The Use of Filters

The Novell^® Internet Access Server 4.1 routing software supports filtering to control the service and route information that is accepted or advertised by a router. Filters are useful when you want to limit specific types of traffic to certain parts of your network and when you want to provide a certain level of security. You use FILTCFG to configure the filters for the Internetwork Packet Exchange^TM (IPX^TM) protocol, IP, AppleTalk*, and the source route bridge to selectively discard packets sent or received by a router. The following types of filters are supported:

• Packet forwarding ---Prevents selected data packets from being forwarded by the router. Packet forwarding filtering is available for IPX and TCP/IP.

• Service information ---Limits the services added to the service information (SAP) tables of specified routers. Service information filtering is available for IPX and AppleTalk.
• Routing information ---Limits the routes added to the routing tables of specified routers. Routing information (RIP) filtering is available for IPX, AppleTalk, and TCP/IP.
• OSPF ---Controls the propagation of routing information from non-OSPF domains (RIP, EGP, and so on) to the OSPF domain.
• EGP ---Defines the routes that a router can share with other EGP peers.

• Protocol ID and ring number ---Filters packets of certain protocol types received by the bridge (Protocol ID filter), and filters packets received from specific rings on a token ring network (ring number filter). Both types of filters are only available for source route bridge.

Table 1 lists the protocol suites and the filter types that you can configure for each with FILTCFG.

Table 1. Filter Types and Protocol Suites