Assessment Wrap-up with RIP Commands (Part 3 of 3)

Can You Easily Identify RIP Config Commands?

Can you recall all the config commands related to RIP Version 2 (RIP-2)? And their important parameters? And, can you list the conditions under which these commands impact whether or not a router will learn routes, and if learned, what routes? As promised, today we'll look at RIP Version 2 (RIP-2) config on Cisco routers, to wrap up this 3-part series about self-assessment.

(If you didn't read the previous two posts, take a quick peek. The short version of the lead in to this post is: What are all the CCNA-level RIP commands, key parameters, and how do they work?)

Self-assessing: Remembering the Commands vs Applying the Commands

When asking yourself if you are ready for the exam, for some major topic like RIP, you must remember the commands, and the key parameters. But to do well on the exam, you need to be able to apply the commands. What happens when you configure RIP-2 correctly? What happens when you make different kinds of mistakes?

To self-assess your readiness to apply the commands, when you review your study material, ask yourself questions like " I wonder what would happen if you changed/omitted/added this command?" If you have lab gear, try to lab out some scenarios, and make those same changes, to check your work. Or, pose the same scenario with questions to the Cisco Learning Network (learningnetwork.cisco.com), which is a great place to discuss such examples.

Next, on to some discussions about self-assessing skills for RIP-2 on the CCNA exam, including some sample questions to ask yourself.

Required Commands for RIP-2

RIP-2 has three commonly remembered commands, because most any CCNA-level config includes these commands:

router rip

 version 2

 network net-id

The first command, router rip, must exist to configure RIP-2. It moves the user into RIP config mode, where you can enter the other two commands.

The second command, version 2, tells the router to use RIP-2 exclusively. Up until Cisco revised CCNA most recently in July 2007, CCNA either included only RIP Version 1 (the very early days), and later both RIP-1 and RIP-2. The current CCNA focuses on RIP-2, so the configs typically just include "version 2" to make each router use RIP-2, and RIP-1 not at all.

Finally, the network command enables RIP on interfaces whose IP addresses are in the listed classful network. EG, network 10.0.0.0 tells the router to look at all its interfaces, and enable RIP on any whose address is in class A network 10.0.0.0. (In an odd quirk of IOS, if you were to type something like network 10.1.1.0, thinking that means subnet 10.1.1.0/24, IOS changes the command to list the network ID of the classful network. The show run command would list "network 10.0.0.0" in this case.)

Optional RIP-2 Commands

For CCNA, a couple of other commands have some impact on whether RIP-2 routers send and learn routes, and which routes they learn. This isn't a list of all commands, just those that I think matter to CCNA:

[no] auto-summary

passive-interface [type number]

ip address addr mask secondary

Of these three commands, the first two are configured in RIP config mode, while the third is configured in interface mode. These commands are listed in order from most important to least important. On a 10-point scale, 10 as most important, the auto-summary command is a 10, the passive-interface command a 6, and the ip address secondary command a 1.

Application and Self-Assessment

So, as a self-assessment exercise, let me toss out a few questions. If you want to post to ask about them, please jump in. If you for sure know about auto-summary and passive-interface, that's probably good enough for self-assessment for CCNA, in my opinion at least. The questions will use the same figure as the last two posts as a backdrop. Note that all the questions assume RIP-2 has been configured on all routers, and on all interfaces.

Auto-summary

Auto-summary is essentially a toggle on a router, either set to auto-summary or no auto-summary. To self-assess, ask yourself:

  1. On which of the three routers will the configuration of the auto-summary command have an impact?
  2. What is that impact, specifically in the case shown in the figure?
  3. On which routers does the configuration of no auto-summary have an impact? And what is that impact?

If you can apply these questions to the figure, and have a good idea of what will happen in that network for each question, then I'd say that's a positive self-assessment of where you sit with auto-summary. If you're a little unsure, it's worth investigating, trying it in lab, reading over examples, or in this particular case, post a comment or question here.

Passive-interface

Examine router R2, and consider the routes learned by each router, assuming that "no auto-summary" is also configured on all three routers. Then, consider three different cases in which R2 has a single passive-interface command configured:

1.     R2 configured with passive-interface f0/0

2.     R2 configured with passive-interface S0/0/0

3.     R2 configured with passive-interface S0/0/1

As an example for self-assessment, ask yourself: what changes occur to the routing table on R1 in each of these 3 cases?

Secondary IP address

The ip address secondary command is a relatively minor command in the context of CCNA. However, it can be used to add another IP address to an interface. For example, if the primary subnet off R1's G0/0 interface, 10.1.1.0/24, ran out of IP addresses, R1 could be configured with an ip address 10.2.2.1 255.255.255.0 secondary command. Then hosts on that LAN could be given IP addresses in this new subnet, and use 10.2.2.1 as their default gateway. R1 then has two subnets off its single G0/0 interface.

So, imagine R1 indeed added a secondary subnet with these commands:

interface g0/0

 ip address 10.2.2.1 255.255.255.0 secondary

For self assessment:

1.     What other config must be added so that all other hosts can communicate with these new hosts, with IP addresses in the 10.2.2.0/24 subnet?

2.     What would be required if that new secondary IP address/mask was instead 192.168.2.1/24?

3.     What would be required if that new secondary IP address/mask was instead 192.168.1.129/25? (For this question, assume that R3's LAN interface attaches to a different subnet, also using a mask of 255.255.255.128.)

Admittedly, question 3 in this section is challenging for CCNA, and driven by a minor command. However, that complexity gets to the heart of some of the key concepts related to RIP-2. But for self-assessment, while it may be unlikely to come across the ip address secondary command, you should have a good understanding of how to advertise those routes with RIP.

Feel free to ask about any of these that you wonder about, or offer your own answers to any of these questions to help out the other folks reading this series. There are no wrong answers here - just toss out your ideas, and I'll be happy to kick them around with you.

Related Posts:

CCENT and CCNA Self-Assessment Wonderings (Plus an Exercise)

Self-Assessing CCNA Readiness (RIP-2, Part 2)

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