I have a host which runs a few docker's containers.
This host has a few network interfaces, my goal is make some exposed ports from containers accessible only by certain interfaces, and prevent access from others.
I would like to use host's iptables for that.
But its imposible to do simply with:
iptables -I INPUT -i vlan2 --dport 80 -j DROP
because packets are forwarded by prerouting.
iptables -t nat -L PREROUTING 2 Chain PREROUTING (policy ACCEPT) target prot opt source destination DOCKER all -- anywhere anywhere ADDRTYPE match dst-type LOCAL Chain DOCKER (2 references) target prot opt source destination DNAT tcp -- anywhere anywhere tcp dpt:mysql to:172.17.0.2:33066 DNAT tcp -- anywhere anywhere tcp dpt:http to:172.17.0.4:80
There are two exposed ports 80 and 3306 to different containers, and I want to make it inaccessible from interface vlan2
After I added this:
iptables -I FORWARD -i vlan2 -p tcp --dport 80 -j REJECT
Web server stopped to work, but
iptables -I FORWARD -i vlan2 -p tcp --dport 3306 -j REJECT
don't prevent connection to mysql, I am still able to connect. And tcpdump proves it:
tcpdump -n -i vlan2 port 3306 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on vlan2, link-type EN10MB (Ethernet), capture size 262144 bytes 22:48:13.066636 IP 126.96.36.199.47259 > 188.8.131.52.3306: Flags [S], seq 3619220560, win 29200, options [mss 1460,sackOK,TS val 90183390 ecr 0,nop,wscale 7], length 0 22:48:13.066740 IP 184.108.40.206.3306 > 220.127.116.11.47259: Flags [S.], seq 2743923517, ack 3619220561, win 28960, options [mss 1460,sackOK,TS val 10989883 ecr 90183390,nop,wscale 7], length 0
And I can't understand the difference between these two rules.
How to use host's iptables to prevent access to containers