Installing and Administering Internet Services

Chapter 8 269
Configuring gated
Configuring the OSPF Protocol
packet to the host must also be specified. (In most cases, the host has
only a single connection to the network so the cost configured has no
effect on routing.)
Figure 8-8 shows an example of a router (A) that is connected to a
non-broadcast, point-to-point network through interface 193.2.1.1.
Figure 8-8 Point-to-Point Router Interface Example
The following is an example of the interface definition in router A’s
/etc/gated.conf file:
interface 193.2.1.1 nonbroadcast cost 5 {
hellointerval 30 ;
routerdeadinterval 30 ;
retransmitinterval 30 ;
pollinterval 30 ;
} ;
Note that if the router (A) were connected to a multicast, point-to-point
network, the nonbroadcast clause and the pollinterval statement
must be omitted.
Stub Areas
By default, AS external link advertisements (routes to destinations
outside the AS) are propagated to every router in every area in the AS.
Certain OSPF areas can be configured as stub areas. AS external link
advertisements are not flooded through stub areas. This reduces the size
of the topology database that must be maintained by internal routers in
the stub area and reduces the protocol traffic through the area. For
example, if all inter-area traffic for an area must go through a single
router, then it is not necessary for all routers in the area to receive
inter-area routing information.
An area border router advertises in the stub area a default route as the
summary of all the IP destinations that are reachable outside the AS.
Summary link advertisements (routes to destinations outside the area
but within the AS) continue to be sent into the stub area.
The stub statement specifies that the area is a stub area. A cost clause
can optionally be defined that specifies the cost associated with the
default route to be advertised in the stub area.
193.2.1.1
193.2.1.2
Router
A
Router
B