CCNA subnetting question

Traditionally, the first and the last subnet (zero subnet and all-ones subnet) were reserved. However, Cisco routers can be configured to override that using the command "ip subnet-zero". This command is enabled by default since IOS version 12.0. For details, please refer to this link:

formatting link


formatting link
- Free CCNA Study Guide

Reply to
Loading thread data ...

kplab napisa³(a):

Yes, but even Cisco is not using this restriction and also learning (CiscoPress, curriculum) not to use it. Its historical.

Reply to

Usually, when we need 7 subnets, we would use the four bit subnet mask, that is 240. Some CCNA examples in the textbook show the use of three bit subnet mask. It uses both the subnet-zero and the broadcast subnet. Is that correct?

Will it cause any confusion?


Reply to

Janice napisa³(a):

What subnet mask you use depends on how many subnets you need to create and how many stations you have to connect in this subnet. If you are creating subnets just for connections between two routers you need two IPs (one for each router) so You'll use subnet mask With four bit subnet mask there'll be 14 IPs for machines connected to this subnet.

There is no such thing as broadcast subnet. There is broadcast IP address in every subnet, and its the last IP in this subnet, ie. for subnet its

There are many schemes of IP addressing you can use in each task, it all depends on how many IPs you need in ever subnet and what subnet you are subnetting. Its OK to use zero-subnet.

Reply to
_PepeR_ Forums website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.