BGP and Building redundancy...

[smitesh kharecha]

Hello Community,

I have a scenario which, I'm not able to figure out the solutions.

Please see the problem statement below:

I have 3 link from 2 different ISP and running BGP. All 3 neighbour gives me default route only.

Out of 3 links, 2 are STM and 1 is DS3.

Now to build redundancy in case of failover, I used as-path prepending. However, my ISP says that it won't work because of the multi-homing and other stuff. In short they will not do anything even if longer as-path is coming though their peer.

As a solution I thought to go for conditional advertisement.

But my bad luck is that since I have 2 link from same ISP having same as-path and only default route, I'm not able to think out how to differentiate whether STM link has gone done or DS3 link has gone done and apply that in AVERTISE-MAP NON-EXIST-MAP solution.

Please guide.

Thanks,

Smitesh

[milan.kulik]

Hi,

what about asking the ISPs to advertise one additional subnet together with the default route from each provider router?

You could use those prefixes for your NON-EXIST-MAPs.

If impossible, what about advertising two more specific subnets covering your IP range over your preferred line?

And one less specific over the non-preferred line?

Example: one /23 over the non-preferred line and two /24s over the preferred line?

The provider would have to use the preferred line as long as it's up!

HTH,

Milan

[smitesh kharecha]

Hi Milan,

Already thought about both of your suggestion.

Today only I have asked both ISP to provide me one  prefix apart from default-route. Even if any one of them give me a single prefix, i would be more than happy...

Also, yesterday have  thought about aggregate route advertisement, however i'm just seeing some minor glitches (not so major that it is unviable option); so current kept that as secondary option.

Just post the query, so explore any other option if available.

Still thanks for your suggestion...

Regards,

Smitesh