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WNR2000v4 keeps changing internal ip address
Hi there, Since a while I have a strange problem with my WNR2000v4. Every now and again the router changes the internal ip address of itself. The standard/default ip address is 192.168.1.1 but fo...
Hi Andy,
I have some more information on this subject from my ISP community. It is a rough translation with google translate, I hope you understand it.
This seemingly "strange phenomenon" can be explained. What I can say at this stage is that both parties have no guilt here. This phenomenon stems from two requirements that a manufacturer must meet when NAT is used with the product. See https://tools.ietf.org/html/rfc4787#section-4.4 for details.
Why you can see this at a modem reset is because the RF interface of the modem is not connected yet to the CMTS. As a result, the DHCP server of the modem itself is active until there is a connection to the CMTS. The WAN interface of your router detects a link down / up event and then try again to obtain an IP address. The WAN interface from your router will then receive a private IP from the modem of the same sequence which is then used your router at that time. The modem does not know that your router uses internally the same private IP range. This clearly presents a problem and configure your router responds correctly by itself with another private IP range. Why is the DHCP server of the modem active when there is no connection to the CMTS? Because you still can logon to the management interface of the modem.
Manufacturers must implement one of the following two things to make it work.
All traffic between internal / exterene clients correct translation and forwarding. This is difficult because you need a solution such as Session Traversal Utilities for NAT server. If the two clients are the same ISP who does double NAT, you are also dependent on the correct NAT hairpinning implementation of the ISP router.
The second solution is automatically ensure that the internal and external IP ranges do not overlap / are identical.
Manufacturers logically opt for the second easy solution. How can you solve this problem permanently? If your local network eg. 192.168.0.0 Class C network can be used eg. Set your router to use IP network 192.168.1.0.
Where there several of those messages or just one? For a complete TCP transaction I would expect some response if it’s a legitimate message.
I suppose one last thing you could do if you have not done so already is to capture traffic between the modem and the PC when the modem boots up.
I will pass your comments on to Kenneth.
Hi Andy,
No, I got only those, there is "never" an answer to it. Kinda like a one-way street so to speak.
When I switched the computer from the router to the modem it did not connect. I had to reset de modem by pulling the power. After that I directly took a look at the IP configuration which outputed an internal IP address of 192.168.1.10. This is not my static address I normally use. When I looked again I got the external address of 94.213.*.*. So this made me wonder is there is some internal routing capability within the modem and uses the 192.1681.1 range to establish a connection before you are connected.
As I see it now, the modem requests an IP address from my ISP and when received it will route/give the signal to my netgear router. When it does use an internal routing procedure in the range 192.168, then that might be the problem. However, I'm wondering how the modem can "leak" the 192.168. range to the router.
Hi Andy,
I think I have it. It was as before, I needed to reset the router because I had no connection. I had Wireshark running on the router or to watch the router and it changed it's IP address to 10.0.0.0 range. I have the logs if you want to take a look at them, this file I can e-mail to you. It is small enough.
What will commonly happen with a DOCSIS modem is that before a connection is established with the ISP equipment, the modem may temporarily allocate a 192.168.100.x IP address, and it may also do this if the connection to the ISP fails, this allows for easy communication / diagnostics with the modem.
I suspect that you modem may well be allocating a 192.168.1.x IP address during startup, to be replaced by your public IP shortly afterwards.
With many cable modems, it is necessary to reboot the modem when the connected equipment changes, or the connected MAC address changes.
So I would expect that the Netgear router will change its LAN subnet during the period that the modem reboots, does this match with your observations?
It does now. I do not know if the modem is using DOCSIS, I know the routers are like cisco and some others but not the modems.
I would like to confirm this, so I will contact my ISP again for information. After that I will report back.
Thanks Andy
Hi Andy,
I'm waiting for a respons of the ISP community but according to the helpdesk of my ISP the modem has an internal routing function to let the main signal thru. However, they do not know which address this is because it is automaticly generated.
I will change my internal IP to another range so this can not happen again.
Since I do not like any survey thingies I will give my feedback here.
Andy, thank you for helping me and I have learned a lot. As for service from Netgear, it is great! Keep it up :-)
Well thanks very much for that.
If you do find out any more information about the modem I would be interested, but I think your idea of changing the router LAN subnet to avoid the issue un future is sound.
Regards,
Andy
Hi Andy,
I have some more information on this subject from my ISP community. It is a rough translation with google translate, I hope you understand it.
This seemingly "strange phenomenon" can be explained. What I can say at this stage is that both parties have no guilt here. This phenomenon stems from two requirements that a manufacturer must meet when NAT is used with the product. See https://tools.ietf.org/html/rfc4787#section-4.4 for details.
Why you can see this at a modem reset is because the RF interface of the modem is not connected yet to the CMTS. As a result, the DHCP server of the modem itself is active until there is a connection to the CMTS. The WAN interface of your router detects a link down / up event and then try again to obtain an IP address. The WAN interface from your router will then receive a private IP from the modem of the same sequence which is then used your router at that time. The modem does not know that your router uses internally the same private IP range. This clearly presents a problem and configure your router responds correctly by itself with another private IP range. Why is the DHCP server of the modem active when there is no connection to the CMTS? Because you still can logon to the management interface of the modem.
Manufacturers must implement one of the following two things to make it work.
All traffic between internal / exterene clients correct translation and forwarding. This is difficult because you need a solution such as Session Traversal Utilities for NAT server. If the two clients are the same ISP who does double NAT, you are also dependent on the correct NAT hairpinning implementation of the ISP router.
The second solution is automatically ensure that the internal and external IP ranges do not overlap / are identical.
Manufacturers logically opt for the second easy solution. How can you solve this problem permanently? If your local network eg. 192.168.0.0 Class C network can be used eg. Set your router to use IP network 192.168.1.0.- Yes, that’s pretty much how I understand it to work. For me it’s very rare for the ISP connection to fail, but on those rare occasions in the past before I had an intervening router I would find that the attached PC would have a 192.168.100.x IP address which allowed me to access the modem and see what the issue was. Since getting a router I have always operated my LAN with a subnet of 192.168.12.x and this has never caused any issues even with several changes of modem model.
Babylon5 wrote:
Yes, that’s pretty much how I understand it to work. For me it’s very rare for the ISP connection to fail, but on those rare occasions in the past before I had an intervening router I would find that the attached PC would have a 192.168.100.x IP address which allowed me to access the modem and see what the issue was. Since getting a router I have always operated my LAN with a subnet of 192.168.12.x and this has never caused any issues even with several changes of modem model.I didn't know this. For me it is a first. Although I have to say that I had never problems with a modem before. A router is another story though.
Anyway, thank you! The last thing to do for me is to mark an answer to be the solution. But which one? I assume the best one is the one which help others too. Any ideas on that?
- I would suggest your post 41.