Novell NETWARE 6-DOCUMENTATION Manual page 1873

Figure 1 Outgoing RIP Filters
Filtering
Router R1
(filtered)
Network 1
Network 2
Incoming Routing Information Filters
End Station
E1
Filtering
Router R2
Network 3
The route to Network 1 is filtered out in Router R1's advertisement to Network
3. If End Station E2 sends a packet to Network 1, Router R2 drops that packet
because it does not have a route. If End Station E1 sends a packet to Network
1, Router R1 forwards it because it does have a route. End Station E1 can send
a packet to Network 1 only if it has a route to that network. End station E2 can
see only Networks 2, 3, and 4. End station E1 can see both Networks 1 and 2.
When IPX is used, route information filters affect both clients and routers. A
client will make a route request that passes through the same filters as for the
routinely transmitted route information. However, if a client is attached
locally to a router that is performing outbound route information filtering and
the client is using software that can use static routing, the client can send
packets to Network 1 through Router R1 because R1 knows about Network 1
in its routing tables. If only standard IPX route lookups are done (true for a
majority of sites), a path to the filtered networks is not possible.
Incoming routing information filters limit the routing information accepted by
a router from its neighboring routers.
When incoming routing information filters are enabled on a router, the router
accepts only the allowed routes from each neighboring router, thereby hiding
specified routes from some routers and from certain parts of the network.
However, incoming routing information filters cannot be used to filter out
directly connected networks.
End Station
E2
Network 4
13
Understanding