[j-nsp] Ideas on failure detection for a peering exchange shared between two routers.

[Gert Doering]

Hi,

On Tue, Mar 02, 2021 at 09:06:22PM +0000, Jonathan Call wrote:
> Two MX80 routers participate in the same peering exchange. (A
> Primary and Secondary) Each has an interface configured in the same
> IP network within that IX. During a random bad event (maintenance
> error or fiber failure within the IX) the primary router loses
> access to everything on the IX network but it's link stays up. The
> secondary router is not impacted by the event. When this happens
> BGP on the primary router detects the loss of connectivity to its
> peers and updates all of its routes based on the BGP table from the
> secondary router. But because the peering link on the primary router
> is still UP/UP, the forwarding table says the next-hop is available
> via the bad interface. Here is an example of a Google route being
> learned on the IX:

next-hop-self

(aka "have the other IXP router set its loopback IP as next-hop when
sending the prefix via iBGP")

Note: some people recommend always using next-hop-self, but there are
situations when you don't want it, and I do not want to start that particular
discussion now :-) - it improves *this* situation, and it also saves you
from having to carry the IXP LAN in your internal routing.

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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