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CLI (Command Line Interface)
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NXA-ENET24 - Software Management Guide
IP ACL Commands (Cont.)
Command Function
mask
(IP ACL - Cont.)
Command Usage: Packets crossing a port are checked against all the
rules in the ACL until a match is found. The order in which these packets
are checked is determined by the mask, and not the order in which the ACL
rules were entered.
First create the required ACLs and ingress or egress masks before map-
ping an ACL to an interface.
If you enter dscp, you cannot enter tos or precedence. You can enter both
tos and precedence without dscp.
Masks that include an entry for a Layer 4 protocol source port or destina-
tion port can only be applied to packets with a header length of exactly five
bytes.
Example: This example creates an IP ingress mask with two rules. Each
rule is checked in order of precedence to look for a match in the ACL
entries. The first entry matching a mask is applied to the inbound packet:
Console(config)#access-list ip mask-precedence in
Console(config-ip-mask-acl)#mask host any
Console(config-ip-mask-acl)#mask 255.255.255.0 any
Console(config-ip-mask-acl)#
Example:
This shows that the entries in the mask override the precedence in which
the rules are entered into the ACL. In the following example, packets with
the source address 10.1.1.1 are dropped because the “deny 10.1.1.1
255.255.255.255” rule has the higher precedence according the “mask
host any” entry:
Console(config)#access-list ip standard A2
Console(config-std-acl)#permit 10.1.1.0 255.255.255.0
Console(config-std-acl)#deny 10.1.1.1 255.255.255.255
Console(config-std-acl)#exit
Console(config)#access-list ip mask-precedence in
Console(config-ip-mask-acl)#mask host any
Console(config-ip-mask-acl)#mask 255.255.255.0 any
Console(config-ip-mask-acl)#
Example:
This shows how to create a standard ACL with an ingress mask to deny
access to the IP host 171.69.198.102, and permit access to any others.
Console(config)#access-list ip standard A2
Console(config-std-acl)#permit any
Console(config-std-acl)#deny host 171.69.198.102
Console(config-std-acl)#end
Console#show access-list
IP standard access-list A2:
deny host 171.69.198.102
permit any
Console#configure
Console(config)#access-list ip mask-precedence in
Console(config-ip-mask-acl)#mask host any
Console(config-ip-mask-acl)#exit
Console(config)#interface ethernet 1/1
Console(config-if)#ip access-group A2 in
Console(config-if)#end
Console#show access-list
IP standard access-list A2:
deny host 171.69.198.102
permit any
Console#