Bay Networks NauticaRS Reference Manual page 38

NauticaRS 5.5R Reference Guide
1-8
Many client/server-based network protocols broadcast Idle (no
data being sent) or Hello (ready and active) frames regularly,
making them unsuitable for cost-effective bridging or routing
across ISDN by constantly bringing up lines for non-important
calls. The Nautica routers solve this by filtering broadcast and
multicast frames, while intelligently routing and spoofing
protocols.
The IP RIP protocol causes routers to send out their updated
routing tables every 30 seconds. While this does not matter for
leased line connections, it is an important consideration for
routers connected over ISDN links, because the ISDN links then
become active every 30 seconds to transmit this information.
Nautica series routers have developed an advanced spoofing
solution to overcome this overhead. It works on the basis that
changes to the network occur rarely, so routing table updates need
not be sent every 30 seconds, but can be transferred with real data
when the link becomes active. This is known as a piggyback
update.
Normally routes learned from routing updates, IP Routing
Information Protocol (RIP) and Novell's Internet Packet
Exchange (IPX) RIP, are aged and removed from the table if no
update is received in 180 seconds. However, when routing
updates are only received when an ISDN data call is connected, it
is likely that there would be insufficient calls made to ensure that
routes were not removed after the 180-second time-out had
expired. The Nautica series overcomes this by making ISDN
routes semi-permanent, so that they can be updated, but never
expire due to time-out.
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