CCNA Exploration: Routing Protocols and Concepts Chapter 7 Case Study
Objectives:
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Consolidate RIPv2 knowledge and understanding.
Describe the use and necessity of the no auto-summary command.
Intro:
As you already expected, Tred Inc. needs a new routing protocol to be run into their networks.
Current Topology:
© 2009 Cisco Learning Institute
CCNA Exploration: Routing Protocols and Concepts Chapter 7 Case Study
Scenario:
As you know, Tred has 3 physically separate offices. From a network perspective, they are identified as
Branch 1 (B1), Branch 2 (B2) and Main (M). Main was the first office created and it has a connection to
Internet. As shown on the topology above, B1 and B2 reach Internet via M.
Tred hired 2 512Kb WAN links from the telephony company to interconnect all 3 sites. The first WAN link
connects B1 to B2 and the second, B2 to M. A third 2Mb link connects M to the internet.
In order to provide a second redundant path to M, a third 1Mb/s link was hired. The new link connects B1
directly to M.
M is responsible for providing Internet connectivity to all Tred Inc. sites and for routing packets to/from
Network 3 (192.168.50.64/27).
Tred’s network is taking advantage of an optimized VLSM addressing scheme.
On your last visit you implemented VLSM on Tred’s network but since IGRP is currently running on it and
it does not support variable length subnet mask (VLSM), a new routing protocol must be configured.
Because RIP version 2 (or simply RIPv2) carries both the network address and the subnet mask, it does
not need to summarize these networks based on class boundaries (class A, B, C, etc). Routers running
RIPv2 no longer need to use the inbound interface's mask to determine the subnet mask in the route
advertisement. The network and the mask are explicitly included in each and every routing update. In
networks that use a VLSM addressing scheme, a classless routing protocol is essential to propagate all of
the networks along with their correct subnet masks.
You choose RIPv2 as the new Tred’s routing protocol.
Question 1:
What are the main RIPv2 advantages if compared to RIPv1?
Answer: Next-hop addresses included in the routing updates; use of multicast addresses in sending
updates; authentication option available
Step 1 – Configuring RIPv2
You start configuring RIPv2 on Tred’s routers while keeping IGRP running for now. The reason why IGRP
is kept running is productivity: Tred’s network can’t be stopped and this strategy will ensure a smooth
migration from IGRP to RIPv2.
Starting at router M, you issue a show ip protocols command to confirm IGRP configuration. Everything
looks as expected.
You configure RIPv2 based on the topology shown above and document the commands as below:
© 2009 Cisco Learning Institute
CCNA Exploration: Routing Protocols and Concepts Chapter 7 Case Study
M(config)# router
M(config-router)#
M(config-router)#
M(config-router)#
rip
version 2
network 192.168.50.0
no auto-summary
Still on M, you issue a show ip protocols command to confirm RIPv2 configuration. Everything looks good.
Question 4:
Why is the no auto-summary command necessary?
Answer: The RIPv2’s default behavior is to summarize all routes based on their classful boundaries.
Since VLSM is being used on the topology, the automatic summarization must be disabled to avoid wrong
RIPv2 route advertisements.
From M, you connect to B2 via telnet and configure RIPv2 too. Once more, you keep IGRP configuration
on B2. The commands are documented below:
B2(config)# router
B2(config-router)#
B2(config-router)#
B2(config-router)#
rip
version 2
network 192.168.50.0
no auto-summary
Question 5:
Even though the no auto-summary command exists, only one network statement, with no mask
information was configured. Is that correct? Why?
Answer: Yes. RIPv2 is just an improvement of RIPv1. The network command is a classful based
command and tells RIPv2 to add any network/interface within the 192.168.50.0/24 network range to the
RIPv2 advertisements. If auto-summary is disabled, RIPv2 will add the subnet mask configured on the
router’s interface to its advertisements, instead of dealing with classful based subnet masks.
Question 6:
What is the administrative distance of RIPv2 routes?
Answer: 120, the same administrative distance of RIPv1 routes.
Because of your strategy of keeping IGRP running, the network is still running. From B2 you issue a
telnet to B1. You configure B1’s RIPv2 process and check its routing table. No RIPv2 routes were placed
at B1’s routing table.
B1(config)# router
B1(config-router)#
B1(config-router)#
B1(config-router)#
rip
version 2
network 192.168.50.0
no auto-summary
© 2009 Cisco Learning Institute
CCNA Exploration: Routing Protocols and Concepts Chapter 7 Case Study
Question 7:
Why no RIPv2 were placed into the routing table? Is this the expected behavior?
Answer: Yes, it is expected. Since IGRP routes have smaller administrative distance than RIPv2 routes,
IGRP routes are kept into the routing tables.
You issue a show ip protocols command into B1, B2 and M to confirm RIPv2 configuration. Everything
looks good.
Since RIPv2 is working, it is time to remove IGRP from the routers using the command no router IGRP
100. You are already connected to B1 and start by it. Then you remove IGRP from B2 and finally from M.
A look at the routers configuration, routing tables and routing protocols confirms IGRP was successfully
removed and RIPv2 runs smoothly. A few more successful pings show the connectivity is still
guaranteed.
A quick look at the routers routing table shows the RIPv2 magic in action: M’s, B1’s and B2’s routing
tables have routes with different subnet masks in use.
Question 2:
Is RIPv2 really the ultimate routing protocol?
Answer: Even though RIPv2 is an improvement if compared to RIPv1 (multicast messages,
authentication support and VLSM support), it still has big flaws. The way it calculates metrics and its
convergence time are good examples of RIPv2.
© 2009 Cisco Learning Institute