Summary Link State Advertisements; External Link State Advertisements - 3Com corebuilder 3500 Implementation Manual

Summary Link State
Advertisements
External Link State
Advertisements
Area border routers can generate two types of summary link state
advertisements:
Summary link state advertisements that report the cost to a single
subnetwork number outside the area. These advertisements are
identified as Type 3 in the link state advertisement header.
Summary link state advertisements that report the cost to a single
autonomous system boundary router (ASBR). These advertisements
are identified as Type 4 in the link state advertisement header.
Each summary link state advertisement includes this information:
LSID (Link State ID) — Possible values:
For Type 3 summary link advertisements, this is the IP network
number.
For Type 4 summary link advertisements, this is the ASBR's
router ID.
Router ID — ID of the router that originated the LSA.
LS Seq (Link State Sequence) — The sequence number of the
advertisement. Used to detect old or duplicate link state
advertisements.
LS age — The time, in seconds, since the LSA was generated.
Network Mask — For Type 3 summary link state advertisements, this
is the destination network's IP address mask. For Type 4 summary link
state advertisements, this parameter is set to 0.
Metric — The cost of the specified route.
Each autonomous system boundary router generates an external link
state advertisement for each network destination (known to the router)
outside the AS. AS boundary routers use these external link state
advertisements to describe routes to destinations outside the AS. For
these advertisements, the Link State ID field in the advertisement header
specifies an IP address.
Link State Databases 389