3Com Switch 4800G 24-Port - Page 289

Introduction to OSPF 289
Figure 89 Network LSA format
Major fields:
■ Link State ID: The interface address of the DR
■ Network Mask: The mask of the network (a broadcast or NBMA network)
■ Attached Router: The IDs of the routers, which are adjacent to the DR,
including the DR itself
■ Summary LSA
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 format
of type 3 and 4 summary-LSAs is identical.
Figure 90 Summary LSA format
Major fields:
■ 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
Network mask
...
Attached router
LS age
Linke state ID
Advertising Router
Options 2
LS sequence number
LS checksum Length
0 7 15 31
Network mask
...
TOS
LS age
Linke state ID
Advertising Router
Options 3or4
LS sequence number
LS checksum Length
TOS metric
0 metric
0 7 15 31