My firewall is blocking network connections from t

Question

For me this is a very standard setup, I had a ubuntu machine running docker and ufw as my firewall.

If my firewall is enable the docker instances is unable to connect to outside

$ docker run -i -t ubuntu /bin/bash
WARNING:  Docker detected local DNS server on resolv.conf. Using default external servers: [8.8.8.8 8.8.4.4]
root@d300c5f17207:/# apt-get update
Err http://archive.ubuntu.com precise InRelease
0% [Connecting to archive.ubuntu.com]
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/precise/InRelease  
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/precise/Release.gpg  Temporary failure resolving 'archive.ubuntu.com'
W: Some index files failed to download. They have been ignored, or old ones used instead.

Here is the ufw log showing the blocked connections from the docker container.

$ sudo tail /var/log/ufw.log
Jun 30 15:41:56 localhost kernel: [61609.503199] [UFW BLOCK] IN=testbr0 OUT=eth0 PHYSIN=veth8Rj8Nh MAC=fe:ff:ed:42:b0:01:0a:7c:42:7c:a6:72:08:00 SRC=172.16.42.2 DST=8.8.8.8 LEN=64 TOS=0x00 PREC=0x00 TTL=63 ID=14886 DF PROTO=UDP SPT=60192 DPT=53 LEN=44 
Jun 30 15:42:01 localhost kernel: [61614.500867] [UFW BLOCK] IN=testbr0 OUT=eth0 PHYSIN=veth8Rj8Nh MAC=fe:ff:ed:42:b0:01:0a:7c:42:7c:a6:72:08:00 SRC=172.16.42.2 DST=8.8.4.4 LEN=64 TOS=0x00 PREC=0x00 TTL=63 ID=16137 DF PROTO=UDP SPT=44812 DPT=53 LEN=44 
Jun 30 15:42:06 localhost kernel: [61619.498516] [UFW BLOCK] IN=testbr0 OUT=eth0 PHYSIN=veth8Rj8Nh MAC=fe:ff:ed:42:b0:01:0a:7c:42:7c:a6:72:08:00 SRC=172.16.42.2 DST=8.8.8.8 LEN=64 TOS=0x00 PREC=0x00 TTL=63 ID=14887 DF PROTO=UDP SPT=60192 DPT=53 LEN=44

I had try adding a rule using the ip.

$ sudo ufw allow in from 172.16.42.2
$ sudo ufw allow out from 172.16.42.2

And have no change is still blocked.

How can I esily allow all connections from the container to outside with a ufw rule?

Answer 1

Edit /etc/ufw/before.rules as follows:

In the *filter section, after the first block of required lines, add:

# docker rules to enable external network access from the container
# forward traffic accross the bridge 
-A ufw-before-forward -i docker0 -j ACCEPT
-A ufw-before-forward -i testbr0 -j ACCEPT
-A ufw-before-forward -m state --state RELATED,ESTABLISHED -j ACCEPT

At the end of the file, after the line that says COMMIT, add the following section:

*nat
:POSTROUTING ACCEPT [0:0]
-A POSTROUTING -s 172.16.42.0/8 -o eth0 -j MASQUERADE
# don't delete the 'COMMIT' line or these rules won't be processed
COMMIT

After saving the file, restart ufw with sudo ufw disable && sudo ufw enable

Answer 2

Maybe this is due to the current version, but the current answer doesn't work on my system (Docker 0.7.2 with base Ubuntu image).

The solution is explained here in the official Docker documentation.

For the lazy ones:

• edit /etc/default/ufw to change DEFAULT_FORWARD_POLICY's value to "ACCEPT",
• reload with [sudo] ufw reload.

This ensures ufw forward your traffic to the Docker's bridged network (as of my current understanding of these things...).

Answer 3

Are you sure that ufw allow the connection on the port concerned ?

Answer 4

This fixed it for me:

 ufw allow in on docker0