Block from ARIN

Hello our company has registered with ARIN and we have a block of IPV6 addresses. My question is since we have a global unicast address, is there any reason to use the unique local addresses? Reading the one blog, “The big difference with IPv6 is that we have so much address space that we can use global unicast addresses on any device in the network.”

Just trying to make sure I design this properly. Thanks!

Hello Chad

The primary purpose of IPv4 private addresses in conjunction with NAT, is to deal with IPv4 address exhaustion. With IPv6, that problem has disappeared, so why do we need unique local addresses, which are the counterpart of private IPv4 addresses?

Well, the reasoning behind unique local addresses for IPv6 is not to solve the address space exhaustion problem, but to enable enterprises to use IPv6 within their networks, without having to obligatorily register an IPv6 address range as you have done.

Unique local addresses can be freely used without registration. Of course, you can choose a random block of global unicast IPv6 addresses and use those without any problems, but there is a slight chance that one of those addresses will be used on the Internet at some point. If that’s the case, you may find that you’ll have connectivity problems to any services delivered using that IPv6 address.

Unique local addresses ensure that such a situation will not occur.

Now if you have registered a block of IPv6 addresses for use in your enterprise, and you have enough of them to serve your internal hosts, then by all means use them, since registration is not an obstacle for your particular organization.

I hope this has been helpful!


Thanks Laz for the clarification. That makes complete sense. I will continue to use my global unicast addresses that are assigned to us.


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