network: Updates to IPv6 address pools

- a ULA prefix is used if there's no IPv6 in default-address-pools
- restrictions on IPv6 subnet size and number of pools have been removed

Signed-off-by: Rob Murray <rob.murray@docker.com>

content/config/daemon/ipv6.md

@@ -12,6 +12,12 @@ IPv6 is only supported on Docker daemons running on Linux hosts.
 
 - Using `docker network create`:
 
+  ```console
+  $ docker network create --ipv6 ip6net
+  ```
+
+- Using `docker network create`, specifying an IPv6 subnet:
+
   ```console
   $ docker network create --ipv6 --subnet 2001:db8::/64 ip6net
   ```
@@ -43,8 +49,9 @@ Hostname: ea1cfde18196
 IP: 127.0.0.1
 IP: ::1
 IP: 172.17.0.2
+IP: 2001:db8::2
 IP: fe80::42:acff:fe11:2
-RemoteAddr: [fe80::42:acff:fe11:2]:54890
+RemoteAddr: [2001:db8::1]:37574
 GET / HTTP/1.1
 Host: [::1]
 User-Agent: curl/8.1.2
@@ -94,8 +101,9 @@ Hostname: ea1cfde18196
 IP: 127.0.0.1
 IP: ::1
 IP: 172.17.0.2
-IP: fe80::42:acff:fe11:2
-RemoteAddr: [fe80::42:acff:fe11:2]:54890
+IP: 2001:db8:1::242:ac12:2
+IP: fe80::42:acff:fe12:2
+RemoteAddr: [2001:db8:1::1]:35558
 GET / HTTP/1.1
 Host: [::1]
 User-Agent: curl/8.1.2
@@ -107,11 +115,16 @@ Accept: */*
 If you don't explicitly configure subnets for user-defined networks,
 using `docker network create --subnet=<your-subnet>`,
 those networks use the default address pools of the daemon as a fallback.
-The default address pools are all IPv4 pools.
 This also applies to networks created from a Docker Compose file,
 with `enable_ipv6` set to `true`.
 
-To enable dynamic subnet allocation for user-defined IPv6 networks,
+If no IPv6 pools are included in Docker Engine's `default-address-pools`,
+and no `--subnet` option is given, [Unique Local Addresses (ULAs)][wikipedia-ipv6-ula]
+will be used when IPv6 is enabled. These `/64` subnets include a 40-bit
+Global ID based on the Docker Engine's randomly generated ID, to give a
+high probability of uniqueness.
+
+To use different pools of IPv6 subnets for dynamic address allocation,
 you must manually configure address pools of the daemon to include:
 
 - The default IPv4 address pools
@@ -135,20 +148,7 @@ The default address pool configuration is:
 
 The following example shows a valid configuration with the default values and
 an IPv6 pool. The IPv6 pool in the example provides up to 256 IPv6 subnets of
-size `/112`, from an IPv6 pool of prefix length `/104`. Each `/112`-sized
-subnet supports 65 536 IPv6 addresses.
-
-> **Note**
->
-> Be aware that the following known limitations exist for IPv6 pools:
->
-> - The `base` value for IPv6 needs a minimum prefix length of `/64`.
->   This is due to an integer overflow in the Docker daemon.
->   See [moby/moby#42801](https://github.com/moby/moby/issues/42801).
-> - The difference between the pool length and the pool size can't be larger
->   than 24. Defining an excessive number of subnets causes the daemon to
->   consume all available memory.
->   See [moby/moby#40275](https://github.com/moby/moby/issues/40275).
+size `/64`, from an IPv6 pool of prefix length `/56`.
 
 ```json
 {
@@ -160,18 +160,19 @@ subnet supports 65 536 IPv6 addresses.
     { "base": "172.24.0.0/14", "size": 16 },
     { "base": "172.28.0.0/14", "size": 16 },
     { "base": "192.168.0.0/16", "size": 20 },
-    { "base": "2001:db8::/104", "size": 112 }
+    { "base": "2001:db8::/56", "size": 64 }
   ]
 }
 ```
 
 > **Note**
 >
-> The address `2001:db8` in this example is
+> The address `2001:db8::` in this example is
 > [reserved for use in documentation][wikipedia-ipv6-reserved].
 > Replace it with a valid IPv6 network.
+>
 > The default IPv4 pools are from the private address range,
-> the IPv6 equivalent would be [ULA networks][wikipedia-ipv6-ula].
+> similar to the default IPv6 [ULA][wikipedia-ipv6-ula] networks.
 
 [wikipedia-ipv6-reserved]: https://en.wikipedia.org/wiki/Reserved_IP_addresses#IPv6
 [wikipedia-ipv6-ula]: https://en.wikipedia.org/wiki/Unique_local_address