[c-nsp] Peering + transit backup between 2 ISPs

[james edwards]

> 2. serve as backup transit one for the other: each ISP would have one
> upstream only, and when the unique upstream goes down, it would then (and
> only then) use the other ISP for transit
>
> Is this feasible? I can't really figure out how this could be achieved
> without having both ISPs offering transit to each other all of the time.

Take a look at "BGP Conditional Advertisement":

http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a00800b5d54.html

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a0080094309.shtml