The simple explanation
Type 6 was introduced for MOSPF, the multicast extensions to OSPF. That Cisco does not support.
The technical explanation
We have now reached LSA 6. And yes, this one is a little bit awkward.
Type 6 was introduced for MOSPF, the multicast extensions to OSPF. Its job was to carry information about members of multicast groups. Sounds useful, right?
Well, the problem is that Cisco doesn't support it. So while the other LSAs are busy doing their jobs, LSA 6 is standing outside the party asking:
- Hello? Am I invited?
- Cisco: No.
Type 6 is called a Group Membership LSA. In MOSPF, it was used to distribute information about multicast group membership so routers could figure out where multicast traffic needed to go.
And just like LSA 1 and LSA 2, LSA 6 are area specific. They do not get flooded outside the area where they originated.
So if you only remember three things about LSA 6:
- It belongs to MOSPF.
- It carries information about multicast group membership.
- Cisco does not support MOSPF/Type 6 LSAs.
LSA 6 is technically part of the story. It just never got invited to the Cisco party.
Protocol reference: RFC 2328 (OSPFv2). NSSA reference: RFC 3101.
logic
The local correspondent whose story needs approval before the international edition.
Example
A branch NSSA redistributes a local external route. The NSSA carries Type 7 information; a qualifying translated Type 5 advertises it outside.