[c-nsp] Default Route recalculated every 60 seconds.

[Robert Raszuk]

Hi Bradley,

>From my cisco days I recall that you should not be seeing RIB being updated
over and over with the same route even if BGP keeps sending you implicit
withdraws in the form of new BGP UPDATEs. Of course I will not tell you if
the above is still identical today on all XE, NX & XR :)

However the above only works if your next hop is stable. If you are
recursing your routes over BGP (double recursion) then yes you will see
this churn going on into RIB.

But there is simple fix/test - just set a static route matching next hop of
received BGP prefixes towards your eBGP peer with interface and IP address
and see if it helps.

Cheers,
R.



On Sat, Apr 18, 2020 at 8:10 AM Bradley Ordner <bradinusa at hotmail.com>
wrote:

> I am about to leave an Enterprise environment due to Pre Covid-19
> redundancy and I just need to find the root cause of this issue before I
> leave.
>
> We recently built a Layer 2 Circuit over a Providers SDN Backbone so we
> could get a 2Gb Internet link. We peered with this neighbor and filtered a
> partial table, so we get about 30000 routes. For some reason, every 30
> seconds the default route uptime resets to 00:00 in the routing table. I
> spoke with Carrier, they made a few changes and one was the BGP
> advertisement timer. It is now set to 60 seconds and now the default route
> resets every 60 seconds.
>
> The carrier, keeps blaming my side so I opened a Cisco TAC case and they
> haven't got around to looking at it yet, probably because it really sounds
> like it is the carrier side. I took some packet captures and indeed every
> 60 seconds an update with the default is sent. Our router constantly
> accepts this, recalculates and enters it into the routing table.
>
> I can't seem to figure out if this is some type of bug or not. The router
> has been rebooted and is due for IOS upgrade shortly, but wanted to see if
> anyone has seen this or point me in the right direction.
>
> Thanks
>
> Brad
>
>
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