TMS zl Management and Configuration Guide ST.1.0.090213

9-31
Routing
OSPF
All routers generate Type 1 LSAs, which they use to advertise their own links.
A Type 1 LSA includes the following:
■ Link ID—in a point-to-point link, the neighboring router’s ID (typically
its loopback VLAN address); in a link to a network, the network IP address
■ Type of link—point to point, stub network, transit network
■ Link status
■ Metric—the cost for crossing the link, usually based on inverse band-
width
Other important LSAs are Type 3 LSAs, which include the following:
■ IP address and subnet mask for a network or range of networks
■ Cost of the link to the network or networks
An ABR summarizes the networks in an area and then advertises a link to that
range of networks in a Type 3 LSA. The ABR sends only the summary to routers
in a different area from that of the networks advertised in the LSA. Type 3
LSAs allow routers to generate inter-area routes.
The ABR automatically advertises a default route to internal routers in stub
areas. Routers in total stub areas receive only this Type 3 LSA, which they use
to generate a default route for all traffic outside their area.
Type 5 LSAs advertise connections to external networks and are not received
by routers in stub areas. Stub routers use their default route for external traffic
A special Type 7 LSA allows routers in NSSAs to receive summary routes to
external networks.
5—summary
external links
• External network or
range of external
networks
• Cost for the link
• External 1 (E1) routes,
which include external
cost and the cost to the
ASBR
• External 2 (E2) routes,
which only include
external cost
An ASBR External
network
address
• All ABRs
• All internal routers in normal areas
and the backbone
• Not sent to internal routers in stub
and total stub areas
LSA Type Contains Originated By Link State ID Flooded To