Usernet Internal - Docker

Containers on user-defined --internal networks

These are the rules for two containers on different --internal networks, with and without inter-container communication (ICC).

Equivalent to:

docker network create \
  -o com.docker.network.bridge.name=bridgeICC \
  --internal \
  --subnet 192.0.2.0/24 --gateway 192.0.2.1 bridge1
docker run --network bridgeICC --name c1 busybox

docker network create \
  -o com.docker.network.bridge.name=bridgeNoICC \
  -o com.docker.network.bridge.enable_icc=true \
  --internal \
  --subnet 198.51.100.0/24 --gateway 198.51.100.1 bridge1
docker run --network bridgeNoICC --name c1 busybox

Most rules are the same as the network with external access:

<details> <summary>Full table ...</summary>

table ip docker-bridges {
	map filter-forward-in-jumps {
		type ifname : verdict
		elements = { "docker0" : jump filter-forward-in__docker0,
			     "bridgeICC" : jump filter-forward-in__bridgeICC,
			     "bridgeNoICC" : jump filter-forward-in__bridgeNoICC }
	}

	map filter-forward-out-jumps {
		type ifname : verdict
		elements = { "docker0" : jump filter-forward-out__docker0,
			     "bridgeICC" : jump filter-forward-out__bridgeICC,
			     "bridgeNoICC" : jump filter-forward-out__bridgeNoICC }
	}

	map nat-postrouting-in-jumps {
		type ifname : verdict
		elements = { "docker0" : jump nat-postrouting-in__docker0,
			     "bridgeICC" : jump nat-postrouting-in__bridgeICC,
			     "bridgeNoICC" : jump nat-postrouting-in__bridgeNoICC }
	}

	map nat-postrouting-out-jumps {
		type ifname : verdict
		elements = { "docker0" : jump nat-postrouting-out__docker0,
			     "bridgeICC" : jump nat-postrouting-out__bridgeICC,
			     "bridgeNoICC" : jump nat-postrouting-out__bridgeNoICC }
	}

	chain filter-FORWARD {
		type filter hook forward priority filter; policy accept;
		oifname vmap @filter-forward-in-jumps
		iifname vmap @filter-forward-out-jumps
	}

	chain nat-OUTPUT {
		type nat hook output priority dstnat; policy accept;
		ip daddr != 127.0.0.0/8 fib daddr type local counter jump nat-prerouting-and-output
	}

	chain nat-POSTROUTING {
		type nat hook postrouting priority srcnat; policy accept;
		iifname vmap @nat-postrouting-out-jumps
		oifname vmap @nat-postrouting-in-jumps
	}

	chain nat-PREROUTING {
		type nat hook prerouting priority dstnat; policy accept;
		fib daddr type local counter jump nat-prerouting-and-output
	}

	chain nat-prerouting-and-output {
	}

	chain raw-PREROUTING {
		type filter hook prerouting priority raw; policy accept;
	}

	chain filter-forward-in__docker0 {
		ct state established,related counter accept
		iifname "docker0" counter accept comment "ICC"
		counter drop comment "UNPUBLISHED PORT DROP"
	}

	chain filter-forward-out__docker0 {
		ct state established,related counter accept
		counter accept comment "OUTGOING"
	}

	chain nat-postrouting-in__docker0 {
	}

	chain nat-postrouting-out__docker0 {
		oifname != "docker0" ip saddr 172.17.0.0/16 counter masquerade comment "MASQUERADE"
	}

	chain filter-forward-in__bridgeICC {
		ct state established,related counter accept
		iifname != "bridgeICC" counter drop comment "INTERNAL NETWORK INGRESS"
		counter accept comment "ICC"
	}

	chain filter-forward-out__bridgeICC {
		ct state established,related counter accept
		oifname != "bridgeICC" counter drop comment "INTERNAL NETWORK EGRESS"
	}

	chain nat-postrouting-in__bridgeICC {
	}

	chain nat-postrouting-out__bridgeICC {
	}

	chain filter-forward-in__bridgeNoICC {
		ct state established,related counter accept
		iifname != "bridgeNoICC" counter drop comment "INTERNAL NETWORK INGRESS"
		counter drop comment "ICC"
	}

	chain filter-forward-out__bridgeNoICC {
		ct state established,related counter accept
		oifname != "bridgeNoICC" counter drop comment "INTERNAL NETWORK EGRESS"
	}

	chain nat-postrouting-in__bridgeNoICC {
	}

	chain nat-postrouting-out__bridgeNoICC {
	}
}

</details>

The filter-forward-in chains have rules to drop packets originating outside the network. And, with ICC disabled, the final verdict is drop rather than accept:

	chain filter-forward-in__bridgeICC {
		ct state established,related counter accept
		iifname != "bridgeICC" counter drop comment "INTERNAL NETWORK INGRESS"
		counter accept comment "ICC"
	}

	chain filter-forward-in__bridgeNoICC {
		ct state established,related counter accept
		iifname != "bridgeNoICC" counter drop comment "INTERNAL NETWORK INGRESS"
		counter drop comment "ICC"
	}

The nat-postrouting-out chains have no masquerade rules:

	chain nat-postrouting-out__bridgeICC {
	}

	chain nat-postrouting-out__bridgeNoICC {
	}