Brocade Communications Systems ServerIron ADX 12.4.00a - Manual (Page 81)

ServerIron ADX Security Guide 67
53-1002440-03
Modifying ACLs
2
Modifying ACLs
When you use the Brocade device’s CLI to configure any ACL, the software places the ACL entries in
the ACL in the order you enter them. For example, if you enter the following entries in the order
shown below, the software always applies the entries to traffic in the same order.
ServerIronADX(config)# access-list 1 deny 209.157.22.0/24
ServerIronADX(config)# access-list 1 permit 209.157.22.26
If a packet matches the first ACL entry in this ACL and is therefore denied, the software does not
compare the packet to the remaining ACL entries. In this example, packets from host
209.157.22.26 will always be dropped, even though packets from this host match the second
entry.
You can use the CLI to reorder entries within an ACL by individually removing the ACL entries and
then re-adding them. To use this method, enter “no” followed by the command for an ACL entry,
and repeat this for each ACL entry in the ACL you want to edit. After removing all the ACL entries
from the ACL, re-add them.
This method works well for small ACLs such as the example above, but can be impractical for ACLs
containing many entries. Therefore, Brocade devices provide an alternative method. The alternative
method lets you upload an ACL list from a TFTP server and replace the ACLs in the device’s
running-config file with the uploaded list. Thus, to change an ACL, you can edit the ACL on the file
server, then upload the edited ACL to the device. You then can save the changed ACL to the
device’s startup-config file.
ACL lists contain only the ACL entries themselves, not the assignments of ACLs to interfaces. You
must assign the ACLs on the device itself.
NOTE
The only valid commands that are valid in the ACL list are the access-list and end commands. The
Brocade device ignores other commands in the file.
To modify an ACL by configuring an ACL list on a file server.
1. Use a text editor to create a new text file. When you name the file, use 8.3 format (up to eight
characters in the name and up to three characters in the extension).
NOTE
Make sure the Brocade device has network access to the TFTP server.
2. Optionally, clear the ACL entries from the ACLs you are changing by placing commands such as
the following at the top of the file.
no access-list 1
no access-list 101
When you load the ACL list into the device, the software adds the ACL entries in the file after
any entries that already exist in the same ACLs. Thus, if you intend to entirely replace an ACL,
you must use the no access-list <num> command to clear the entries from the ACL before the
new ones are added.
3. Place the commands to create the ACL entries into the file. The order of the separate ACLs
does not matter, but the order of the entries within each ACL is important. The software applies
the entries in an ACL in the order they are listed within the ACL. Here is an example of some
ACL entries.