Refer to the Exhibit
In the exhibit, a working Layer 3 VPN exists between all routers. No OSPF domain IDs are
configured or attached in advertisements.
What can be configured on the PE routers to allow the internal OSPF routes in Area 3 to show up
as summary (Type 3) LSAs in CE2?
A.
Assign a domain ID of 1.1.1.1 to all routes injected into the Layer 3 VPN on PE1.
B.
The routes will show up as summary LSAs by default.
C.
Configure PE2 to have a different domain ID than PE1.
D.
Configure a sham link between PE1 and CE1.
Explanation:
Answer is A.
When a PE router receives a route, it redistributes and advertises the route as either a Type 3 LSA or a Type 5 LSA, depending on the following:
If the receiving PE router sees a Type 3 route with a matching domain ID, the route is redistributed and advertised as a Type 3 LSA.
If the receiving PE router sees a Type 3 route without a domain ID (the extended attribute field of the route’s BGP update does not include a domain ID), the route is redistributed and advertised as a Type 3 LSA.
If the receiving PE router sees a Type 3 route with a non-matching domain ID, the route is redistributed and advertised as a Type 5 LSA.
If the receiving PE router sees a Type 3 route with a domain ID, but the router does not have a domain ID configured, the route is redistributed and advertised as a Type 5 LSA.
If the receiving PE router sees a Type 5 route, the route is redistributed and advertised as a Type 5 LSA, regardless of the domain ID.
If PE1 doesn’t have a domain-id configured, then configuring a domain-id on PE2 will cause the router to be advertised to CE2 as a type 3 LSA. >> Answer C.
lack of domain ID causes implicit match. Answer B
Thanks qrz. I was reading it wrong.
The answer is B, of course.