将RIP协议配置成单播

see:http://fengnet.com/book/cisco.ios.cookbook.2nd/I_0596527225_CHP_6_SECT_9.html

RIP v1可以接受V1和V2的RIP路由信息。

但是V2是多播发送的。

而V1是广播的方式发送的。

那么启用了V1的路由器之所以能收听广播方式的V2信息，是因为接口上加入了224.0.0.9多播组。

可以使用show int xx查看

2511#sh ip int s0
Serial0 is administratively down, line protocol is down
Internet address is 10.1.1.1/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500 bytes
Helper address is not set
Directed broadcast forwarding is disabled
Multicast reserved groups joined: 224.0.0.9

Recipe 6.8. Unicast Updates for RIP

Problem

You want to exchange routing information with one device on a network, but not with any others.

Solution

You can configure RIP to send its updates to a neighboring router using unicast instead of broadcast or multicast packets. This is useful in two situations. First, on Nonbroadcast Multiple Access (NBMA) networks, you can't use the standard broadcast or multicast methods for distributing information because the media doesn't support it. Second, sometimes you need to exchange routing information with one or more specific devices on a segment, but you don't trust the rest to give you reliable information. This feature is rarely used, but it can be extremely valuable in these types of situations:

Router1#configure terminal  Enter configuration commands, one per line.  End with CNTL/Z. Router1(config)#router rip Router1(config-router)#passive-interface FastEthernet0/1 Router1(config-router)#neighbor 172.22.1.4 Router1(config-router)#end Router1#

Discussion

This recipe uses the passive-interface command discussed in Recipes 6.6 and 6.7 to prevent the router from sending routing information to the interface in general. Note that it does not prevent the router from receiving routing information from other devices on the segment. We will discuss how to solve that problem in a moment.

A debug trace helps to show how the unicast update option works:

Router1#debug ip rip RIP protocol debugging is on Router1# Aug 11 02:41:13.632: RIP: sending v1 update to 255.255.255.255 via FastEthernet0/0.1 (172.25.1.5) Aug 11 02:41:13.636: RIP: sending v1 update to 255.255.255.255 via Serial0/0.2 (172.25.2.1) Aug 11 02:41:13.644: RIP: sending v1 update to 172.22.1.4 via FastEthernet0/1 (172.22.1.3)

Here you can see that this router sends its updates to the general broadcast address, 255.255.255.255, for all of the other interfaces, but for FastEthernet0/1, the update goes directly to 172.22.1.4. We note in passing that this is RIP Version 1. If it were Version 2, it would send updates using the multicast address 224.0.0.9, instead of the general segment broadcast address by default. However, the unicast option for Version 2 would work exactly the same as shown here.

The output of the show ip protocols command includes information about any unicast neighbors:

Router1#show ip protocols  Routing Protocol is "rip"   Sending updates every 30 seconds, next due in 21 seconds   Invalid after 180 seconds, hold down 180, flushed after 240   Outgoing update filter list for all interfaces is not set   Incoming update filter list for all interfaces is not set   Redistributing: rip   Neighbor(s):     172.22.1.4   Default version control: send version 1, receive any version     Interface             Send  Recv  Triggered RIP  Key-chain     FastEthernet0/0.1     1     1 2                                       Serial0/0.2           1     1 2                                     Automatic network summarization is in effect   Maximum path: 4   Routing for Networks:     172.22.0.0     172.25.0.0   Passive Interface(s):     FastEthernet0/1   Routing Information Sources:     Gateway         Distance      Last Update     172.25.1.7           120      00:00:26     172.25.2.2           120      00:00:14     172.22.1.4           120      00:00:07   Distance: (default is 120)  Router1#

As we noted in Recipe 6.6, just making an interface passive does not prevent it from listening for updates. But one of the most common reasons for using unicast neighbors with RIP is to ensure that the router accepts routing information only from specific devices on a segment. So we need to configure the router to reject incoming RIP information from all other devices. This is most easily accomplished by using an access list, as follows:

Router1#configure terminal  Enter configuration commands, one per line.  End with CNTL/Z. Router1(config)#access-list 101 permit udp host 172.22.1.4 any eq rip Router1(config)#access-list 101 deny udp any any eq rip  Router1(config)#access-list 101 permit ip any any  Router1(config)#interface FastEthernet0/1 Router1(config-if)#ip access-group 101 in Router1(config-if)#end Router1#