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dabomb4097

@comcast.net

[IPv6] Comcast IPv6 Gives Address But No Default Gateway

tl;dr - Motorola SB6121 + Cicso E3200 Router gets IPv6 IP address and DNS Servers but no Default Gateway.

The whole story:

So, I recently moved a couple miles away and transferred my Comcast service.

At my previous house I had a leased UBee DDM3513 modem with a Cisco/Linksys E3200 router. I had fully functional native dual-stack IPv6 connectivity.

At the new house, the tech swapped the UBee for a Cisco DPC3000 that does not support IPv6 during some troubleshooting. I asked for a v6 modem but he said that was all he had on his truck.

I fixed this by purchasing my own v6 compatible Motorola SB6121 to replace the non-v6 Cisco, and eliminate the monthly rental fee. The modem activated just fine, but I can't get IPv6 working. My E3200 router receives an IP Address (2601: ...) and DNS servers on the v6 side, but it shows 0:0:0:0:0:0:0:0 for the Default Gateway, like its not getting one.

IPv4 works fine. Any ideas why I'm getting an IP and DNS but no Default Gateway when I enable IPv6 on my Cisco E3200 router?



NetFixer
Snarl For The Camera Please
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join:2004-06-24
The Boro
Reviews:
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1 recommendation

Go into your SB6121 "Logs" tab and find your CMTS MAC address. Then go to »www.coffer.com/mac_find/ and find out who manufactured the CMTS. I am connected to a Cadant (Arris) CMTS; if you are connected to a Cisco CMTS, that might explain your problem.

It might also help if you post a screen shot of your Cisco E3200's IPv6 setup page. If you do that perhaps someone with the same or similar router can confirm if your settings are correct. I know that I have to explicitly setup both my Netgear and D-Link routers to use DHCP (simply using auto-detect does not work).
--
We can never have enough of nature.
We need to witness our own limits transgressed, and some life pasturing freely where we never wander.


dabomb4097

join:2012-12-13
Willowbrook, IL

1 edit

Click for full size
Options on the IPv6 Setup Page
Click for full size
The status page with an IP and DNS but no Gateway.
The CMTS MAC is registered to 0001C = CADANT INC. according to that site.

The router setup only has one option. "IPv6 - Automatic" Enabled or Disabled. The page also shows a DUID, which looks like a longer MAC Address or something. When this was enabled it worked fine in at my other house with the UBee modem.

There are also options for 6rd Tunnel, but this is grayed out and disabled when "IPv6 - Automatic" is Enabled and the router is in Native IPv6 mode. I understand what I am doing, and am NOT confusing Native IPv6 configurations for Tunneling configurations.

Sorry about the double post, I accidentally posted as anonymous the first time and went back and redid it after I signed in.

Thanks again for the help.


NetFixer
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·Comcast Business..
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2 edits

1 recommendation

said by dabomb4097:

The CMTS MAC is registered to 0001C = CADANT INC. according to that site.

The router setup only has one option. "IPv6 - Automatic" Enabled or Disabled. The page also shows a DUID, which looks like a longer MAC Address or something. When this was enabled it worked fine in at my other house with the UBee modem.

There are also options for 6rd Tunnel, but this is grayed out and disabled when "IPv6 - Automatic" is Enabled and the router is in Native IPv6 mode. I understand what I am doing, and am NOT confusing Native IPv6 configurations for Tunneling configurations.

Sorry about the double post, I accidentally posted as anonymous the first time and went back and redid it after I signed in.

Thanks again for the help.

Unfortunately, if your only configuration options are as shown, then you are totally at the mercy of the Linksys automatic firmware algorithms being compatible with Comcast's native dual stack implementation. The instructions from Comcast for the Linksys E4200v2 on their »mydeviceinfo.comcast.net/?homegateway page seems to indicate that selecting "IPv6 - Automatic" Enabled is all you need (or can) do with a Cisco/Linksys router.

In my D-Link and Netgear routers, I have to manually select DHCP settings, or Comcast's IPv6 does not work, but Cisco/Linksys does not seem to make such options available.

I have a Motorola SB6121 on a Cadant CMTS (and Comcast has said that all of their Arris/Cadant boxes are now fully IPv6 functional), so that should not be a limiting factor.

Since there are no user configurable options in the SB6121, and apparently only an "On" or "Off" option in the E3200, the only suggestion I have is to try doing a factory default reset followed by power cycles on both the modem and the router and see if that wakes some sleeping function up. If that "Hail Mary" action does not help, hopefully someone who is more familiar with your particular router will notice your thread(s) and offer some better advice.

EDIT:
Do the PC(s) behind your router get public IPv6 addresses, gateways, etc, but IPv6 connectivity terminates at the router? Or do the PC(s) only get private IPv4 IP addresses, gateways, etc?

--
We can never have enough of nature.
We need to witness our own limits transgressed, and some life pasturing freely where we never wander.


NetDog
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reply to dabomb4097

Make sure you don't have a firewall blocking ICMPv6 packets.. It is odd that I have seen a couple of people having this same issue where the user is not getting the default route. Please PM me your public IP's or cable modem MAC address, I would like to see if your on the same CMTS as others with the same issue.


dabomb4097

join:2012-12-13
Willowbrook, IL
reply to NetFixer

said by NetFixer See Profile
Do the PC(s) behind your router get public IPv6 addresses, gateways, etc, but IPv6 connectivity terminates at the router? Or do the PC(s) only get private IPv4 IP addresses, gateways, etc?[/BQUOTE :

Yes, PC's receive public IPv6 addresses and can communicate amongst themselves, there's just no route beyond the E3200.



NetFixer
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Reviews:
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1 edit

said by dabomb4097:

said by NetFixer See Profile
Do the PC(s) behind your router get public IPv6 addresses, gateways, etc, but IPv6 connectivity terminates at the router? Or do the PC(s) only get private IPv4 IP addresses, gateways, etc?

Yes, PC's receive public IPv6 addresses and can communicate amongst themselves, there's just no route beyond the E3200.

Well, hopefully now that NetDog See Profile has noticed your thread (that is even better than someone familiar with the E3200 responding to your thread), he can check out your CMTS after you supply the requested information. Some kind of misconfiguration (or failure) in your CMTS is a good possibility.
--
We can never have enough of nature.
We need to witness our own limits transgressed, and some life pasturing freely where we never wander.


NetDog
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reply to dabomb4097

said by dabomb4097:

said by NetFixer See Profile
Do the PC(s) behind your router get public IPv6 addresses, gateways, etc, but IPv6 connectivity terminates at the router? Or do the PC(s) only get private IPv4 IP addresses, gateways, etc?[/BQUOTE :

Yes, PC's receive public IPv6 addresses and can communicate amongst themselves, there's just no route beyond the E3200.

PM me your cable modem MAC address so I can look at this.. I need to find out if the issue is a cable modem issue or what the problem is.

dabomb4097

join:2012-12-13
Willowbrook, IL

Sent the requested info. Thanks again for your help!



koitsu
Premium,MVM
join:2002-07-16
Mountain View, CA
kudos:23

1 recommendation

reply to dabomb4097

With IPv6, the default gateway isn't obtained as part of DHCP (like it is with DHCP on IPv4), but is obtained via IPv6 route announcements and NDP (network discovery protocol). This methodology works using ICMPv6.

So as long as Comcast has their RA advertisements set up correctly (and it sounds like NetDog See Profile is going to check on that), if your router isn't picking up the announcement, then quite simply this would be a firmware bug in your router. Make it Linksys' problem (although Comcast should probably engage Linksys on this matter as well), and make sure you're using the latest firmware for your router.

Also, the fact that you've edited your screenshots heavily, as well as cropped out useful information, does not help the situation. Please do not do this. I cannot stress this enough, especially with IPv6. For example it would really help to know if you're getting both the /64 route announcement as well as the /128, but you've hidden all the information that's needed and for no good reason.
--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.


dabomb4097

join:2012-12-13
Willowbrook, IL

said by koitsu:

Also, the fact that you've edited your screenshots heavily, as well as cropped out useful information, does not help the situation. Please do not do this. I cannot stress this enough, especially with IPv6. For example it would really help to know if you're getting both the /64 route announcement as well as the /128, but you've hidden all the information that's needed and for no good reason.

There is no additional information on any of the pages pertaining to the IPv6 connection. Just that single enable/disable button and the status information shown. I'm running the latest firmware available from Linksys/Cisco.

Where do you think I might find this route announcement data? I've been through every page and tab, those two snippets are the only IPv6 information this particular router allows you to set or read.


koitsu
Premium,MVM
join:2002-07-16
Mountain View, CA
kudos:23

said by dabomb4097:

There is no additional information on any of the pages pertaining to the IPv6 connection. Just that single enable/disable button and the status information shown. I'm running the latest firmware available from Linksys/Cisco.

I will gladly admit I don't know enough about the E3200's native firmware to know if it will show you both the advertised /64 and the individual /128 announced by Comcast. Some routers show this, others do not. Here's an example of one which does:

»forums.comcast.com/t5/image/serv···-1&px=-1

said by dabomb4097:

Where do you think I might find this route announcement data? I've been through every page and tab, those two snippets are the only IPv6 information this particular router allows you to set or read.

It's not something that's shown (in any firmware) in the GUI. It's handled purely by the kernel/firmware when it receives it across the wire. Even on third-party firmwares like TomatoUSB this information isn't available in the GUI or via any other means (on TomatoUSB you simply have to use tools like tcpdump on the router itself, watching for ICMPv6 traffic, then decode the results yourself, or write the capture to a file and then open the file in Wireshark). So basically what I'm saying is: there is no way for you to determine if you're actually seeing RAs or not. You just have to cross your fingers and hope.
--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.

dabomb4097

join:2012-12-13
Willowbrook, IL

said by koitsu:

I will gladly admit I don't know enough about the E3200's native firmware to know if it will show you both the advertised /64 and the individual /128 announced by Comcast. Some routers show this, others do not. Here's an example of one which does:

»forums.comcast.com/t5/image/serv···-1&px=-1

Ah okay, on the Local Network tab it shows:
Prefix Address: 2601:d:3000:44::/64

Does that offer any additional insight?

dabomb4097

join:2012-12-13
Willowbrook, IL
reply to koitsu

said by koitsu:

I will gladly admit I don't know enough about the E3200's native firmware to know if it will show you both the advertised /64 and the individual /128 announced by Comcast. Some routers show this, others do not. Here's an example of one which does:

»forums.comcast.com/t5/image/serv···-1&px=-1

Oh ok, yeah now that you mention it on the Local Network page it says the following:

Prefix Address: 2601:d:3000:44::/64

Does that offer any additional insight?


koitsu
Premium,MVM
join:2002-07-16
Mountain View, CA
kudos:23

That means you're at least picking up the /64 prefix delegation that Comcast hands you (which is the IPv6 network block that should be used by systems on your LAN for direct IPv6 connectivity), so that means at least some RAs are working.

I have no explanation for why there's no default IPv6 gateway other than a network misconfiguration on Comcast's side or a firmware/router bug in the E3200. An alternate possibility is that Cisco DPC3000 is incorrectly filtering or messing with some kinds of IPv6 packets (strange but possible), even though cable modems aren't supposed to screw with layer 3 traffic passed through to the underlying LAN port. That's about all I can do with the information here -- IP network technicians have to figure out the rest. I'd wait for NetDog See Profile at this point.
--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.



Mike Wolf

join:2009-05-24
Beachwood, NJ
kudos:3
reply to dabomb4097

I'm using a Cisco EA4500, have tested E3200's, and have not had any problems so I think it's an issue with how the modem is giving out the IPv6 address from the CMTS. Try restarting the modem and seeing if that works, as well as connecting the modem directly to a desktop and see if that receives an IPv6 address.



NetDog
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reply to dabomb4097

I am thinking it is not a CPE router issue but a modem issue at this point. I have one other person with the same issue same modem firmware. I have also emailed customers with IPv6 running on both CMTS's and they are not having any issues with IPv6. So let me send some emails and track down people next week to work on this one.

FYI.. the modem is SB6121\SB6120 1.0.6.8, so if anyone else has a SB6121\SB6120 and IPv6 please PM me or post here.. I would like to know if others are having or not having issues with IPv6.

dabomb4097,

Can you manually add the default route? Does the E3200 give you that access? I can get the link local address for you if you can.



koitsu
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join:2002-07-16
Mountain View, CA
kudos:23

I have a SB6121 and have used IPv6 on my router (RT-N16 running TomatoUSB with appropriate IPv6 fixes) in the past. At the time I was using a SB6120 and it was running 1.0.6.0 or earlier (I forget). Of course, all my IPv6 settings (on the LAN systems) I configured manually (still learning IPv6), but that's not really relevant -- I can check all the settings on the router itself (looking at IPv6 routes, etc.). On the other hand, I'm not in Illinois or off of that CMTS.

If my location/setup is sufficient for testing, I'm happy to spend a little time providing analysis/insights if need be. Let me know, NetDog See Profile.
--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.



NetFixer
Snarl For The Camera Please
Premium
join:2004-06-24
The Boro
Reviews:
·Cingular Wireless
·Comcast Business..
·Vonage

2 edits
reply to NetDog

said by NetDog:

I am thinking it is not a CPE router issue but a modem issue at this point. I have one other person with the same issue same modem firmware. I have also emailed customers with IPv6 running on both CMTS's and they are not having any issues with IPv6. So let me send some emails and track down people next week to work on this one.

FYI.. the modem is SB6121\SB6120 1.0.6.8, so if anyone else has a SB6121\SB6120 and IPv6 please PM me or post here.. I would like to know if others are having or not having issues with IPv6.

I am using an SB6121:
Firmware Name: SB_KOMODO-1.0.6.8-SCM01-NOSH
Boot Version: PSPU-Boot(25CLK) 1.0.12.18m3
Hardware Version: 5.0

I connect to a Cadant CMTS: (CMTS-MAC=00:01:5c:3c:f4:48) located in Murfreesboro, TN.

I have no problems with Comcast's native dual stack using a D-Link DIR655 (Hardware Version: B1 Firmware Version: 2.10NA).

I also use a Comcast/Netgear WNR1000v2-VC (Firmware Version V1.2.2.56NA) as a guest router, and except for an annoying anomaly where the router's WAN IPv6 address (but not its prefix) and its corresponding PD LAN prefix (but not its local IPv6 address) randomly change every couple of weeks (which is apparently a Comcast/Netgear firmware problem), IPv6 is working for and behind that router which is connected to the same SB6121 cable modem (I have a "c05" modem config file) through Netgear FS105 and ZyXEL GS105S switches.

If it helps to visualize my connection, you can see my current network diagram at: »www.dcs-net.net/image/DCS-networ···gram.gif
--
We can never have enough of nature.
We need to witness our own limits transgressed, and some life pasturing freely where we never wander.

dabomb4097

join:2012-12-13
Willowbrook, IL
reply to NetDog

said by NetDog:

Can you manually add the default route? Does the E3200 give you that access? I can get the link local address for you if you can

Unfortunately, the router only has provisions to add IPv4 routes, there are no advanced v6 options.

So, here's the next fun question...if it is a cable modem firmware problem, how can I correct that? I have a customer-owned modem, and I'm reading conflicting reports on whether or not Comcast will push firmware updates to them. If Comcast will not push a firmware update to a customer-owned modem, is there a way I can update it from my end? If I will be stuck with this non-working firmware forever please let me know, I'm still in the 30-day return window where I can exchange this modem for a different brand/model that will work if need be. Or is the firmware problem just an incompatibility with my particular router, and getting a different router will fix it?


NetFixer
Snarl For The Camera Please
Premium
join:2004-06-24
The Boro
Reviews:
·Cingular Wireless
·Comcast Business..
·Vonage

1 recommendation

said by dabomb4097:

So, here's the next fun question...if it is a cable modem firmware problem, how can I correct that? I have a customer-owned modem, and I'm reading conflicting reports on whether or not Comcast will push firmware updates to them. If Comcast will not push a firmware update to a customer-owned modem, is there a way I can update it from my end? If I will be stuck with this non-working firmware forever please let me know, I'm still in the 30-day return window where I can exchange this modem for a different brand/model that will work if need be.

Comcast definitely pushes updated firmware to customer owned modems. I also have my own SB6121 (with the same 1.0.6.8 firmware as you have) that I installed in September, and I have already had two firmware updates pushed to it.
--
We can never have enough of nature.
We need to witness our own limits transgressed, and some life pasturing freely where we never wander.


koitsu
Premium,MVM
join:2002-07-16
Mountain View, CA
kudos:23
reply to dabomb4097

If it's a cable modem firmware issue, Comcast is the one who will push the firmware update to you. You have absolutely no control over this. Folks like SteveTeow See Profile and jlivingood See Profile will need to get involved. Be aware there is a very large amount of politics/procedures with regards to Comcast's relationship with the modem manufacturer to get firmware updates (the same applies to Motorola, UBee, Zoom, and any other brands that work with Comcast).

But like two of us have already said -- the SB6120 and SB6121 are not blocking these kinds of packets. I live in Silicon Valley and I do not have the issue you report, and NetFixer See Profile lives in Tennessee and does not have the issue you report. I think focusing on "modem firmware problem" is barking up the wrong tree. We don't have hard evidence at this point that that's the root cause.

I'm waiting on NetDog See Profile's response to me WRT if he needs me to test IPv6. My router (Linux-based) has tcpdump and I am a senior UNIX SA + NA, so I have no problem proving the existence of ICMPv6 RAs and prefix delegation if need be.
--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.



NetDog
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join:2002-03-04
Parker, CO
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reply to dabomb4097

said by dabomb4097:

So, here's the next fun question...if it is a cable modem firmware problem, how can I correct that?

Comcast will push the firmware to you on approved cable modems, and yes the SB6120\SB6121 is approved.
said by dabomb4097:

Or is the firmware problem just an incompatibility with my particular router, and getting a different router will fix it?

I am going to try and recreate the issue on Monday so standby, if I can recreate the issue then we can go from there.


NetDog
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join:2002-03-04
Parker, CO
kudos:77
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reply to NetFixer

said by NetFixer:

I am using an SB6121:
Firmware Name: SB_KOMODO-1.0.6.8-SCM01-NOSH
Boot Version: PSPU-Boot(25CLK) 1.0.12.18m3
Hardware Version: 5.0

I connect to a Cadant CMTS: (CMTS-MAC=00:01:5c:3c:f4:48) located in Murfreesboro, TN.

I have no problems with Comcast's native dual stack using a D-Link DIR655 (Hardware Version: B1 Firmware Version: 2.10NA).

This is great thanks for the info, this will be me a place to start..


koitsu
Premium,MVM
join:2002-07-16
Mountain View, CA
kudos:23

As for my setup, so that you can use it as a datapoint as well:

Model Name: SB6121
Vendor Name: Motorola
Firmware Name: SB_KOMODO-1.0.6.8-SCM01-NOSH
Boot Version: PSPU-Boot(25CLK) 1.0.12.18m3
Hardware Version: 5.0

I connect to CMTS-MAC=00:01:5c:32:6e:44, which is also a Cadent unit. I've been trying for months to get a concise geographic location of where the head-end is, but I'm connecting out of Mountain View, CA.

Router model is an Asus RT-N16, presently running TomatoUSB Toastman firmware tomato-K26USB-1.28.0500.5MIPSR2Toastman-RT-N-Ext.trx with IPv6 disabled (and if you need me to enable + test it let me know -- I have done so in the past with 100% success, but with these firmware/router adjustments needing to be applied to make things work).
--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.



Mike Wolf

join:2009-05-24
Beachwood, NJ
kudos:3
reply to NetDog

The SB6121 connected to the Cadant I'm on is running the 1.0.6.8 firmware and the IPv6 is working just fine with my various Linksys routers. CMTS mac address is 00:01:5c:24:1d:ce
Currently on a Linksys EA4500 running 2.0.37 build 131047 2012-03-22 04:24


dabomb4097

join:2012-12-13
Willowbrook, IL
reply to NetDog

Thanks!

My router is an Cisco/Linksys E3200 Hardware 1.0 with firmware 1.0.04 build 1 Apr 10, 2012.

And I'm not sure if its a coincidence or not, but I woke up this morning and found both my TV and HSI completely out. There appears to be no signal, TV or Internet, on the line coming into my house at all.



Mike Wolf

join:2009-05-24
Beachwood, NJ
kudos:3

Maybe something outside (or somewhere on Comcast's end) was failing and causing the IPv6 to not pass through, and when it completely failed it resulted in complete loss of service. Are your neighbors affected too?



NetDog
Premium,VIP
join:2002-03-04
Parker, CO
kudos:77
Reviews:
·Comcast

said by Mike Wolf:

Maybe something outside (or somewhere on Comcast's end) was failing and causing the IPv6 to not pass through, and when it completely failed it resulted in complete loss of service. Are your neighbors affected too?

Mike,

I have checked with other customers that this users CMTS and they are working fine. So it is only this user and one other user on a totally different CMTS. From what I can see so far they are not receiving the RA's from the CMTS. Very odd..


NetDog
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Parker, CO
kudos:77
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1 recommendation

reply to koitsu

said by koitsu:

Router model is an Asus RT-N16, presently running TomatoUSB Toastman firmware tomato-K26USB-1.28.0500.5MIPSR2Toastman-RT-N-Ext.trx with IPv6 disabled (and if you need me to enable + test it let me know -- I have done so in the past with 100% success, but with these firmware/router adjustments needing to be applied to make things work).

I have been told people got Tomato working with DHCPv6-PD support.. Have you tried it lately? Latest code that is..