DES-3326S Layer 3 Fast Ethernet Switch User’s Guide

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.

FieldDescription

 

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

The

cost

of

this

route.

 

 

Expressed

in

the

same

 

 

units

as

the

interface

 

 

costs in the router links

 

 

 

 

 

 

 

 

 

 

Switch Management and Operating Concepts

 

 

 

 

 

 

163

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D-Link DES-3326S manual Summary Link Advertisement, 163