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Baffling port forwarding problem

Hi all, I've got an ubuntu LXC container set up with a bridged NIC to run Plex. The container grabs an IP on the LAN and from other hosts I can hit plex at port 32400 just fine. The really weird thing is that if I forward 32400 from my router to the container's IP, it doesn't seem to work. No connection is made and the connection attempt seems to hang forever. If I use netcat to listen on 32400 on the antsle itself and forward to that it works fine. I wouldn't expect there to be any iptables shenanigans needed on the antsle if I am using a bridge, is there something I'm missing?

Make sure the VM operating system has a default gateway pointing to the router.

I had papered over the problem with iptables rules on the host but I finally got around to trying your suggestion. After removing the rules I added and replacing the default route going through the internal interface with one to my router, everything works as expected. I would never have figured that out, thanks.

I think I'm having a similar issue.... Here is my work up on it.... Unfortunately, I don't know how/where I should change the route to make it work.

Antsle / pfSense Issue


I’m not entirely sure where the issue is, so I will describe the environment and the symptoms

of what is happening.



I’ve eliminated most of my other network from the equation, unplugging other switches and

connected machines to make sure it isn an external interaction that is causing this.

If have a Netgate pfSense (7100 1U) Firewall appliance connected to my business internet

router.  It is configured in a pseudo-bridge mode to hand a small range (13 in all) of static IPs

to my firewall, which then routes them to various internal interfaces sub-nets that are NATted

with an internal IP.  All of this works.


I have a Port Forward from my Firewall to an internally connected machine on their respective sub-net

and vice-versus.  This provides me access FROM the internet to my internal boxes and vice-versus.

BTW, the HTTP/80 is the only port I’m allowing thru.  All of this works.


If I plug my Antsle into a Firewall switch port, instead or alongside the machine that is able to receive

a port forward, it will also reside on the same sub-net, receive it’s IP via DHCP and gain access to

the outside world by exiting thru the NATted sub-net on the firewall.  All of this works.


I can then also setup an additional Port Forward to my Antsle from the outside (internet) and access

my Antsle main interface and login to my Antsle from the Internet.  All of this works.

I created an antlet and added an additional virtual NIC, so that I can obtain an additional IP directly

on my internal sub-net via DHCP. I then setup a http (NGINX) server on this antlet on port 80.  From my

internal sub-net on a different machine, I am able to access the web site running on this antlet.  I am also

able to curl to this assigned IP that was assigned directly to my antlet and obtain the page.  All of this works.




If I setup a Port Forward to the IP that is directly attached to the antlet OR if I change a previous Port

Forward to point to it instead of my Antsle, then I CANNOT access my antlet web site from the outside

world.  I have confirmed that the firewall allows the rule thru (both for a new port forward or a previously

changed one, just in case I made a typo somewhere on the firewall rule).  It appears that the connection

goes thru the firewall, but never returns.


What I don’t know is if the Antsle is somehow ignoring the connection, or if it’s return routing is not allowing

the antlet to talk back to the firewall directly, or does some internal routing need to be configured.  I don’t

understand why this works on the main Antlse page, but not for the bridged NIC IP.  This issue ONLY exists

with connections coming THRU the firewall.  If I do a connection from a machine on the current sub-net,

then I am able to talk to the antlet.  If I do a connection THRU the firewall and talk to the Antsle OR any other

web-site NOT on an antlet, then the connection works too.


More Info…:


I don’t know if this is relevant as everything else seems to work.  If I ssh into my antlet (the one with the two

interfaces) (first one is bblv and the 2nd one is br0 which correspond to eth0 and eth1 respectively), both

interfaces are present and have the correct IPs obtained by DHCP. If I issue a command of:


ping -I eth0


then everything seems to go out and back, acknowledging the pings.


If I use a command of:


ping -I eth1


then I get a “Destination Host Unreachable”


Sample output:


root@externtest:~# ping -c 3 -I eth0

PING ( from eth0: 56(84) bytes of data.

64 bytes from ( icmp_seq=1 ttl=52 time=12.2 ms

64 bytes from ( icmp_seq=2 ttl=52 time=13.7 ms

64 bytes from ( icmp_seq=3 ttl=52 time=17.1 ms

--- ping statistics ---

3 packets transmitted, 3 received, 0% packet loss, time 2002ms

rtt min/avg/max/mdev = 12.250/14.393/17.174/2.064 ms





root@externtest:~# ping -c 3 -I eth1

PING ( from eth1: 56(84) bytes of data.

From ( icmp_seq=1 Destination Host Unreachable

From ( icmp_seq=2 Destination Host Unreachable

From ( icmp_seq=3 Destination Host Unreachable

--- ping statistics ---

3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2072ms

pipe 3






So…. I’m at a lost as to what is going on and whether this issue is with my firewall (pfSense) or with

the internal routing on my Antsle.  Any assistances would be greatly appreciated.


Quote from W Glen Boyd on December 2, 2019, 11:19 am

I think I'm having a similar issue.... Here is my work up on it.... Unfortunately, I don't know how/where I should change the route to make it work.


So…. I’m at a lost as to what is going on and whether this issue is with my firewall (pfSense) or with  the internal routing on my Antsle.  Any assistances would be greatly appreciated.

As cardboard42 said, it is probably wrong routing in the vm. Your VM should have a default gateway on the interface that connects directly to your router, not the internal one that goes through Antsle's NAT. If you added the second interface and never changed the default settings on the first one, it is almost certainly the case that the default gateway points to wrong interface.

What is probably happening is that connections from the local LAN work because the VM OS knows that the source IP is on a directly attached network. However, when something comes from the Internet, the source IP will be on the Internet. The packet will go to the VM's bridged interface as expected. But the VM has no interface on the network the packet came from, so it will send the response to the default gateway. If the default gateway points to the Antsle side, the response will get dropped because it isn't part of a connection the Antsle's NAT knows about.

In addition, when you open a connection to the Internet from the VM it will "work" but will be going through two NAT translations, one in the Antsle and one in your firewall. If the default gateway is the direct-to-LAN one there will be only one translation in the firewall.

Not being able to ping out the second interface from the Antsle itself is normal. The Antsle OS itself won't have an IP associated with that interface, only the VM's attached to it will.