vlan segregation

Unanswered Question
Jan 9th, 2008

Hi frds

i have a subnet of, i want to futher segregat it so that i can get around 30 hosts in a subnet and around 170 hosts in other . Is it possible and if it is, than how ?

can u guys help me


I have this problem too.
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Jon Marshall Wed, 01/09/2008 - 23:34

Hi Jagdev

No it is not possible. You can get the 30 host subnet but you can't get the 170 host subnet because the largest you could support would be a /25 ie.

which gives hosts -> + broacast of


Kevin Dorrell Thu, 01/10/2008 - 01:50


As Jon says, it is not possible to divide the address space asymetrically because you have to split it on a bit boundary. However, if your objective is to split the space into two VLANs, there is a slightly messy trick you could use: split it three ways (one /25 and two /26) and put two subnet (the /25 and a /26) on one VLAN.

In the following example, VLAN 221 handles the address space from to, and VLAN 222 handles the address space from to

int vlan 221

ip address


int vlan 222

ip address

ip address secondary

Of course, you have to avoid issuing addresses that conflict with any of the base addresses, gateway addresses, or directed broadcast addresses.

For the hosts in VLAN 222, there are two ways you could configure them:

1. You could give them different gateway addresses depending on which subnet they fall into,

2. You could give them all a /24 mask and tell them to use or as gateway - it doesn't matter which. In this case, if they wanted to talk to any hosts in VLAN 221, they would be relying on proxy-arp responses from the switch.

Kevin Dorrell



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