Usernet Portmap Natunprot - Docker

Container on a nat-unprotected network, with a published port

Running the daemon with the userland proxy disable then, as before, adding a network running a container with a mapped port, equivalent to:

docker network create \
  -o com.docker.network.bridge.name=bridge1 \
  -o com.docker.network.bridge.gateway_mode_ipv4=nat-unprotected \
  --subnet 192.0.2.0/24 --gateway 192.0.2.1 bridge1
docker run --network bridge1 -p 8080:80 --name c1 busybox

The filter table is:

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 DOCKER-USER  all  --  any    any     anywhere             anywhere            
2        0     0 DOCKER-FORWARD  all  --  any    any     anywhere             anywhere            

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         

Chain DOCKER (2 references)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 DROP       all  --  !docker0 docker0  anywhere             anywhere            
2        0     0 ACCEPT     all  --  !bridge1 bridge1  anywhere             anywhere            

Chain DOCKER-BRIDGE (1 references)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 DOCKER     all  --  any    docker0  anywhere             anywhere            
2        0     0 DOCKER     all  --  any    bridge1  anywhere             anywhere            

Chain DOCKER-CT (1 references)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 ACCEPT     all  --  any    docker0  anywhere             anywhere             ctstate RELATED,ESTABLISHED
2        0     0 ACCEPT     all  --  any    bridge1  anywhere             anywhere             ctstate RELATED,ESTABLISHED

Chain DOCKER-FORWARD (1 references)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 DOCKER-CT  all  --  any    any     anywhere             anywhere            
2        0     0 DOCKER-INTERNAL  all  --  any    any     anywhere             anywhere            
3        0     0 DOCKER-BRIDGE  all  --  any    any     anywhere             anywhere            
4        0     0 ACCEPT     all  --  docker0 any     anywhere             anywhere            
5        0     0 ACCEPT     all  --  bridge1 any     anywhere             anywhere            

Chain DOCKER-INTERNAL (1 references)
num   pkts bytes target     prot opt in     out     source               destination         

Chain DOCKER-USER (1 references)
num   pkts bytes target     prot opt in     out     source               destination

<details> <summary>iptables commands</summary>

-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-N DOCKER
-N DOCKER-BRIDGE
-N DOCKER-CT
-N DOCKER-FORWARD
-N DOCKER-INTERNAL
-N DOCKER-USER
-A FORWARD -j DOCKER-USER
-A FORWARD -j DOCKER-FORWARD
-A DOCKER ! -i docker0 -o docker0 -j DROP
-A DOCKER ! -i bridge1 -o bridge1 -j ACCEPT
-A DOCKER-BRIDGE -o docker0 -j DOCKER
-A DOCKER-BRIDGE -o bridge1 -j DOCKER
-A DOCKER-CT -o docker0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A DOCKER-CT -o bridge1 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A DOCKER-FORWARD -j DOCKER-CT
-A DOCKER-FORWARD -j DOCKER-INTERNAL
-A DOCKER-FORWARD -j DOCKER-BRIDGE
-A DOCKER-FORWARD -i docker0 -j ACCEPT
-A DOCKER-FORWARD -i bridge1 -j ACCEPT

</details>

Differences from nat mode:

In the DOCKER chain:
- Where nat mode appended a default-DROP rule for any packets not accepted by the per-port/protocol rules, nat-unprotected appends a default-ACCEPT rule. setDefaultForwardRule
  - The ACCEPT rule is needed in case the filter-FORWARD chain's default policy is DROP.
- Because the default for this network is ACCEPT, there is no per-port/protocol rule to ACCEPT packets for the published port 80/tcp, setPerPortIptables doesn't set it up.
  - If the userland proxy is enabled, it is still started.

The nat table is identical to nat mode.

<details> <summary>nat table</summary>

Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 DOCKER     all  --  any    any     anywhere             anywhere             ADDRTYPE match dst-type LOCAL

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 DOCKER     all  --  any    any     anywhere            !loopback/8           ADDRTYPE match dst-type LOCAL

Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 MASQUERADE  all  --  any    !bridge1  192.0.2.0/24         anywhere            
2        0     0 MASQUERADE  all  --  any    !docker0  172.17.0.0/16        anywhere            

Chain DOCKER (2 references)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 DNAT       tcp  --  !bridge1 any     anywhere             anywhere             tcp dpt:http-alt to:192.0.2.2:80


-P PREROUTING ACCEPT
-P INPUT ACCEPT
-P OUTPUT ACCEPT
-P POSTROUTING ACCEPT
-N DOCKER
-A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER
-A OUTPUT ! -d 127.0.0.0/8 -m addrtype --dst-type LOCAL -j DOCKER
-A POSTROUTING -s 192.0.2.0/24 ! -o bridge1 -j MASQUERADE
-A POSTROUTING -s 172.17.0.0/16 ! -o docker0 -j MASQUERADE
-A DOCKER ! -i bridge1 -p tcp -m tcp --dport 8080 -j DNAT --to-destination 192.0.2.2:80

</details>