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DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
Table 5-14. Hello Packet
The Database Description Packet
Database Description packets are OSPF packet type 2. These packets are exchanged when an
adjacency is being initialized. They describe the contents of the topological database. Multiple packets
may be used to describe the database. For this purpose a poll-response procedure is used. One of the
routers is designated to be master, the other a slave. The master seconds Database Description packets
(polls) that are acknowledged by Database Description packets sent by the slave (responses). The
responses are linked to the polls via the packets’ DD sequence numbers.
Database Description Packet
Version No.
2 Packet Length
Router ID
Area ID
Authentication Type
Authentication
Authentication
Checksum
Options
DD Sequence No.
Reserved
Reserved
Link-State Advertisement Header ...
IM
MS
Figure 5-27. Database Description Packet
Field Description
Options The optional capabilities supported by the router.
I – bit The Initial bit. When set to 1, this packet is the
first in the sequence of Database Description
packets.
M – bit The More bit. When set to 1, this indicates that
more Database Description packets will follow.
MS – bit The Master Slave bit. When set to 1, this indicates
that the router is the master during the Database
Exchange process. A zero indicates the opposite.
DD Sequence Number User to sequence the collection of Database
Description Packets. The initial value (indicated by
the Initial bit being set) should be unique. The DD
sequence number then increments until the
complete database description has been sent.
Table 5-15. Database Description Packet
The rest of the packet consists of a list of the topological database’s pieces. Each link state
advertisement in the database is described by its link state advertisement header.
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