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App Note A: Use of IP Restrictions
SNMP Access Gateway User’s Manual - v1.0 -- 11/99 - Page 50
App Note A. Use of IP Restrictions
IP Restrictions can be established to limit which IP Addresses are allowed access to the SNMP Access Gateway.
The IP Restrictions menu can be found in the Networking section of the SETUP menu. By using this menu you can
enter in IP addresses into a table to specify which addresses are allowed access and which addresses are denied
access to the unit.
The following rules apply to IP addresses entered into this table.
1) By default, there are no entries in the IP Restriction table. With no entries in the table, all IP addresses are
allowed access to the unit. However, once any entry is placed into the IP Restriction table, only those IP addresses
which are explicitly specified in the table will be allowed access to the unit. For this reason you should be very
careful with this feature to avoid accidentally prohibiting your own network access to the unit.
1) A ZERO placed anywhere in the IP address acts as a wildcard to ALLOW access to any IP address matching the
other values of that table entry. For example, 192.168.100.0 entered into the table will allow access to any IP
address starting with 192.168.100 and prohibiting access in any form from ALL other IP addresses.
2) A 255 placed anywhere in the IP address acts as a wildcard to PROHIBIT access to any IP address matching the
other values of that table entry. For example, 192.168.200.255 entered into the table will prohibit access to any IP
address starting with 192.168.200.
3) A full address entered into the table will explicitly allow access to that IP address. For example, entering
192.168.200.001 explicitly allows that address access to the unit.
4) Each IP address attempting access to the unit is evaluated against the table of entries, from the first entry down to
the last entry of the table. The first match which explicitly PROHIBITS an IP address will immediately cause access
to the unit to be denied. The first match found which explicitly ALLOWS an IP address will immediately cause
access to be allowed. You need to be careful that the logical order of your entries does not cause an earlier entry to
deny access to a latter entry which you allow access to, and vice versa.
5) If no match is found by the time all entries of the table have been examined, the IP address will be denied access
to the unit. However, you can approach it in the opposite fashion if you place 0.0.0.0 as the last entry in the table.
Then, all prior entries can be those for which access is specifically denied, with all other addresses being allowed
access.
6) If you make a mistake and deny your own IP address access, you will have to fix this using the dialup connection
or the local command mode connection to change the IP restriction back so you can have access again.
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