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In IPv4, do private address ranges have a default subnet mask?

In this expert response, Silvia Hagen explains the relationship between private IP address range and default subnet masks. She also informs us about new address types coming up in IPv6 that will make subnetting and addressing easier.

QUESTION: In IPv4, do the private addresses of range 10 series, 172 series, and 192 series have a default subnet mask?

For example: 10 series belongs to Class A IP addressing, but can we use default subnet mask of Class C 255.255.255.0 for it?

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No they do not. Many companies in fact use addresses out of the 10 range but subnet them like a Class C address depending on the requirements of their networks.

With IPv6, there are no private address ranges defined anymore. NAT is something we should get rid of, because it breaks the end-to-end model. With IPv6 there are new address types used. For instance, you could use the link-local or site-local IPv6 address for internal communication that doesn't have to be routed to the Internet.

This was first published in September 2008

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