ELSA LANCOM Business LC-4X00, Manual

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Operating modes and functions
ELSA LANCOM Business
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unknown to the workstation computer if there are several routers in a network.
Occasionally, however, this default router cannot reach the destination network itself but
does know another router which can find this destination.
How can you assist the workstation computer now?
By default, the router sends the computer a response with the address of the router
which knows the route to the destination network (this response is known as an ICMP
redirect). The workstation computer then accepts this address and sends the data packet
straight to the other router.
Certain computers, however, do not know how to handle ICMP redirects. To ensure that
the data packets reach their destination anyway, use local routing (in
ELSA LANconfig in
the 'TCP/IP' configuration section on the 'Routing' tab or in the /
Setup/IP-router-
module/Local-routing
menu). This is how you tell the router to send the data
packet to the other router itself. The router will then no longer send any ICMP redirects.
This may seem to be a good idea in principle, but local routing should still only be used
as a last resort, since this function leads to doubling of the number of data packets being
sent to the destination network required. The data is first sent to the default router and
is then sent on from here to the router which is actually responsible.
Dynamic routing with IP RIP
In addition to the static routing table ELSA routers also have a dynamic routing table
containing up to 128 entries. Unlike the static table, you do not fill this out yourself, but
leave it to be dealt with by the router itself. It uses the routing information protocol (RIP)
for this purpose. This protocol is used by all routers with RIP in a local network to
exchange information regarding the reachable routes.
What information is propagated by IP RIP?
A router uses the IP RIP information to inform the other routers in the network of the
routes it finds in its own static table. The following entries are ignored in this process:
쮿
Rejected routes with the '0.0.0.0' router setting.
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Routes running on other routers in the local network.
쮿
Routes linking individual computers to the LAN by proxy ARP.
Although the entries in the static routing table are set manually, this information changes
according to the connection status of the router and so do the RIP packets transmitted.
쮿
If the router has established a connection to a remote station, it propagates all the
networks which can be reached via this route in the RIPs with the distance '1'. Other
routers in the LAN are thus informed by these means that a connection to the remote
station has been established on this router which they can use. The establishment
of additional connections by routers with dial-up connections can be prevented, thus
reducing connection costs.