A question that I often face - what IS a traceroute? Most individuals know that it represents the “hops” or routers along the path from a system’s IP to the destination IP entered. What’s most often misunderstood is the response time numbers printed for each hop. Some assume that it is the time any packet takes to make that leg of the journey. But, that just isn’t the case.

Those times actually measure the time elapsed from when the packet was sent to when a response was received. In today’s Internet, most routers have very strict limits on how many of these responses they can generate in any particular time period. So a lack of response isn’t indicative of the latency of that leg, also because the router may use a very different part of its “brain” to generate these control responses than it would to simply forward a normal packet the times may be misleading. This means that a router under modest load may respond with wildly different times, as its busy doing other “housework.”

So how do we know where the lag is coming from with a traceroute? Only end-to-end pings can really show latency or packet loss. But, certain patterns in a traceroute can help pinpoint a possible source.

One method of detection is a cliff-like increase in latency that builds from one hop forward. In other words, the traceroute suddenly has a steady jump in the return times of each hop from one spot to the next. Notice I didn’t say stars in the route. In today’s Internet landscape, stars don’t reflect the certain issue they once did. Certain providers have restrained the routers so much that they constantly throw stars.

If you see every hop after a line is throwing stars then that link may be losing packets. An end-to-end ping showing this loss is just about the only way to verify that for sure. As if all these rate limits weren’t enough to render our poor traceroutes meaningless, there’s another issue making it even more difficult.

The Internet often involves paths that get somewhere a different way than they get back. In other words the Internet is asymmetric. This asymmetry means that the packet you sent to the hop in the traceroute got to the router one way - through one set of providers, links, etc. - and the router’s response got back to you another way. This means a lack of response, the star, or latency could indicate an issue with either path. It also means that the cliff I spoke of earlier could mean that past that hop the return path has an issue not the actual route you see. Yes, traceroute can only show you the outbound path. This is a weakness in the technique it uses. Only the outbound path is visible to the tracing packets. This makes diagnosing or finding the offending hop difficult if it’s located in the return path.

So how do we find the issue? Anyone that’s opened a network-related ticket with The Planet knows we like to have traceroutes (to indicate the path), then pings of 100 or so, from the IP at The Planet seeing the problem to the IP on the Internet. And if possible, and we know this isn’t very easy, the same from the Internet side of the issue back to The Planet IP.

If we have this sort of information we can usually determine where the problem exists. Of course like taking your car to the shop many times these traces and pings don’t show the problem because it is intermittent. They are still useful and at least give us a baseline to work from when we’re looking into the issue. Intermittent issues can also be helped by reporting times of day the issue happens and/or if it is limited to certain IPs or servers.

So the next time someone tells you that a 380ms spike in hop 5 means that the router is overloaded, or that a star in line 10 shows that we’re losing packets, you might let them know that it’s never that simple in today’s Internet.

- Turbo

The first time I saw the inside of a data center I had already worked in Web hosting sales for nearly two years. A member of our executive management team had decided that if we were going to sell dedicated servers we should probably have some concept of what they looked like.

I knew the building well; we’d once had a company-wide meeting in the lobby at 7:00 AM on a Saturday, so until our field trip I associated data centers with stale coffee and discontent over early weekend meetings. Although the data center and I had shared a less-than-stellar first encounter, when I finally stepped through the door that separated our then 14,000 or so servers from the rest of the world I never wanted to leave.

For those who have never had the pleasure or opportunity, visiting a large data center is something akin to a religious experience. Everything is so clean and sanitized. There are thousands of machines lined up in perfectly symmetrical rows and racks that tower above you, all connected by miles upon miles of a brilliant cable rainbow. The words you speak die in mid-air, absorbed by the sound of an electrified, whirring wonderland.

But in spite of the majesty of our data center’s sights and sounds, the part that struck me most was the smell. Imagine the new-plastic smell your CPU gives off when you plug a home computer for the first time, multiplied by many thousands, floating through perfectly filtered air. Within the first five minutes I wanted every customer to come and visit. They had to see and hear and, most importantly, smell what I was experiencing.

So when I read this article about the rising popularity of rub and sniff marketing my first thought was that we needed a way to recreate the smell of our data centers and include it in our print ads. We would be pioneers in olfactology for IT businesses!

Before this idea could come to fruition, it was pointed out to me that the smell of the data center really doesn’t do it for everyone. Although I cannot imagine why, some people even find it downright unpleasant, preferring smells like vanilla and sandalwood to plastic and electricity. One of our data center managers has even told me that while the CPUs and the electricity were contributing factors, most of what I smell is the fan belts on the air conditioning units, but that sounds much less romantic.

Still, the data center experience is more widely available to our customers than ever before. We now have a data center tour, starring actual Planet employees and filmed in our very own data centers. Click the button that says, “Take the Tour” on http://www.theplanet.com/ and enjoy our video, scent not included. For that part, you still need to make the trip to Texas and schedule a guided tour … break room coffee included.