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

[Gert Doering]

Hi,

On Sat, Apr 18, 2020 at 06:06:49AM +0000, Bradley Ordner wrote:
> 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.

If you can see the default route being announced by the carrier, it's
(very obviously so) not your router who is causing this  (if you see
an outgoing route refresh request, and then an update of *everything*,
things would be different).  There is no mechanism in BGP to tell the
other end "of all routes you sent me, please refresh just the default 
route".

Do not let carriers bullshit you into believing "it's all your fault".


Now for "why is it sending an update" - it might be attributes changing
(due to something oscillating in the carrier network), or just a dumb
implementation on their side.  Try looking at the attributes for two
consecutive updates (metric, communities, ...) and see if something
changes.

(OTOH, except for academic interest, I would not worry too much about
it either - one route recalculation every 60 seconds which leads to the
same result "out to that carrier" will not negatively affect your 
network)

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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