CGNM-3552 wifi to lan issue

[Loux]

Hi,

I can't establish a TCP connection (ssh, http, ...) from devices on the Wifi (Android, ubuntu) to devices on the LAN (Ubuntu). It seems to be linked to an arp issue ? If i add the arp entry of the LAN device on the Wifi device, I'm able to connect.

Anyone else has issue this issue ?

Louis

modem : CGNM-3552

Firmware 4.5.8.22 (same issue with 4.5.8.21)

Security Firewall : level Minimum, Ping from WAN Allow

***EDITED LABELS***

[RogersCorey]

Hi @Loux!

Welcome to our Community Forums!

I personally don't have a lot of experience with Ubuntu and that OS does fall outside of our regular scope of support.

Perhaps another Community member has encountered this issue and could share some insight? 

Regards,

RogersCorey

[Loux]

Hi,

let me rephrase, am I the only one having issue trying to connect from a Wifi device to a LAN device on the same network with the CGNM-3552 modem ?

Regards,

Louis

[Gdkitty]

It isnt specifically something that i have heard from other users, at least on here.

[Loux]

Hi,

from the Wifi Device, if i query the port 80 of the lan device, i don't even see the tcp pkt coming with tcpdump (on the lan device).

Regards,

Louis

[RogersCorey]

Hi @Loux!

As far as I'm aware, this port is reserved on residential connections. If you're looking to host a server, you may need to look into getting a business Internet account or attempt to specify an alternate port.

Regards,

RogersCorey

[Loux]

@RogersCorey, you don't seem to understand. I'm not trying to do anything with the outside world (called port forwarding or NAT).

I'm talking about communication (TCP to be precise) between my inside/private Wifi network (from the rogers modem) to my inside/private LAN network (from the rogers modem). All the equipments are on the same IP network 192.168.0.0/24.

There is an issue with ARP

Regards,

Louis

[RogersDave]

Loux,

I looked at your issue and I don't think there is a modem problem. If ARP was broken between WiFi to LAN (internally these are 2 distinct interfaces bridged together), it would have an impact to many users given the fact that it would break everybody trying to use any wired device from WiFi (NAS, printer, media streaming).

That being said, I am sure you do have an issue so let's try to figure it out and let's start with the root cause of why your WiFi device is not getting responses. A couple of starter questions:

1. On your WiFi device ARP table, do you have an entry for the gateway (192.168.0.1)?

2. On your LAN device ARP table, do you have an entry for the gateway (192.168.0.1)?

3. Are you using DHCP on all devices (both the LAN and the WiFi)?

4. Did you change the LAN subnet on the gateway?

And the most important one...

5. Can you confirm that all devices have the same subnet mask, especially if not using DHCP on a device?

Based on my experience, ARP issues are caused 90% of the time by an incorrect subnet mask. Other 10% is a firewall (software or hardware) is blocking communication (Windows public mode for example). I've also seen, very rarely but seen it, a device on the network acting as a honey pot and trying to hijack ARP responses to intercept traffic.

Dave

[Loux]

Hi,

all devices are on the same network, they are all connected to the rogers modem and use dhcp, they are all on 192.168.0.0/24 with a netmask of 255.255.255.0.

It is hard to see the arp table of the android device (connected with Wifi).

But with my laptop, connected on the wifi, if i replace the arp entry of the PC (connected on LAN) i can reach him (ssh connection). With the default arp entry provided by the rogers modem, i've got connection refused.

Regards,

Louis

[RogersShaun]

Hi @Loux,

@RogersDave might not have seen your response.  Just a friendly reminder to use the @ symbol, then type or click on a username when replying to someone if you'd like them to get notified of your response. 

Have a great one!

RogersShaun

[Loux · Accepted solution]

Hi @RogersDave , @RogersShaun

i found it ! If my PC server on the LAN is using the modem dhcp with a static address provided by the rogers modem outside of the range (ex: let's says 192.168.0.2 while the dhcp range is 192.168.0.10-200) then there will be an ARP issue with devices connected on the Wifi trying to talk to the LAN.

Regards,

Louis

[RogersMoin]

Hello, @Loux

When you use DHCP Reservation to assign a static IP, by default the modem will only provide IPs from the defined range say between 192.168.0.10 - 192.168.0.200 unless manually assigned outside the range. I'm glad you were able to figure out the outside range IP causing the issue and updating the Community. 

Cheers,

RogersMoin