Configuring Access Control Lists 593
Using IP and MAC Address Masks
Masks are used with IP and MAC addresses to specify what should be
considered in the address for a match. Masks are expanded internally into a
bit mask and are applied bit-wise in the hardware even though they are
entered in decimal or hexadecimal format. Masks need not have contiguous 0
or 1 bits. A 0 bit value in the mask indicates that the address field in the
packet being compared must match the address bit exactly. A 1 value in the
mask indicates a wildcard or don't care value, i.e. the access bits are not
compared and match any possible value. For example, an IP address of 3.3.3.3
with a mask of 0.0.0.0 indicates that the ACL matches on all four bytes of the
IP address. Likewise, a MAC address of 68:94:23:AD:F3:18 with a mask of
00:00:00:00:00:ff indicates that the first five bytes must match (e.g.,
68:94:23:AD:F3) and the last byte may take on any value from 0x00 to 0xff
(0–255) and still be considered a match.
The following ACL equivalents are noted:
0x08 EGP
0x09 IGP
0x11 UDP
Address Mask Equivalent Address
0.0.0.0 255.255.255.255 any
x.x.x.x host x.x.x.x
0:0:0:0:0:0 ff:ff:ff:ff:ff:ff any
Table 20-3. Common IP Protocol Numbers (Continued)
IP Protocol Number Protocol
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