Changing subnet mask in an ASA interface

Answered Question
Aug 8th, 2012
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Hi,

We have an ASA 5520, working fine.

One of the interfaces is connected to users PCs and printers mainly. Last months the number of devices has grown rapidly, and we would like to make some changes in it in order for it to be able to host new devices.We thought on change subnet mask of actual subnet (10.0.2.0/24) to 10.0.2.0/23, so it can hold as many devices.

I understand I have to make some changes in the ASA, but my question is:

What will happend to the acces rules I have created?

Will I need to create them again?

There are some objects which carry information about subnet mask, so I suppose I will need to redefine them, but for those without any subnet mask information, will I have to redefine them?

Thank you very much for your answers.

Kind Regards.

David Fernandez

Correct Answer by Jennifer Halim about 5 years 1 week ago

Your access rules will remain the same, you don't have to create them again. Access rule that has subnet mask of 255.255.255.0, you would need to change to 255.255.254.0 to cater for the additional host.

Your existing host, you would also need to change the subnet mask to match the ASA mask once you change it.

For those object which carry information on subnet mask, just change the subnet mask to the new one. Others without any subnet mask, you don't need to worry.


Hope that answers your question.

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Correct Answer
Jennifer Halim Wed, 08/08/2012 - 09:28
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  • Cisco Employee,

Your access rules will remain the same, you don't have to create them again. Access rule that has subnet mask of 255.255.255.0, you would need to change to 255.255.254.0 to cater for the additional host.

Your existing host, you would also need to change the subnet mask to match the ASA mask once you change it.

For those object which carry information on subnet mask, just change the subnet mask to the new one. Others without any subnet mask, you don't need to worry.


Hope that answers your question.

david.fernandez... Wed, 08/08/2012 - 09:41
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Hi Jennifer,

It quite well responds my question.Thank you very much.

So I will apply the new configuration.

Thank you very much and best regards.

David Fernandez.

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