07-31-2018 10:57 AM
I have a L3 switch that is doing BGP peering with two other routers, RouterA and RouterB. I am learning a default route (via BGP) from RouterA and devices that use my L3 switch as their default gateway are able to reach the Internet without issue.
Now, I am trying to "re-advertise" the default route I am learning from RouterA and push that into the BGP routing table running on RouterB. On my L3 switch, if I go into my BGP routing instance and configure "default-information originate", and then if I do "show ip bgp neighbor RouterB advertised-routes", I see a default route being pushed to RouterB. But, the tech that manages RouterB says he doesn't see a default route come in from my L3 switch. If I configure a static 0.0.0.0 route on my L3 switch and then do "redistribute static" in my BGP routing process, RouterB starts to pick up the default route from my L3 switch but at the same time, I create a routing loop between my L3 switch and RouterA and so I lose my Internet connection.
I'm hoping someone can help me sort this out.
08-01-2018 09:45 AM
08-01-2018 10:24 AM
You said the following on the original post: If I configure a static 0.0.0.0 route on my L3 switch and then do "redistribute static" in my BGP routing process, RouterB starts to pick up the default route from my L3 switch but at the same time, I create a routing loop between my L3 switch and RouterA and so I lose my Internet connection. It seems to me that there is no filter on RouterB side of the configuration.
It would be very helpful for us to look at the BGP configurations.
07-31-2018 12:57 PM
No problem that you are not up to speed on BGP. It can be complicated. It is very helpful to know that the AS number you use is different from the number you use for A and for B. In that case both would be EBGP. To help us understand could you post your BGP configuration? mask out sensitive information like public IP addresses and post the rest of the config.
07-31-2018 01:10 PM
07-31-2018 01:47 PM
If this is all EBGP then each device should set itself as the next hop IP when advertising to an EBGP peer and so if the EBGP peerings are up then they should know how to reach the next hops.
If the tech for router B does a “sh ip bgp” does he see the default route ?
Could you get the BGP configuraton for your switch and router B ?
08-01-2018 09:46 AM
07-31-2018 01:51 PM
One other point.
If you are receiving default from router A why are you trying to originate the route on your switch ?
Why not just pass on the default route ?
08-01-2018 09:50 AM
07-31-2018 02:55 PM
Awesome, although we will still need to know more about the BGP ASNs for each site. Some people put their MPLS clouds in one AS, some people make every site a different AS.
Please let us know the ASN of each of these sites including router a, router b, and your l3 switch. Posting configs is always good if you can do it. Also, does site 2 (DR site) peer with router B?
07-31-2018 12:36 PM
Are these eBGP or iBGP peering relationships? What are you advertising as the next hop from from your L3 switch to Router B? Without seeing any configuration/technical details, my first thought would be to ensure your next hop is set correct and reachable from router B.
07-31-2018 12:51 PM
07-31-2018 01:08 PM - edited 07-31-2018 01:11 PM
Looks like you guys got it sorted. Geez you guys are fast!
If everything is eBGP then some type of filtering is likely going on that is blocking the default route OR it doesn't meet the criteria to be added to the BGP table on router B...most likely its being filtered. Your co-worker can run a "debug ip bgp updates" (and maybe some others) to help determine what is happening with the default route.
EDIT - Also yes, if you can post your config we can take a closer look.
08-01-2018 07:34 PM
08-02-2018 07:33 AM
The info is great but unfortunately I think router B's config is what we really need, the ASNs here are good to see though. From that we can find out if there are any filters and see what peering (internal or external) router B has with the other spokes.
When you post the config for router B be sure to include any route-maps that are applied to neighbors and their associated objects (ACLs, prefix lists, etc). It may also be valuable to post "show ip bgp 0.0.0.0" and "show ip route" on router B.
I am still struggling with the idea that the default route is tagged with the no export community when its handed to you. But I would think if that was the case it would not show up in your advertised routes command output...."show ip bgp 0.0.0.0" output on your router will suffice to eliminate that possibility.
08-02-2018 09:35 AM
Could you share the output of "sh ip bgp 0.0.0.0" from your L3 Switch?
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