Subnetting to lower broadcasts

whiteford · ‎01-29-2008

Hi, we are adding 6 new remote offices on our WAN, these offices range from 20 users to 40 users, for all these 6 offices I was going to use 172.30.1.x\25 to 172.30.6.x\25. This gives each office a maximum of 126 IP's for future expansion.

I was just going to set them as \24 class C and thought would \24, \25 or \26 really make much difference, due to the extra broadcasts etc?

Richard Burts · ‎01-29-2008

Andy

I am not sure that I understand your question. I do not see that whether it is /24 or /25 or /26 has any impact on how many broadcasts. Changing the mask (/24 or /25 or /26) will change how many addresses are reserved for each office but does not change how many broadcasts there are. Perhaps you can help me understand what I do not yet grasp in your question.

HTH

Rick

HTH

Rick

whiteford · ‎01-30-2008

Apologies, it's just my understanding. I just thought the bigger the subnet to allow more hosts the more broadcasts to all IP's in that subnet, whether the IP's are active or not.

I guess there is no difference in me using:

192.168.150.x/24 (class C)

or

172.30.1.x/24 (class B)

Whether classful or classless they are private addresses, I just had it in my head that the smaller the subnet the better due to broadcasts running riot :S

keeleym · ‎01-30-2008

Hi Andy

I think that whether you use a /24 or a /26 or indeed a /16 will not matter as far as broadcast traffic is concerned.

I think this will be set by the number of hosts which you place on these subnets. If each subnet is a broadcast domain and has 20 hosts, there could only be broadcast traffic from 20 hosts on a particular subnet. Granted a /16 or /24 will allow you to place more hosts on a particular subnet than a /26 will. But the scope of the subnet will not affect how much broadcast traffic is seen on a subnet. As mentioned above I think it will be down to the number of hosts.

Best Regards,

Michael