R12001 route updates the route announcement of the same router interface with different subnet masks (two interfaces belong to the same primary route)

The router interface receives a route update. Check whether the route entry belongs to the same master-class network and the same master-class network.

Tutorial topology:

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The subnet mask of the port is used as the subnet mask of the learned route entry. If the learned route entry and the route of the Local interface do not belong to the same primary network. Then, determine the primary route that the learned route belongs to. A <B c belongs to Class A, and use the subnet mask of Class A as the subnet mask of the route.

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Analysis of experimental phenomena:

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View the R4 route table:

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Q: Why didn't I learn the networks 172.16.2.0/24 and 172.16.1.0/24 on R4?

Cause: Observe the two interface addresses of R3.

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F0/0 is/24 network F0/1 is/25 Network

R12001 does not connect the left and learned route entries (these route entries belong to the same primary network as the IP address of F0/1. In this example, all are B-type networks,

The reason is: if such a route entry is advertised from F0/1, when R4 receives the route update message, view these B-type networks and find that my F0/1 belongs to the same main class 172.16.0.0. So I used the/25 of my own interface as the route entry advertised by R3 (172.16.1.0 172.16.2.0) therefore, the Routes learned by R4 are 172.16.2.0/25 and 172.16.1.0/25, but the network does not exist. That is to say, the route entries learned by R4 are incorrect, therefore, in order to avoid such errors, r3f0/0/24 networks are not directly advertised from F0/1/25 of R3, however, the premise is that F0/0 and F0/1 of R3 must be in the same primary network, 172.16.0.0 in this example. 650) This. width = 650; "src ="/e/u261/themes/default/images/spacer.gif "alt =" r00001.pkt "class =" editor-attachment "style =" Background: URL ("/e/u261/lang/ZH-CN/images/localimage.png") No-repeat center; Border: 1px solid # DDD; "/>

Similarly, R3 will not advertise the network route information of/25 on the Right To R2.

Then, R4 learns the class C/24 network on R2. this is because the network where these 192.168.1.0 192.168.10.0 networks and r3d interfaces are located is not the same primary network, so R3 will advertise these routing messages to R4,

Finally, R4 learned the l0 172.16.10.0/25 on R3.

This is because the F0/1 of R3 is the/25 interface. Therefore, the routing information of the same subnet mask that belongs to the same class B network of the same primary network will be advertised to R4, when you view a route query message on R4, it is found that the local interface and the Local interface belong to the same primary network. Then, the/25 of the current interface will be used as the subnet mask of the 172.16.10.0 network, 172.16.10.0 is originally a/25 network, so no aforementioned error occurs.

This article is from the "8144301" blog, please be sure to keep this source http://8154301.blog.51cto.com/8144301/1551357

R12001 route updates the route announcement of the same router interface with different subnet masks (two interfaces belong to the same primary route)