IPv6: Things that fix themselves

In a January post, I commented on trying to make the new Internet Protocol (IPv6) work in my household.

Despite some detailed sleuthing, I could not get IPv6 working reliably on my WiFi/Ethernet local area network with its connection to our ISP, Comcast.  The router would give up after a day or so, reporting ICMP6 checksum errors and shutting down IPv6 service.  (IPv4 worked well, regardless.)

I had tried swapping out a lot of my devices, including routers, but nothing seemed to keep the service going for more than 24 hours.  Lacking more elaborate packet inspection tools, I put the whole thing on the shelf.

Now, after 5 months of computer / Internet life, I thought I'd check in again.  What do you know -- IPv6 is stable now.  There have been quite a few updates to operating systems, routers, and other components since January, so it's not possible to say what made the difference.  And Comcast may have secretly changed its service in a way that cured my bug.  (The log still reports bursts of ICMP6 checksum errors, by the way.)

We may never know what happened, and that's a shame because it is good to know where the weak links are (or were) to help plan future developments.

Meanwhile, laissez les bon temps rouler!  We are ready for the next century.

p.s. This is mainly a hobby activity.  There is practically nothing you can do with IPv6 that you can't do with the common IPv4.  (You can test your own IPv6 capability here.) Over time, since the IPv4 system is now almost out of available new addresses, new services will have to be provided on IPv6 only.  But that may be a while yet.

IPv6: Light my Fire!

Our IPv6 story continues.  We removed our Asus RT-N66U router and showed that the problem (long periods of dropped IPv6 connectivity) was not in the Asus device.   The problem continued when we went back to the Comcast/Cisco DPC 3941T router, alone.   The Comcast device has very poor facilities for diagnosing network problems or anything that might confuse the general Comcast users.  It gives a log that says there were some problems seen by the firewall and that's about it.

So we put the Asus device back in operation, switching the Cisco to bridge mode.  The Asus demonstrated the same IPv6 problems as before, but now it was time to scrutinize the log a little better.

We noticed a lot of ICMPv6 checksum errors like the following:

Jan 20 10:20:35 kernel: nf_ct_icmpv6: ICMPv6 checksum failed
Jan 20 10:20:35 kernel:  <0>nf_ct_icmpv6: ICMPv6 checksum failed
Jan 20 10:20:35 kernel: IN= OUT= <1>SRC=ff02:0000:0000:0000:0000:0001:ff6e:d2d3 DST=2601:0183:4002:0987:0000:0000:0000:0001 <1>LEN=64 TC=0 HOPLIMIT=255 FLOWLBL=0 PROTO=ICMPv6 TYPE=136 CODE=0

They repeat up to once a second, when they start coming. All the erroneous packets originated from the ...d2d3 address.  With a little work, we found...

The Guilty Party

The Amazon Fire tablet seemed like a good value at its ~$50 price.  Unfortunately, it appears to be sending the malformed IPv6 packets.  Powering off the Fire (or using airplane mode) cuts the errors, and seems to have stabilized the network.

Kindle's version of Android gives you very little to adjust, and you can't shut off v6.  We tried unloading most of the non-Amazon apps just in case one of them was causing the problem, but that had no effect.

Maybe $50 is just too cheap? That would be one moral of this story.

Another moral: Don't expect a Comcast router to help you fix your network if something goes wrong.

Still slogging on Internet Issues

While trying to understand why IPv6 is (still) not reliable on my Comcast / Xfinity service, I rediscovered DSL Reports.  This is a great place to go to get your technical / support questions answered for DSL or Cable connections.

I have a post in for Comcast's attention.  Meanwhile, I ran the nice speed test tool, which gave me the highest-ever speed report.

More Network Fun: Asus, HP, and Xfinity

Asus RT-N66U (l), Cisco/Xfinity DPC3941T (r)

...in which we demote the Asus RT-N66U.

Faithful readers know about my efforts get reliable networking here at home (last post).  I want IPv6 to work well, and I'd like all my devices to freely work together, with good Internet access.

We took 2 steps forward, and then 1 back.  IPv6 worked, but not reliably when I set up the Cisco DPC3941T for "bridging mode" and gave the routing function to the Asus RT-N66U.  ICMPv6 packets were displaying lots of errors.

We ran the house that way for about a month.  Everybody was happy (in an IPv4 way), but there was one significant problem. Our HP LaserJet Pro MFP M127fw printer was not working reliably.

HP LaserJet Pro MFP M127fw

This is an "all in one" B&W laser printer / scanner / fax system offering lots of capability for a reasonable price.  It offers WiFi, Ethernet, or USB interfacing.

Everything works fine on Windows.  After a detour through HP's website, it works on Linux, too.  It works with Google's Cloud Print service, and HP's ePrint.

It worked for a while, but then would go catatonic and refuse new jobs after a period of minutes or hours.  You could always get it back by cycling the AC power.  We lived with this for some time, but it's pretty annoying to start a print job from the other end of the house, only to find out later that it did not go through.

So we tried a lot of tricks, adjusting the printer's setup, the router's setup, and even the Linux driver installation.  (The problem showed up with either Linux or Windows.)  We updated the printer's firmware. We tried both WiFi and Ethernet connections. 

Cut to the chase.  Eventually we cut out the Asus router, and there was progress.  Using the Cisco/Xfinity/Comcast router by itself, the printer worked -- and IPv6 worked, too!  It is clear that the Asus/Cisco combination (if not the Asus alone) is problematic for HP and IPv6.

So we retreat another half step.  We still use the Asus box as our main WiFi access point.  The Cisco 2.4 GHz WiFi transmitter is much weaker (nearly 20 dB weaker) that Asus, and it's built-in antenna system is doubtful.  (The Cisco box may actually be defective.)

For the moment, printing works, IPv6 works, and we will stop there.  The problems we had originally with Xfinity's DHCP and other issues of that sort are still there, but overall it's time to relax.

Comcast IPv6 - Asus RT-N66U Troubles

We were a dual-stack household -- for a while.  Comcast is one of the leaders in the evolution of Internet services from the old IPv4 to the new IPv6 service.

The old IPv4 network has run out of easy-to-allocate IP addresses (the numerical kind, like 130.132.20.1, that are roughly equivalent to your telephone number).  Among other advantages, the new IPv6 allows for gazillions of new addresses.  It will be a key enabler of the new "Internet of Things" that you may have heard about.

As this transition occurs (slowly, as there are so many v4-only systems installed), many of us will need to operate "dual stack" systems that are capable of using both forms of addressing.  Any modern desktop PC (Windows 7 and onward, Linux, etc.) already knows how to do this.  The weak link for many users will be their Internet Service Provider (ISP) that will have to reorganize itself to provide IPv6 services.  So, the good news -- our Comcast system does offer IPv6.

We were able to run dual-stack pretty well with the gateway device that Comcast rents us, a Cisco DPC-3941T.  (We need their gateway, because we use their VOIP telephone service.  That's another story.)  Our Linux operating system (and probably Windows, too) will prefer to use IPv6 over IPv4, when a given Internet service offers both.  Google sites all seem to offer IPv6, for example.

But it wasn't going to be that simple for us, because the Cisco gateway is "crippled". Comcast seems to have decided that a downgraded gateway can offer more security with fewer support issues for the 99% of customers who have simple needs.  It does not support a moderately complicated home network, like ours, where you might want to use specific IP addresses, firewall setups, etc.  In this situation, Comcast recommends that you operate their gateway in a non-routing mode and that you attach your own WiFi router that will be more configurable to local needs.

Enter the Asus RT-N66U.  On paper, this looks like a fine choice for us, offering very good dual-band WiFi and lots of configuration control.  With its standard setup (IPv4), we've had no problems.  (The VOIP service stays with the Comcast gateway.)  When we enable IPv6, things worked well, too, despite the lack of documentation or help files from Asus.

Worked well, that is, for a number of hours.  After a time, the IPv6 service just stopped.   The good news is that Internet service continued with only minor delays using the old IPv4 protocol.  The bad news is that IPv6 isn't reliable using the RT-N66U.  It starts up again if you reboot the router, but it will eventually die with the same symptoms.

According to the router system log, the router starts encountering ICMPv6 checksum errors.  After some substantial number of such errors have been reported, the router decides to drop IPv6 entirely.  That's my interpretation, anyway.  Where the errors arise is not clear.  It could be the Asus router itself, or it could be an interaction with the Cisco device, or something even further upstream.

I have tried all variants of IPv6 setup that I could think of -- enabling/disabling DHCP, response to Internet pings, etc.  Sometimes IPv6 seemed stay up for longer, but eventually it always dropped out.

So despite the initial excitement of operating a cutting-edge dual-stack household, we are back to plain old IPv4 for now.  Maybe someone will suggest a better router configuration, or maybe we will get a firmware update that fixes things.  Meanwhile, we're coasting along on tried and true IPv4.

Note added: To keep things in perspective, there is no great reason to run IPv6 at the present time.  It's just a game, until a significant number of services begin to be offered exclusively on IPv6.  That will happen eventually as the address exhaustion begins to be felt, but for now essentially all IPv6 services are also available via IPv4.