ACL is a mechanism for controlling access and functions of the node based on call-signs. This is done based on two numerical values, the "Mask" value and the "Default" value.
For example, if you enter your own call-sign with the default value, you get access under all circumstances. If you enter a call-sign with a value higher than the Default value, it is subject to evaluation with the Mask Value.
ACL * 0 < Assigns an ACL Default value
ACL & 127 < Assigns an ACL Mask value
ACL WX9BAD + 127 < Enters this call-sign and value to the ACL list
This means that WX9BAD will not be able to make an incoming or outgoing AX.25 connection (necessary to initiate a Net/Rom circuit), and will ignore the SSID. This corresponds to bit 0 +1, bit 1 +1, and bit 6 +1, which is 127.
The Mask means that your our node will only bar incoming and outgoing AX.25 connections, and will ignore the SSID of the listed station when checking the call-sign. Now we can get a little tricky.
I mentioned before that it is possible to keep everyone (including the sysop) from connecting to the node. Let's say, for examlple, that I am the Sysop of this node. I can prevent this from happening by the addition of this command:
ACL * 7 < Set the Default value at 7
ACL & 0 < Set the Mask value at 0 - No Mask used
ACL WX9GUD-5 + 64 < Set the ACL Value for this station to 64
Now we are guaranteed to be able to connect and make Level 3 and 4 connections to WX9GUD-5. Note that we have not set the "Ignore the SSID" Bit, so this entry only applies to WX9GUD-5. WX9GUD-3 would not be permitted these priveleges. Why?
There are reasons for doing this, mostly for network management. In the first example, we denied access to and from a node that is unreliable. In the second, we guaranteed access to a known, reliable node and made sure it was part of the network.
To change or deactivate the Default or Mask values, just enter a new value of 0. Here are a few examples:
ACL WX9BAD - < Removes WX9BAD from the ACL list.
ACL * 0 < Removes the Default value.
ACL & 0 < Removes the Mask value.
ACL - < Shuts off all ACL functions.
If you must use it, be sure to make certain that you use the above example of 0 default, your desired mask, and set several call-signs as 0 so that selected Sysops can connect to the node. I say "selected Sysops" just in case something happens when you are out of town or something prevents you from operating the node. You should have at least two other people set up to be able to Sysop the node if something keeps you from maintaining the node. Otherwise, your node may be inaccessable to the rest of the network. In Part 3, we'll continue our discussion with ADC.
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