acl wildcard masks

nathan8

what wildcard mask would you use to specify the whole 192.168.6.0 /30 network.
I thought it would be 0.0.0.3 as a 30 bit subnet mask is 255.255.255.252
and 256 - 252 = 4 and it would be 1 less which is 3 so 0.0.0.3

Please help

nathan

marlon23

192.168.6.0 255.255.255.252 is subnet-zero so be carefull about its usage. (#ip subnet-zero <-- global configuration mode command to enable it).

Wildcard mas is correct 0.0.0.3, but the formula is little different. Calculation is "255.255.255.255 minus subnet-mask"

so:
255.255.255.255
- - - -
255.255.255.252
= = = =
0 . 0 . 0 . 3

with this math you can cover whole subnet with wildcard mask, and its so easy and really fast.

Hope this formula was clear to understand