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The TCP/IP Guide  9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)       9  TCP/IP Internet Layer (OSI Network Layer) Protocols            9  TCP/IP Routing Protocols (Gateway Protocols)                 9  TCP/IP Interior Routing Protocols (RIP, OSPF, GGP, HELLO, IGRP, EIGRP)                      9  Open Shortest Path First (OSPF)

OSPF General Operation and Message Types 1 2 3 4 5 6 7 Other Interior Routing Protocols

Database Description Message Format

These messages have a Type value of 2 in the header, and the body structure depicted in Table 128 and Figure 186.

Table 128: OSPF Database Description Message Format

Field Name	Size (bytes)	Description
Interface MTU	2	Interface MTU: The size of the largest IP message that can be sent on this router's interface without fragmentation.
Options	1	Options: Indicates which of several optional OSPF capabilities the router supports.
Flags	1
DD Sequence Number	4	DD Sequence Number: Used to number a sequence of Database Description messages so they are kept in order.
LSA Headers	Variable	LSA Headers: Contains link-state advertisement headers, which carry information about the LSDB. See near the end of the topic for more information on LSAs.

Figure 186: OSPF Database Description Message Format

OSPF General Operation and Message Types 1 2 3 4 5 6 7 Other Interior Routing Protocols

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