Summary Link Advertisements; Autonomous Systems External Link Advertisements - D-Link DGS-3600 Series User Manual

Field
Network Mask
Attached Router

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.
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
Network Mask
ToS
Metric

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
xStack DGS-3600 Series Layer 3 Gigabit Ethernet Managed Switch
Description
The IP address mask for the network.
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
Link-State Age
Advertising Router
Link-State Sequence Number
Link-State Checksum
TOS
Figure 8- 37. Summary Link Advertisements
Description
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.
The Type of Service that the following cost is relevant to.
The cost of this route. Expressed in the same units as the interface costs in
the router links advertisements.
Options
Link-State ID
Length
Network Mask
Metric
180
2