What is IPv6 Dual stack? What does IPv6 dual stack exactly mean?

What is IPv6 dual stack ? From some questions and comments on the website, I understand that there is a confusion about it. So, what does exactly dual stack IPv6 mean ? IPv6 is not a luxury anymore. It is not avoidable for the Service Providers especially. The biggest problem for the Service Providers is IPv4 address exhaustion.

If a provider requests an IPv4 public address, RIRs (Regional Internet Registries) cannot provide anymore an IPv4 public addresses. All available addresses are allocated. Does it mean, operators have to deploy IPv6 ? Of course not ! Still there are many methods to postpone the deployment of IPv6. These are; Buying an IPv4 public addresses from the other companies – This is real, in fact, some of my customers purchased public IPv4 address blocks.

They are in Middle East and currently they don’t have any problem with their new address blocks. I see many companies doing LSN (Large Scale NAT) or it is more commonly known as CGN (Carrier Grade NAT). There are more problems with LSN than purchasing an IPv4 address blocks from market space. I won’t go to details of alternatives of IPv6 in this post but will continue with the definition of IPv6 dual stack.

If you say that we have IPv6 dual stack, it means , the customer access network device (Modems, ONUs, Phones) , provider network devices , applications inside the operator network, Internet peering and transit links , everything are running both IPv4 and IPv6.

I see many different deployment models on my customer and the students networks, and those who have deployed IPv6 only on their networking devices and the transit links are saying that they have an IPv6 dual stack deployment. This is not true. They just deployed IPv6 on the operator network and the upstream operator connections. But most of their users are not using IPv6, since they don’t provide an IPv6 addresses to their customers.

Having IPv6 ready core network doesn’t mean , your users are using IPv6 path to reach destinations. Destination can be Internet , Customer VPN sites , SP Datacenter and so on. IPv6 have to be deployed on all these locations. Of course IPv4, alongside with IPv6 need to be deployed for dual stack. But this is not always possible. Do you know why ? Read my ‘ Is IPv6 dual stack really a best approach for IPv6 deployment ‘ post.

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Orhan Ergun

Orhan Ergun, CCIE/CCDE Trainer, Author of Many Networking Books, Network Design Advisor, and Cisco Champion 2019/2020/2021

He created OrhanErgun.Net 10 years ago and has been serving the IT industry with his renowned and awarded training.

Wrote many books, mostly on Network Design, joined many IETF RFCs, gave Public talks at many Forums, and mentored thousands of his students.  

Today, with his carefully selected instructors, OrhanErgun.Net is providing IT courses to tens of thousands of IT engineers. 

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