D-Link DES-3326SR User Manual page 150

DES-3326SR Layer 3 Fast Ethernet Switch User's Guide
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 Advertisemen
Link-State Age
Link-State Sequence N
Link-State Checksum
TOS
Figure 5-31. Summary Link Advertisement
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.
ts
Op tions
Link-State ID
Advertising Router
umber
Length
Network Mask
Metric
When describing a default
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2