Why is eBGP receiving updates with
Is this normal or just an OS bug?
Cisco IOS Software, 3700 Software (C3745-ADVIPSERVICESK9-M), Version 12.4(25d),
RELEASE SOFTWARE (fc1)
Routes show up as
Origin IGP for one of these reasons:
network x.x.x.x command under the bgp process, the routes naturally show up as
Origin IGP. This makes sense, because bgp typically finds those routes in the IGP (of course they could be statics as well)
Origin incomplete to
Origin IGP using a route-map
So the question might be asked, "who cares what the BGP Origin code is?"; the Origin code matters in certain cases. If you look at the BGP Path Selection algorithm, origin code is considered at step 6 of the 10-step algorithm;
Origin IGP is considered the lowest if the weight, local-preference, and AS-path length are all the same.
BGP admins typically set
Origin IGP on all ingress prefixes to avoid routes with
Origin incomplete. If you have routes with
Origin incomplete, it potentially short-cuts these decision points: lowest MED, EBGP vs IBGP, lowest IGP cost to the BGP next-hop, and lowest BGP router-id.
So the short answer is people manually force
Origin IGP so bgp behaves more rationally. For instance, setting all routes to
Origin IGP helps facilitate Hot Potato Routing
Just for grins, I'm including the BGP path selection algorithm below... notice that the Origin code is at step 6, but there are very relevant decision points below.