Subnetting - Extend existing network

[Patrik Nechajev]

Hello,

I have ran into following issue. We have subnet 10.0.0.0/24 which is currently divided into 3 networks:

• One customer 10.0.0.0/27 (GW .1, Broad .31)
• Second customer 10.0.0.32/27 (GW .33, Broad .63)
• Third customer 10.0.0.64/27 (GW .65, Broad .95)

Problem is that we need to extend network for third customer to /26 so it will be:

• One customer 10.0.0.0/27 (GW .1, Broad .31)
• Second customer 10.0.0.32/27(GW .33, Broad .63)
• Third customer 10.0.0.64/26 (GW .65, Broad .127)

Will it cause any problems? No overlapping? Also i would like to minimize downtime as much as possible, what would be best approach? At first change subnet mask for active hosts and then change mask on vlan interface itself? There is no DHCP.

Thank you.

[Elliot Dierksen]

That should not be a problem since the third network was already in a segment that lines up as a /26. The sequence of changing the subnet mask for existing hosts doesn't matter until you start using IP's that are outside the original /27 range. Where you will see issues if a host does not have the subnet mask changed is talking between hosts in the old range and hosts in the new portion of the range.

[Patrik Nechajev]

Hello Elliot, thank you for explanation. So it should be just about changing the subnet mask to right value.

[Elliot Dierksen]

Yes, that should be it.

[Patrik Nechajev]

However /26 is lowest I can use, /25 would overlap with others, right? 

[Reza Sharifi]

/25 would overlap unless you want to go with 10.0.0.128/25 which would be from 129-254

HTH