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 [email protected]
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