User’s
Manual 249
source-port
Check the protocol source port field.
destination-port
Check the protocol destination port field.
port-bitmask
Protocol port of rule must match this bitmask. (Range: 0-65535)
control-flag
Check the field for control flags.
flag-bitmask
Control flags of rule must match this bitmask. (Range: 0-63)
Default
None
Command Mode
IP Mask
Usage Guidelines
Use this command to check packets crossing a port against the rules set in the ACL until it finds a match.
The order the rules entered in the ACL file do not determine the order the packets are checked.
You must first create the required ACLs and ingress or egress masks before mapping 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 destination port only apply 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)#
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)#
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