3Com 4007, Руководство по внедрению, Страница: 528 / 684

528 C
HAPTER
20: IPX R
OUTING
RIP Policies Each router maintains a table of current routing information (the routing
table). The routing protocols receive or advertise routes from the
network. RIP policies control the flow of routing information among the
network, the protocols, and the routing table manager.
Routing policies allow you to define:
■
The import policies that specify which routes the router places into the
routing table.
■
The export policies that specify the routes that the router propagates
to the network.
■
Import/export policies for each peer.
RIP Import Policies
Before the router adds a route to the routing table, it follows these steps:
■
The protocol receiving the route forwards the route to the routing
table manager.
■
The routing table manager compares the route to the import policy to
determine whether to accept or drop the route.
■
If the routing table manager accepts the route, it stores the route in
the routing table.
The default import policy is none; that is, the router places all routes into
the routing table.
RIP Export Policies
At certain times, such as when the routing table changes, the protocol
asks the routing table manager for routes to advertise to other routers.
The routing table manager follows these steps:
■
It compares the route to the export policy to determine whether to
advertise the route to the network.
■
If it accepts the route, the manager propagates it to the network.
The default import policy is none; that is, the router advertises all routes
in the routing table.