Exam 4A0-101 topic 3 question 24 discussion

Type 1 Router LSA format Options:- represents the optional capabilities supported by the router, such as option E that is used to indicate if the origination router area type is a backbone, transit or non-stub area. Bit E :- This bit is used to determine whether this router is an ASBR. Note that this is different from the options E bit.

E-bit: Type-5 AS external link advertisements are not flooded into/through OSPF stub and NSSA areas. The E-bit ensures that all members of a stub area agree on that area configuration. The E-bit is meaningful only in OSPF Hello packets. When the E-bit is reset in the Hello packet sent out a particular interface, it means that the router will neither send nor receive type-5 AS external link state advertisements on that interface (in other words, the interface connects to a stub area). Two routers will not become neighbors unless they agree on the state of the E-bit.

The E-bit (Edge Bit) of the Options field should be set if and only if the attached area is capable of processing AS-external-LSAs. Router LSA of ASBR will have “E-bit” set in router-lsa packet All the routers should have “E-bit” set to 0 in their hello packets to form adjacency.