Null Route

[pavan.kumar]

Dear All,

Any one of you please explain Why we have to specify Null route ?

what is the importance of it?

If i allow a network in BGP , I do specify a null route for that perticular network.

Sometimes if i face any browsinig problem pertaining to that block , i will remove that null statement then it starts working .

Please respond

Regds

VKSP

[Georg Pauwen]

Hello,

the null route in BGP is typically used when you want to advertise a classfull network on a BGP router that has auto-summary enabled. Without a component route from the classfull network in the routing table, the network will not be advertised. The component route can either be coming from an IGP, or from a static route. Here is an example:

router bgp 1

network 172.17.0.0

auto-summary

If you do not add a static route, e.g.:

ip route 172.17.1.0 255.255.255.0 null 0

the classfull network 172.17.0.0/16 will not be added to the BGP table and advertised to neighbors.

When you have your null routes, make sure that at least a classfull route to your destination network is advertised and present in the BGP table. Can you post the output of ´show ip route´ when the problem occurs, together with the IP address of the website you are unable to reach ?

Regards,

Georg

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