Re: Question about normal ops - BGP Flaps nightly

[Mark Tinka <mark.tinka () seacom mu>]

On 21/Nov/19 19:59, Saku Ytti wrote:

> As there are best path algorithms which consider route age, BGP reset
> impact may be indefinite.

A practical problem we've seen with Cisco's BGP-SD implementation is
that 0/0 and ::/0, when learned via BGP, are installed last.

So consider a situation where BGP flaps a session on IOS or IOS XE
running BGP-SD. Even though the full BGP table is being held in RIB only
(which can take about 10 minutes to fully download with the CPU
performance of, say, an ME3600X or an ASR920), a default route coming in
over an iBGP session will get loaded only after all more specific routes
have been installed and a best path algorithm ran against them.

If you write only default into FIB on these platforms, you're basically
blackholing traffic for as long as it takes for BGP to reconverge.

So yes, while the fundamental design for this by Cisco is inherently
flawed, unnecessary session resets are not ideal.

Mark.