We have all heard the same questions at one point in our careers, “Is the Internet down?” or “Getting to X site is slow.” You scramble to a browser to see if Google, ESPN or the NY Times websites are up. Then you fire up traceroute. In some cases, the pages might load slowly, in other cases not at all. These two situations are often downstream fallout of two connectivity issues: latency and packet loss. Latency is the time it takes for a packet to get from source to destination. The speed of light says the latency for one packet to get across the USA from New York to San Francisco is normally between 70-90ms [1]. Packet loss occurs when packets do not make it from their source to destination, being lost along the way. Many factors can contribute to packet loss, including overloaded routers and switches, service interruptions, and human error. ...

I started to write this post, explaining how I upgraded my home network setup with a dhcpd server, multiple dns servers communicating securely via tsig keys along with dynamic dns, but the post became unwieldy and would have been thousands of words. Instead, I’ll post some links and gotcha’s and hints on how to make it work a lot easier. Links scoured and re-read in the process: Securing zone tranfers with TSIG Bind Security: Transaction Signatures (TSIG) Configuration Security Zone Transfers With Bind 9 Hints: ...

I was having issues trying to get Nagios to more easily query my APC UPS with the APC-provided MIB. It took me a while to figure out the right bits both on the file system and in my query to have the MIB ‘processed.’ I still don’t know how to add that MIB to the “automatically process me too if snmpwalk is run” piece of the puzzle. But for what I have running a home, some notes for myself and others who ripped out enough hair already. ...

TL;DR: How to hand out DNS servers in different orders to different clients based upon MAC address. Background: I was connected into my office’s VPN a few months ago and was noticed some very slow DNS resolution of host names back at the office. I would attempt to ssh into another host, and the connection would sit there for more than a few seconds before finally proceeding. This didn’t happen for just ssh, but also for making http requests. I dug into my resolv.conf locally and tried sending a few DNS queries via dig to the two DNS servers I was provided. The first one failed, the second one returned immediately with the correct response. I swapped the two entries and DNS resolution locally was back to where I would expect it, very fast. I alerted our IT group and the issue was fixed (the first DNS server had become hung, and needed a process restart). ...

For those who have spent time debugging their Comcast Internet connection, we all know the frustration of trying to explain to Comcast that something on their end is the problem. In this case, more data is better: latency history, ping times, traceroutes, etc. You can run Smokeping to monitor latency between your home connection and a remote Internet IP address for example. You can also print out traceroute examples and email them if you have an astute support contact. But if you want to monitor the data your cable modem is seeing, you need to look at the signal to noise ratio of your connection. This ratio refers to how much of your signal has been disturbed by noise on the physical line (Thanks Wikipedia). Newer cable modems will use multiple channels along the same line to increase your download and upload speed, and each channel can be disturbed independently. ...