[c-nsp] Best Practices for quickly removing routes when BGP peer drops

[Gert Doering]

Hi,

On Wed, Dec 10, 2025 at 09:29:34AM -0500, Shawn L via cisco-nsp wrote:
> We currently have a couple of Internet feeds (full tables) and peering
> sessions to most of the major streaming networks, etc.  When our peering
> sessions go down for whatever reason (lately it's been fiber cuts) it takes
> a couple of minutes for our routers to process all of the routing changes
> and for streaming sessions to start up again.
> 
> I'm wondering what others are doing to try to reduce this time.  In the
> past I was always told that reducing the BGP timers was a bad idea.  Is
> that still the case?  BFD?

There's a number of aspects to it

 - determine that a session is down -> use BFD for that (with reasonable
   timers, don't go for "50ms" because that will just lead to spurious
   flaps on some platforms)

 - propagate that information
   (this can be sped up with TCP PMTUd between routers, using full segments)

 - reconverge with new information
   (this can be sped up by having backup paths available all the time, 
   trading in memory for convergence speed - BGP add-path, BGP 
   fast-external-fallover, ..., depending on platform)

 - reduce the amount of information that needs to be processed
   (not receive full-tables from everyone but only relevant routes for
   that network)

also, "it takes a few minutes for streaming to restart" could be on the
*other* end as well - BFD might help with that, the rest is not under
your control.

gert
-- 
"If was one thing all people took for granted, was conviction that if you 
 feed honest figures into a computer, honest figures come out. Never doubted 
 it myself till I met a computer with a sense of humor."
                             Robert A. Heinlein, The Moon is a Harsh Mistress

Gert Doering - Munich, Germany                             gert at greenie.muc.de
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