User manual

xStack DES-3800 Series Layer 3 Stackable Fast Ethernet Managed Switch
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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 8- 24. 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.