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S2989G-24TX Operation Manual

Chapter 4 Routing Protocol Related Configuration

4-14

back to Switch 1. When Switch 1 receives these datagrams, it will forward them back to

Switch 2. Thus, loopback exists. To solve this problem, Black Hole Routing can be

introduced on Switch 2.

ip route 192.168.0.0/21 null0 50

Then Switch 2 will drop the datagrams from interface VLAN1 that match the Black

Hole Routing rule. And loopback routing is prevented.

Configuration steps are listed as below:

Switch#config

Switch(config)#ip route 192.168.0.0/21 null0 50

4.3.4

Black Hole Routing Troubleshooting

When configuring the Black Hole Routing function, the configuration may not work

due to some reasons such as incorrect network address mask, and incorrect

management distance. Attention should be paid to the following items:

 IPv6 should be enabled before IPv6 Black Hole Routing can work.

 It is suggested that the length of the network address mask should be longer than that

of normal routing configuration, in order to prevent the Black Hole Routing from

intervening other routing configuration.

 When the network address mask of Black Hole Routing configuration is the same with

some other configuration, it is suggested that the distance of Black Hole Routing is

set lower.

For problems that cannot be fixed through above methods, please issue the

command show ip route distance and show ip route fib, and show l3. And copy and paste

the output of the commands, and send to the technical service center of our company.

4.4

ECMP

4.4.1

Introduction to ECMP

ECMP (Equal-cost Multi-path Routing) works in the network environment where there

are many different links to arrive at the same destination address. If using the traditional

routing technique, only a link can be used to send the data packets to the destination

address, other links at the backup state or the invalidation state, and it needs some times

to process the mutual switchover under the static routing environment. However, ECMP

protocol can use multi-links under such network environment, it not only implements the