Check out AT&T's Valentine's Day Gift Guide for ideas & deals on the new Samsung Galaxy S23!
Get superfast AT&T Fiber internet
alex.49.98's profile

New Member

 • 

4 Messages

Sunday, November 13th, 2022 2:53 PM

Port forwarding behind 2 routers

I have an ISP modem/router (BGW210-700). How terrible this modem/router is a separate story so eventually I decided to connect my own router (WNDR4500), which is old but always works great, to it and setup everything there.

Thus, I have BGW210 facing internet with x.x.x.x IP and having its own 192.168.1.254 IP. Then I connected WNDR4500 and setup BGW210 to give it a static/fixed/permanent IP 192.168.1.100. WNDR4500 in its turn has its own 192.168.2.1 IP and all devices connected to it are on 192.168.2.x network. I have only one device connected to BGW210, it is WNDR4500 and I set up IP Passthrough to WNDR4500 MAC, all other devices connected to WNDR4500. Then I setup port forwarding on WNDR4500 to forward particular ports to static/fixed/permanent 192.168.2.10.

From the internet connection standpoint everything is good. All devices have internet access but port forwarding doesn't work. Requests don't reach my 192.168.2.10 server if I send requests to x.x.x.x internet IP, however if I use 192.168.1.100 port forwarding works but of course it makes very little sense. If I try 192.168.2.1 port forwarding does not work again but probably it shouldn't.

If I do tracert I get a very unexpected result 192.168.2.1 goes before 192.168.1.254 and 192.168.2.1 is not in the list.

    tracert x.x.x.x
    
    Tracing route to x.x.x.x [x.x.x.x] over a maximum of 30 hops:
    
      1     1 ms    <1 ms    <1 ms  192.168.2.1   
      2     9 ms     2 ms     1 ms  192.168.1.254   
      3  192.168.1.254  reports: Destination host unreachable.

This is what I get if I telnet to internet IP

    telnet x.x.x.x 5555
    Connecting To x.x.x.x...
    Could not open connection to the host, on port 5555: Connect failed

And this is what I get if I telnet to 192.168.1.100

    telnet 192.168.1.100 5555
    220-FileZilla Server 1.5.1

an expected reply from my FTP server sitting behind.

All that seems as if packets go directly from x.x.x.x to 192.168.2.1 but they all should go to 192.168.1.100 first for port forwarding to work. Maybe I'm mistaken but something is definitely wrong.

Does anybody have a solution to this problem or at least an idea what to try? I'm thinking about creating a static IP route on WNDR4500 but I don't understand how it should look. It seems BGW210 doesn't support static routes.

tonydi

ACE - Guru

 • 

9.6K Messages

3 months ago

I'm having a hard time following what you've done here but obviously something is wrong.  I'd say let's start with a clean sheet of paper by doing a factory reset on both the AT&T gateway (hold the Reset button down for >15 secs) and on the Netgear.

Then use this tutorial on setting up IP Passthrough on the BGW series gateways.

Don't make any other changes, no static IPs, nothing. 

Then set up the Netgear with the port forwarding you need and see what happens.

New Member

 • 

4 Messages

3 months ago

   I doubt factory reset would help especially if you didn't understand the essence of the problem. Let me know what is not clear and I'll be happy to explain.

Alex

bogar90706

Teacher

 • 

115 Messages

3 months ago

Ok I always like to break things down to see if there something amiss... 

Thus, I have BGW210 facing internet with x.x.x.x IP and having its own 192.168.1.254 IP

Okay I'm with you so far. The BGW210 by default assigns its LAN Ip to 192.168.1.254 for you to make changes to the gateway

Then I connected WNDR4500 and setup BGW210 to give it a static/fixed/permanent IP 192.168.1.100

By my understanding, you have assigned your own router a fixed private LAN IP address, which in turn any device behind your WNDR4500 are now subject to Double NAT, a point that reiterates your next statement 

WNDR4500 in its turn has its own 192.168.2.1 IP and all devices connected to it are on 192.168.2.x network

Here is where you throw me a curveball

 I have only one device connected to BGW210 (I'll refer from here and on as 'the gateway'), it is WNDR4500 and I set up IP Passthrough to WNDR4500 MAC

IP passthrough mode means that the gateway literally shares its public IP address with whichever device you choose based on the MAC address. (There are other IP passthrough modes too, such as manual, dchp dynamic, but ill skip these). Pretty much it bridges the gateway (not really but lets say yes) and all port fowarding is now handled by your router. Your router would no longer be a LAN client of the gateway, it will be on this own. 

Perhaps you mean a different allocation mode? Could you mean Default Server? That is pretty a DMZ mode where your device will still have lan address but all port traffic is forwarded to your device

New Member

 • 

4 Messages

3 months ago

   You understood everything right, that was exactly what I meant, and this is exactly what I expected "IP passthrough mode means that the gateway literally shares its public IP address with whichever device you choose based on the MAC address." However, that didn't happen. I don't know what happened and I hoped that tracert could shed a light and somebody could understand what is wrong. You see the first hop is 192.168.2.1 and then 192.168.1.254 which is unreachable. I would expect either 192.168.1.254 not to be on the list or the first hop to be either 192.168.1.100 or straight to 192.168.1.254. I guess something is messed up here and my requests to my server don't even come to the port forwarding on WNDR4500. I didn't really figured out yet how to confirm that I receive a request on my WNDR4500 irrespective to port forwarding.

   Later I played with other modes and when I set Default Server almost everything worked. Almost means that if I send a request to my server via x.x.x.x external IP address when I'm on any network which in not my home network the request reaches the server (pay attention it doesn't reach the server if I use IP passthrough) however if I'm on my home network and send a request to my server via x.x.x.x external IP address it doesn't reach the target.

(edited)

bogar90706

Teacher

 • 

115 Messages

3 months ago

I'm curious to ask when you selected IP Passthrough as the allocation mode, which passthrough mode did you attempt to use when setting your netgear router? I found this blog where this user was encountering similar issue to yours, where no matter what, his device would not get the public ip address.

https://spin.atomicobject.com/2021/02/19/ip-passthrough-bgw210-700/

(edited)

bogar90706

Teacher

 • 

115 Messages

3 months ago

It just hit me that there could be another reason of why your device is not getting the public ip address you were expecting in IP passthrough. On your first post you mentioned this:

I connected WNDR4500 and setup BGW210 to give it a static/fixed/permanent IP 192.168.1.100

This could be the very main reason why your device is not getting the public IP address, since the MAC address is already assigned

a private LAN address.

Not finding what you're looking for?
New to AT&T Community?
New to the AT&T Community? Start by visiting the Community How-To.
New to the AT&T Community?
Visit the Community How-To.