Cabletron Systems CSX100 series, User Manual, Page: 110 / 153

ISDN Router 96
IP Routing
IP routing support provides the ability to process TCP/IP frames at the
network layer for routing. IP routing support includes the Routing
Information Protocol (RIP) which allows the exchange of routing information
on a TCP/
IP network. The router receives and broadcasts RIP messages to adjacent
routers and workstations. Since IP sends out periodic RIP frames that could
keep dial-up links permanently connected, filtering and spoofing are
performed to minimize these broadcasts on the WAN links. The router uses
the ‘piggyback method’ to send RIP update packets to the WAN port. The
piggyback method means that RIP update packets are sent only when the dial-
up link is established because of data traffic.
IPX Routing
Internetwork Packet Exchange (IPX) Routing support provides the ability to
process IPX frames at the network layer. This support includes the Routing
Information Protocol (RIP)* which allows the exchange of routing
information on an Internetwork, and the Service Advertising Protocol (SAP),
which provides a means of exchanging Internetwork service information. The
router receives and broadcasts RIP and SAP messages to adjacent routers and
workstations so that clients on the network can determine what services (file,
print, etc.) are available on the network and obtain the Internetwork address
of the servers.
Since IPX sends several types of control packets that could keep dial-up links
permanently connected, control of updates, and spoofing techniques are
employed to reduce this traffic. Specifically, RIP, SAP, Watchdog, and
serialization frames are filtered and spoofed. RIP and SAP update frames are
only sent piggybacked with data packets. SAP requests for the nearest server
are spoofed, serialization frames are dropped, and Watchdog frames are
spoofed.
* IPX-RIP is similar to IP-RIP except IPX-RIP includes a time delay in
addition to a hop count