DXS-3326GSR Gigabit Layer 3 Switch
values that are not specified defaults to the TOS 0 cost. Metrics must be listed in order of increasing TOS encoding. For
example, the metric for TOS 16 must always follow the metric for TOS 8 when both are specified.
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 multi-access network that has more than one attached router. The network
links advertisement is originated by the network’s Designated router. The advertisement describes all routers attached to
the network, including the Designated Router itself. The advertisement’s Link State ID field lists the IP interface address of
the Designated Router.
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:
Link-State Age
Options
Link-State ID
Advertising Router
Link-State Sequence Number
Link-State Checksum
Length
Network Link Advertisements
2
Network Mask
Attached Router
Figure 7- 26. Network Link Advertisements
Field
Description
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.
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.
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