D-Link DES-3326SR User Manual page 152

DES-3326SR Layer 3 Fast Ethernet Switch User's Guide
Autonomous Systems External Link Advertisements
Autonomous Systems (AS) link advertisements are Type 5 link
state advertisements. These advertisements are originated by
AS boundary routers.
each destination known to the router, that is external to the
AS.
AS external link advertisements usually describe a particular
external destination. For these advertisements the Link State
ID field specifies an IP network number.
advertisements are also used to describe a default route.
Default routes are used when no specific route exists to the
destination. When describing a default route, the Link Stat ID
is always set the Default Destination address (0.0.0.0) and the
Network Mask is set to 0.0.0.0.
The format of the AS External Link Advertisement is shown
below:
AS External Link Advertis
Link-State Age
Link-State Sequence N
Link-State Checksum
E TOS
Forwarding Address
Figure 5-32. AS External Link Advertisement
A separate advertisement is made for
AS external link
ements
Op tions
Link-State ID
Advertising Router
umber
Length
Network Mask
Metri c
External Route Tag
140
5