Hi,
Need your help with the attached scenario I am currently testing in a lab.
LSA-1 X.X.X.X/24 is advertised by CE-3 to PE-3 which is redistributed from OSPF to BGP on the PE-3. PE-3 advertise the prefix to both PE-1 and PE-2. Both PE-1 and PE-2 advertise the prefix to their respective CEs. However, both CE-1 and CE-2 have backdoor OSPF connectivity to each other. The following occurs:
- CE-1 learns the X.X.X.X/24 route as Inter-area route which it then advertised to CE-2
- CE-2 prefers CE-1 to reach X.X.X.X/24
- CE-2 advertise the route to PE-2
- PE-2 learn the route from CE-2 and also PE-3
- Due to route preference (AD), OSPF route is preferred on PE-2 which it then advertise back to BGP
- PE-1 sees the route from PE-2 and PE-3 but still prefers PE-3 due to BGP metric.
When I shutdown the link between CE-1 and PE-1; CE-1 learns X.X.X.X/24 from CE-2. No routing loop in this case. When I re-active the CE-1 -- PE-1 link, CE-1 still prefers CE-2 to reach X.X.X.X/24 and the whole routing loop process start all over but in this case on PE-1.
I have configured tags to prevent loops but that doesn't seems to be working. I have configured domain-vpn-tag but that doesn't work as that is applicable to LSA type 5 and 7. I have tried using different ospf processes with redistribution between each other, still not working as expected.
Could anyone share an insight into this please?
Thanks.