Symptom
In a MPLS environment a PE router receives a prefix from an eBGP neighbor first, the local RIB does not have the mpls-vpn flag set. When this prefix is redistributed into OSPF, the DN bit is not set. Now if eBGP neighbor goes down, the iBGP learnt route is preferred and installed in RIB; however, the DN flag is still not set.
Conditions
MPLS EBGP redistribution into OSPF
Workaround
You can mitigate this by removing and re-applying the redistribution under OSPF
Further Problem Description
Type-5 AS External Link States
LS age: 98
Options: 0x2 (No TOS-capability, No DC) << No DN Bit set
LS Type: Type-5 AS-External
Link State ID: x.x.x.x (Network address)
Advertising Router: x.x.x.x
LS Seq Number: 0x80000002
Checksum: 0xe56d
Length: 36
Network Mask: /32
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 1
Forward Address: 0.0.0.0
External Route Tag: 3489725440
