D-Link TM DES-6500, Manual

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DES-6500 Chassis-based Layer 3 Ethernet Switch Manual
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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 The cost of this route. Expressed in the same units as the interface
costs in the router links advertisements.
Autonomous Systems External Link Advertisements
Autonomous Systems (AS) link advertisements are Type 5 link state advertisements. These advertisements are originated
by AS boundary routers. A separate advertisement is made for 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. AS external link 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:
Link-State Age
Options
Link-State ID
Advertising Router
Link-State Sequence Number
Link-State Checksum
Length
Network Mask
TOS Metric
AS External Link Advertisements
5
Forwarding Address
External Route Tag
E
Figure 6- 127. AS External Link Advertisements