Problem rt-n66 with cable modem dcm-475

[Mistermoonlight]

It seems that the cable modem is not friendly with the router. When there is a power failure very often, the router is not able to get an ip automatically very often (i think that this happens when both powerup at the same time). it seems too be timing critical, depending how long for the modem to boot and connect to the cable network. If i powerup the router after, it will work most of the time. The router wan is set to automatically get an ip address (dhcp).

I am using a merlin firmware.

Anybody have seen a similar issue?

 

[RMerlin]

It seems that the cable modem is not friendly with the router. When there is a power failure very often, the router is not able to get an ip automatically very often (i think that this happens when both powerup at the same time). it seems too be timing critical, depending how long for the modem to boot and connect to the cable network. If i powerup the router after, i will work most of the time. The router wan is set to automatically get an ip address (dhcp).

I am using a merlin firmware.

Anybody have seen a similar issue?

I'm using a DCM475 myself, and have zero problem with it.

Try setting your DHCP frequency to "Normal" instead of "Aggressive" on the WAN page. Some ISPs like Charter will aggressively blacklist MACs that issue too many DHCP requests in a short period of time.

 

[Mistermoonlight]

I don't have a choice to set agressive/normal dhcp setting on the wan page (internet connection tab). I could only set it to 'automatic ip' (with no sub option). I am running the very stable (for me with 2 open vpn server, uptime was many months while i was adsl, i recently switch to cable), version 3.0.0.4.270.26. I guess it is a newer setting in newer versions?

What could be a very stable release that could have this setting (even if not the currently test build. I prefer to have stability than up to date features)?

I am only getting this problem after a power failure. Once both devices are connected, it is rock solid. I could maybe attempt to get a wireshark trace of the devices attemting to connect together to see what is happening. But i have notice while testing that if i am connecting the modem to my pc directly (which is power on), it is always working, but if i am changing to the router after already connected to the modem-pc, i can't usually get a new address (mac change was discovered and not appreciate i guess ).

 

[RMerlin]

I don't have a choice to set agressive/normal dhcp setting on the wan page (internet connection tab). I could only set it to 'automatic ip' (with no sub option). I am running the very stable (for me with 2 open vpn server, uptime was many months while i was adsl, i recently switch to cable), version 3.0.0.4.270.26. I guess it is a newer setting in newer versions?

yes, 270.26 is antique. The list of issues that have been fixed since then is nearly endless, if you look at the changelog. Upgrade to the latest version.

 

[Mistermoonlight]

I guess i would have to clear all NVRAM parameters with an update coming from so far?

 

[RMerlin]

Definitely.

 

[MilkManX]

I am running the latest Merlin on my RT-N66U and its rock solid.

 

[Mistermoonlight]

yes, 270.26 is antique. The list of issues that have been fixed since then is nearly endless, if you look at the changelog. Upgrade to the latest version.

I have updated to the latest 50 beta 1 version. I have tried both wan settings (normal and agressive) and still have the issue most of the time. Maybe i don't have the same dcm475 firmware version that you have?

Example:
I am getting a power failure. I am turning on both the cable modem and the router at the same time. I am never getting a wan address. I can see on the wan page that it is renewing, but after 5mn, still no wan ip. If i am clicking on the wan switch to the the internet off and turn it on after that, i am getting an ip instantly. So the router must doing something the cable modem does not like?

 

[L&LD]

You should update to the latest Beta 2.


And also try leaving your modem off between 10 minutes to half an hour, depending on your ISP and how long it takes them to notice your modem is offline and resets itself once it is on.

 

[Mistermoonlight]

You should update to the latest Beta 2

Nothing in the change log is related to this issue.

I have tried 2 differents firmware (a 2 years old one and one form last month). Both have the same problem. The fact that turning off the wan internet in the router gui for 15 secs and turning it back on within another 15 secs give back instantly a wan ip tells me that there is something wrong happening (the router was not able to get one by itself after waiting 5mn, but this trick solves the problem instantly).

 

[L&LD]

Doesn't have to be in the change log to have been (inadvertently) fixed.

 

[Mistermoonlight]

See that thread for additionnal info:

http://forums.smallnetbuilder.com/showthread.php?t=22533

 

[john9527]

You should update to the latest Beta 2.


And also try leaving your modem off between 10 minutes to half an hour, depending on your ISP and how long it takes them to notice your modem is offline and resets itself once it is on.

Did you try this suggestion when changing routers? A lot of problems like this have been solved by powering down the modem for a while (I always suggest closer to half an hour) when changing routers (or router MACs).

 

[Mistermoonlight]

Did you try this suggestion when changing routers? A lot of problems like this have been solved by powering down the modem for a while (I always suggest closer to half an hour) when changing routers (or router MACs).

No i didn't. But i only changed router after i finished all the testing with the asus router (i already got a lot of problems with the asus router before i had the idea to change router). As soon as i changed with the dlink router (without waiting neither), no more problems. I have tested it multiple times with the dlink router without changing back to the asus router (successfully).

This wrong behavior is really a pain because i am suffering here for many power failure every year and the setup simply is not restarting by itself many times at powerup (i have to manually restart). I will verify but i am not sure if that the wan agressive mode changes something in the dhcp sequence timing... Having voip adapter means that no more phone is coming back at powerup for the family until i get repair the situation myself

 

[john9527]

No i didn't. But i only changed router after i finished all the testing with the asus router (i already got a lot of problems with the asus router before i had the idea to change router). As soon as i changed with the dlink router (without waiting neither), no more problems. I have tested it multiple times with the dlink router without changing back to the asus router (successfully).

This wrong behavior is really a pain because i am suffering here for many power failure every year and the setup simply is not restarting by itself many times at powerup (i have to manually restart). I will verify but i am not sure if that the wan agressive mode changes something in the dhcp sequence timing... Having voip adapter means that no more phone is coming back at powerup for the family until i get repair the situation myself

I'd say it's worth a try (only a little bit of your time)......your ISP may be remembering the dlink....and need to learn the asus.....

 

[Mistermoonlight]

Is there anyway to keep (using a script of some sort) wan disconnected until a certain time (let's say turn it on ~45 secs after boot). This would be a workaround. I am pretty confident that if i enable wan access on the router when the cable modem is already linked with the isp, it would probably work. In fact we can see in the wireshark logs i have posted that the router is getting 2 dhcp addresses (one private at the beginning and one public once the modem is linked to the network). The asus router is always succeeding at getting the private dhcp address, so if this step is postponed a little in time, it would get a public address instead...

 

[RMerlin]

Personally, I recommend buying an entry level UPS. Something in the 60$ range should be able to give you close to two hours of uptime with a cablemodem + router.

 

[Mistermoonlight]

Yes i have already followed the ups idea to help with this situation, but power failure is really a pain in my location (it's like we are living somewhere in north of hudson bay ).

Merlin, any way to script a delayed wan enable at powerup?

When the system is not restarting (if ups battery exausted) loosing voip phones is really annoying. Ups helps but it's not perfect all the time. In last december, we had a power failure that spent several hours (half of the night)...

 

[Mistermoonlight]

According to my isp, there is no timing of some sort that would prevent to get a public ip address from them. The only constraint that most cable modems have is that they will provide a public dhcp address to the 1st mac address they have seen that asked for it. It is not possible to get another one after from a new mac address without powering off the modem.

So i am looking into wireskark logs to see if there is any sign of wrong behavior there.

 

[RMerlin]

According to my isp, there is no timing of some sort that would prevent to get a public ip address from them. The only constraint that most cable modems have is that they will provide a public dhcp address to the 1st mac address they have seen that asked for it. It is not possible to get another one after from a new mac address without powering off the modem.

That, and some ISPs like Charter will blacklist your MAC if you send too many DHCP queries within a short period of time. This is what forced me to add the DHCP query setting, where you can set it to Normal (Aggressive being the original default behaviour).