Case Study A Basic RIPv2 Configuration

By default, a RIP process configured on a Cisco router sends only RIPvl messages but listens to both RIPvl and RIPv2. This default is changed with the version command, as in the following example:

router rip version 2

network 172.25.0.0 network 192.168.50.0

In this mode, the router sends and receives only RIPv2 messages. Likewise, the router can be configured to send and receive only RIPvl messages:

router rip version 1

network 172.25.0.0 network 192.168.50.0

The default behavior can be restored by entering the c ommand no version in config-router mode. Case Study: Compatibility with RIPvl

The interface-level "compatibility switches" recommended by RFC 1723 are implemented in Cisco IOS with the commands ip rip send version and ip rip receive version.

The internetwork in Figure 7.10 contains routers speaking both RIPv1 and RIPv2. Additionally, Pojoaque is a Linux host running routed, which understands only RIPv1. The configuration of Taos is:

Figure 7.10. Taos is running RIPv2 but must also speak version 1 to some devices.

Figure 7.10. Taos is running RIPv2 but must also speak version 1 to some devices.

interface Ethernet0 ip address 192.168.50.129 255.255.255.192 ip rip send version 1 ip rip receive version 1

interface Ethernet1 ip address 172.25.150.193 255.255.255.240 ip rip send version 1 2

interface Ethernet0 ip address 192.168.50.129 255.255.255.192 ip rip send version 1 ip rip receive version 1

interface Ethernet1 ip address 172.25.150.193 255.255.255.240 ip rip send version 1 2

interface Ethernet2 ip address 172.25.150.225 255.255.255.240

router rip version 2

network 172.25.0.0 network 192.168.50.0

Because router Laguna is a RIPv1 speaker, E0 of Taos is configured to send and receive RIPv1 updates. E1 is configured to send both version 1 and 2 updates, to accommodate the RIPv1 at Pojoaque and the RIPv2 at Sandia. E2 has no special configuration; it sends and receives version 2 by default.

In Figure 7.11, debug ip rip is used to observe the messages sent and received by Taos. There are several points of interest here. First, notice the difference between the traps for RIPv1 and RIPv2 messages. The address mask and the Next Hop and Route Tag fields (both set to all zeros, in this case) of the RIPv2 updates can be observed. Second, it can be observed that interface E1 is broadcasting RIPv1 updates and multicasting RIPv2 updates. Third, because Taos has not been configured to receive RIPv1, the updates from Pojoaque (172.25.150.206) are being ignored. (Pojoaque has been misconfigured and is broadcasting its routing table.) [9]

[9] Intentionally misconfigured for this example actually, with the routed -s option.

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