Intel ER8100STUS - Express 8100 Router, Reference Manual

Page: 98 / 150

Reference.bok : Chapter09 86 Wed Apr 22 10:58:08 1998
86
Routing Information Protocol (RIP)
Novell IPX Routing
Routing Information
Routers exchange routing information to inform each other about the network to-
pology in the following situations:
■
When powered on, initial broadcasts to directly attached segments and WAN
links are sent.
■
To receive routing information from other routers, Initial Routing Requests
are sent.
■
To inform about each other’s existence, periodic broadcasts are typically sent
every minute.
■
Immediately after a network topology change, triggered updates are sent.
Updating periods
Each router sends updated routing information in periods of one minute (by de-
fault) on its associated LAN. In case of a router shut-down, all other routers de-
lete the routing entry after approximately 3 minutes (or 3 times the normal
interval of 1 minute). This allows a router to miss at least 2 packets in case the
network is heavily loaded. Note that routers never send routing information back
to networks they received the routing information from, as this would create
loops.
Triggered updates
A triggered update is routing information exchanged due to changes in the net-
work topology, for example if a link fails.
Cost factor
The costs for exchanging routing information on packet switched networks can
be high, as the carrier charges you for every byte transmitted.
RIP Filtering
Introduction
Routing information entering and leaving a Intel Express 8100 Router can be fil-
tered to remove unwanted routing information. For example, this may be done to:
■
restrict access between certain networks
■
reduce the amount of routing information traffic
Implementation RIP filters are implemented for both WAN and LAN links, and are implemented
for both received (Rx) and transmitted (Tx) routing information.
RIP Rx filters
RIP Rx filters can be used to remove selected incoming routing information be-
fore it is entered into the routing table for the router. Routing destinations re-
moved in this way are not accessible via the router, and the routing information
is not passed on to other routers.
RIP Tx filters
RIP Tx filters can be used to remove selected routing information before it is
passed on to other routers. Routing destinations removed in this way are accessi-
ble via the router but the routing information is not passed on to other routers.