D-Link DES-6500 - Switch User Manual page 162

Link State Advertisement Header
All link state advertisements begin with a common 20-byte header. This header contains enough information to uniquely identify
the advertisements (Link State Type, Link State ID, and Advertising Router). Multiple instances of the link state advertisement
may exist in the routing domain at the same time. It is then necessary to determine which instance is more recent. This is
accomplished by examining the link state age, link state sequence number and link state checksum fields that are also contained in
the link state advertisement header.
The format of the Link State Advertisement Header is shown below:
Field
Link State Age
Options
Link State Type
Link State ID
Advertising Router
Link State Sequence
Number
Link State Checksum
Length
xStack DES-6500 Modular Layer 3 Chassis Ethernet Switch User Manual
Link-State Advertisement Header
Link-State Age
Link-State Checksum
Figure 6- 127. Link State Advertisement Header
Description
The time is seconds since the link state advertisement was originated.
The optional capabilities supported by the described portion of the
routing domain.
The type of the link state advertisement. Each link state type has a
separate advertisement format.
The link state type are as follows: Router Links, Network Links,
Summary Link (IP Network), Summary Link (ASBR), AS External Link.
This field identifies the portion of the internet environment that is being
described by the advertisement. The contents of this field depend on the
advertisement's Link State Type.
The Router ID of the router that originated the Link State Advertisement.
For example, in network links advertisements this field is set to the Router
ID of the network's Designated Router.
Detects old or duplicate link state advertisements. Successive instances
of a link state advertisement are given successive Link State Sequence
numbers.
The Fletcher checksum of the complete contents of the link state
advertisement, including the link state advertisement header by accepting
the Link State Age field.
The length in bytes of the link state advertisement. This includes the 20-
byte link state advertisement header.
Options
Link-State ID
Advertising Router
Link-State Sequence Number
Length
147
Link-State Type