Our leaf set up is fairly straight forward. We have two routers at each leaf site for redundancy that receive a default route from our hub router via eBGP. Router1 is the "primary", we use local preference of 200 on it. Router2 is the "secondary", we use local preference of 100 on that. Both routers have OSPF for the igp for iBGP reachability, they are directly connected and peer with their loopbacks. OSPF is configured on both routers to advertise a default route via default-information-originate with metric-type 1 for the downstream L3 distribution switches. Here's where things get strange and we have this deployed at many sites....
-At some sites Router2 will prefer the default advertised from Router1 via iBGP.
-At some sites Router2 will prefer the default advertised from Router1 via OSPF.
In the configs nothing has been changed to tweak a routing protocols admin distance. There is not PBR or any otherwise config that would cause this. They are identical configurations aside from IP addresses quite literally.
I would expect that Router2 prefers the default route from Router1's OSPF advertisement since local preference on Router1 is higher, this iBGP route is the preferred BGP path on Router2. The iBGP (200 AD) route would not be installed in the routing table since there is OSPF route available (110 AD). With that said I can't imagine any scenario that would cause the iBGP route to be preferred over OSPF at some sites, especially when I look at the tables they look nearly identical aside from the ones preferring OSPF show a rib failure in BGP which is to be expected. What's going on here or have I forgotten something about OSPF and BGP's relationship?
Example, SiteA (iBGP preferred)
router1# show ip route
Gateway of last resort is (eBGP neighbor) to network 0.0.0.0
B* 0.0.0.0/0 [20/0] via (eBGP neighbor), 8d16h
router1#show ip bgp
Network Next Hop Metric LocPrf Weight Path
*> 0.0.0.0 (eBGP neighbor) 200 0 65001 65002 i
router2#show ip route
Gateway of last resort is (iBGP Neighbor) to network 0.0.0.0
B* 0.0.0.0/0 [200/0] via (iBGP Neighbor), 8d16h
router2#show ip bgp
Network Next Hop Metric LocPrf Weight Path
*>i 0.0.0.0 (iBGP Neighbor) 0 200 0 65001 65002 i
* (eBGP neighbor) 100 0 65000 65002 i
Example Site B, (OSPF preferred)
router1#show ip route
Gateway of last resort is (eBGP neighbor) to network 0.0.0.0
B* 0.0.0.0/0 [20/0] via (eBGP neighbor), 6w4d
router1#show ip bgp
Network Next Hop Metric LocPrf Weight Path
*> 0.0.0.0 (eBGP neighbor) 200 0 65001 65002 i
router2#show ip route
Gateway of last resort is (router1) to network 0.0.0.0
O*N1 0.0.0.0/0 [110/12] via (router1), 6w4d, TenGigabitEthernet0/1/0
router2#show ip bgp
Network Next Hop Metric LocPrf Weight Path
r>i (iBGP Neighbor) 0 200 0 65001 65002 i
r 0.0.0.0 (eBGP neighbor) 100 0 65000 65002 i
Get same result as you,
the R2 show prefix learn from O E2 even if it learn from R3 (ebgp) directly.
I check now solution.
only make weight for any prefix learn from eBGP Peer higher that default value which is 32768
I make it 65535 and immediate the router now learn the prefix direct from eBGP not from iBGP neighbor via OSPF (O E2)
thanks
MHM
