Link-State Age
Options Link-State Type
Link-State ID
Advertising Router
Link-State Sequence Number
Link-State Checksum
Length
Routers Links Advertisements
Reserved Reserved Number of Links
Link ID
Link Data
Type No. Of TOS TOS 0 Metric
TOS
Metric
...
TOS
Metric
...
Link ID
Link Data
0
0
V BE
Figure 5-28 Routers Links Advertisements
In router links advertisements, the Link State ID field is set to the router’s OSPF Router ID. The T-bit is set in the
advertisement’s Option field if and only if the router is able to calculate a separate set of routes for each IP Type of
Service (TOS). Router links advertisements are flooded throughout a single area only.
Parameter Description
V-bit
When set, the router is an endpoint of an active virtual link that is using the described
area as a Transit area (V is for Virtual link endpoint).
E-bit
When set, the router is an Autonomous System (AS) boundary router (E is for External).
B-bit
When set, the router is an area border router (B is for Border).
Number of Links
The number of router links described by this advertisement. This must be the total
collection of router links to the area.
The following fields are used to describe each router link. Each router link is typed. The Type field indicates the
kind of link being described. It may be a link to a transit network, to another router or to a stub network. The values
of all the other fields describing a router link depend on the link’s Type. For example, each link has an associated
32-bit data field. For links to stub networks, this field specifies the network’s IP address mask. For other link types,
the Link Data specifies the router’s associated IP interface address.
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