ELSA LANCOM Business 6000, Manual

Page: 142 / 174

Technical basics
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ELSA LANCOM Business 6000
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142
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7.4.9 IPX packet filters
With the entries in the routing table, it can be determined which other
networks are accessible. These networks are also accessible for such data
packets which are not actually required in the network of the remote station.
These packets can result in establishing undesired connections thus entailing
costs.
Therefore, appropriate filters must be used. For example, data packets which
are only used for internal communication of the networks can be excluded
from data transmission via WAN or at least restricted:
Propagated frames
These special data packets use protocols which cannot actually be
routed. In order to become a part of the common routing, this data is
encapsulated in normal IPX packets and transmitted as a broadcast.
Sometimes these packets are not desired when routing. Therefore, you
can explicitly adjust whether this packet type should be routed or filtered.
Socket filter
Each data packet in an IPX network not only contains target and source
addresses but also target and source sockets. Sockets designate the
processes for which the data in the packet are determined.
For the sockets from local as well as remote networks, there is a
corresponding filter table which contains the filters, with which
individual target sockets or complete socket groups can be excluded from
data transmission. Several sockets, which are known to be frequently
used for undesired connections, are entered by default in the socket filter
table.
RIP and SAP information
Via RIPs, a router informs other routers of all known routes (routes in
other networks) according to the split horizon principle. This includes not
only the entries from its own routing table, but also all routes which the
router acquired from other routers. It acquires routes not only from
routers from local networks, but also from remote networks. The router
enters all available routing information in its internal RIP table.
In SAP information, the servers provide their services. The various
services are represented within the SAP information by numbers. Each
service (e.g. file server or print server) has a distinct number. The router
includes the information on available services in the internal SAP table,