[nsp] BGP backup transit link

[Nick Kraal]

We have 2 transit links and running BGP and receiving about 110,000 prefixes
from both providers. We are trying to use only one provider as our primary
transit link and the other only when the first link is kaput.

This is as:
1. the primary link is actually 5x larger than the secondary (which was the
old primary link before an upgrade). so we do see the secondary link
bordering congestion. we have tried as_prepending at our upstream (up to 4x
prepend -is this enough?) and inbound as_path filters restricting installing
routes further than 3 as_hops away. we see that inbound traffic is the main
culprit here -duh.
2. then this will then lead avoid a very obvious asymmetrical return route
problem/issue -which in this part of the world can lead from jumps from 20ms
to a sudden 300ms as traffic wants to return via the south pole.

Any ideas or is tweaking with as_prepends the only way we have. been looking
at BGP link bandwidth but i think this is the secret recipe between two
autonomous systems only.

Thanks in advance.

-nick/