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ccna 4 final 2012 (95%)

EWAN Final Exam – CCNA Exploration: Accessing the WAN (Version 4.0)
1

Refer to the exhibit. Communication between two peers has failed. Based on the output that is shown, what is the most likely cause?

ccna 4 final 2012

interface reset

unplugged cable

improper LMI type

PPP negotiation failure

2

Refer to the exhibit. A network administrator is tasked with completing the Frame Relay topology that interconnects two remote sites. How should the point-to-point subinterfaces be configured on HQ to complete the topology?

ccna 4 final 2012

frame-relay interface-dlci 103 on Serial 0/0/0.1
frame-relay interface-dlci 203 on Serial 0/0/0.2

frame-relay interface-dlci 301 on Serial 0/0/0.1
frame-relay interface-dlci 302 on Serial 0/0/0.2

frame-relay map ip 192.168.1.1 103 broadcast on Serial 0/0/0.1
frame-relay map ip 192.168.2.2 203 broadcast on Serial 0/0/0.2

frame-relay map ip 192.168.1.1 301 broadcast on Serial 0/0/0.1
frame-relay map ip 192.168.2.2 302 broadcast on Serial 0/0/0.2

3
Which data link layer encapsulation protocol is used by default for serial connections between two Cisco routers?

ATM

Frame Relay

HDLC

PPP

SDLC

4

Refer to the exhibit. Company ABC expanded its business and recently opened a new branch office in another country. IPv6 addresses have been used for the company network. The data servers Server1 and Server2 run applications which require end-to-end functionality, with unmodified packets that are forwarded from the source to the destination. The edge routers R1 and R2 support dual stack configuration. What solution should be deployed at the edge of the company network in order to successfully interconnect both offices?

ccna 4 final 2012

a new WAN service supporting only IPv6

NAT overload to map inside IPv6 addresses to outside IPv4 address

a manually configured IPv6 tunnel between the edge routers R1 and R2

static NAT to map inside IPv6 addresses of the servers to an outside IPv4 address and dynamic NAT for the rest of the inside IPv6 addresses

5
Which variable is permitted or denied by a standard access control list?

protocol type

source IP address

source MAC address

destination IP address

destination MAC address

6

Refer to the exhibit. The link between the CTRL and BR_1 routers is configured as shown in the exhibit. Why are the routers unable to establish a PPP session?

The clock rate must be 56000.

The usernames are misconfigured.

The IP addresses are on different subnets.

The clock rate is configured on the wrong end of the link.

The CHAP passwords must be different on the two routers.

Interface serial 0/0/0 on CTRL must connect to interface serial 0/0/1 on BR_1.

7
Which three statements accurately describe a security policy? (Choose three.)

It creates a basis for legal action if necessary.

It defines a process for managing security violations.

It defines acceptable and unacceptable use of network resources.

The remote access policy is a component of the security policy that governs acceptable use of e-mail systems.

It is kept private from users to prevent the possibility of circumventing security measures.

It provides step-by-step procedures to harden routers and other network devices.

8
A network administrator has changed the VLAN configurations on his network switches over the past weekend. How can the administrator determine if the additions and changes improved performance and availability on the company intranet?

Conduct a performance test and compare with the baseline that was established previously.

Interview departmental secretaries and determine if they think load time for web pages has improved.

Determine performance on the intranet by monitoring load times of company web pages from remote sites.

Compare the hit counts on the company web server for the current week to the values that were recorded in previous weeks.

9

Refer to the exhibit. Headquarters is connected through the Internet to branch office A and branch office B. Which WAN technology would be best suited to provide secure connectivity between headquarters and both branch offices?

ccna 4 final 2012

ATM

VPN

ISDN

Frame Relay

broadband DSL

10
Which statement about a VPN is true?

VPN link establishment and maintenance is provided by LCP.

DLCI addresses are used to identify each end of the VPN tunnel.

VPNs use virtual Layer 3 connections that are routed through the Internet.

Only IP packets can be encapsulated by a VPN for tunneling through the Internet.

11
A company is deciding which WAN connection type it should implement between its main office and branch offices. The company wants to use a cost-effective service that provides virtual circuits between each office. The company also wants to be able to transmit variable-length packets on these circuits. Which solution best meets these requirements?

ATM

HDLC

ISDN

Frame Relay

12
A technician is talking to a colleague at a rival company and comparing DSL transfer rates between the two companies. Both companies are in the same city, use the same service provider, and have the same rate/service plan. What is the explanation for why company 1 reports higher download speeds than company 2 reports?

Company 1 only uses microfilters at branch locations.

Company 1 has a lower volume of POTS traffic than company 2 has.

Company 2 is located farther from the service provider than company 1 is.

Company 2 shares the connection to the DSLAM with more clients than company 1 shares with.

13

Refer to the exhibit. What is placed in the address field in the header of a frame that will travel from the DC router to the Orlando router?

DLCI 123

DLCI 321

10.10.10.25

10.10.10.26

MAC address of the Orlando router

14

Refer to the exhibit. This router is being configured to use SDM, but the SDM interface of the router cannot be accessed. What is the cause of the problem?

The VTY lines are not configured correctly.

The HTTP timeout policy is not configured correctly.

The authentication method is not configured correctly.

The username and password are not configured correctly.

15
Which two devices can be used by teleworkers who need to connect to the company network across the PSTN for a few hours a day? (Choose two.)

router

CSU/DSU

DSL modem

cable modem

access server

dialup modem

16
An administrator is configuring a dual stack router with IPv6 and IPv4 using RIPng. The administrator receives an error message when trying to enter the IPv4 routes into RIPng. What is the cause of the problem?

When IPv4 and IPv6 are configured on the same interface, all IPv4 addresses are over-written in favor of the newer technology.

Incorrect IPv4 addresses are entered on the router interfaces.

RIPng is incompatible with dual-stack technology.

IPv4 is incompatible with RIPng.

17
What is the function of an intrusion detection system on a network?

to restrict access to only authorized users

to detect attacks against a network and send logs to a management console

to prevents attack against the network and provide active defense mechanisms

to detect and prevent most viruses and many Trojan horse applications from spreading in the network

18

Refer to the exhibit. All devices are configured as shown in the exhibit. PC1 is unable to ping the default gateway. What is the cause of the problem?

The default gateway is in the wrong subnet.

STP has blocked the port that PC1 is connected to.

Port Fa0/2 on S2 is assigned to the wrong VLAN.

S2 has the wrong IP address assigned to the VLAN30 interface.

19
When Frame Relay encapsulation is used, what feature provides flow control and exchanges information about the status of virtual circuits?

LCP

LMI

DLCI

Inverse ARP

20
A system administrator must provide Internet connectivity for ten hosts in a small remote office. The ISP has assigned two public IP addresses to this remote office. How can the system administrator configure the router to provide Internet access to all ten users at the same time?

Configure DHCP and static NAT.

Configure dynamic NAT for ten users.

Configure static NAT for all ten users.

Configure dynamic NAT with overload.

21
A company is looking for a WAN solution to connect its headquarters site to four remote sites. What are two advantages that dedicated leased lines provide compared to a shared Frame Relay solution? (Choose two.)

reduced jitter

reduced costs

reduced latency

the ability to burst above guaranteed bandwidth

the ability to borrow unused bandwidth from the leased lines of other customers

22
What will be the result of adding the command ip dhcp excluded-address 192.168.24.1 192.168.24.5 to the configuration of a local router that has been configured as a DHCP server?

Traffic that is destined for 192.168.24.1 and 192.168.24.5 will be dropped by the router.

Traffic will not be routed from clients with addresses between 192.168.24.1 and 192.168.24.5.

The DHCP server will not issue the addresses ranging from 192.168.24.1 to 192.168.24.5.

The router will ignore all traffic that comes from the DHCP servers with addresses 192.168.24.1 and 192.168.24.5.

23

Refer to the exhibit. A host connected to Fa0/0 is unable to acquire an IP address from the DHCP server. The output of the debug ip dhcp server command shows “DHCPD: there is no address pool for 192.168.3.17″. What is the problem?

The address 192.168.3.17 address is already in use by Fa0/0.

The pool of addresses for the 192Network pool is configured incorrectly.

The ip helper-address command should be used on the Fa0/0 interface.

The 192.168.3.17 address has not been excluded from the 192Network pool.

24

Refer to the exhibit. From the output of the show interfaces and ping commands, at which layer of the OSI model is a fault indicated?

application

transport

network

data link

physical

25
What three questions can be answered using data gathered from a baseline on a new network? (Choose three.)

Are areas of the network experiencing high error rates?

Will the disaster recovery procedures work correctly?

What parts of the network have the highest volume?

Does the organization require more network technicians?

How does the network perform during peak periods?

Are there any devices working at top capacity?

What networks are the most susceptible to security attacks?

26
Which type of ACL will permit traffic inbound into a private network only if an outbound session has already been established between the source and destination?

extended

reflexive

standard

time-based

27

Refer to the exhibit. R1 is performing NAT overload for the 10.1.1.0/24 inside network. Host A has sent a packet to Web Server. What is the destination IP address of the return packet from Web Server when received at R1?

10.1.1.2:80

10.1.1.2:1234

172.30.20.1:1234

172.30.20.1:3333

28
An administrator issues the command show interfaces s0/1/0 on a router that is configured for Frame Relay. Which console output may indicate an LMI mismatch?

Serial0/1/0 is administratively down

Serial0/1/0 is up, line protocol is up

Serial0/1/0 is up, line protocol is down

Serial0/1/0 is down, line protocol is down

29
A recently patched application server is experiencing response time problems. The network on which the application server is located has been experiencing occasional outages that the network team believes may be related to recent routing changes. Network and application teams have been notified to work on their respective issues. Which statement applies to this situation?

Only results from the software package should be tested as the network is designed to accommodate the proposed software platform.

Scheduling will be easy if the network and software teams work independently.

It will be difficult to isolate the problem if two teams are implementing changes independently.

Results from changes will be easier to reconcile and document if each team works in isolation.

30

Refer to the exhibit. Branch A has a non-Cisco router that is using IETF encapsulation and Branch B has a Cisco router. After the commands that are shown are entered, R1 and R2 fail to establish the PVC. The R2 LMI is Cisco, and the R1 LMI is ANSI. The LMI is successfully established at both locations. Why is the PVC failing?

The PVC to R1 must be point-to-point.

LMI types must match on each end of a PVC.

The frame relay PVCs cannot be established between Cisco and non-Cisco routers.

The IETF parameter is missing from the frame-relay map ip 10.10.10.1 201 command.

31

Refer to the exhibit. Which VLAN will carry untagged traffic on FastEthernet 0/1?

VLAN 1

VLAN 2

VLAN 11

VLAN 12

VLAN 30

VLAN 999

32
What is an accurate description of CHAP when used with PPP on a serial connection between two routers?

A username and password are sent to the peer router, which replies with an accept or reject message.

A username and password are sent to the peer router. If these match the configuration in the peer, the peer in turn provides a username and password to the initiating router.

A challenge message is sent to the peer router, which responds with its username and a calculated value based on a shared secret. This value is then compared by the challenger to its own calculations.

An encrypted password is sent to the peer router, which decrypts it and compares it to a shared secret. If the decrypted passwords match, the peer sends the encrypted password back to the initiating router.

33
Where does a service provider assume responsibility from a customer for a WAN connection?

local loop

DTE cable on router

demarcation point

demilitarized zone

34

Refer to the exhibit. An ACL called Managers already exists on this router. What happens if the network administrator issues the commands as shown in the exhibit?

The commands are added to the end of the existing ACL.

The existing Managers ACL will be overwritten by the new ACL.

The router will output an error message and no changes will be made.

A duplicate Managers ACL will be created that will contain only the new commands.

35
Which statement is true about PAP in the authentication of a PPP session?

PAP uses a two-way handshake.

The password is unique and random.

PAP conducts periodic password challenges.

PAP uses MD5 hashing to keep the password secure.

36
Which combination of Layer 2 protocol and authentication should be used to establish a link without sending authentication information in plain text between a Cisco and a non-Cisco router?

PPP with PAP

PPP with CHAP

HDLC with PAP

HDLC with CHAP

37
Which option correctly defines the capacity through the local loop guaranteed to a customer by the service provider?

BE

DE

CIR

CBIR

38
Which wireless solution can provide mobile users with non line-of-sight broadband Internet access at speeds comparable to DSL or cable?

Wi-Fi

WiMAX

satellite

Metro Ethernet

39

Refer to the exhibit. EIGRP has been configured as a routing protocol on the network. Users on the 192.168.1.0/24 network should have full access to the web server that is connected to 192.168.3.0/24 but should not be allowed to telnet to router R3. Verifying the configuration, the network administrator realizes that users on network 192.168.1.0/24 can successfully telnet to the router. What should be done to remedy the problem?

The ACL 101 statements 10 and 20 should be reversed.

The ACL 101 should be applied on R3 VTY lines 0 4 in the inbound direction.

The ACL 101 should be applied on R3 VTY lines 0 4 in the outbound direction.

The ACL 101 should be applied on R3 Serial0/0/1 interface in the outbound direction.

The ACL 101 statement 10 should be changed to: permit ip 192.168.1.0 0.0.0.255 any

40
What does an access control list determine when used with NAT on a Cisco router?

addresses that are to be translated

addresses that are assigned to a NAT pool

addresses that are allowed out of the router

addresses that are accessible from the inside network

41
Which IP address and wildcard mask combination can be used in an ACL statement to match the 172.16.0.0/30 network?

172.16.0.0 0.0.0.1

172.16.0.0 0.0.0.3

172.16.0.0 0.0.0.7

172.16.0.0 255.255.255.252

42
Which security solution has the responsibility of monitoring suspicious processes that are running on a host and that might indicate infection of Trojan horse applications?

antivirus application

operating system patches

intrusion prevention system

Cisco Adaptive Security Appliance

43

Refer to the exhibit. A network administrator is trying to connect R1 remotely to make configuration changes. Based on the exhibited command output, what will be the result when attempting to connect to R1?

failure to connect due to Telnet not being enabled

failure to connect due to incomplete configuration for Telnet

a successful connection and ability to make configuration changes

a successful connection but inability to make configuration changes because of the absence of an enable secret password

44

Refer to the exhibit. Results of the show vlan and show vtp status commands for switches S1 and S2 are displayed in the exhibit. VLAN 11 was created on S1. Why is VLAN 11 missing from S2?

There is a Layer 2 loop.

The VTP domain names do not match.

Only one switch can be in server mode.

S2 has a higher spanning-tree priority for VLAN 11 than S1 does.

45
A technician has been asked to run the Cisco SDM one-step lockdown on a customer router. What will be the result of this process?

Traffic is only accepted from and forwarded to SDM-trusted Cisco routers.

Security testing is performed and the results are saved as a text file stored in NVRAM.

All traffic that enters the router is quarantined and checked for viruses before being forwarded.

The router is tested for any potential security problems and all recommended security-related configuration changes will be automatically applied.

46

Refer to the exhibit. Which data transmission technology is being represented?

TDM

PPP

HDLC

SLIP

47
A network administrator is instructing a technician on best practices for applying ACLs. Which two suggestions should the administrator provide? (Choose two.)

Named ACLs are less efficient than numbered ACLs.

Standard ACLs should be applied inside the core layer.

Place standard ACLs as close to the destination as possible.

ACLs applied to outbound interfaces require fewer router resources.

Extended ACLs should be applied closest to the source that is specified by the ACL.

48

Refer to the exhibit. Which configuration command would result in the output in the exhibit?

ip nat inside source static 10.1.200.254 172.16.76.3

ip nat inside source static 10.1.200.254 192.168.0.10

ip nat inside source static 172.16.76.3 10.1.200.254

ip nat inside source static 172.16.76.3 192.168.0.10

ip nat inside source static 192.168.0.10 172.16.76.3

ip nat inside source static 192.168.0.10 10.1.200.254

49
What are three important reasons to establish a network baseline? (Choose three.)

to determine the time it takes for the network to self recover from a failure

to determine which areas in the network are underutilized or overutilized

to determine the performance of the network during the normal hours of operation

to determine what thresholds should be set for the devices that need to be monitored

to determine the areas in the network which should not be included in the monitoring process

to determine the number of users whose access to network resources should be restricted

50
Which two statements are true about creating and applying access lists? (Choose two.)

There is an implicit deny at the end of all access lists.

One access list per port, per protocol, per direction is permitted.

Access list entries should filter in the order from general to specific.

The term “inbound” refers to traffic that enters the network from the router interface where the ACL is applied.

Standard ACLs should be applied closest to the source while extended ACLs should be applied closest to the destination.

51
While troubleshooting a problem with an e-mail server, an administrator observes that the switch port used by the server shows “up, line protocol up”. The administrator cannot ping the server. At which layer of the OSI model is the problem most likely to be found?

application layer

network layer

data link layer

physical layer

52

Refer to the exhibit. Router RT is not receiving routing updates from router RTA. What is causing the problem?

The ip rip authentication key-chain command specifies exam rather than test.

The name of the keystring is not the name of the neighboring router.

The key chains are given the same name on both routers.

The passive-interface command was issued for RTA.

Domain Knowledge – Weighted Score

Max Points: 102
Earned Points: 97
Percentage: 95.1%

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Continuing from a previous story – StarCrab SandFerry

Abby and Fedy again travel to Paradise RedCrab to meet with Febb and CeCe. They discuss the positive feedback they have received from their elders. Febb and CeCe acknowledge that the feedback they received from their elders were also very similar and very positive. First, they worked on the new StarCrab Numbering method and came up with the following resolution:

1. LoneStar Numbers: From now on, citizens of Laguna LoneStar kingdom will use a range of numbers between 0 and 127 to uniquely identify themselves. All numbers belonging to LoneStar should be preceded by ls to identify the kingdom of LoneStar. Therefore, citizens of LoneStar can use any number between ls-1 and ls-126. However, citizens will not be allowed to use ls-0 or ls-127, the first and the last number of the range as their individual number. ls-0 is a reserved number and would be used to identify the entire kingdom and ls-127  represents all the citizens within the kingdom and would be used as an alias to send a message at once to everyone within the kingdom, instead of sending the same message one at a time to every citizen. This is very similar to using Fefy as an alias during emergency. They also wanted to reserve a number for group conversations, but instead decided to work on it in the near future.
2. RedCrab Numbers: On the other hand, citizens of Paradise RedCrab kingdom will use a range of numbers between 0 and 255 to uniquely identify themselves. All numbers belonging to RedCrab should be preceded by rc to identify the kingdom of RedCrab. Therefore, citizens of RedCrab can use any number between ls-1 and ls-254. However, citizens will not be allowed to use ls-0 and ls-255, the first and the last number of the range as their individual number. ls-0 is a reserved number and would be used to identify the entire kingdom and ls-255 would be used as an alias to send a message at once to everyone within the kingdom, instead of sending the same message one at a time to every citizen.
3. Flexible than Birth Names: The new numbering method would be flexible, meaning an individual can change her own number anytime she wishes as long as no one else is using the same number. However, individuals are discouraged to change their number without notifying everyone, especially those who may seek their assistance or other services.
4. LoneStar FerryQueen: They’ve elected Abby to perform the duties of a FerryQueen for the LoneStar kingdom. This is only a temporary assignment for her. They realize that Abby, one of the brightest young starfish, is too busy with her school and research and her help is needed for further development of the new conversation etiquette. Later on, due to the new and flexible numbering system her number could be assigned to someone else trained to perform the duties of a FerryQueen. For now, Abby would be assigned a new number ls-22.
5. RedCrab FerryQueen: For the time being, Febb has volunteered to be the FerryQueen for the RedCrab kingdom. Febb would be assigned a new number rc-33.
6. ClamSpotter: In the LoneStar kingdom they have a ClamSpotter, whose job is to spot clams during their migratory season. This very important role is assigned to Beby. Starfish relied on her during clam harvesting season and she has done a marvelous job of spotting clams and providing that information to starfish. However, there was one problem. When Beby is on vacation or becomes sick, someone else would take over her responsibilities, but it has been always difficult and challenging to announce the new Spotter’s name to all starfish. Even after several announcements, some starfish would not pay attention and some would forget the new spotter’s name. So these starfish would always ask for Beby for directions but Beby would no not be available. This problem maybe resolved by assigning ls-5 to Beby and having everyone in LoneStar kingdom to ask for ls-5 instead of Beby to help in spotting clams. If Beby becomes sick then she could easily assign her number to someone else who can perform the duties of a ClamSpotter. This way an emergency announcement would not have to be made anytime Beby is unavailable. At this time, it has become apparent that the ClamSpotter could also provide clam news to citizens of RedCrab as long as the citizens know what number to ask, in this case ls-5, for the news.
7. WeatherGirl: The RedCrab kingdom has a weather person responsible for monitoring the weather. Her birth name is Dede and she has been assigned a new number rc-12. Now, if everything works according to plan, the citizens of LoneStar should be able get the updated news from rc-12. This may also help in creating a joint Alert System that both starfish and crabbies talked about before.
8. The all new StarCrab Conversation Etiquette (StarCrEt): This is a higher level conversation based on the existing Starfish Conversation Etiquette(StarEt).  This is considered a higher level because from now on either starfish or crabbies will no longer be able to use their birth names to start or continue a conversation.  They must use the new numbering method to address one another. It would be rude to use birth names at these higher level of conversations. Proper etiquette is to address everyone by respective numbers. During the lower or more casual level of conversation they would identify their corresponding birth names and send the message to the appropriate individual. Developing StarCrEt has been more difficult than they originally thought it would be, since it involves not only the local conversations but also those conversations meant for citizens of another kingdom. But nothing is too difficult for starfish and crabbies when they get their heads together. The difficulties and the solutions to the challenges would be discussed shortly.

In the starfish kingdom there has been a uproar when the news of a new numbering method came out. They questioned why they have to use a cumbersome numbering method to identify themselves on the top of their birth names. They also resented the fact that they have to use a “so called” higher lever conversation etiquette to address each other by numbers, otherwise they would considered unsophisticated. Starfish are proud individuals and they proud of their birth names and believe in free speech. They don’t want anyone, rumor has it that crabbies are behind this to destroy their heritage, especially from the outside world to tell them what they can say and how they can say it. It infringes on their “1st addition,” also known as “free to speak,” one of the core principles on which LoneStar kingdom was built.

The elders along with Abby and Fedy,  immediately called a town hall meeting to calm the fears of their citizens. The elders explained that they themselves went through similar oppositions when they were building the Sand Tunneling System for the Starfish Conversation Etiquette (StarEt). Sand Tunneling and StarEt allowed them to instantaneously start conversations or send messages to one another, instead of using trained clams as messengers which used to take months. Sometimes the messages would take more than a year or the messages will not arrive at all. The reason being some clams, although trained, lose their way during their journey, some would be inadvertently eaten by other starfish due to mistaken identity. Also, there were reports that some clams were too lazy to deliver the message, found someone and gotten married and then decided to take a break from their hectic lives and retire in the wilderness of the LoneStar kingdom. The elders then added that it is hard to believe that there were starfish who had preferred trained clams instead of instant messaging.

Abby and Fedy then get a chance to talk to the opposition directly. They told them that they realize that it would be difficult to remember or manage their own individual numbers, number of the FerryQueen, number of their friends and so forth, but they’re doing research to make their life easier so they do not have to remember too many numbers. Then Abby added that in the future they may not have to remember any number at all. They are already very exited about connecting to the new world and also started to think about some futuristic concepts, such as StarShack or CrabShack, where individuals from different kingdoms can hangout and have fun. Using the SandTunneling, SandFerry and StarCrab Numbering it may all become a reality very soon.

It seemed that the elders’, Abby and Fedy’s  reasoning hit home and the opposition realized that they must give the new numbering a chance. After all, it is a very small price to pay for what future has to offer to them. The elders agreed that the numbering is cumbersome and it may take a little while of getting used to, but they think that the days of calling each other by birth names are numbered. The new numbering will allow them to converse with a new world and perhaps more than a single kingdom in the near future.

StarCrab Academy(StaC)

Since the introduction of StarCrab Numbering and the StarCrEt have caused so much confusion among the citizens of both LoneStar and RedCrab kingdoms that the elders from both kingdoms thought that it would be wise to establish an organization dedicated to developing new ideas and also to educating and training their citizens. After all, informed and educated citizens are their best assets. Therefore, the StarCrab Academy, also would be known as StaC in short,  has been  created. The smartest and brightest citizens from both kingdoms are lured to run the StaC and Fedy, Abby, Febb and CeCe became some of its founding members. The StaC would very soon become a highly prestigious institution.

In StaC’s first inaugural meeting, the founding members have decided to find a way to efficiently inform the citizens of both kingdoms about new and upcoming changes to their conversation etiquette. They’ve also decided to routinely distribute to their citizens a “Q&A” on different subjects, so it may help them better understand the new ways of communication.

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Continuing from a previous story – StarCrab Numbering

StarCrEt has been developed mostly by Abby and Fedy in collaboration with Febb and CeCe from the RedCrab kingdom. It starts with the basic tried and proven functionality of StarEt as elders have stipulated. If you recall, StarEt allows starfish to communicate with each other using their birth names, also known as BirthNames. This would remain the ultimate method of exchanging messages or having a conversation between starfish using the existing SandTunnels.

However, a higher level conversation etiquette such as StarCrEt became necessary when the StarCrab Numbering was introduced. As you may know, StarCrab Numbering was invented so starfish could have a conversation and send or receive messages to someone outside of their kingdom and to the new world. StarCrEt and StarCrab Numbering are the foundation for all conversation etiquette that everyone must follow  inside or outside of the kingdom.  It takes advantage of SandFerry to send a message across another kingdom.

While testing the new StarCrEt using the numbering method, it became apparent to Abby and Fedy that a very small and portable black book  is needed for everyone to carry to have a sound conversation. It became impossible for a starfish to remember all the birth names which are now associated with the new numbers. It has been decided that for the ease of conversation a startfish would record an individual’s number along with the corresponding birth names in the little black book. This black book would be known as StarCrab TynyBB. TynyBB would be very small, so they may need to erase any old number that they do not currently need and replace it with numbers of individuals involved in current conversations. Abby and Fedy promised that more details and the side benefits of TynyBB would be announced very shortly. TynyBB is a major feet in making the StarCrab Numbering dynamic and flexible and easier to use during conversation. It also made transferring a number from one starfish to another hassle free. This would become apparent, for example, when several individuals may be needed to perform the duties of a ClamSpotter.

The Guts of StarCrEt: The following is a summary and a detailed description of sophisticated StarCrab Conversation Etiquette. In this scenario, Eddy and the ClamSpotter will be starting a conversation. Eddy and Beby have been assigned the numbers ls-11 and ls-5 respectively. Everyone has been told from now on to inquire with ls-5, the ClamSpotter,  instead of Beby directly, if one needed help in spotting clams. Using ls-5 instead of Beby’s name allows Beby to transfer or assign her number to someone else to fill in for her in case she becomes unavailable. As mentioned previously, now it is a proper etiquette to use the new assigned number to start a conversation with another. It is no longer a proper etiquette to address anyone with her birth name at the start of any conversation. Eventually, one would need to know the birth name (BirthName) that is associated with the new number to be able to send a message to the other person. It is important to note that StarCrEt only works on the higher level of conversation where individuals must address each other by using the number assigned to them; StarCrEt eventually takes advantage of the existing StarEt, as shown in the example below,  to continue the conversation at the lower level where it uses the BirthNames to identify each other. StarCrEt also plays an important role when an individual needs to send a message to another kingdom. We’ll get to know more about this shortly.

In the following example, Eddy starts a conversation with the ClamSpotter because he needs help in hunting for clams.

Summary of StarCrEt

1. Eddy first starts by asking everyone in LoneStar Kingdom for the identity (BirthName) of the assigned number ls-5.
2. Only Beby responds by identifying herself with her BirthName.
3. In case he forgets, Eddy pencils down ls-5 and associates it with Beby in his TynyBB.
4. Eddy asks for help.
5. Beby responds by telling Eddy to look at his 2 o’clock where some clams are trying to hide.

Spilling the Beans on TynyBB

The new StarCrab Numbering provided a great opportunity for starfish and RedCrab to communicate with each other and perhaps, in the future, with other kingdoms. However, it also provided a few drawbacks. One of them being difficult to remember the numbers and their corresponding BirthNames of all the individuals involved in a conversation. TynyBB was created to address this particular issue. A starfish may know the number of the other starfish with who to communicate with but may not always know the corresponding BirthName to identify the other starfish. It is important to know the corresponding BirthName before starting a conversation. Therefore, before starting a conversation a starfish must make a Public Announce (PANN) in the LoneStar kingdom for the individual to respond with her BirthName who has been assigned the number????. After knowing the BirthName, the starfish makes an entry in his TynyBB. This allows a starfish to have an instant and confidential conversation with another starfish without having to remember his or her corresponding BirthName. The bottom line is, if you only know the number and not the BirthName of the starfish with whom you would like to have a conversation, then just ask. An example of TynyBB entry made by Eddy is shown below:

• StarCrab Number               BirthName
• ls-5                                                 Beby
• ls-13                                               Deby

Yelling Yeee-Whoo

Within a few days of implementing the StarCrab Conversation Etiquette, all starfish have?????? come to realize that they are very often using the PANN (Public Announcement) to know the identity (BirthName) of a given number. In the past, they mostly used the PANN for emergencies. Some of the starfish, mostly the elders became agitated at first with all the yelling going on in the SandTunnels but they have become used to it when they realized that they can simply ignore the call to identify as long as it is not meant for them. A precocious teenage starfish, later became known as Billy the Starfish,  coined the term yelling “Yeee-Whoo” for anyone using the PANN to find the BirthName of a starfish who has been assigned a known number. The same kid later also coined another term yelling “Flip-Yeee-Whoo” for anyone using the PANN to find the assigned number of a starfish whose BirthName is known. At the time, little was known as to why anyone would need to yell “Flip-Yeee-Whoo,” but soon they’ll find out why.

StaC Q&A

1. Which of the following are some of the benefits of implementing the StarCrab Numbering? (Select all that apply)

• A. Starfish would be able to talk to RedCrabs
• B. It makes BirthNames obsolete
• C. Numbers are easier to switch than BirthNames

2. Which of the following is a characteristic of an assigned number?

• A. A number assigned to a starfish could be temporary
• B. A number assigned to a starfish is always permanent
• C. Only a starfish without a BirthName can be assigned a number

3. Beby, the Clam Spotter, became sick during the clam hunting season. What can Beby do so starfish asking for help locating clams can still get help?

• A. Temporarily assign her number to someone else capable of becoming a Clam Spotter.
• B. Make a public announcement that Beby is sick.
• C. Starfish cannot get help when Beby is sick.

what is the dis-adv of sc numbering to – cumbersome, complicate, not easy to remember, etc

TynyBB to the rescue

yeee-whoo – Know the number, need to know the corresponding BirthName, remmember most of the time you’ll know the number, it will be posted on their forehead, t-shirt, birthnae is hidden due to privacy

flip-yeee-whoo – Know the BirthName, need to know the number

© 2010-2011 ccnablog.org.  All rights reserved.

[Tech Fiction]

In the year 452, Emperor Valentinian III of Rome, in order to seek peace, sends a messenger in a hurry to Attila the Hun, who is by then ravaging cities near Venice. After a while, when the messenger does not return, Valentinian begins to worry. Not knowing the fate of the 1st messenger, he again sends another messenger equipped with elaborate maps to meet Attila. When the 2nd messenger also fails to return on time, Valentinian grows very nervous and out of desperation sends a 3rd messenger, an experienced and well traveled high Roman official named Leo the Great, to see Attila.

Within a few days, Leo returns with a good news for Valentinian. According to Leo, he was able to convince Attila not to attack Italy, doing so – Attila was told – he and his army could suffer severe repercussions. With curiosity Valentinian asked Leo, how he was able to return so quickly and he then inquired about the fates of the previous messengers. Leo then summarized the following to the emperor:

1. The 1st messenger left ill equipped, since the emperor was in a hurry and forgot to tell him which main gate to use to exit the kingdom towards Venice. Leo thinks the messenger began to wonder and eventually died of exhaustion.
2. The 2nd messenger was well equipped and was told exactly which main gate to use to exit the kingdom towards Venice. He was able to meet Attila, however, Attila was furious to see him since the messenger was only a low ranking Roman official. Attila then asked him to get lost immediately, otherwise, threatened to throw him in jail. Fearing for his life, he left Attila in a hurry. Attila neglected to tell him which gate to take to exit Venice and, therefore, he began to wonder and eventually may have died of exhaustion.
3. Leo was able to return quickly, since he knew exactly which gate to use to exit the kingdom; after the meeting,  pleased Attila was kind enough to tell Leo which gate to use to exit Venice on his way back to Rome.

The moral of the fiction – More often than not, when a messenger doesn’t return, we automatically assume that the messenger had trouble reaching the destination. We very often neglect the fact that the messenger indeed reached the destination but had trouble finding his way back. We must assume both possibilities equally.

The fiction above also emphasizes the fact that – when we dispatch a messenger outside of the kingdom – we must notify the messenger which gate to use to exit the kingdom. Once the messenger reaches its destination, it is also important to notify the messenger which gate to use to exit the visiting kingdom to be able to return safely. Reaching a foreign destination doesn’t guarantee a messenger’s return.

© 2010-2011 ccnablog.org.  All rights reserved.

[Tech Fiction]

In the late 30′s, at the height of genetic research, a few scientists from Belgium decide to travel to Congo to do some serious research on rats. Rats, according to their belief, possesses more intelligence than humans. The scientists, fearful that some day rats may take over the humans and eventually rule the planet Earth, concocts a plan to turn them into a generation of benign rats. To do so, they decide to inject a few captive rats with a special blend of herbal drink saturated with high fructose corn syrup. This made the rats happy – at the same time slowed their brain functionality – it also made them lazy. These rats are no longer capable of searching intelligently for their own food. If a rat becomes hungry, it has to be told exactly where to go to look for food. At the end of the meal, the same rat, now due to the lack of memory retention, has to be told exactly which path to take to go back to its own burrow. “What a simple and harmless potion to control the minds of foolish rats,” – one scientist quipped.

Elated by their initial test results, the scientists decide to break the news to the world, although, they still need to figure out how to inject every single rat on the planet with the same potion.

The moral of this fiction – Non-intelligent rats cannot guide themselves, they must be guided by someone to each and every destination.

Similarly, IP packets are non-intelligent electronic objects. Even with a source and a destination IP address contained in them, they cannot guide themselves to their destination from one network to another. They must be steered and propelled from junction to junction by the routers in different networks until they reach their final destination.

© 2010-2011 ccnablog.org.  All rights reserved.

[Tech fiction]

A little girl, named Maddie, learns how to make a paper boat from her mom. After several tries, she becomes successful in making her 1st paper boat on her own. Overjoyed, she takes the paper boat and runs to the bayou at the back of her house. It is a beautiful quiet afternoon in New Orleans and the water in the bayou is calm.

Maddy puts her paper boat in the water and watches it float. She creates a small wave with her soft little hands and then watches the rocking boat with a glee. She then pushes the boat in one direction – the boat sails for a few seconds and then stops. She walks over to the boat in her less than knee-high water and pushes the boat again – the boat sails again and then stops after a few seconds. She pushes the boat around for a while in the bayou’s shallow water until her best friend Soledad shows up. Excited and eager to play with the paper boat, Soledad joins Maddie and starts to push the boat towards each other.

In the late afternoon, Maddie hears her mom calling her to come home. The little girls, though unwilling, decided to call it the day – they had to – since by this time the paper boat became wet and soggy and it would no longer float in the water. Maddie decides to come back the next day and promises to teach Soledad how to make her won paper boat.

As Maddie walks back home, she wonders – if there is something she could do to the paper boat so it would sail on its own – she doesn’t like to push the boat all the time.

The moral of the fiction – A paper boat can’t move on its own and it has no sense of directions. Someone needs to push it in the right direction for it to reach its destination.

© 2010-2011 ccnablog.org.  All rights reserved.

A common misconception regarding an IP Packet is that, since each packet carries a source and a destination IP address,  it automatically knows how to navigate itself to its destination. It would be very similar to saying – an ordinary airline passenger with a ticket from San Diego to Chicago automatically knows which plane to get on and is also capable of navigating the plane from San Diego to Chicago.

An IP packet, similar to a paper boat, requires two things to successfully reach its destination – a direction and a push (propulsion). An IP packet, similar to a paper boat, requires from someone or something a constant direction and a push going from one place to the next, until it arrives at its final destination.

One may ask, “What is the purpose of the source and the destination IP addresses?” And, “Who is going to provide the direction and the propulsion.”

Haha! – I knew you’re going to ask me that! I’ll use several analogies below and all of them will explain the same thing. I must warn you now, pay attention. Cisco will not allow you to pass CCNA without knowing the following fundamental concept. I promise, you’ll be asked, by Cisco, the same question over-and-over again but in different ways. This is why I’ll be using several analogies.

Analogy 1: Let’s assume for a moment that someone buys a ticket to go from Los Angeles to New York City. When she arrives at the airport with a ticket which has “LA to NYC” printed on it, she is directed to go to her proper gate and board an aircraft destined for NYC. During her trip, she will always be carrying the same ticket - it will not change until she finally reaches New York City.

Analogy 2: Graduated at 15, Trixi, a very smart teenager from Los Angeles, decides to attend NYU to study journalism. Her mom Jenny is worried, since Trixi would be traveling alone to New York City for the first time. Jenny’s other concern is that she could only buy a ticket for an indirect flight. This would require Trixi, a forgetful teenager with many luggage,  to take 3 connecting flights before finally reaching her destination. To calm her mom’s anxieties, Trixi decides to wear a T-Shirt which has “To NYC” printed at the front and “From LA” printed on the back. All the airlines involded are notified of her travel and since Trixi is a minor traveling alone wearing a distinct t-shirt, the courteous airline attendants did not have any trouble spotting Trixi and guiding her to the appropriate aircraft at each gate. Trixi had to change aircraft at Salt Lake City, Denver and Chicago, then finally arriving at New York City. Although she went through three cities, she did not have to change her t-shirt which had from LA to NYC printed on it.

Analogy 3: KSS, a small but very advanced coal-loading systems manufacturer in the US gets a rare contract from China. KSS puts all the equipment for export in a standard 40′ cargo container and seals it. It then prints “From: Los Angeles, USA” and “To: Shenyang, China” on the outside of the container. The container is carried by a truck to a nearby seaport. It is then put on a ocean going cargo vessel bound for China. The container would eventually be off loaded onto 2 other cargo vessels before it would arrive at the port of Shenjeng. Although, the cargo would be transferred into 3 different vessels, the “To:” and the “From:” printed on the container remained the same.

Analogy 4: The US postal service in San Diego, receives a mail to be delivered to Gobi, Mongolia, a remote location of South Mongolia where the nomadic shepherds live. The mail traveled in car, train, bus, airplane, boat, horse back and eventually on a camel back to reach its final destination. The “From” and the “To” addresses printed on the envelope did not change, however, the mail traveled 7 countries and 3 continents.

Fact: Every IP packet contains some sort of cargo. Its source and destination IP addresses contained (printed) on the packet never change – only the underlying carrier changes from port to port, which guides the packet towards its final destination.

Concept: An IP packet, while traveling, never changes its source or destination IP addresses.

Think: It would be very confusing if the To/From addresses on a letter keeps changing en route to its destination.

Know: The source and the destination IP addresses are similar to the To & From addresses printed on a letter. They never change.

Food for thought: There must be some underlying mechanisms or invisible addressing scheme the postal services use to deliver a mail traveling several cities or countries

Once on transit the IP packets are at the mercy of the handler to guide them to their destination. Packets cannot travel without the help of their handler (guides).

The postman has just dropped off my mail today. One of my mails came from Carol Stream, IL. It is my AT&T bill. I inspected both the front and the back of the envelope and it is very clean. I was hoping to see some king of a seal stamped on the envelope, indicating what route the mail took to come all the way from Illinois to San Diego, CA – but there is none. Only the “From” and “To” addresses are prominently printed on the envelope.

 

© 2010-2011 ccnablog.org.  All rights reserved.

Cisco wants you to understand this concept down cold and will ask you many questions related to this concept. However, the answer is always the same. The concept is as follows:

An IP packet with a source and a destination IP address contained in it, sometimes has to travel through several networks before it can reach its final destination. The question is, does the IP packet keep changing its source and destination IP addresses until it reaches its final destination.

The answer is no. The IP packet does not keep changing its IP addresses from network to network until it reaches its final destination. However, the underlying MAC addresses, which is mostly invisible to us, contained in the IP packet do.

To remember this, lets look at the the previous analogy made about The Postman and the mail (bill) I’d received from AT&T in Carol Stream, IL. It is obvious that the mail went through several post office sorting facilities before it arrived in San Diego. It is a mystery, how the mail traveled all the way from Illinois to California without any indication on the mail itself. Now lets ask ourselves the question, “Do we think that the mail kept changing its “From” and “To” addresses printed on the envelope until it reached San Diego.” The obvious answer is no. But, it is clear that the post office uses some sort of underlying mechanism, which is invisible to us, that allowed the mail to travel several cities and states before finally arriving in San Diego.

We can think of the “From” and the “To” addresses printed on the envelope as the “Source” and “Destination” IP addresses of an IP packet – these addresses never change while on transit. On the other hand, the post office’s underlying mechanism could be thought of as the MAC addresses, which are continually changing while the IP packet is traveling from one network to the next until it reaches its final destination. The changing of MAC addresses remains mostly invisible to us. We’ll very soon look at how MAC addresses help IP packets to reach its final destination.

© 2010-2011 ccnablog.org.  All rights reserved.

 

There are two different IP addressing schemes used on the Internet. They are, IPv4 (also known as just IP) and IPv6. No need to worry about IPv1-3 and IPv5, they are non-existent. IPv4 is the older of the two and more widely used. I do not have a figure, but if I were to guess, I’d say that 90% of the devices that are currently connected to the Internet are using IPv4 addressing. Although IPv4 has been in existence for many decades and for the most part has served us well, it is currently exhausted. IPv4 utilizes a 32-bit addressing scheme which yields about 4.3 billion addresses. As of February, 2011, ICANN, the authority that gives out new IP addresses, announced that they no longer  have  new IPv4 addresses to give out. This was anticipated for a long time and hence IPv6 addressing was created several years ago to deal with this exact issue and a few other things. Although, IPv6 is designed to produce more IP addresses than we’ll ever need in our lifetime, I’ll let time to be the judge of that.

Most of the Cisco networking equipment support concurrent addressing in both IPv4 and IPv6 format. This is also true for some major PC and other IP device (PDA, Cell phone, etc.) manufacturers and Operating Systems such as Windows 7 and Linux. From ground up, IPv6 was designed to co-habit with the existing IPv4, so the migration from IPv4 to IPv6 becomes easier.

One may ask, “What’s the point of spending time in learning IPv4 addressing, since it’s going to be phased out soon?” It would be phased out for sure, because it has to, but not very soon. We expect to see IPv4 still dominating the Internet for at least 5 to 7 more years before it is completely phased out. Also, without a good working knowledge of IPv4, it would be impossible to pass the “CCNA1: Network Fundamentals” course (1st of 4 CCNA courses), let alone the CCNA certification exam. All CCNA courses (CCNA1-CCNA4) are based on IPv4.  In addition, companies will be looking for network engineers with IPv4 knowledge for many years to come.

A Typical Home Addressing: Before learning IPv4 addressing, lets first look at how a typical home addressing works here in America. For simplicity, I’ve used the word “home,” but it could be an office, an apartment or a farm, etc. This will be used as an analogy to describe how IPv4 addressing works.

Example 1:

Cisco Systems, Inc.

170 West Tasman Dr.

San Jose, CA 95134

USA

The address above has, more or less, five (5) identifiers*, and they are, Name, Street, City, State & Country. Traditionally, we’ve been writing an address following the format shown above because we are told to do so by the post office. This makes it easier for the postman and, especially, the postal scanners (computers) to sort out the mails for proper destinations. Although the address above is written from top-to-bottom, it would be safe to assume that the sorting machines actually read the address from bottom-to-top. Bottom being more general and towards the top being more specific address identifiers.

To be able to make my analogy of home addressing to the IPv4 addressing, let me write the identifiers of the above address in a single line as shown below, separating each identifier by a dash. Also, to have some fun with it, lets just call it the dashed representation of a typical home address , where the traditional address identifiers are written in a single line, from left-to-right, left being more general and the right being more specific.

Example 2: A dashed representation of a typical home address

USA - CA 95134 – San Jose – 170 West Tasman Dr.* - Cisco Systems, Inc.

Note: The ‘*’ is not part of the address, it is there just to be able to make a point later.

Looking at this dashed addressing, it would be safe to conclude that,  “USA - San Jose – CA 95134 - 170 West Tasman Dr. -” is the general part of the address and “Cisco Systems, Inc.” is the most specific part, the final destination of the mail. Therefore, we can say that in example 2, four (4) identifiers (from left to right) was used to represent the general part of the address, which leaves the 5th identifier to be the most specific part of the address, the final destination. Now that we had fun with it, lets look at another address shown below, which has four (4) identifiers instead of five (5).

Example 3: Another example of a dashed representation of a typical home address   

CA 92128 – San Diego – 12001 Bing Crosby Avenue* Unit #2 – Willie Smith

The address above indicates that Willie Smith lives in Unit #2 of the building labeled as 12001 Bing Crosby Dr. Since there could be more than one person by the name Willie Smith living in 12001 Bing Crosby Dr., Unit #2 has to be included as a part of the most specific address, the 4th identifier. Therefore, in example 3 above, about 2-2/3 identifiers represent the general part of the address and rest 1-1/3 identifier represents the most specific part of the address.

One may ask, “What is the big fuss about noticing the general part and the most specific part of an address?” This is where I need your patience to pay attention to how we (humans) think and how it differs from computers’ thinking. In example 2, we started to read the address from left-to-right, then we took a split second pause at the asterisk, before concluding that Cisco Systems, Inc. is the final  destination. In example 3, we repeat the same process, but this time include Unit #2, the last 1/3 part of the 3rd identifier, before concluding that Unit #2 & Willie Smith is the final destination. In example 3, we also ignored the fact that USA is missing from the beginning of the address. We process this information with ease because we are trained to do so. Also, what helps our brain is the type setting, the font, casing, spaces, dashes, periods, numbers and other queues like the two-letter state abbreviation followed by a 5-digit ZIP code, etc.

Note: The asterisk shown above is not part of the address, it is there only to show exactly where our brain may take a pause to separate the two main parts of an address.

Now, hold on to your seats cowboys and cowgirls, and try to solve the following brain teasers.

Example 4a:

usaca95134sanjose170westtasmandrciscosystemsinc

Example 4b:

ca92128sandiego12001bingcrosbyavenueunit2williesmith

In the examples above, I’ve removed all the spaces, dashes and periods, and changed all alphabets to small letters. You may still be able to use your perceptions to figure out who the address belongs to. This may not have been too difficult because you possess the power of human perception. But, “Who is there to say that the address in example 4a does not belong to ‘sco systems inc’?” Now, lets try to solve another puzzle shown below.

Example 5:

01110101011100110110000101100011011000010011100100110101001100010011001100110100
01110011011000010110111001101010011011110111001101100101001100010011011100110000
01110111011001010111001101110100011101000110000101110011011011010110000101101110
01100100011100100110001101101001011100110110001101101111011100110111100101110011
01110100011001010110110101110011011010010110111001100011

Can you tell me who the above address belongs to? Example 5 displayed the same address as in example 4a, but in a binary format, a language that only computers communicate in. But here is the dilemma. Since computers do not possess, or at least not most computers, the same kind of perceptions as we humans do, how would it know that the address belongs to “cisco systems inc” and not to “sco systems inc” or “isco systems inc” or “drcisco systems inc” or something else which may be very meaningless. As a matter of fact, the computer would not know unless we tell it how to separate the general part from the most specific part of an address. Very shortly, we’ll see how we instruct the computer to do that.

So far, we have established the fact that a home address is divided into two(2) specific parts. First being the general part and the 2nd being the specific part, the person (thing) the address belongs to. We are also faced with a challenge, that is, the computer must know how to decipher the general part of an address from its specific part, so there are no confusions.

QuizTime:

Let’s take a short quiz to solidify our understanding before moving on. All the questions are based on what we’ve discussed so far.

Q 1. A  typical home address has the following parts: (select all that apply)

(a) general & specific  (b) significant and non-significant

Q 2. The general part of the address remains on which side of the main address:  (select all that apply)

(a) left side    (b) right side  (c) in the middle

Q 3. The specific part of the address remains on which side of the main address:  (select all that apply)

(a) left side    (b) right side  (c) in the middle

Q 4. The general part of the address represents:  (select all that apply)

(a) the area where the house is located   (b) the person (thing) the address belongs to

Q 5. The specific part of the address represents:  (select all that apply)

(a) the area where the house is located   (b) the person (thing) the address belongs to

Q 6. When humans read an address, deciphering the general from the specific part is not an issue due to:  (select all that apply)

(a) humans think the same way computers do  (b) addresses are written in plain English (c) humans possess perceptions

Q 7. When computers read an address, deciphering the general from the specific part is not an issue due to:  (select all that apply)

(a) computers think the same way humans do  (b) unless told, computers cannot decipher (c) computers possess perceptions

Q8. When humans read an address, deciphering the general from the specific part is not an issue due to:  (select all that apply)

(a) humans do it subconsciously with ease  (b) adults are aware of Post Office rules (c) humans know it by birth

Answers: 1-a, 2-a, 3-b, 4-a, 5-b, 6-b&c, 7-b, 8-a&b.

 

This leads our discussion to IPv4 addressing. We’ll also look into how IPv4 addressing has overcome some of the challenges discussed above.

 

IPv4 addressing: An IPv4 address is used to uniquely  identify a computer which is connected to the Internet and regardless of where the computer is physically located in the world. It is designated by four(4) distinct addressing identifiers, where each identifier is separated by a period (dot). The following example is a symbolic representation of an IP address.

Example 5:  A symbolic representation of an IPv4 address

Identifier1 . Identifier2 . Identifier3 . Identifier4

In the example above, each identifier represents eight(8) bits of information and they are a combination of zeros(0) and ones(1), also known as binary digits or bits. The following example is a binary representation of an IP address. It is commonly known as the binary format of an IPv4 address.

Example 6: An IPv4 address (in binary format)

11000000 . 10101000 . 00011101 . 00000001

Observing the IPv4 address displayed above, we humans, or most of us,  immediately feel an awkwardness with the zeros(s) and ones(1). Also, it would be a chore to type and enter all these zeros and ones to identify a computer. So to make it easier, the scientists who had developed IPv4 addressing, decided that instead of using zeros and ones we could use the decimal equivalent of these binary numbers represented in each identifier, leaving the conversion from decimal-to-binary up to the computer. The example below shows the format used to represent or describe an IPv4 address. This way of representing an IPv4 address is also known as dotted decimal notation. Dotted, because each identifier is separated by a dot, and decimal, because the binary value in each identifier has been replaced by a corresponding and equivalent decimal value.

Example 7: An  IPv4 address, same as in example 6, (in dotted decimal notation)

192 . 168 . 29 . 1

Don’t we feel more comfortable in looking at the numbers shown in example 7 instead of the numbers shown in example 6? We definitely do, but don’t get too comfortable, because understanding the binary representation of an IPv4 address is fundamental to understanding how IPv4 works. And unfortunately, there is no short cut. For now, let’s not worry too much about it, I’ll try to make it very easy for you to understand and deal with binary numbers when we get to it. Coming soon, there would be a blog entry showing you the techniques to follow and practice for a few days to become an expert in IPv4 addressing and sub-netting. You can be 99.9% certain that you would be asked a question regarding IPv4 addressing during a job interview for a network engineering position.

 

An IPv4 address differs from a typical home address in several important ways as discussed below:

(1) In an IPv4 address, the number of address identifiers are always fixed, and it is always four(4). This is in contrast to a home address where the number of address identifiers may vary significantly, especially, for addresses outside of United States.

(2) IPv4 addresses are strictly managed so that a computer (device), which may be located anywhere in the world and which is also connected to the Internet, can be uniquely identified. This means, IPv4 addresses are not duplicated. Everyone in the world follows the same standards, rules and regulations defined by ICANN. The same cannot be said for home addresses. Although there are some similarities, our home addressing formats are different than those formats in other countries.

(3) IPv4 identifiers use only decimal notations separated by dots. On the other hand, a typical home address has a combination of numbers, letters, spaces, dashes, the pound(#) sign, commas(,), etc.

It is important to note that there is one aspect of IPv4 addressing which is distinctly different than a typical home addressing. That is, in a typical home addressing, each identifier represents a unique attribute, such as a Country, a State, or a City, etc. However, in an IPv4 addressing, identifiers do not represent unique attributes such as Country, State or City. Instead, the general address represents a unique geographical location where there is a computer uniquely identified by the specific address. If you did not understand this clearly, do not worry, because we will go into this in more detail very shortly.

So far, we have discussed some of the characteristics of IPv4 addresses. We still have not resolved the challenge and that is, to instruct the computer on how to separate the general from the specific part of an IPv4 address. A computer (device) will fail to connect to a network since an IPv4 addressing will not be complete without the additional instruction.

 

QuizTime:

Let’s take a short quiz based on the discussions above and solidify our understanding before moving on.

Q1. How many address identifiers does an IPv4 address have ? (select all that apply)

(a) 4  (b) 5  (c) It is not fixed

Q2. What is the common way to write an IPv4 address? (select all that apply)

(a) dashed decimal notation  (b) dotted binary notation  (c) dotted decimal notation

Q3. Like a home address, an IPv4 address identifiers represent Country, State, City, etc. (True/False)

(a) True   (b) False

Q4. Two computers (devices) connected to the Internet can have the same IPv4 address, as long as they are in two different countries.  (True/False)

(a) True   (b) False

Q5. Due to which of the following reasons IPv4 addresses are strictly managed ? (select all that apply)

(a) To stunt Internet growth   (b) To prevent address duplication (c) Available IPv4 addresses were depleting rapidly

Q6. An IPv4 address includes which of the following parts? (select all that apply)

(a) The general part   (b) The specific part (c) both general & specific parts

Q7. Just by looking at an IPv4 address, the general part can be identified easily. (True/False)

(a) True   (b) False

 

Answers: 1-a, 2-c, 3-b, 4-b, 5-b&c, 6-c, 7-b.

 

I hope you did well with the quiz. Now, lets look at IPv4 addressing in more detail.

Now, it’s time to resume the talk about the challenge, which we had discussed earlier, of informing the computer on how to separate the general part from the specific part of an IPv4 address. But before we do that, lets look at a possible solution for the dilemmas we humans may have with the addresses depicted in examples 4a & 4b. For convenience, they are duplicated as shown below in examples 8a & 8b accordingly.

Example 8a:

usaca95134sanjose170westtasmandrciscosystemsinc

Example 8b:

ca92128sandiego12001bingcrosbyavenueunit2williesmith

As discussed earlier, without any preconceived notion, it would be hard to tell  who the address in example 8a belongs to. We also pointed out that the address could possibly belong to not only “cisco systems inc” but also to “isco systems inc” or even “sco systems inc.” One of the possible solutions is to be able to embed a special character, such as an asterisk (*) in between the general part and specific part of the address as shown in examples 9a & 9b. This would make it obvious that the address in example 9a belongs to “cisco systems inc.” Similarly, the address in example 9b would clearly belong to “unit 2 willie smith.”

Example 9a: 1st solution of identifying the general part of a home address

usaca95134sanjose170westtasmandr*ciscosystemsinc

Example 9b: 1st solution of identifying the general part of a home address

ca92128sandiego12001bingcrosbyavenue*unit2williesmith

Another possible solution is to count, from left to right, the total number of characters that belong to the general part of a given address. This number, enclosed in parenthesis, could then be appended at the end of the address to indicate the general part of the address. This possible solution is shown below in examples 10a & 10b.

Example 10a: 2nd solution of identifying the general part of a home address

usaca95134sanjose170westtasmandr ciscosystemsinc(32)

Example 10b: 2nd solution of identifying the general part of a home address

ca92128sandiego12001bingcrosbyavenue unit2williesmith(36)

If we follow the 2nd solution, as in example 10a, we can be certain that the address belongs to “cisco systems inc.” Likewise, example 10b would indicate that the address belongs to ” unit 2 willie smith.” Whew! Thank you for your patience!

You would be right if you say it is foolish to go through all these examples and complicate a typical home address. However, what is not foolish is the concept that in either a home address or an IPv4 address, an Address Separator – to coin a term – is needed to be able to separate two important parts of an address. For home addresses, it is not necessary to explicitly add an Address Separator. Our brains do it automatically with ease, because we are trained to do so since grade school. Remember, writing a letter to someone special who lives in North Pole?

In an IPv4 address, on the other hand, the Address Separator must be stated explicitly. The Address Separator merely indicates the length of the general part of the corresponding IPv4 address. In an IPv4 address, this length is from leftmost-to-right. Anything after the general part is considered to be the specific part of the IPv4 address. This is how the computer knows how to separate the two important parts of an IPv4 address. I hope you have noticed before that I’ve coined the term Address Separator. In IPv4 addressing, the corresponding technical term is known as Subnet Mask or Netmask.

 

IPv4 Subnet Mask: The IPv4 Subnet Mask, also referred to interchangeably as just subnet mask or netmask, is a part of IPv4 addressing. In functionality, it works like an Address Separator discussed earlier. It merely indicates the length, from leftmost-to-right, of the general part of the address and doing so makes the specific part of the address obvious. In IPv4 addressing, the technical term that is used to describe the general part of an address is called the network portion of the address. Similarly, the technical term that is used to describe the specific part of an address is called the host portion of the address. Therefore, in an IPv4 address of a computer, the network portion indicates where the computer is physically located, and the host portion uniquely identifies the computer itself. It is important to note that, each IPv4 address has a corresponding subnet mask. Also, a host means a computer, a cell phone, a PDA or some kind of a network device or an interface that is connected to the network.

To reiterate, an IPv4 address has two(2) distinct components, a network portion and a host portion. The corresponding subnet mask is used to separate these two portions. Without a corresponding subnet mask it would be difficult to identify which computer(device) a given IPv4 address belongs to.

To explain how a subnet mask works, lets recall the IPv4 addresses discussed earlier.

Example 11a: An IPv4 address (in binary format )

11000000 . 10101000 . 00000001 . 00011101

Example 11b: The same IPv4 address as in example 11a (in dotted decimal notation)

192 . 168 . 1 . 29

As discussed earlier, in example 11a, the binary format of an IPv4 address has four (4) parts and each part is represented by zeros(0) and ones(1). These zeros and ones are also known as binary digits or simply bits. Each part of the address is also known as an octet, since each octet represents eight(8) bits. Therefore, as shown in example 11a, a binary format of a typical IPv4 address is represented by four(4) octets, each separated by a dot (period). The leftmost octet is known as the 1st octet which makes the rightmost octet as being the 4th.

In example 11b, the IPv4 address is identical to example 11a, except it is represented in dotted decimal notation. This type of IPv4 representation also has four(4) parts, each part representing the equivalent decimal value of the corresponding octet of the binary format of the address.

Now, if we look at the addresses shown in example 11a & 11b, it would be impossible to know which computer those addresses belong to without knowing the corresponding subnet mask. Without it, one could arbitrarily say that the network portion of the IPv4 address shown above is “192.168.” or “192.168.1.” or even just “192.” This would make “1.29″ or “29″ or even “168.1.29″ accordingly, to be the host portion of address.

The format of a subnet mask is identical to an IPv4 address. It can be represented in either a binary format or a dotted decimal notation. There is a 3rd way of representing a subnet mask known as the CIDR notation, which will be discussed later. A subnet mask contains a series of consecutive bits of  ’1′s ending with a series of consecutive bits of  ’0′s. The number of ’1′s, counting from leftmost-to-right, indicates the length of the network portion of the corresponding IPv4 address. The ending series of ’0′s represent the host portion of the IPv4 address.

Note, in a binary format, a subnet mask almost always starts with a series of consecutive ’1′s and ends with consecutive ’0′s.

Below is the IPv4 address shown in example 11a with a corresponding subnet mask.

Example 12a: An IPv4 address and a corresponding subnet mask (in binary format )

IPv4 Address:  11000000 . 10101000 . 00000001 . 00011101

Subnet Mask:   11111111    . 11111111     . 11111111 . 00000000

Example 12b: The same IPv4 address as in example 12a and the corresponding subnet mask (in dotted decimal notation)

IPv4 Address: 192 . 168 . 1 .  29

Subnet Mask:  255. 255. 255 . 0

In example 12a, the subnet mask shows that there are twenty-four consecutive ’1′s, counting from left-to-right, which represent the length of the network portion of the IPv4 address. The rest of the ’0′s, in this case a total of eight(8) bits, represent the host portion of the address.

In example 12a, the decimal value of 255 in the subnet mask represents eight(8) consecutive ’1′s. Hence, twenty-four consecutive ’1′s followed by eight(8) ’0′s are represented by 255.255.255.0.

The following examples show the same IPv4 addresses discussed above but the subnet masks are shown in CIDR notations.

Example 13a: An IPv4 address (in binary format ) and a corresponding subnet mask shown in CIDR notation.

IPv4 Address:  11000000 . 10101000 . 00000001 . 00011101/24

Example 13b: The same IPv4 address as in example 13a, with a corresponding subnet mask in CIDR notation

IPv4 Address: 192 . 168 . 1 .  29/24

In examples 13a & 13b, ‘/24′ represents the subnet masks of the corresponding IPv4 addresses. ‘/24′ means a series of consecutive ’1′s, counting from leftmost-to-right, representing the length of the network portion of the IPv4 address. The rest of the bits, a total of eight (32-24=8), can be assumed (implied) to be a series of consecutive ’0′s, which would represent the host portion of the address.

It sure looks like the CIDR notation is the way to go in understanding subnet masks. In a way it is, but not quite so. To understand how an IPv4 addressing works, as I’ve mentioned before, there cannot be any jumping over binary numbers.

Please pay attention to the following discussions very carefully. Understanding it, would separate the best IP network engineers from the rest of the pack. Notice that so far I’ve been using the terms “network portion” and the “host portion” of an IPv4 address. However, I did not define or mention the corresponding “network address” and the “host address” which are also something we need to find out.

The following includes the corresponding network addresss and host addresses of the IPv4 addresses shown in examples 12a & 12b.

Example 14a: An IPv4 address, subnet mask, network address and host address (in binary format )

IPv4 Address:  11000000 . 10101000 . 00000001 . 00011101

Subnet Mask:   11111111    . 11111111     . 11111111 . 00000000

Network Address: 11000000.10101000.00000001.00000000

Host Address: 11000000 . 10101000 . 00000001 . 00011101

Example 14b: An IPv4 address, subnet mask, network address and host address (in dotted decimal notation)

IPv4 Address: 192 . 168 . 1 .  29

Subnet Mask:  255. 255. 255 . 0

Network Address: 192 . 168 . 1 . 0

Host Address: 192 . 168 . 1 . 29

In examples 14a & 14b, the network address is the network portion of the address followed by a series of consecutive ‘o’s, which originally represented the host portion of the address. And the host address is the network portion of the address followed by the number represented by the host portion of the address.

“That’s it? So, what was the big deal?,” one may ask. Congratulations! It was easy for you because you have patiently either read this article or other books on IPv4 addressing and it shows that you have come a long way. It was also easier due to the fact that, all along I’ve been using an IPv4 address with a very simple subnet mask. This type of IPv4 address and the corresponding subnet mask is known as the IPv4 Class C addressing. In IPv4 Class C addressing, it is easier to extract the network address from the network portion of the address and host address from the host portion of the address. It so happens that most of the network engineers start out by learning Class C addressing and move on to IPv4 subnets or subnetting, where they need to dissect a bigger network into several smaller networks. Although, Class C IPv4 addressing is the right place to start, more often than not the distinction between the concepts “network portion” and “network address” gets blurred. The same is true between “host portion” of an address and a “host address.” Blurring these concepts will make learning subnetting very difficult or challenging.

For now, just remember and memorize the following. Keeping these in mind will help you learn IPv4 subnetting faster.

The “network portion” of an address is not the same as the “network address.”

The “host portion” of an address is not the same as the “host address.”

The “network portion” of an address may not readily reveal what the “network address” may look like.

The “host portion” of an address may not readily reveal what the “host address” may look like.

The “network portion” of an address may reveal more than one “network address.”

The “host portion” of an address may reveal more than one “host address.”

 

Coming up next – IPv4 Subnets.

 

 

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