CCNA 3.2.a: Prefix

Overview:

A prefix is simply the network address. In a routing table, the prefix is the destination network address.  A prefix-length is just the shorthand way to express a subnet mask using CIDR notation.  If the subnet mask is 255.255.255.0 than the prefix-length is /24.

 

Study Notes:

Show IP Route Image

 

  • Reading the routing table from top to bottom you can see the prefixes and prefix-lengths for the destination networks:
    • 0.0.0.0/0    The prefix is 0.0.0.0 and the prefix-length is /0
    • 172.16.0.0/16    The prefix is 172.16.0.0 and the prefix-length is /16, but this isn't a route just a summary
    • 172.16.1.0/24    The prefix is 172.16.1.0 and the prefix-length is /24
    • 172.16.1.1/32    You got this
    • 172.16.2.0/24    I'll show a couple more to make sure
    • 172.16.3.0/24
    • 172.16.4.0/28
    • 192.168.0.0/16    The prefix is 192.168.0.0 and the prefix-length is /16
    • 209.165.200.0/24
    • 209.165.200.224/30
    • 209.165.200.224/32
    • 209.165.200.225/32    The prefix is 209.165.200.225 and the prefix-length is /32
    • 209.165.200.228/30
    • 209.165.200.232/30
    • 209.165.200.233/32
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