Wildcard Masks


When compared to an IP address, a wildcard mask will identify what addresses get matched for placement into an area:

  • A 0 (zero) in a wildcard mask means to check the corresponding bit in the address for an exact match.

  • A 1 (one) in a wildcard mask means to ignore the corresponding bit in the addresscan be either 1 or 0.

Example 1. 172.16.0.0 0.0.255.255
 172.16.0.0  = 10101100.00010000.00000000.00000000 0.0.255.255 = 00000000.00000000.11111111.11111111 ----------------------------------------------------------------------      Result = 10101100.00010000.xxxxxxxx.xxxxxxxx               172.16.x.x (anything between 172.16.0.0 and 172.16.255.255) 

Tip:

An octet of all zeros means that the address has to match exactly to the address. An octet of all ones means that the address can be ignored.


Example 2. 172.16.8.0 0.0.7.255
172.168.8.0 = 10101100.00010000.00001000.00000000 0.0.0.7.255 = 00000000.00000000.00000111.11111111 ----------------------------------------------------------------------      Result = 10101100.00010000.00001xxx.xxxxxxxx    00001xxx = 00001000 to 00001111 = 815    xxxxxxxx = 00000000 to 11111111 = 0255               Anything between 172.16.8.0 and 172.16.15.255 




CCNA Self-Study(c) CCNA Portable Command Guide
CCNA Portable Command Guide
ISBN: 1587201585
EAN: 2147483647
Year: 2006
Pages: 261
Authors: Scott Empson

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