How do I allow VNC from one subnet to another?

  • pfSense box: single WAN in, four port NIC out with four different subnets, and they are normally not allowed to interact. The server is connected to two of them, 192.168.1.x and 192.168.10.x But the last is blocked in Routing and remote access, so the server does not give access to it on the internal network (192.168.0.x).

    That means that I have to VNC to the server and then use a VNC client on the server to control what's there. I would like to go from the 192.168.1.x subnet to he pfSense box and directly over to the 192.168.10.x and I think it's possible. I have tried to create rules in the pfSense box so that any address on the 192.168.1.x network is allowed to VNC to any client on the 192.168.10.x network, but it doesn't work. Do I need to mess with reverese DNS or something like that to achieve this?

  • LAYER 8 Rebel Alliance

    Show us a screenshot of your Firewall Rules.
    VNC per default is TCP Port 5900 and 5800.
    Maybe you have Asymmetric Routing going on there....check your Firewall Logs.


  • LAYER 8 Global Moderator

    @mastiff said in How do I allow VNC from one subnet to another?:

    But the last is blocked in Routing and remote access

    Blocked in routing? Huh?? Pfsense has the network attached it will know how to get there.. Are you saying your policy routing via firewall rules and show connections out a gateway?

    As with pretty much all firewall related questions - post up a pic of your rules if you actually want valid help.

  • Rico, here you go:0_1543586149718_3fc624fe-8bf5-4da6-9844-c2c7741e5f93-bilde.png

    I tried to add 5800 too, but that didn't help any. I'm using 5900, btw. Egetnett is the subnet that the server has as it's WAN. It didn't work with "any" as the source either.

    Johnpoz, I just meant that I can't use the Windows Server role Routing and remote acces on the server to get to this subnet, like I could if I had the server NIC on the 192.168.10.x subnet marked with "Enable NAT on this interface". But I see that I shouldn't really have mentioned that, it just clouds the issue.

  • LAYER 8 Global Moderator

    How would egetnett EVER be source into airplay interface..

    If you want egetnett to get to airplay then those rules would go on the egetnett interface not airplay..

    Rules are evaluated as traffic enters and interface from the network the interface is attached too.. First rule to trigger wins, no other rules are evaluated..

    In NO scenario would the egetnett IPs ever be source inbound into your airplay interface..

  • Silly me. I thought it was the other way around, that you opened up on the interface you wanted to GET to. So I have made this rule, but it still doesn't work, probably something else I have missed:


  • Nothing?

  • LAYER 8 Global Moderator

    I don't see any hits on that rule see the 0/0
    Do you have any floating rules?
    Are you hitting 5900 or 5800? VNC could use both - one is the java port.

  • Thanks for answering! Right, so that's what those numbers are! Eh...not as far as I know. Not if they're not built in, because I have never heard about them, so I haven't made any myself.

  • LAYER 8 Global Moderator

    So sniff on egetnett for your source IP, try and open up your vnc... Do you see traffic?.. Are you suing some fqdn.. Maybe that resolve to public IP or something..

    Are you putting in IPaddress that is on your airplay net? If so that rule would see a hit ie would change from 0/0

    That rule would allow traffic to port 5900..

  • I don't see anything at all in the log either. But is the rule enough, or is there some kind of an "outbound NAT" if that's even a thing that's necessary to get to the other subnet?

    I am pretty sure there's nothing in the system that can resolve to a public IP, no. And 5900 is for VNC, yeah.

    When I capture, I get this in Wireshark, in red:

    14 1.776350 TCP 66 52111 โ†’ 5900 [SYN] Seq=0 Win=64240 Len=0 MSS=1460 WS=256 SACK_PERM=1

  • LAYER 8 Global Moderator

    Ok you sent syn.. Sniff on the airplay interface when you do that... Do you see the syn going to the IP, the thing you wan to to vnc too... If you do but you see no answer, then that means its not listening on 5900, or it has a firewall... Or its not using pfsense as its gateway.

    No there is no outbound nat to do, pfsense does not NAT between local networks. Unless you put some gateway on pfsense interface for your local networks - they are LAN side network and no there would be no nat between them, unless you messed with the outbound nat rules.

  • Thanks! I set up a VM on the server directly on the 1.x segment, and it turned out that I could both sniff and get to the 10.x segment from that. So it seems the problem is in my server, which is kind of logical when I think about it. The Windows Server 2016 needs to know that requests to 10.x should go through the 1.x network. I tried setting up a static route in Routing and remote access on the server, but that didn't work, so I have to experiment a bit more to find out how I can route that.

  • LAYER 8 Global Moderator


    So you have multihomed server, ie it have interfaces in more than 1 network? Why would it go through your 1 network if its on the 10 network already??

    Why don't you draw up how you have this server actually connected... Multihoming a server is normally BAD IDEA!!!!

  • The server does not have (shared/NAT-ed/routed) interfaces in more than one network. The pc I want to connect from is on the server's internal network, 192.168.0.x, the server uses the 1.x segment from the pfSense box as it's WAN, and then I wanted to go like this:

    Pc on --> Server internal NIC --> Server WAN --> pfSense egetnett (the server's wan) --> pfSense Airplay 192.168.10.x

  • LAYER 8 Global Moderator

    If your server is a downstream router... Then its wan this 192.168.1 network becomes a transit.. There should be NO hosts on this network.. It is a transit network between routers.. If your going to put hosts on it.. Then this server (router) would need to nat traffic from the 192.168.0 to 192.168.1.x (its wan address).. If you expect the 192.168.10 to know how to get back to it..

    If you do not nat, then pfsense needs to know to get to the 192.168.0 network to talk to this servers (downstream router) IP on the 192.168.1 network.

  • The server sees the .1 network as a pure WAN, yeah. The server has no outgoing DNS, DHCP or anything else to that net, everything there is controlled by the pfSense box.

    But I'm afraid I need it dumbed a bit down, sorry... Do you mean that I need to put some kind of a static route from the 10.x network to the 0.x network with the server's external IP as the gateway? I thought the 10.x network would see the contact coming from the server's external IP on the 1.x network (192.1681.4), and that the rest had to be done in the server.

  • LAYER 8 Global Moderator

    If your server nats the 192.168.0 netework to to its WAN ip 192.168.1.x then you have not problems. If it is NOT natting this and pfsense is seeing a source IP of 192.168.0 on its egetnett interface then for starters you need to allow for that.. Since 192.168.0 is NOT egetnett network 192.168.1

    And pfsense also needs to know how to get to 192.168.0 via a route and a gateway..

    where did you sniff this

    14 1.776350 TCP 66 52111
    If you sniffed that on pfsense then your server is NOT natting to its 192.168.1 address.

    And its not a static route from the 10 network.. Its route on PFSENSE saying hey to get to 192.168.0 talk to 192.168.1.x
    So you need a gateway setup. And you need to create the route... And then you will need to enable the rules on egetnett to allow for 192.168.0
    And if you want 192.168.0 to get to the internet you would have to make sure that pfsense does outbound natting of this 192.168.0 network

    For the life of me have no idea why you would do it this way... Why not just directly connect 192.168.0 to pfsense - what is the point of this server doing routing downstream of pfsense?

    So you have other devices on this egetnett? If so them talking to stuff on the 192.168.0 is going to be asymmetrical..

  • I understand. I see that nothing happens in the Firewwall log when I try to VNC out, and there's no mentioning anywhere in the firewall logs about a 0.x segment, only (the server's external network) so that should mean that the server should NAT to the WAN.

    The sniffing was done on the internal network, on the same 0.50 pc that's trying to get to the VNC's on the 10.x network.

    And 0.x has always gotten to the Internet, that's a problem. It's just getting from the internal network via the Server and to the 10.x segment that doesn't work. Which led me to think that I needed a static route to the 10 network. pfSense sees "hey, on the Egetnett wants to talk to somebody on the .10 net, so I'll route it". And it can. So I think this is a matter of finding out how the Server can be aware that it needs to go to the pfSense on to get to the 10.x network. I guess that's what you're saing in the bottom added part, right?

  • LAYER 8 Global Moderator

    OMG dude...

    Sniff on pfsense egetnett interface for 5900 tcp... Try and get to your 192.168.10 address from your 192.168.0 address.

    Do you see traffic?? What is the source IP?

    Now sniff on the airplay interface for tcp 5900 and try and get there again... Do you see pfsense send on the traffic???

    "hey, on the Egetnett wants to talk to somebody on the .10 net, so I'll route it".

    Pfsense KNOWS how to route to any network connected to it... You do not have to create any routes... You have to allow it via a firewall rule on egetnett interface.

    You say that 192.168.0 can get to the internet... So how is the default gateway of this server your 192.168.0 behind NOT pfsense IP address in the 192.168.1 network?? If its NOT then NO its never going to get to the 10.. Does this server your 192.168.0 have some other default gateway.. Does it have some other connection to the internet that you say the 192.168.0 can get to?

    This is your network???

  • I need to set up something that can sniff on that network. I'll try to do that tomorrow and see if I can find out something.

    The default gateway to Internet in my internal network is the server ,, and the default gateway for Window's Routing and remote access (and NAT) on the server is, which is the pfSense box. And the 0 segment has no other way to the internet than Server --> pfSense --> ISP Internet router

  • LAYER 8 Global Moderator

    Sniff on pfsense egetnett when you try and got vnc on the 192.168.10 address... If pfsense does not SEE this then no you can never get there.. Maybe your server is blocking it from going out?

    This is really 30 seconds to figure out with simple packet capture on pfsense to validate traffic gets there and is sent on..

  • Sorry, I answered before you put in that network pic. Yeah, that's basically my network, at least the part of it that I am trying to get to work now.

    I hadn't seen the package capture function on pfSense before, but I tried it now. I did packet capture on the Egetnett and nothing was shown that tried to go from 0.50 to the 10.x segment. Then I tried a VM that's connected directly to the 1.x segment (physically on the server, but totally separate from the 0.x network), and there I could see the packages going back and forth.

    So it seems obvious that the server has no idea where to send stuff to 10.x segment, I need to figure out how to tell it that.

  • LAYER 8 Global Moderator

    @mastiff said in How do I allow VNC from one subnet to another?:

    from 0.50 to the 10.x segment.

    OMG dude... No shit you would not see traffic from 0.x your server is NATTING the traffic to - how else could stuff on the 0 get to the internet... Pfsense has NO clue to the 192.168.0 network..

    Your server has only its default gateway right (pfsense) so it sends ALL traffic there that is not local.. Do you maybe have this 192.168.0 with a /16 mask or something??

  • No, it's a 24 mask. But I meant that I don't see any VNC traffic AT ALL when when trying to get from 0.50 to the 10.x segment. So there's no VNC traffic coming out of 1.4 either.

  • LAYER 8 Global Moderator

    Well then you need to figure that out on your downstream server - pfsense can not let you into the 10 network on port 5900 if it never gets there.

    Seems pretty impossible if your default gateway is pfsense, unless your server is blocking traffic to rfc1918 space.. Can your box ping say

    You would have to allow that on your egenett rules.. I don't recall what they were now..

    From the rules you listed - sorry but its not possible for those 192.168.0 boxes to be getting internet through pfsense.. Since rules on that interface only allow access to the egetnet address.. So unless you were using proxy?? On pfsense?

    Unless you have rules below what you posted for 5900 dest..

  • Yeah, I know. It has to be lost somewhere on the server, I guess that's because it doesn't know where to send requests to the 10.x subnet. I tried to set up static routes to do that, but it didn't do anything.

    And yes, I can ping both the pfSense box and the VM that's running on the Egetnett. So the server should not block 1918. I am not using proxy. And yes, I have other rules, I just cut out the rule for the 5900. Default LAN to any rule should cover that, right? Also now for testing I have a rule on Egetnett allowing anything to Airplay net.

  • FOUND IT! It was the server, and I saw it when I used route print. An old, static route from an experiment several weeks ago was overriding the new static route I had set up. I deleted the old route, and now it works. Thanks for you help! ๐Ÿ˜€

    Edit: The weird thing is that the old route was taking presedence over the new route, which I had with metric 1. I have no idea why.

  • LAYER 8 Rebel Alliance

    9 days ago in #2 I told you about Asymmetric/check your Routing. ๐Ÿ˜


  • Rico, turned out that it wasn't that at all. The routing I thought was wrong was only for internal use on the server, I didn't check the RAS routing table, which was correct. So something strange happened in the pc. But now I'm back with the problem, only different. After fiddling with the rules for both airplay and egetnett I see what seems to be happening. I see the VNC packages on the Airplay net, but they are blocked. Because I get this:

    Dec 9 20:43:58	AIRPLAY	Default deny rule IPv4 (1000000103)	TCP:SA

    Now that confuses the heck out of me, because I keep getting that even with this rule on the very top of Airplay:


    Shouldn't that rule let everything through? Also I can't understand why I'm seeing the internal IP of the client, and not the IP of the server, but perhaps that's the way it is so that the server can send it on to the correct client?

  • LAYER 8 Global Moderator

    SA screams of Asymmetrical traffic!!!

    Shouldn't that rule let everything through?

    NOT when it is not SYN... You do NOT need rules on airplay to allow return traffic that is started from egetnett... The state will allow the return traffic...

    Like I said draw up your network.. If your seeing SA.. Means you are asymmetrical.. Ie send the Syn,ACK back to firewall where the SYN came from some other path that the firewall did not SEE.

  • I will try. What is the software/website you're using to make your drawings? It seems quick and easy compared to the stuff I've tried.

  • LAYER 8 Global Moderator

    I use visio.. But there are plenty of places to do online drawing..

    Here is ascii art one that is pretty slick

    there is giffy

    Here is the thing if your multihoming shit - then you going to have issues with asymmetrical traffic unless you KNOW what your doing.. Its real simple to not have asymmetrical traffic... ONLY put stuff on 1 network, and any upstream/downstream routers would be connected with transit networks

  • Thanks for the drawing tips! But it seems like I don't need them this time. โ˜น I really don't get this. The 10.4 NIC is still nowhere in the RRAS routing table, but I can see that it is assymetrical traffic. So for now I have given up on using the clients for VNC and instead VNC into the server and then from that to the 10.x devices. At least that way I will keep the bulletproff failsafe in the totally static 10.x network for my automation. I am going to find out how to avoid this in a Windows Server forum. Thanks for the patience, I'll put on my flame retardant raincoat and you now get to say "I told you so".

  • LAYER 8 Global Moderator

    If your 192.168.1 is only transit, and your server has connection to it and its .0 network behind it.. And this .0 network is not connected to anything else then its not possible for you to have asymmetrical traffic.

    How would traffic get to the 10 devices other then via pfsense connection?

    Do you have multiple layer 3 over the same layer 2 network? Ie do you have devices with different IPs plugged into the same dumb switch? And thinking they are on different networks?

  • That's the confusing thing. The only assymetric way I should be able to get from the clients on the 0 network would be through the going like this:

    Client...................RRAS server NIC...........Server NIC excluded from RAS -- -> --------------> -------------------> 192.168.10.x

    And that's what I don't understand. I think I'll have to get down to the technical room and go over the connections. I recently moved the server from one rack to another (I needed more space for the whole house audio amps, they got HOT because they were to close together, so I split the system over two racks) and it is possible that there is a wrongly plugged cable connecting the 1.x and the 10.x network, or perhaps even the 0.x and the 10.x network. That's the only think I can imagine. That would be a lot of hours wasted on a network cable...

  • LAYER 8 Global Moderator

    Your server is multihomed - it has a connection in the 10.. As I stated doing such a thing leads to problems - especially if you do not fully understand how the protocol works and will not be coming to a device on the 10 from another direction.

    You do understand that if its directly connected then there is a ROUTE!!!!

    You hit the server and tell the server hey, send this to 192.168.10.X

    Server - sure directly connected to that network, and hey I arp for X and its here on this network... Let me throw that SYN out to it for you..

    10.X sees that SYN from Say hey yeah I listen on that 5900 port, let me move that traffic up the stack for you hey... Hey it says yeah lets talk,, he sent me this syn,ack he wants me to send back to you.. Oh lets see hmmm I don't know how to get there.. Let me send that to my friendly default gateway pfsense at - he will know how to get it to the 0 network..

    Pfsense - says sees the SA... Sorry bud NO state.. Dropped!!!

  • I do know that. And I too think that's what happening. The thing is that what's a route locally on the server and what's a route on Routing and Remote Access, dealt out to the clients of the server, at least in theory should be two different things. That's why there are totally different route tables for RRAS and Route print on a server. So the clients shouldn't even be able to go through the 10.4 NIC as long as that's blocked in RRAS.

    But I will check the cabling, and I'll see if I can find out if RRAS routes and local server routes are to be totally separate, and that it may be a configuration mistake on my server. I have put in a question about that on a server forum. This is something new for me, even after almost 20 years of running "indows server (from 2000 Advanced Server) at my home and my cabin.

  • LAYER 8 Global Moderator

    Dude we stopped using RRAS like 20 some years ago... I have supported "server" since NT 3.51 days... Got my MCSE back on NT 4 and 2k..

    There are much easier ways to route traffic then using windows that is for damn sure.. For starters your using one - pfsense..

    Not sure what you think putting device behind windows is getting you other then more complexity?

  • Somebody forgot to tell Micro$ft and some tens of milliones customers about that... ๐Ÿ˜ My server is a combination of RRAS, DHCP, DNS, VM host, storage host, media host, media server and several special programs for work and automation that can't run on anything but a physical Windows computer. If I didn't do it this way, I'd have to use at least three boxes.