Null interface

[minumathur]

Hi.

Can anybody tell me why we put null interface route in router.

S 213.31.195.206 is directly connected, Null0

I know it mean discard, but i wanted to know , if it is discard then why we publies this route in the network.

i hope you understand my point

[leonvd79]

Hello mnumathur,

When you advertise a summary-route, the routing protocol installs a static route to Null0 in the local routing table.

This is to prevent blackholing traffic. So when you advertise a summary for the subnet 192.168.1.0/24 i.e. 192.168.0.0/23 the router prevents from blackholing traffic to 192.168.0.0/24 since it does not have an entry in it's local routing table.

Another reason could be policy-based routing. If you want to block certain traffic for host 213.31.195.206, you can set the interface to Null0. The Null0 is treated as a thrashcan.

HTH

--Leon

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