D-Link DGS-3627G Product Manual - Page 228

xStack® DGS-3600 Series Layer 3 Managed Gigabit Ethernet Switch 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. Summary Link Advertisements Link-State Age Options 2 Link-State ID Advertising Router Link-State Sequence Number Link-State Checksum Length Network Mask TOS Metric Figure 4- 48. Summary Link Advertisements 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. 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 212