Novell NETWARE 6-DOCUMENTATION Manual page 1880

AppleTalk Routing Information Filters
20
Filter Configuration
If filtering for that device or service location is enabled, the router drops the
NBP reply so that a user or application cannot get the network address of these
services. Without the NBP reply, the application cannot know about the
existence of the device.
NOTE:
Device hiding filters provide a low level of security, but they do have
limitations. Because filtering is enabled on a router, if the client machine requesting
the address is on the same network as the service, the NBP reply goes directly to
the client and the router has no opportunity to filter it out. Additionally, if a client
machine knows the address of a specific service, it does not need the NBP reply
to access the service.
You can configure AURP routers to filter service information traveling
through an IP tunnel. If a filter is enabled on the tunnel, all networks accessible
through the tunnel are affected by service information filters configured for
the AURP router.
AppleTalk routing information filters restrict the exchange of routing
information between routers by limiting the routes added to the routing tables
of specified routers. These filters increase security by limiting the visibility of
selected networks or zones and reduce the network bandwidth consumed by
the periodic exchange of routing information between routers. There are two
types of AppleTalk routing information filters:
Outgoing route filters
Incoming route filters
AppleTalk uses Routing Table Maintenance Protocol (RTMP) as its primary
routing protocol. This protocol is similar to the RIP used by TCP/IP and IPX.
The routing tables maintained by RTMP contain an entry for every known
route. These routing tables acquire routing information in two ways:
For directly connected networks, through AppleTalk configuration
For networks not directly connected, through the routing updates from
each of a router's neighboring routers
When all routing information filters are not enabled, an AppleTalk router
learns all the routes known by its neighboring routers through periodic routing
table updates (sent by RTMP). In this way, every router on the internetwork
acquires the routing information from all other routers on the internetwork.