This may be connected to another networks issue #18901.
docker version:

Client:
 Version:      1.9.1
 API version:  1.21
 Go version:   go1.4.2
 Git commit:   a34a1d5
 Built:        Fri Nov 20 13:12:04 UTC 2015
 OS/Arch:      linux/amd64

Server:
 Version:      1.9.1
 API version:  1.21
 Go version:   go1.4.2
 Git commit:   a34a1d5
 Built:        Fri Nov 20 13:12:04 UTC 2015
 OS/Arch:      linux/amd64

docker info:

Containers: 0
Images: 6
Server Version: 1.9.1
Storage Driver: aufs
 Root Dir: /var/lib/docker/aufs
 Backing Filesystem: extfs
 Dirs: 6
 Dirperm1 Supported: false
Execution Driver: native-0.2
Logging Driver: json-file
Kernel Version: 3.13.0-35-generic
Operating System: Ubuntu 14.04.3 LTS
CPUs: 4
Total Memory: 7.676 GiB
Name: hermes
ID: K5FF:7DYK:R4CX:SYUC:EWJD:4BIO:DOOC:IWEL:3PZI:7HYD:DHKB:F6EP
WARNING: No swap limit support

uname -a:
Linux hermes 3.13.0-35-generic #62-Ubuntu SMP Fri Aug 15 01:58:42 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

1. In the beginning sudo iptables -L:

   Chain INPUT (policy ACCEPT)
   target     prot opt source               destination         
   
   Chain FORWARD (policy ACCEPT)
   target     prot opt source               destination         
   DOCKER     all  --  anywhere             anywhere            
   ACCEPT     all  --  anywhere             anywhere             ctstate RELATED,ESTABLISHED
   ACCEPT     all  --  anywhere             anywhere            
   ACCEPT     all  --  anywhere             anywhere            
   
   Chain OUTPUT (policy ACCEPT)
   target     prot opt source               destination         
   
   Chain DOCKER (1 references)
   target     prot opt source               destination 
   

2. Execute docker network create A

3. Execute docker network rm A

4. Check again sudo iptables -L:

   Chain INPUT (policy ACCEPT)
   target     prot opt source               destination         
   
   Chain FORWARD (policy ACCEPT)
   target     prot opt source               destination         
   DOCKER     all  --  anywhere             anywhere            
   ACCEPT     all  --  anywhere             anywhere             ctstate RELATED,ESTABLISHED
   ACCEPT     all  --  anywhere             anywhere            
   ACCEPT     all  --  anywhere             anywhere            
   DOCKER     all  --  anywhere             anywhere            
   ACCEPT     all  --  anywhere             anywhere             ctstate RELATED,ESTABLISHED
   ACCEPT     all  --  anywhere             anywhere            
   ACCEPT     all  --  anywhere             anywhere            
   
   Chain OUTPUT (policy ACCEPT)
   target     prot opt source               destination         
   
   Chain DOCKER (2 references)
   target     prot opt source               destination    
   

5. In fact, if you do this many times:

for i in `seq 1 50`;
do
    docker network create N
    docker network rm N
done

Docker looses connectivity:
docker run -it --rm debian ping 8.8.8.8:

PING 8.8.8.8 (8.8.8.8): 56 data bytes
92 bytes from d986949dfb23 (172.17.0.1): Destination Host Unreachable
92 bytes from d986949dfb23 (172.17.0.1): Destination Host Unreachable
92 bytes from d986949dfb23 (172.17.0.1): Destination Host Unreachable

P.S. I have not figured out how to restore it yet. sudo iptables -F && sudo service docker restart does not help.