Enabling dualstack connections

When working with Fastly, you can enable IPv6 to allow for dualstack connections, meaning traffic to your websites and applications can be served over both IPv4 and IPv6. This can be done without any changes to your backend infrastructure and shouldn’t negatively impact performance as most modern clients implement an approach called Happy Eyeballs. With this approach, clients connect over either IPv4 or IPv6, whichever is faster, choosing IPv6 over IPv4 when all else is equal.

To enable traffic to be served over IPv6 and IPv4 addresses, follow the instructions below appropriate to your CNAME record. If you're using one of our TLS products, you can find your CNAME records in the HTTPS and network tab, under DNS details. If the name ends in map.fastly.net, it is a customer-specific hostname. Otherwise, it is a Fastly-shared hostname.

Once enabled, test that you can connect over IPv6.

Limitations and considerations

Note the following limitations and considerations:

• Fastly only supports IPv6 connections to origin servers in Compute.
• If you use our Anycast IPv4 addresses for apex domains, contact Fastly support and we’ll provide you with the appropriate Anycast IPv6 addresses.
• Fastly's geolocation features work with IPv6 addresses.
• You can track whether a request came in as an IPv6 request with the req.is_ipv6 VCL variable as well as by the IPv6 format itself when logging %h.

Enabling dualstack for Fastly-shared hostnames

You can enable IPv6 dualstack (IPv4 and IPv6) functionality for your hostname by prefixing your CNAME record with dualstack. For example, if you have traffic on an IP address pool nicknamed j.sni (which supports a minimum TLS version of 1.2, a maximum TLS version of 1.3, does not support 0RTT, and offers HTTP/2), then you could use the following dualstack options:

• dualstack.j.sni.global.fastly.net (dualstack global map)
• dualstack.j.sni.us-eu.fastly.net (dualstack NA/EU)

If you are using m.ssl (which supports a minimum and maximum TLS version of 1.2 and HTTP/1.x only), then you could use the following dualstack options:

• dualstack.m.ssl.global.fastly.net (dualstack global map)
• dualstack.m.ssl.us-eu.fastly.net (dualstack NA/EU)

Enabling dualstack on customer-specific hostnames

If you have a customer-specific hostname, contact support and we'll provide you with a parallel IPv6 map or enable dualstack on your current one. By default, maps will be HTTP/2 enabled and have a global billing region set. Be sure to specify any required changes when having a new map created.

Testing IPv6

Once you’re up and running with IPv6, test IPv6 by entering a dig command in a terminal application to make sure your map returns AAAA records. For example, you can type something similar to this:

$ dig www.example.com AAAA +short

where www.example.com is the domain that you’re testing.

Your output should appear similar to the following:

2606:2800:220:1:248:1893:25c8:1946

You can also use a tool like What's my DNS and choose the AAAA option to see how clients around the world are resolving to your CNAME record.