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CM3008 Modem - The Saga Continutes

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CM3008 Modem - The Saga Continutes

Lets see how long this stick around before hits the archives...


Linksys CM3008    H/W Ver 1A  S/W Ver

Downstream Bond (port 1 2 3 4) 9 10 11 12

Upstream Bond (port 1 2 3 4) 4 3 2 1

There are a few corrected errors on each of the downstream bonded channels.  The uncorrectables are 631, 643, 632, 630. 

Signal Strengths (port 1 2 3 4) 7.479 7.404 7.165 6.986

Signal to Noise Ratio (port 1 2 3 4) 37.636  37.936  38.258  38.605

Upstream Signal Strength (port 1 2 3 4)45.000  45.000   45.000   46.500  It makes me think that 45dbmv is going to be the base level, and modem will adjust over time. 


Problem: Since initial provision, modem has bootlooped.  Meaning that it would start up, communicate on base channels, bond to up and downstream channels, status goes 'hot' as indicated by solid status light.  30 seconds later, ethernet light stays off, and modem reboots, ad-infinitum.  Occasionally, the modem will stay online...Until you try and route through it, then it reboots.  Note, computer can be connected / disconnected, and behavior stays the same. 


Linksys had sent another modem, a CM3016, that is working on the firmware / config.  It is a "loaner" for the time being.  I still have the CM3008.  Many calls and tickets have been opened with the "Advanced Repair" team, and tonight we also apparently have engineers online.  To further cloud the works, Linksys had indicated that they do *NOT* block the diagnostic page after modem is provisioned. can still be pinged.  You just cannot access that port after the modem is fully provisioned / up and running with bonded channels.


Until Now.


You can access the diagnostics page through a round a bout way of doing things.  Setup the *ethernet* connection manually.  IP# will be  Subnet Gateway drop into a terminal window (with admin rights, if needed) and run ipconfig.  The ethernet adapter should come back with the data. 


Now you can access the diag / info pages until you get tired of it.  Note that at this point, your computer is connected to the modem via ethernet, and since your adapter is manually configured for a 192xxx address, it isn't going to route.  I suspect that this is actually going to be dependent on the subnet range, but I haven't explored that far yet. An alternative, which is likely going to be much easier to implement, is putting a switch between the modem and router.  Then I can always have a port to plug into without taking the router offline.  Hmm, I may be able to create a virtual wlan configured would port (:80) forwarding to


I was just about to say that the modem has been operational for the last hour.  Changed my eth0 congig to dhcp, was assigned the IP# from Comcast.  Tried to goto and....reboot / boot loop cycle has started again.  The modem was stable  as long as I had the 192xxx address configured and viewing information pages. 


More to come...


(BTW, how to attach html files?  )

Modem: Linksys CM3008
Router: Linksys WRT54G OpenWRT
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Re: CM3008 Modem - The Saga Continutes

Additional Findings...


It appears that DHCP is main component that crashes the router.  It is able to remain online without boot looping, this is likely due to something that has been done on Comcast side. Prior, a cold start with only power and coax connections yielded a continuous reboot process.  Currently, if nothing is connected on Ethernet, it remains online.  S/W version


If I configure laptop Ethernet for the IP, Gateway, subnet, DNS then I cannot route, but modem stays online.


If I configure laptop Ethernet for assigned IP (recorded from prior history), Gateway (also from prior history), subnet, DNS the modem will stay online and I can route with a great throughput.


The moment I change Ethernet adapter settings back to DHCP and renew IP, router crashes.  If I leave as DHCP, it will boot loop.  If settings are changed to static (see above), router boots normally and stays online.


Observation: noticed that Ethernet indicator on router will sometimes flash blue for an instant prior to crashing.  The adapter in laptop is gigabit compatible, there maybe some handshaking errors occurring during DHCP.  Will be exploring that today. Will attempt to slow adapter down to 10 and 100 in laptop settings.


FEC uncorrectable are still at high levels, 600+, quickly after reset to zero.

Still haven't figured out how to attach HTML pages to messages. Unable to convert to image files since page scrolls.

Modem: Linksys CM3008
Router: Linksys WRT54G OpenWRT
Frequent Visitor

CM3008 Modem - The Saga Continutes - RESOLVED

Resolved.  Root Cause is way the CM3008 handles DNS, possible affects similar models.


I think that Linksys may have been blowing smoke at us, modem is now working just fine on version firmware / configuration file.  I am sure the comcast tech staff tweaked something on the back end, my downstream channel numbers switched, uncorrectable error count went to zero.  Upstream power also dropped a bit as well.  Maybe the modem finally settled into its routine.


Something was gnawing at the back of my head regarding the diag page at  It could be pinged, but you just couldn't route to it.  I suspected that it was something to do with a different subnet after provisioning.  I was able to test all 3 speeds on my laptop (JMicron PCI Express Giganet on Asus Laptop), trying static 192, static 73 (public), DHCP, and variations of the three with and without dns, and using 3rd party dns.  The 3rd party dns is what did the trick.  Once (Comcast DNS, port 53) was dumped, and I started using Google and OpenDNS, the modem began behaving like it should.  The only time that I saw a reboot was when changing speeds on the adapter.  See attached file, if I can get it to attach.


Long story short, if you find your modem rebooting often or even bootlooping, you might try specifying a different DNS in your device / router.  You can also connect direct to the modem, set your ethernet IP for and gateway for, subnet should populate as  As long as you are set up for manual configuration, you should not have any problems accessing the modem diag page.  This has also been confirmed using an old DLink 4 port switch (not a router, not a hub) between my modem and the router.  Router got its info as needed from modem (DNS was specified though) and while the router was passing data to / from the internet, I was able to plug into the switch with my manually configured adapter and was able to observe modem performance.  Pretty Cool.  Try It.


Linksys has told me that the modem that was loaned is now mine to keep.  They will not be able to do any advanced troubleshooting with it and return back to me.  Though it will be analyzed, return is not going to be possible. 


On a sidenote, I was able to knock my cm3008 modem offline altogether by using a known exploit.  There is not any protection at this point in time for the CM3008 / 3016 /3032 modems.  An update is being developed, but nothing ready to be released as of this moment.


Have a good night.


Linksys CM3016 Modem

MBR95 Mobile Router w/ Fallback

Linksys WRT54G version 3 running OpenWRT firmware

Modem: Linksys CM3008
Router: Linksys WRT54G OpenWRT

Re: CM3008 Modem - The Saga Continutes - RESOLVED

FWIW, DNS can not affect straight cable modems. They are simply layer 2 bridges that merely forward / return DNS queries / replies to the DNS servers / network clients.

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Re: CM3008 Modem - The Saga Continutes - RESOLVED

Agreed, that was my understanding as well, that the modems are bottom 2 or 3 layers on the network stack.  None the less...the data points to a different conclusion. Though wasn't part of results, same reaults achieved with different laptop (Lenovo Think pad) running Linux to verify my findings. I wasn't able to switch its adapter to higher speed since driver didn't support (though windows did).  Again, same results including modem crash when port sped changed.  Partial verification achieved with android device (actually a modded fire stick), but without adapter speed changes, using an OTG adapter for physical link.


I heard back from 'Grim' at Linksys, after leaving a message for him to return my call.  Presented with my findings, I asked what exactly was difference between over 10 and 13 for this modem.  Was advised that 10 is Linksys version, 13 is Comcast.  When I queried that why didn't Linksys release the 13 version, was told that 13 is encrypted and Comcast wouldn't provide keys or similar.  Personally, I would think manufacturer would have access regardless.  


There is more going on inside the modem than is apparent.  There is the presence of the diag pages both prior to and after the modem is provisioned and online. Access is impeded when public IP is issued.  Prior posting indicated that I was still able ping the 192 address despite having been issued a 73.x.x.x .  I was still able to access diag page after provisioning but had to use a computer configured for static address (see previous post) connected to a switch placed between modem and router.  That tells me there is additional function as well. 


I had found another address that pinged, and could route to on the modem, though I forget what it is.  I think I mentioned it in previous message as well.  That page through up a login screen, with host being indicated as NVR.  I suspect this maybe a programming port used by manufacturer to preconfigure a modem/ router.  The Linksys 'engineer' refused to address any queries regarding this port / page.  Unfortunately, I can't play with the CM3008 anymore as its on its way to Linksys.  I do plan on 'evaluating' the CM3016 that was supposed to be a loaner, but is now a replacement / keeper.  Not exactly happy about it due to Puma 6 chip set, but it will support going a lot faster if I ever see the need to.



How does one go about attaching a 'single page' HTML file to the messages? 

Modem: Linksys CM3008
Router: Linksys WRT54G OpenWRT