I have set up a docker container with a vpn. I added another container with a Squid proxy using the --net option, sharing the same network as the vpn. Running a traceroute from within the container I am able to see that traffic is routed through the vpn. Squid is running in the proxy container on it's default port 3128. If I configure a firefox to use this proxy, 172.17.0.2:3128, it will use the proxy to access the Internet using the vpn. However, why does this only work on my docker host machine? If I try this from my workstation I get a timeout. I can try the same thing using telnet,
On the docker host the following results in a timeout,
torbjorn@base telnet 192.168.1.100 3128
On the docker host the following result in a connection,
torbjorn@base telnet localhost 3128
I made further attempts with tcpdump and route and I get to the conclusion that packets get lost in the first case. One possibility that comes to mind is that perhaps docker added a route so that packets from the docker host is routed back to the host. Is it possible that packets originating somewhere else are routed down the vpn? What can I do to resolve this situation so that I can use this http proxy from other machines than the docker host?
I enabled ip forward on the docker host and on the docker containers.
Creating the docker containers
docker run --cap-add=NET_ADMIN --device /dev/net/tun --name vpn -p 3128:3128 --expose=3128 --volume /home/torbjorn/docker/troyc-openvpn-client:/vpn -d troyc/openvpn
docker run --cap-add=NET_ADMIN --device /dev/net/tun --name proxy -p 3128:3128 --expose=3128 --net=container:vpn --volume /home/torbjorn/docker/squid/cache:/var/spool/squid3 -d sameersbn/squid:3.3.8-5
Checking the containers
torbjorn@base:~$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
72273f554ce7 sameersbn/squid:3.3.8-5 "/sbin/entrypoint.sh 2 weeks ago Up 6 minutes proxy
36161a9eb125 troyc/openvpn "openvpn --cd /vpn - 2 weeks ago Up 6 minutes 0.0.0.0:3128->3128/tcp vpn
routing table of the docker host, containers are running
torbjorn@base:~$ sudo iptables -t nat -L -n
Chain PREROUTING (policy ACCEPT)
target prot opt source destination
DOCKER all -- 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type LOCAL
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
DOCKER all -- 0.0.0.0/0 !127.0.0.0/8 ADDRTYPE match dst-type LOCAL
Chain POSTROUTING (policy ACCEPT)
target prot opt source destination
MASQUERADE all -- 172.17.0.0/16 0.0.0.0/0
MASQUERADE tcp -- 172.17.0.2 172.17.0.2 tcp dpt:3128
Chain DOCKER (2 references)
target prot opt source destination
DNAT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:3128 to:172.17.0.2:3128
torbjorn@base:~$ sudo iptables -L -n
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
DOCKER all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
Chain DOCKER (1 references)
target prot opt source destination
ACCEPT tcp -- 0.0.0.0/0 172.17.0.2 tcp dpt:3128
Gateways of the docker host
torbjorn@base:~$ route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default DD-WRT.local 0.0.0.0 UG 0 0 0 eth0
172.17.0.0 * 255.255.0.0 U 0 0 0 docker0
192.168.1.0 * 255.255.255.0 U 1 0 0 eth0
Gateways on the docker container
root@36161a9eb125:/# route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default 10.114.0.1 128.0.0.0 UG 0 0 0 tun0
10.114.0.0 * 255.255.0.0 U 0 0 0 tun0
128.0.0.0 10.114.0.1 128.0.0.0 UG 0 0 0 tun0
172.17.0.0 * 255.255.0.0 U 0 0 0 eth0
se3.mullvad.net 172.17.42.1 255.255.255.255 UGH 0 0 0 eth0
Some experiment with ip route
root@36161a9eb125:/# ip route get to 192.168.1.100 from 172.17.0.12
192.168.1.100 from 172.17.0.12 via 10.114.0.1 dev tun0
cache
torbjorn@base:~/docker$ ip route get to 172.17.0.12 from 192.168.1.100
172.17.0.12 from 192.168.1.100 dev docker0
cache
torbjorn@base:~/docker$ ip route get to 192.168.1.100 from 172.17.0.12
RTNETLINK answers: Invalid argument
tcpdump
torbjorn@base:~$ docker exec -it proxy tcpdump -vv -n -i any port 3128|tee tcpdump_local.txt
tcpdump: listening on any, link-type LINUX_SLL (Linux cooked), capture size 65535 bytes
17:46:56.045708 IP (tos 0x0, ttl 64, id 7053, offset 0, flags [DF], proto TCP (6), length 60)
172.17.42.1.42855 > 172.17.0.12.3128: Flags [S], cksum 0x825e (incorrect -> 0x2a32), seq 1327404614, win 29200, options [mss 1460,sackOK,TS val 46042571 ecr 0,nop,wscale 7], length 0
17:46:56.045744 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto TCP (6), length 60)
172.17.0.12.3128 > 172.17.42.1.42855: Flags [S.], cksum 0x825e (incorrect -> 0x388b), seq 284840194, ack 1327404615, win 28960, options [mss 1460,sackOK,TS val 46042571 ecr 46042571,nop,wscale 7], length 0
17:46:56.045773 IP (tos 0x0, ttl 64, id 7054, offset 0, flags [DF], proto TCP (6), length 52)
172.17.42.1.42855 > 172.17.0.12.3128: Flags [.], cksum 0x8256 (incorrect -> 0xd792), seq 1, ack 1, win 229, options [nop,nop,TS val 46042571 ecr 46042571], length 0
17:46:56.045902 IP (tos 0x0, ttl 64, id 7055, offset 0, flags [DF], proto TCP (6), length 130)
172.17.42.1.42855 > 172.17.0.12.3128: Flags [P.], cksum 0x82a4 (incorrect -> 0x65bd), seq 1:79, ack 1, win 229, options [nop,nop,TS val 46042571 ecr 46042571], length 78
17:46:56.045923 IP (tos 0x0, ttl 64, id 56520, offset 0, flags [DF], proto TCP (6), length 52)
172.17.0.12.3128 > 172.17.42.1.42855: Flags [.], cksum 0x8256 (incorrect -> 0xd746), seq 1, ack 79, win 227, options [nop,nop,TS val 46042571 ecr 46042571], length 0
17:46:56.046150 IP (tos 0x0, ttl 64, id 56521, offset 0, flags [DF], proto TCP (6), length 2948)
172.17.0.12.3128 > 172.17.42.1.42855: Flags [.], cksum 0x8da6 (incorrect -> 0x0688), seq 1:2897, ack 79, win 227, options [nop,nop,TS val 46042571 ecr 46042571], length 2896
17:46:56.046177 IP (tos 0x0, ttl 64, id 7056, offset 0, flags [DF], proto TCP (6), length 52)
172.17.42.1.42855 > 172.17.0.12.3128: Flags [.], cksum 0x8256 (incorrect -> 0xcbc7), seq 79, ack 2897, win 274, options [nop,nop,TS val 46042571 ecr 46042571], length 0
17:46:56.046190 IP (tos 0x0, ttl 64, id 56523, offset 0, flags [DF], proto TCP (6), length 674)
172.17.0.12.3128 > 172.17.42.1.42855: Flags [P.], cksum 0x84c4 (incorrect -> 0xb67b), seq 2897:3519, ack 79, win 227, options [nop,nop,TS val 46042571 ecr 46042571], length 622
17:46:56.046210 IP (tos 0x0, ttl 64, id 7057, offset 0, flags [DF], proto TCP (6), length 52)
172.17.42.1.42855 > 172.17.0.12.3128: Flags [.], cksum 0x8256 (incorrect -> 0xc943), seq 79, ack 3519, win 296, options [nop,nop,TS val 46042571 ecr 46042571], length 0
17:46:56.046308 IP (tos 0x0, ttl 64, id 56524, offset 0, flags [DF], proto TCP (6), length 52)
172.17.0.12.3128 > 172.17.42.1.42855: Flags [F.], cksum 0x8256 (incorrect -> 0xc987), seq 3519, ack 79, win 227, options [nop,nop,TS val 46042571 ecr 46042571], length 0
17:46:56.046464 IP (tos 0x0, ttl 64, id 7058, offset 0, flags [DF], proto TCP (6), length 52)
172.17.42.1.42855 > 172.17.0.12.3128: Flags [F.], cksum 0x8256 (incorrect -> 0xc940), seq 79, ack 3520, win 296, options [nop,nop,TS val 46042572 ecr 46042571], length 0
17:46:56.046477 IP (tos 0x0, ttl 64, id 56525, offset 0, flags [DF], proto TCP (6), length 52)
172.17.0.12.3128 > 172.17.42.1.42855: Flags [.], cksum 0x8256 (incorrect -> 0xc984), seq 3520, ack 80, win 227, options [nop,nop,TS val 46042572 ecr 46042572], length 0
^C
12 packets captured
12 packets received by filter
0 packets dropped by kernel
torbjorn@base:~$ docker exec -it proxy tcpdump -vv -n -i any port 3128|tee tcpdump_remote.txt
tcpdump: listening on any, link-type LINUX_SLL (Linux cooked), capture size 65535 bytes
17:47:11.169767 IP (tos 0x0, ttl 64, id 10042, offset 0, flags [DF], proto TCP (6), length 60)
192.168.1.100.43194 > 172.17.0.12.3128: Flags [S], cksum 0x6e58 (incorrect -> 0xff57), seq 633650090, win 43690, options [mss 65495,sackOK,TS val 46046352 ecr 0,nop,wscale 7], length 0
17:47:12.166358 IP (tos 0x0, ttl 64, id 10043, offset 0, flags [DF], proto TCP (6), length 60)
192.168.1.100.43194 > 172.17.0.12.3128: Flags [S], cksum 0x6e58 (incorrect -> 0xfe5d), seq 633650090, win 43690, options [mss 65495,sackOK,TS val 46046602 ecr 0,nop,wscale 7], length 0
17:47:14.170364 IP (tos 0x0, ttl 64, id 10044, offset 0, flags [DF], proto TCP (6), length 60)
192.168.1.100.43194 > 172.17.0.12.3128: Flags [S], cksum 0x6e58 (incorrect -> 0xfc68), seq 633650090, win 43690, options [mss 65495,sackOK,TS val 46047103 ecr 0,nop,wscale 7], length 0
17:47:18.174355 IP (tos 0x0, ttl 64, id 10045, offset 0, flags [DF], proto TCP (6), length 60)
192.168.1.100.43194 > 172.17.0.12.3128: Flags [S], cksum 0x6e58 (incorrect -> 0xf87f), seq 633650090, win 43690, options [mss 65495,sackOK,TS val 46048104 ecr 0,nop,wscale 7], length 0
17:47:26.190369 IP (tos 0x0, ttl 64, id 10046, offset 0, flags [DF], proto TCP (6), length 60)
192.168.1.100.43194 > 172.17.0.12.3128: Flags [S], cksum 0x6e58 (incorrect -> 0xf0ab), seq 633650090, win 43690, options [mss 65495,sackOK,TS val 46050108 ecr 0,nop,wscale 7], length 0
17:47:42.206355 IP (tos 0x0, ttl 64, id 10047, offset 0, flags [DF], proto TCP (6), length 60)
192.168.1.100.43194 > 172.17.0.12.3128: Flags [S], cksum 0x6e58 (incorrect -> 0xe107), seq 633650090, win 43690, options [mss 65495,sackOK,TS val 46054112 ecr 0,nop,wscale 7], length 0
17:48:14.270363 IP (tos 0x0, ttl 64, id 10048, offset 0, flags [DF], proto TCP (6), length 60)
192.168.1.100.43194 > 172.17.0.12.3128: Flags [S], cksum 0x6e58 (incorrect -> 0xc1b7), seq 633650090, win 43690, options [mss 65495,sackOK,TS val 46062128 ecr 0,nop,wscale 7], length 0
^C
7 packets captured
7 packets received by filter
0 packets dropped by kernel
