Script to fix Docker iptables on Synology NAS

docker-iptables-fix.sh

#!/bin/bash
currentAttempt=0
totalAttempts=10
delay=15

while [ $currentAttempt -lt $totalAttempts ]
do
	currentAttempt=$(( $currentAttempt + 1 ))
	
	echo "Attempt $currentAttempt of $totalAttempts..."
	
	result=$(iptables-save)

	if [[ $result =~ "-A DOCKER -i docker0 -j RETURN" ]]; then
		echo "Docker rules found! Modifying..."
		
		iptables -t nat -A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER
		iptables -t nat -A PREROUTING -m addrtype --dst-type LOCAL ! --dst 127.0.0.0/8 -j DOCKER
		
		echo "Done!"
		
		break
	fi
	
	echo "Docker rules not found! Sleeping for $delay seconds..."
	
	sleep $delay
done

So, which rules to use? The originals from @pedrolamas, the ones suggested by @flo-mic, or the last ones from @Maypul?

For example if im trying to open ports 6000 tcp and range 1000:1100 udp to a container in docker:

iptables -t nat -A PREROUTING -p tcp --dport 6000 -m addrtype --dst-type LOCAL -j DOCKER
iptables -t nat -A PREROUTING -p udp --match multiport -–dports 1000:1100 -m addrtype --dst-type LOCAL -j DOCKER

This would be ok? Or still I need this?

iptables -t nat -A PREROUTING ! -d 127.0.0.0/8 -m addrtype --dst-type LOCAL -j DOCKER

Hi,

Anyone spent some more time here to figure out the best alternative for this?

Thx
Stefan

@pedrolamas any updates to the questions above?

@kevindd992002 these worked fine at the time I wrote this, however I have since moved away from this type of setup and so can't test the proposed alternatives.

Having said that:

• @ben-ba is most likely right, that second rule right now looks suspiciously useless...
• @Maypul version targets only specific ports, so seems to me the best (tighter / more secure) approach to the whole problem!

@kevindd992002 these worked fine at the time I wrote this, however I have since moved away from this type of setup and so can't test the proposed alternatives.

Having said that:

* @ben-ba is most likely right, that second rule right now looks suspiciously useless...

* @Maypul version targets only specific ports, so seems to me the best (tighter / more secure) approach to the whole problem!

Do you mind sharing what you're using now so that the real client IP is reflected in AGH or pihole?

What I meant is that I am not hosting these apps inside the Synology NAS, but am instead using a completely separate system.

Gotcha!

Having the same headaque, tried this script but could not get it to work on DSM: 7.1.1-42962 Update 4.

I started to wonder if I'm missing anything as this (having real IP being forwarded to Docker containers) should be something common that many people would want to achieve -- just thinking of analytic or security usecases, however, when I search I don't see much search results...

FYI, I have my NAS IP added to Security > Trusted proxy as I saw someone doing that using Nginx as a reverse proxy, but no joy...

Thanks for sharing this!
I noticed in my nextcloud logs that LAN-local IP addresses are still not being shown and instead the IP of the reverse proxy.. I wasn't able to find a solution for this yet.

@domigi
Thats the way a reverse proxy work.

@ben-ba Not sure if we're talking about the same idea.
In my nextcloud container it seems to only see the XFF IP if it's an external/public IP.
For example here two request:

Client	Proxy	Service	Request appears to be from
10.0.0.2	172.16.0.2	172.30.1.2	172.16.0.2
42.199.8.17	172.16.0.2	172.30.1.2	42.199.8.17

(My local LAN is 10.0.0.0/24)

What I would like to achieve: In the example above the first request should also appear to be from 10.0.0.2 and not how it currently is 172.16.0.2.

@domigi Thats the way a reverse proxy work.

in this case, it's not a reverse proxy issue. This happens within the NAT mechanism of the firewall of the Synology box (OSI layer 3), a reverse proxy would be an app getting the incoming connections and forwarding 'em, i.e. a HTTP rev-proxy (OSI layer 7)

this works for a synology 1621+ DSM 7... kudos!

@Maypul
Thank you lots! This helped me to get the actual IPs in traefik and stopped crowdsec to block all connections!

I've testen iptables -t nat -A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER and it worked for me => saw the "real" ip in the traefik access log.
After a reboot i've promted the same command, but this time it didn't work. I am getting the internal docker ip's in the traefik access log.
recreated the containers but still no "real" ip's ...
what do i miss?

FINNALY! Been searching so long for this and now it works! Thanks

I've been wasting so much time this week getting NGINX reverse proxy manager to work properly on Synology. If you want IP-whitelisting then being aware of actual outside IP's is essential and I just could not get it to work. Got headaches from macvlan in Docker and still it did not work. Thank you!

Is this problem unique to Synology?
The rule that I applied is the first suggestion by Pedro:
sudo iptables -t nat -A PREROUTING -m addrtype --dst-type LOCAL -j DOCKER
sudo iptables -t nat -A PREROUTING -m addrtype --dst-type LOCAL ! --dst 127.0.0.0/8 -j DOCKER

However I have a few thoughts.

The first one is security.
It seems that this is a bit of a brute force method that risks exposing other ports of other containers to the network. An attacker would have to break through the port forwarding of my router which does seem like an unlikely event. Then the solution by @Maypul to only script the ports that you are actually going to use sounds like smart paranoia.

The second thought I have is about complexity.
After a while there are so many tweaks to a system that without proper documentation to self (or others) somebody else or even myself is never going to figure out what or why these tweaks were done in case of a system reset or rebuild. Thus, it might be a smart move to install the docker containers that need to be aware of the outside IP to another system like a Raspberry Pi that runs somewhere in the network in more or less default config and that is dedicated to these tasks. That way it becomes clear what the purpose of that machine is and why it is setup the way that it is.

Anyway, just my thoughts but I'm curious about comments.

This doesn't work when trying to access the container from a reverse proxy

Awesome @Maypul thank you!

The change bypassing the synology firewall is understandable and the default docker behaviour.

Other rules added to the FORWARD chain, either manually, or by another iptables-based firewall, are evaluated after the DOCKER-USER and DOCKER chains. This means that if you publish a port through Docker, this port gets published no matter what rules your firewall has configured

https://docs.docker.com/network/packet-filtering-firewalls/#add-iptables-policies-before-dockers-rules

It should only affect ports that you published with docker.

I have my home network on eth0 and another network on eth1. For this reason I only want to accept connections from eth0.

adding the -i eth0 flag does the trick.

iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 80 -m addrtype --dst-type LOCAL -j DOCKER
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 443 -m addrtype --dst-type LOCAL -j DOCKER
iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 53 -m addrtype --dst-type LOCAL -j DOCKER
iptables -t nat -A PREROUTING -i eth0 -p udp --dport 53 -m addrtype --dst-type LOCAL -j DOCKER

None of these iptables rules have worked for me :(

I'm using a DS918+ and running DSM 7.2.

When I run the iptables script, the X-Forwarded-For IP address becomes the address of my router for some reason. So I don't get the client IP, but the IP of my router.

Does anyone know a fix? I've also tried disabling userland-proxy in the docker daemon, but that didn't work either. Or maybe I did something wrong.

@ben-ba Not sure if we're talking about the same idea. In my nextcloud container it seems to only see the XFF IP if it's an external/public IP. For example here two request:

Client Proxy Service Request appears to be from
10.0.0.2 172.16.0.2 172.30.1.2 172.16.0.2
42.199.8.17 172.16.0.2 172.30.1.2 42.199.8.17
(My local LAN is 10.0.0.0/24)

What I would like to achieve: In the example above the first request should also appear to be from 10.0.0.2 and not how it currently is 172.16.0.2.

Have you got any fix on this ?