Fast Down Detection

Fast down detection or sub-second link failure detection is needed in a modern networks. Network operators of modern networks require that they can detect failure in sub-second and react to either soft or hard failures as quickly as possible.

The following are the two categories of fast down detection.

1. Polling

One of the method […]

MPLS VPN: Different OSPF Domain ID

As I mentioned in this post MPLS VPN: Same OSPF Domain ID, OSPF domain ID is the same with OSPF process ID by default. By altering the domain ID or process ID, it also alters the behaviour of the OSPF routes. So the rule is if the domain IDs are different on the PE routers […]


On a Layer 3 MPLS VPN using OSPF as an IGP between PE and CE, OSPF domain ID is equivalent to the OSPF process ID by default. Therefore, OSPF routes are seen as OSPF inter-area (Type 3 OSPF LSA). By considering this behaviour, it is easy to distinguish real external routes in the VPN.

In […]