Adding additional documentation for fixed-cidr networking

Docker-DCO-1.1-Signed-off-by: Frederick F. Kautz IV <fkautz@alumni.cmu.edu> (github: fkautz)

Signed-off-by: Alexandr Morozov <lk4d4@docker.com>

daemon/config.go

@@ -51,7 +51,7 @@ func (config *Config) InstallFlags() {
 	flag.BoolVar(&config.EnableIpForward, []string{"#ip-forward", "-ip-forward"}, true, "Enable net.ipv4.ip_forward")
 	flag.StringVar(&config.BridgeIP, []string{"#bip", "-bip"}, "", "Use this CIDR notation address for the network bridge's IP, not compatible with -b")
 	flag.StringVar(&config.BridgeIface, []string{"b", "-bridge"}, "", "Attach containers to a pre-existing network bridge\nuse 'none' to disable container networking")
-	flag.StringVar(&config.FixedCIDR, []string{"-fixed-cidr"}, "", "IPv4 subnet for fixed IPs (ex: 10.20.0.0/16)\nthis subnet must be nested in bridge subnet (which is defined by -b or --bip)")
+	flag.StringVar(&config.FixedCIDR, []string{"-fixed-cidr"}, "", "IPv4 subnet for fixed IPs (ex: 10.20.0.0/16)\nthis subnet must be nested in the bridge subnet (which is defined by -b or --bip)")
 	flag.BoolVar(&config.InterContainerCommunication, []string{"#icc", "-icc"}, true, "Enable inter-container communication")
 	flag.StringVar(&config.GraphDriver, []string{"s", "-storage-driver"}, "", "Force the Docker runtime to use a specific storage driver")
 	flag.StringVar(&config.ExecDriver, []string{"e", "-exec-driver"}, "native", "Force the Docker runtime to use a specific exec driver")

docs/man/docker.1.md

@@ -49,6 +49,10 @@ unix://[/path/to/socket] to use.
 **-g**=""
   Path to use as the root of the Docker runtime. Default is `/var/lib/docker`.
 
+
+**--fixed-cidr**=""
+  IPv4 subnet for fixed IPs (ex: 10.20.0.0/16); this subnet must be nested in the bridge subnet (which is defined by \-b or \-\-bip)
+
 **--icc**=*true*|*false*
   Enable inter\-container communication. Default is true.
 

docs/sources/articles/networking.md

@@ -54,6 +54,9 @@ server when it starts up, and cannot be changed once it is running:
  *  `--bip=CIDR` — see
     [Customizing docker0](#docker0)
 
+ *  `--fixed-cidr` — see
+    [Customizing docker0](#docker0)
+
  *  `-H SOCKET...` or `--host=SOCKET...` —
     This might sound like it would affect container networking,
     but it actually faces in the other direction:
@@ -365,17 +368,25 @@ By default, the Docker server creates and configures the host system's
 can pass packets back and forth between other physical or virtual
 network interfaces so that they behave as a single Ethernet network.
 
-Docker configures `docker0` with an IP address and netmask so the host
-machine can both receive and send packets to containers connected to the
-bridge, and gives it an MTU — the *maximum transmission unit* or largest
-packet length that the interface will allow — of either 1,500 bytes or
-else a more specific value copied from the Docker host's interface that
-supports its default route.  Both are configurable at server startup:
+Docker configures `docker0` with an IP address, netmask and IP
+allocation range. The host machine can both receive and send packets to
+containers connected to the bridge, and gives it an MTU — the *maximum
+transmission unit* or largest packet length that the interface will
+allow — of either 1,500 bytes or else a more specific value copied from
+the Docker host's interface that supports its default route.  These
+options are configurable at server startup:
 
  *  `--bip=CIDR` — supply a specific IP address and netmask for the
     `docker0` bridge, using standard CIDR notation like
     `192.168.1.5/24`.
 
+ *  `--fixed-cidr=CIDR` — restrict the IP range from the `docker0` subnet,
+    using the standard CIDR notation like `172.167.1.0/28`. This range must
+    be and IPv4 range for fixed IPs (ex: 10.20.0.0/16) and must be a subset
+    of the bridge IP range (`docker0` or set using `--bridge`). For example
+    with `--fixed-cidr=192.168.1.0/25`, IPs for your containers will be chosen
+    from the first half of `192.168.1.0/24` subnet.
+
  *  `--mtu=BYTES` — override the maximum packet length on `docker0`.
 
 On Ubuntu you would add these to the `DOCKER_OPTS` setting in

docs/sources/reference/commandline/cli.md

@@ -55,6 +55,7 @@ expect an integer, and they can only be specified once.
                                                    use 'none' to disable container networking
       --bip=""                                   Use this CIDR notation address for the network bridge's IP, not compatible with -b
       --fixed-cidr=""                            IPv4 subnet for fixed IPs (ex: 10.20.0.0/16)
+                                                   this subnet must be nested in the bridge subnet (which is defined by -b or --bip)
       -D, --debug=false                          Enable debug mode
       -d, --daemon=false                         Enable daemon mode
       --dns=[]                                   Force Docker to use specific DNS servers