1-we have CE device (SBC )that run MCE and is connected to two PEs(NE40E).
2-MBGP and OSPF routing ptotocol is running between CE and PEs.
3-The version of NE40E is V003R006.
4-There is Layer3 vpn configured on both CE (MCE)and PEs but when we check the imported routes from PE into CE vpn table we didnt find any routes.
1-we check the VPN-instance routing table
[SBC] display ip routing-table vpn-instance i-deddicado
-----we didnt find any imorted routes form PE
2-we check option field
display ospf 10 lsdb Network
OSPF Process 10 with Router ID 184.108.40.206
Link State Database
Type : Network
Ls id : 220.127.116.11
Adv rtr : 18.104.22.168
Ls age : 277
Len : 36
Options : D //Dn Bit set
seq# : 80000002
chksum : 0xb094
Link count: 1
Link ID: 22.214.171.124
Data : 255.255.255.255
Link Type: StubNet
Metric : 1
1-We didn’t find any imported routes in the VRF in CE (SBC) because all the routes that received from the PEs had DN bit set so the CE will not import these routes into VRF tables.
2-When DIV gets an upadte about Network x belong to a vpn existing on CE (SBC) ,it will update TER via MB-BGP and also the CE via OSPF and then the CE in turn sends this update again to TER via ospf ,this means that TER will get two updates about network x ,one from the DIV and the other from CE (SBC),By default, the priority of an IGP route is higher than that of an IBGP route. Therefore, TER chooses the OSPF route from CE (SBC)so the loop occurs as TER---SBC----TER and also the same may happen for DIV---SBC--DIV
3-So to prevent the above loop, when DIV updates CE (SBC) it will set DN bit =1 so if the CE resend this upadte again to TER ,TER will first check DN bit then it will discard the update if DN=1.
4.Because the CE is MCE which runs multiple vpn-instance ,when it receives updates from any PEs it will first check the DN bit ,if dn =1 it will discard the updates and that's what happens in this case .
1-Disable loop Detection mechanism on the CE to allow OSPF multiple VPN-Instances to installs the route with DN bit set in the VRF’s tables.
ospf 10 vpn-instnace i-dedicado
2-when we configure Multi-Vpn-Instance on CE we should care about the DN bit