What's the point of prepend communities?

Thu Oct 26 18:55:58 UTC 2017

Hi,

In context of traffic engineering it may be that Network A (customer of
Network B) observes that performance is suboptimal between Network B and
Network C.

If Network B offers some kind of “Prepend to Network C” BGP community,
network A will be able to utilize all of network B except the pieces that
perform less well. (This is ofcourse assuming that Network C picks some
alternative path because of the prepends)

I think prepend communities are useful to empower customers to debug and
perhaps even resolve issues without waiting for action from their supplier.

Prepends are also slightly more graceful than “don’t export”, since if
there are no alternative paths there still is _a_ path - and often any path
is better than no path.

Kind regards,

Job