Subnet Mask Change

[mamuwahig1]

I need to change the subnet mask on a vlan that a customer has from a /26 to a /25.  Before I do that I want to be sure that the only issue I see is that changing this will be that anything configured in the first 64 addresses that has a static IP address means that the old static item will not be able to communicate with the devices in the new upper 64 addreess?  Is that what everyone else sees?

Thanks for your help in advance.

Mamu

[Jon Marshall · Accepted solution]

Mamu

Yes, you are correct. The devices configured with a /26 will think the devices in the other /26 are on a different subnet so will send packets to their defautl gateway.

You may be able to use secondary addressing on the L3 interface as a temporary measure until you change the subnet mask on clients or hopefully in the DHCP scope.

Jon

[Joseph W. Doherty]

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Posting

What could be a problem, your /26 and /25 will disagree about what's the (L3) subnet broadcast address.  In fact, what the /26 will see as its subnet broadcast address the /25 will see as a host address.