10.4 Access Rules
Accesses to data and functions are restricted with access lists (which user gets to use
which services and files).
You define filters for IP packets in order to allow or block access from or to the various
hosts in connected networks. This enables you to prevent undesired connections being
set up via the gateway. Access lists define the type of IP traffic the gateway is to accept or
deny. The access decision is based on information contained in the IP packets, e.g.:
• source and/or destination IP address
• packet protocol
• source and/or destination port (port ranges are supported)
Access lists are an effective means if, for example, sites with LANs interconnected over a
bintec elmeg gateway wish to deny all incoming FTP requests or only allow Telnet ses-
sions between certain hosts.
Access filters in the gateway are based on the combination of filters and actions for filter
rules (= rules) and the linking of these rules to form rule chains. They act on the incoming
data packets to allow or deny access to the gateway for certain data.
A filter describes a certain part of the IP data traffic based on the source and/or destina-
tion IP address, netmask, protocol and source and/or destination port.
You use the rules that you set up in the access lists to tell the gateway what to do with the
filtered data packets, i.e. whether it should allow or deny them. You can also define sever-
al rules, which you arrange in the form of a chain to obtain a certain sequence.
There are various approaches for the definition of rules and rule chains:
Allow all packets that are not explicitly denied, i.e.:
• Deny all packets that match Filter 1.
• Deny all packets that match Filter 2.
• ...
• Allow the rest.
or
Allow all packets that are explicitly allowed, i.e.:
• Allow all packets that match Filter 1.
• Allow all packets that match Filter 2.
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