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Network summary LSAs (Type-3 LSAs) and ASBR summary LSAs (Type-4 LSAs) are originated by
ABRs. Other than the difference in the Link state ID field, the formats of Type 3 and Type 4
summary LSAs are identical.
Figure 35
Summary LSA format
Major fields of the Summary LSA are as follows:
•
Link state ID: For a Type-3 LSA, it is an IP address outside the area; for a Type-4 LSA, it is
the router ID of an ASBR outside the area.
•
Network mask: The network mask for the Type-3 LSA; set to 0.0.0.0 for the Type-4 LSA
•
Metric: The metric to the destination.
A Type-3 LSA can be used to advertise a default route if the Link state ID and Network mask are set to
0.0.0.0.
AS external LSA
An AS external LSA, as shown in Figure 36, originates from an ASBR, and describes routing
information to a destination outside the AS.
Summary of Contents for S9500E Series
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