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DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
Switch Management and Operating Concepts 163
Figure 5-31. Summary Link Advertisement
For stub area, Type 3 summary link advertisements can also be
used to describe a default route on a per-area basis. Default
summary routes are used in stub area instead of flooding a
complete set of external routes. When describing a default
summary route, the advertisement’s Link State ID is always set
to the Default Destination − 0.0.0.0, and the Network Mask is
set to 0.0.0.0.
Separate costs may be advertised for each IP Type of Service.
Note that the cost for TOS 0 must be included, and is always
listed first. If the T-bit is reset in the advertisement’s Option
field, only a route for TOS 0 is described by the advertisement.
Otherwise, routes for the other TOS values are also described.
If a cost for a certain TOS is not included, its cost defaults to
that specified for TOS 0.
Field Description
Network Mask For Type 3 link state
advertisements, this
indicates the destination
network’s IP address
mask. For example,
when advertising the
location of a class A
network the value
0xff000000
TOS The Type of Service that
the following cost is
relevant to.
Metric
T
he cost of this route.
Expressed in the same
units as the interface
costs in the router links