Network Perils

It’s been a week of networking pain. For the past few weeks Comcast has been using a low DHCP lease time. 30 minutes to be exact. This is typical of when they are doing network upgrades/repairs and is what a normal network administrator does. It’s similar to lowering the TTL for DNS.

Renewing the DHCP lease is normally a pretty transparent process, but this time around it’s been causing network connections to drop. While this process is relatively quick, it still resulted in a brief network outage that would kill connections. Occasionally it created a spike when things came back online, which made it feel even longer due to the resulting lag.

No configurations have changed in a long time other than a firmware upgrade a few months ago. Strange I thought. Why is it insisting on on loosing the IP and rediscovering, rather than just renewing? I let it go for a few days hoping Comcast’s low DHCP lease time would be temporary. After 2 weeks I decided to dig deeper.

After a few emails with Motorola’s tech support (Motorola bought Netopia in 2007) they came to the conclusion that the renew-lease ACK packet wasn’t reaching the router. They suspected the firewall wasn’t allowing it to pass, as a result it was dropping the IP, and requesting it again from the DHCP server. They suggested opening up UDP/67 and UDP/68 on the firewall. This seems to resolve the problem. I’m still seeing the lease drop at about 1:00 AM for the past 2 nights, but that’s really a low priority issue and may indeed be on Comcast’s end. It’s possible the router was renewing the hard way every 24-72 hours for a few months, but I know Comcast’s DHCP lease time has been lowered before and the router didn’t exhibit this behavior. Perhaps the firmware upgrade changed the firewalls behavior? I don’t recall that in the docs. Regardless, it’s fixed.

Now today, the UPS for the router, modem and file server’s battery died. Yet another pain. I was able to swap the battery with a similar model UPS from another computer for now. I can deal with that other computer later.

Now maybe I can take my networking hat off for a little while.

Cable Modem Power Level Graphing

As I hinted last week, I graph a fair amount of data, since I find it pretty handy at times, not to mention just interesting to see in a pretty graph form. I’ve been doing this for years and it’s served me well.

One thing I really wanted to get going was monitoring the cable modem’s power levels. This is now implemented:

Cable Modem Power Levels

How pretty is that? I also moved my ping/latency graphs away from MRTG to RRDTool based graphs. Next up is interface traffic (when I get around to figuring out why it didn’t work when I just tried it).

Poor Broadband Performance

For the past several weeks, the cable modem has been getting more and more unstable. Having dealt with this before I knew the signal quality was pretty poor from looking at the stats. By using a different line that goes more direct, it made a real difference as the data below shows (sidenote: I need to start tracking this using RRDtool).


Forward Path:
Signal Acquired at 723.000 MHz
SNR: 27.1 dB
Received Signal Strength: -19.4 dBmV
Bit Error Rate: 0.459 %
Modulation: 256 QAM

Return Path:
Connection: Acquired
Frequency: 31.6 MHz
Power Level: 61.0 dBmV
Channel ID: 4
Modulation: 16 QAM


Forward Path:
Signal Acquired at 723.000 MHz 
SNR: 37.1 dB 
Received Signal Strength: -6.9 dBmV 
Bit Error Rate: 0.000 % 
Modulation: 256 QAM 

Return Path:
Connection: Acquired 
Frequency: 31.6 MHz 
Power Level: 49.8 dBmV 
Channel ID: 4 
Modulation: 16 QAM 

The performance before was getting pretty bad (never more than 10Mbps, often below 4Mbps). Just ran another test and got this:

Comcast Speed

You can see the packet loss was at 100% for several hours yesterday, and was even when up the connection was pretty poor. Around 3:00 it was disconnected while they fixed the coax hookup. You can see the clean connection afterward, with only one small hiccup while I made a little adjustment to the networking cabling that resulted in a few minutes down.
Packet Loss

Pings to this server are still a little high after the tornado incident due to some weird routing on Comcast’s part. Not sure when will get resolved.

April Fools 2008

As usual, my list of April Fools that I saw today:

Comcast Problems?

There are quite a few sites linking to this post about Comcast problems with Mac OS and/or Firefox users. I personally fall under both categories, and haven’t had a problem, though I admittedly have had Comcast for several years, and never installed their software/branding, nor do I use any of their services/websites other than connectivity.

I was curious if this is a big problem for Firefox users. A quick scan of reporter data shows a few reports a day (somewhat high, but they are a portal site for many so volume is expected), and comments on the site are somewhat varied. Most are from a very non-technical audience. I didn’t get the sense that there were certain items that were consistently a problem. My general observations are:

  1. Homepage misrenders at least part of the time.
  2. Games are “optimized” for IE/Windows (at least some appear to be .exe downloads).

Anyone have experiences? They are a somewhat flash centric site, which tends to be pretty good cross platform, making this somewhat of an unusual case. Typically sites that are problematic for Firefox/Mac users are very antiquated sites that still reference Netscape 4.x as “supported”. They on the other hand are relatively modern.

So if you, or someone you know has run across problems, let me know. I’d like to get an idea of what users face on a daily basis.

Upload Bandwidth

I’ve moaned before about the lack of good upload bandwidth despite having rather decent download speeds. Comcast’s new PowerBoost for upload took effect this week, giving a burst of about 1Mbps for uploads for the first part. While this doesn’t quite fix the problem with making remote backups, it does help in some cases.

Hopefully DOCSIS 3.0 or FIOS will come around.

Early Morning Bandwidth

It’s well known cable modems are “shared bandwidth”, meaning if everyone on your neighborhood is downloading Paris Hiltons latest video off the net (ahem… her music video), your connection slows down. Well Comcast’s feature for the past several month allows you to briefly use the excess bandwidth when it’s quiet. So what does it look like at 1:30 AM?


During peak hours it’s really not that much worse. Typically between 7000kbps – 14000kbps. Not to bad. Of course Verizon will eventually roll out 15Mbps sustained with 2Mbps upstream. Comcast just announced “speedburst” for upstream, and it doesn’t really compare to Verizon’s Fiber offering. DOCSIS 3.0 can’t come quick enough.

Take that 56k dialup!

Site Backups And Bandwidth Fun

I keep regular backups of everything on this server just in case something happens. Recently I switched to a more automated and secure (PGP encrypted) solution for this blog due to it’s fast-paced nature. Just the critical stuff (database, media, templates). I choose PGP (implemented using GPG) since it’s easy, and I only have to store the public key on the server, making it safer than most alternatives.

I’m strongly considering moving it all eventually over to Amazon’s S3 storage. At $0.15 per GB-Month of storage used and $0.20 per GB of data transferred it would be very affordable to keep backups in an even more secure fashion. I’d still use my own encryption on top of theirs for extra security. For things like media, I could even see myself hosting it solely at Amazon. It just seems like that may be a more practical and scalable approach.

Unfortunately until either FTTH or DOCSIS 3.0 comes to town, it doesn’t look like Amazon’s S3 will be practical for home backup purposes. This server has a beefy connection to a few large pipes to the internet (Level3, Global Crossing, and Cogent last I checked). They provides high speed connectivity so a backup would take only a few seconds. At home with a cable modem on a DOCSIS 1.1 network (such as Comcast) the bandwidth is just to slim to allow enough upload capacity. Comcast still only allows 384kbps up. Even the top plans in select areas don’t top 1Mbps. Of course these are Comcast’s numbers (the actual performance is often less). In areas that they currently serve, Verizon FiOS (FTTH) is available at 15 Mbps/2 Mbps. Much better suited for such purposes (though more would be welcome). As strange as it may seem pricing is quite competitive, giving cable a run for it’s money. Perhaps one day DOCSIS 3.0 will appear, though that seems to be a while away. Perhaps one day all homes will have 100Mbps full duplex connections with low latency.

The only real way to get around this limitation is to perhaps use rsync to perform backups. Initial backups would still suck, but after that it wouldn’t be too bad. Though that wouldn’t work with services such as Amazon’s S3, which are token based. There is an rsync-like clone, but it’s still not the real thing. Perhaps Google’s upcoming GDrive will be cool enough to allow the use of rsync over SSH (I could dream) in addition to WebDAV (which is what I expect to see). Last I checked rsync doesn’t support WebDAV because WebDAV is done over HTTP. If I understand it right, RFC 3229 would add Delta encoding support to HTTP, making something like rsync over WebDAV possible since it uses delta encoding.

Katrina Relief Online

I’ve been compiling a little list of some ways you can help online. There is a lot going on, so if you find one I haven’t mentioned, leave a comment so I can add it.

  • Flickr Auction – the popular photo sharing site is holding an auction for prints of some donated photo’s. There’s quite a few reflecting some very talented people. If you’ve got some space for a photo and want to help out, this is a great way.
  • eBay is using PayPals to collect money for United Way.
  • Amazon is collecting through it’s “Honor System” making it easy to donate to the Red Cross through your account. Google is pointing to this.
  • Yahoo is also collecting for the Red Cross through it’s website.
  • MSN (Microsoft) is collecting money for the Red Cross.
  • Apple made it easy to donate through it’s iTunes service (link opens in iTunes).
  • Comcast notes a dozen charities which you can donate to (some accept online, some don’t).
  • has been pushed rather extensively by
  • Major League Baseball (MLB) will be holding collections on September 7th (or a day of a teams choosing for teams away on that day).
  • AOL is linking to a bunch of charities through

Feel free to add.