Installing and Administering Internet Services

368 Chapter8
Configuring gated
Configuring the Router Discovery Protocol (RDP)
255.255.255.255, the advertisements contain all IP addresses
configured on the physical interface. If advertisements are being sent to
a net or subnet broadcast, only that net’s or subnet’s address is included
in the advertisement.
An example of the routerdiscovery server statement is shown below.
In the example, the server is being enabled on physical interfaces lan0
and lan2, and the IP addresses 193.2.1.17, 193.2.1.33, and 193.2.1.46 are
to be included in all Router Advertisements that are sent out. Also, the
addresses have a preference of 50.
routerdiscovery server yes {
interface lan1 lan2
maxadvinterval 5 ;
address 193.2.1.17 193.2.1.33 193.2.1.46
broadcast
preference 50 ;
} ;
The RDP Client
The RDP client runs on hosts, listening for Router Advertisements over
the all-hosts multicast address 224.0.0.1 (if it supports IP
multicasting) or on the physical interface’s broadcast address (if the host
does not support multicasting). When a host starts up or has been
reconfigured, it might send some Router Solicitations, requesting
advertisements. When it sends the solicitations, it sends them to the
all-routers multicast address 224.0.0.2 or the interface’s broadcast
address (if multicasting is not supported).
When the RDP client receives a Router Advertisement, the host installs
a default route to each of the addresses listed in the advertisement. If the
advertisement has a preference of ineligible (meaning the addresses
in the advertisement are not eligible to be the default route for any
hosts), or if the addresses are not on an attached physical interface, the
route is marked unusable but is retained. If the preference is a usable
one, that route will be among the routes considered. The route with the
highest preference is the route that will be used. If more than one route
with the same preference is received, the one with the lowest IP address
is used. Note that the default routes are not exportable to other
protocols.
If an RDP client receives a Router Advertisement with a zero lifetime
(meaning that the addresses in the advertisement are no longer valid),
the host deletes all routes with next-hop addresses that it learned from