Wednesday, January 20, 2016

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.

Saturday, January 16, 2016

ARRL President's Award

Lots of comings and goings at the ARRL. Dave Sumner is retiring this year as CEO, and has just received the ARRL President's Award for his many years of service to the League, presented by outgoing President Kay Craigie.

Friday, January 15, 2016

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.

Monday, January 11, 2016

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.

Wednesday, December 16, 2015

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.

Thursday, September 24, 2015

High speed, high cost: it's Comcast!

Comcast (dba Xfinity) is giving us tons of Internet speed these days, at least in our corner of Connecticut.  They gave us a new gateway that is now provides the results shown to the right.  Our current service started out at 50 Mb/s, but has more than tripled with little price increase.

That's all good, but the downside is that they are charging something like $1 per month per megabit per second. High speed is occasionally useful for downloading big files, but we could survive on a fifth of what they are giving.  I suppose a big household where 5 people are all looking at their own HD videos would need this bandwidth.  But that's not us!

The question is whether a downgrade of our "triple play" service would put us at a more reasonable price / performance point.  We'll see.

My home LAN gets used for special ham radio work, servers, and software development, so I need to set up DHCP with some assigned addresses and tailor the network in other ways.  Since Comcast has seen fit to cripple its gateway to prevent me from doing this, I've added a proper Asus RT-N66 WiFi router that runs off the Comcast unit operating in "bridge" mode.  The Asus unit is very nice, including IPv6 service, as you see above.

Tuesday, August 18, 2015

First FreeDV on Flex 6500!


I'm giving an "SDR" talk in a few weeks, and I thought I should try out some new (to me) stuff.  My Flex-6500 supports FreeDV as a built-in "waveform" app with some help from the Windows PC.

Nothing was happening on the magic frequency, 14.236 MHz, so on a lark I gave a call.  To my surprise, I got a quick answer from Walter, K5WH, in Houston TX.  The band was up and down, but he was 90% copy at least, and I seemed to make the grade myself!

FreeDV (FreeDV.org) is an open-source digital voice system, designed especially for minimal bandwidth communications on the HF bands.  Voice fidelity isn't perfect, depending a little on current signal levels, but it's remarkably good for ~1.5 kHz (less than normal analog SSB).

Monday, June 29, 2015

Morse Motivation!

I've been amiss not contributing to the blogosphere for some time -- busy with some writing assignments.

But this article from 7 years ago came into my inbox today.  It reminds me that there's a lot of room for improvement when it comes to Morse communications.  It needs old-fashioned wetware effort.  (No computer CW for me!)

We won't all achieve 140 wpm or anything like it, but I, for one, have been stuck on a plateau around 20 wpm for many years.

A while back I was inspired by a FISTS article IIRC about the guy who made the simple resolution to have at least one Morse QSO every day.  It seems like such an easy thing -- but he had been doing it for many many years. 

I don't know what goal I should set, but I do need one.

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