So, my current situation is that I'm working in a datacenter with 21 racks arranged in three rows, 7 racks long. We have one centralized distribution switch and no patch panels, so everything is run to the switch which lives in the middle, roughly. It's ugly and non-ideal and I hate it a bunch, but it is what it is. And it looks a lot like this.
Anyway, so given this really suboptimal arrangement, I want to be able to more easily identify a particular patch cable because, as you can imagine, tracing a wire is no fun right now.
He wanted advice as to whether the network cables should be labeled with exactly what the other end is connected to, including hostname and port number, or use a unique ID on each cable so that as they move around they don't have to be relabeled.
We write about this in the Data Centers chapter of The Practice of System and Network Administration but I thought I'd write a bit more for this blog.
My reply is after the bump...
Fundamentally you are asking "What is the purpose of a cable label?" If you can answer this question then the labeling scheme becomes self-evident.
I believe the purpose of cable labels is to accelerate tracing. That is, when you need to know "where the other end" having labels means you can read the label instead of physically tracing the cable. If a cable has the same tag on both ends, if you find one end, you can find the other end. The minimum solution is to start numbering cables 1, 2, 3, 4, 5, and so on. Label each end with the same number.
There are other things that COULD be the purpose of the cable labels. I'll list the 2 that come to mind. I think these are POTENTIAL purposes but that they solve problems that are solved better using other methods.
- What is the length, type, and so on. (i.e. Cat6 vs Cat5; 1m vs 6m vs 10m).
- What is connected to each end? (i.e. label each end with "router port 5 to host123")
I would argue that (1) is best done via cable color.
I would argue that (2) is an inventory nightmare: it creates more work than saves. It also solves a problem that doesn't exist. How often have you walked to a computer room to see what is connected to what? Generally you FIRST check the router "cam" table to see the ground truth. That answers your question 99% of the time. You only physically go to the computer room the remaining 1% of the time, and in this case you want to verify what you think you already know, which having a cable number on each end is all you need. In the 1% of the time that THAT is not successful, you end up tracing the cable or just trying a different cable.
On the other hand, this 1% of 1% can be solved by having each end labeled with "routerX port abc:23 connected to host123:eth1". However, maintaining such labels is a huge amount of labor for something that is extremely rare. Without such detailed labels you'd trace the cable (or more likely try a different cable to see if that solves the problem). With such detailed labels you create an inventory nightmare.
Early in my career I tried labeling cables with the name of the two ports on each end. Within a few months the cable labeled "host123" was re-used to connect host "host456" and rather than updating the label we just "lived with it". It was a mess. We eventually just started labeling each end with a unique number. Cables could be reused easily.
If you agree that the only purpose of a label is "to accelerate tracing" then it also means you do not need to keep a database of what each cable is for. You only need to store a single integer: What is the highest number used so far?
If you do choose to keep a database, it will be out of date within days. Even if you make it extremely easy to update, mistakes will happen. Then you'll be tempted to do a yearly database audit, which is a lot of work. Why would you create more work for yourself? Instead, a database that doesn't exist has no errors.
As a side note, this issue seems to be magnified because of the choice to have every machine connected all the way to a single central switch. That is a best practice from years ago that is no longer very popular. The current best practice is to have a switch in each rack (a "TOR" or "Top Of Rack" switch) and then have all the TORs connect to a main switch (the "core" switch). That way you have very short cable runs from the machines to the TORs; so short you might not even need to label them. The only long cable runs are from the TORs to the core switch. These are static and a simple integer-based labeling scheme is fine. I'm sure you have reasons for not going with a flat network instead, but this is one of the trade-offs to be considered.
P.S. There is more information about this in the Data Centers chapter of The Practice of System and Network Administration.