By default the weight parameter is 0.so, what u can do , on both the routers for their ebgp neighbor assign a weight of 1000
Neighbor weight 1000
Why its not recommended to set weight using route-maps, in case of dual ISP setup if by any chance ur AS becomes transit AS then weight value will be propagated further and it can affect the routing at far end.
I am on a public ASN and getting transit off to different SP's.
I have never used weight before as its not really the done thing and never had a need for it.
Weight - if I went with this then in location A I would configure a route-map inbound on the eBGP neighborship, match the default route using a prefix list and set the weight to 100
I would do the exact same thing in location B
This would be a solution I believe.
Weight is neve advertised to any BGP neighbor.
Local Pref - in both locations I would use a route-map again and again match the default route then set the local pref to be 150.
The problem here is when location/router A advertises this to location/router B (and vica versa) the default routes would have matching local preferences and it would go down the order of attributes to decide which one to use, so, part of this solution would need a route map on the iBGP peering to then set the local pref again.
Technically and from a 'text book' approach I think this situation is crying out for weight to be used as I then don't have to change any attributes on the iBGP neighborship, the reason I posted this is because I have never used weight and for some reason (probably because its proprietry) (and becasue it does't propergate through the AS - which is actually the use case here) it has a bad rep and I am relectant to use it.
IMHO, you can use the Weight attribute with the route-map the way you described.
I used that attribute several times in my configs with no problem.
If somebody says it has got a bad reputation, it's possibly because it's not advertised so you might not understand why some router is preferring some profixes without an access to it.
If you insist on using Local preference, you could configure an incoming route-map on the iBGP session which would decrease the default value 100 to 50, e.g.
Don't forget BGP routers advertise only the best prefix. So as long as there will be the default route received from the eBGP neighbor, it will win (LP=100) and will be advertised to any possible neighbor (if there are any others involved).
Also don't forget the prefix received by iBGP will not be advertised to any other iBGP neighbor.
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