
For each link, separate metrics may be specified for each Type of Service (TOS).The metric for TOS 0 must always be included, and was discussed above. Metrics for
Field | Description |
TOS | IP Type of Service that this metric refers to. |
Metric | The cost of using this outbound router link, for traffic of the specified TOS. |
Network Links Advertisements
Network links advertisements are Type 2 link state advertisements.A network links advertisement is originated for each transit network in the area.A transit network is a
The distance form the network to all attached routers is zero, for all TOS.This is why the TOS and metric fields need not be specified in the network links advertisement.
The format of the Network Links Advertisement is shown below:
Network Link Advertisements |
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Advertising Router
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| Figure 6- 108. Network Link Advertisements |
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Network Mask | The IP address mask for the network. | ||
Attached Router | The Router Ids of each of the routers attached to the network. Only those routers that are fully adjacent to | ||
| the Designated Router (DR) are listed.The DR includes itself in this list. |
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Summary Link Advertisements
Summary link advertisements are Type 3 and 4 link state advertisements.These advertisements are originated by Area Border routers.A separate summary link advertisement is made for each destination known to the router, that belongs to the Autonomous System (AS), yet is outside the area.
Type 3 link state advertisements are used when the destination is an IP network. In this case, the advertisement’s Link State ID field is an IP network number. When the destination is an AS boundary router, a Type 4 advertisement is used, and the Link State ID field is the AS boundary router’s OSPF Router ID. Other that the difference in the Link State ID field, the format of Type 3 and 4 link state advertisements is identical.
Allied Telesyn | 115 |