A Modest Proposal for Cisco Interface Naming


If you’re going to be configuring an interface in a switch, which one are you going to use? The interface has a name and a number based on where it is on the device. The numbering part is fairly easy to figure out. The module number comes first, followed by the slot, and finally the port. In the world of Cisco, which is the one I’m the most familiar with, that means a fixed configuration switch usually has interfaces labeled 0/24, with no module and the slot almost always being zero. With a modular switch the interface would be labeled 2/0/28 to indicate the 28th port on the second line card.

The issue arises when you factor in the first part of the interface naming convention. The nomenclature used in the Cisco world since the beginning of time has been the interface speed. If your interface is a 100Mbit Ethernet interface then the interface name is FastEthernet0/48. If you’re using a 1Gbit interface it’s GigabitEthernet0/48. If it’s a 10Gbit interface it becomes TenGigabitEthernet0/48. It’s a progression of interface speeds. Even if the port is capable of using 10/100/1000 the port is referred to at the highest speed. The 10Gbit ports don’t negotiate to a lower speed so they are always TenGigabit.

Now, with the new Catalyst 9000X Series switches you have the option of a port that can do 10/100/1000/2.5G/5G/10G. It’s a multi-gigabit capable port as outlined in this video from a recent Field Day event:

I don’t even want to think about the nightmare of trying to remember the name of the interface in a situation like that. It’s hard enough still to remember what the switches are capable of, whether it’s a gigabit port or a ten gigabit port. It’s hard enough for me but it’s impossible for anyone looking to make a script or automation that needs to be repeatable over a wide variety of switches.

Naming Convention Unity

The obvious solution here is actually present in another Cisco platform already. The Nexus series of switches running Cisco NX-OS already knows how to handle interface naming issues. It’s a problem that occurs when you could be running Gigabit Ethernet or Fibre Channel over Ethernet interfaces.

How does NX-OS fix this? The interface type is always Ethernet. It doesn’t matter what speed the interface is running at because it’s always Ethernet under the hood. So the every interface is labeled Ethernet(module/slot/port). It’s wonderful when you’re working on the device because you never have to make a typo based on the interface speed. It’s also consistent across every platform and module that could be installed.

The solution to the problem actually came from my friend Bruno Wollmann (@WollmanBruno) during the event. It’s well past time to adopt the NX-OS convention in every other version of Cisco IOS. You can alias the old interface names to the new nomenclature to ease the transition if you’d like. Otherwise it’s time to start making people use the basic convention of calling everything Ethernet.

This would ease new users into IOS by making all interfaces the same and focusing on the module/slot/port complexity as the primary place to learn about naming. It also helps with the development of automation and orchestration scripts. Rather than needing to detect device types or write different scripts for NX-OS or IOS-XE you can just use the same logic for both.


Tom’s Take

It’s time we move into the future of interface names. Bruno made an excellent point when he said that it’s time to adopt a standard across the whole line of switches. Cisco may not be ready to do a single OS but having unity between the features will go a long way to making it easier to work on the various platforms. You can do a lot with aliasing in the system to ease the transition but maybe by the time we get to IOS 20 we can use something that’s more manageable for the future.

4 thoughts on “A Modest Proposal for Cisco Interface Naming

  1. In my opinion, it’s well past time that Cisco dropped the ISO command structure and gave use a GUI, for free. The Catalyst commands haven’t changed since the 1990’s. Every other vendor has moved on, except Cisco. That’s another reason for me to change vendors at our next edge-switch replacement.

  2. I totally agree. I see this all the time with device names as well. My conclusion: DO NOT OVERLOAD names with inventory etc. data (attributes, like model #)! Short location code — I value that. But the rest–that’s what NSOT / databases / spreadsheets are for. For interfaces, it is a port, which doesn’t change. Speed is an attribute, a setting, changeable, something you look up to see what the current value.

  3. Pingback: A Modest Proposal for Cisco Interface Naming - Tech Field Day

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