Why Downloads Fail – Part 4 – The Network
Network issues cause download failures. Simple to say, easy to grasp; lose your connection and lose your download.
However, “network issues” can cover a wide range of variables, so we need to define some boundaries. The network, in this case, includes any device between the original host of the content, and the target machine for the downloaded files. Device types include name servers, routers, switches, hubs, firewall devices, VPNs, remote storage mounts (NFS, Samba, etc) security devices (anti-spam, anti-phishing, packet inspectors, etc.) and wireless versions of all of the above.
If you are curious about how many devices are between you and your desired download you should familiarize yourself with a “traceroute” tool. Most operating systems ship with a command implementation of traceroute and there are a number GUI traceroute tools available for those who prefer a visual representation of the network information.
One of the tools I use use is VisualRoute.
Here is a view of the number of devices (that aren’t in stealth mode, between me and the San Jose Mercury News).
As you can see (sorry for the small image), there are at least 13 points along this path that could induce a download failure. An error or disconnect in any one of these devices during a download can cause the file transfer to fail. Errors in data transmission can be caused by faulty hardware, overloaded devices, scheduled maintenance outages, memory limitations, your ISP’s dynamic DHCP lease rotations, and the list goes on.
Some of the devices between you and your target download may even be configured to intentionally block downloads of certain types of files, such as those with executable extensions (.exe, .sh, and others).
The overwhelming majority of the time, we get what we ask for in the download process. These devices work, and the built-in error correction tools that they were designed with handle the problems. But any statistical analysis of the billions of individual transactions that even smallish networks manage daily, forces us to realize that errors do and will occur.
The bigger the file, the longer your download is exposed to potential interruption. This reality is one of the main reason why Akamai exists, and the market for CDN services continues to expand. It’s also why “download managers”, which we discussed in a previous post, exist and are designed segment large files into smaller parallel-processed downloads. Reducing the size and time to complete the download reduces the risk of the transaction failing due to the inevitable everyday errors in the network.
So, on that rare occasion when a download does fail, consider your level of exposure to your network. The Network can be Why Downloads Fail.
