The routes are classless and classless.

Classless and classless Routing

1. When a route is advertised, It is not advertised with the primary subnet mask. When a route is advertised, It is not automatically summarized. Instead, it is advertised with its own subnet mask. Classless routing.

2. After the advertised route is converted into a primary network and the interface advertised for the route is converted into a primary network, this router creates a class border.

3. When the class boundary is generated, if the routing protocol does not support a longer subnet mask, the advertised routes will be summarized as the primary network and advertised.

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Classless Routing

When 10.1.1.0/24 is advertised from f0/1 of R1, It is summarized as 10.0.0.0/8,

This route is a class route.

If 10.1.1.0/24 is still advertised as 10.1.1.0/24

Classless Routing

Class Boundary

When 10.1.1.0/24 is advertised from interface F0/1 of router R1

Because 10.1.1.0 is A Class A address and the default subnet mask is 8 bits, 10.1.1.0/24

You can summarize the network type 10.0.0.0/8.

Similarly, the subnet where F0/0 is located is 12.0.0.0/8. Obviously, these two subnets are not the same subnet.

The class boundary generated on router R1.

Problems caused by classless Routing

When R1 notifies R2 of 10.1.1.0/24 in the form of a class, that is, 10.0.0.0/8

10.0.0.0/8, if R3 also sets 10.1.2.0/24 as a class, that is, 10.0.0.0/8

If it is advertised to R2, there will eventually be a route for 10.0.0.0/8 instead

Detailed routes of CIDR blocks 1.0 and 2.0. When there is 1.0 or 2.0 of traffic from R2 in the network,

It is very likely that the target cannot be found and packet loss occurs.

Solutions to problems arising from classless routing protocols

Use a protocol that supports classless routing, so that you can learn Detailed Routing. Or disable the automatic summary (config-router) # no auto-summary) to prevent classless routes from being aggregated into classes.

Support for classless routing protocols

RIP Version 2 (r00002)

China site

OSPF

IS-IS

BGPv4

Vro protocols

R1_1 IGRP

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