BGP Help

Unanswered Question
Jun 19th, 2007

I have a scope of /24 and another of /25. I want to run BGP and for some reason it it not functioning. If I unplug one cable the other dosn't kick in. I blue all the old config out. So, if someone cal walk me through this, it will be great.

Thank you

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Overall Rating: 3 (1 ratings)
aravindhs Tue, 06/19/2007 - 06:27

More info required. Can you post your config and elaborate a bit on what you are trying to achieve exactly ?

ayussuf Tue, 06/19/2007 - 06:35

My config is as follows....I am trying to have redundancy. Ethernet hand-off is on ether 3/0 and T1 is on ser 3/1...

interface Ethernet3/0

ip address


interface Serial3/1

description TO UUNET




interface Serial3/1.1 point-to-point




router bgp 27241

no synchronization

no bgp log-neighbor-changes

network mask

ip nat translation tcp-timeout 3600

ip classless

ip route Serial3/1.1

no ip http server

ip pim bidir-enable



aravindhs Tue, 06/19/2007 - 06:40

So, you have two internet exits, one on Eth3/0 and the other on Ser3/1.1. And you want all the traffic destined towards the internet to flow out through Ser3/1.1. If this Serial link fails, you want your traffic towards the internet to flow out through Eth3/0. Is this what your requirement is ?

ascinetworks Tue, 06/19/2007 - 10:22

You cannot be able to advertise a /25 subnet with BGP. No subnets smaller than /24 are permitted.

Also, please provide more architecture information. Are you trying to connect a single router to multiple ISPs?

patrickvanham Tue, 06/19/2007 - 18:48

where are your neigbor statements? Can you provide an idea how your architecture is set up?

It may be easier to have specific a /30 each for the physical link to each ISP and use that to peer with and then advertise the /24 en /25 to both as you seem to have your own AS.

mohammedmahmoud Wed, 06/20/2007 - 00:36


Frist of all, is the absence of BGP neighbor command a typo or not ? If not, BGP is not like other routing protocols, it needs manual configuration of its neighbors (uses unicast TCP sessions over port 179 rather than broadcast or multicast).

As for the second part, the policy of the internet is to drop any classes less than /24, you would be able to advertise it to your provider, but the internet will drop this kind of routes.


Mohammed Mahmoud.


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