Interface Nomenclature Guide of Router and Switch

Routers and switches support various types of interfaces for different purposes. Each interface follows a predefined naming convention that allows you to track and configure it separately. This tutorial explains this naming convention and interface nomenclature guide for Cisco routers and switches.

Cisco makes routers and switches with fixed and modular interfaces. A fixed interface comes with the device. It is part of the device. You cannot remove it from the device. A modular interface is a separate interface from the device. You can install it on and remove it from a modular device as needed. A modular device is one with slots for modular interfaces. You can manage modular interfaces only on modular devices.

Naming convention and interface nomenclature guide for Cisco routers

Cisco routers support several media types at the data link layer, including Ethernet, Fast Ethernet, Gigabit Ethernet, ATM, BRI, PRI, Asynchronous, Serial, and more.

Fixed port routers

A fixed port router uses the following interface nomenclature.

Type Port_#

Port numbers always begin at 0 and go up to the last interface. For example, if a router has four fixed FastEthernet interfaces and two fixed serial interfaces, it will use names FastEthernet 0, FastEthernet 1, FastEthernet 2, FastEthernet 3, Serial 0, and Serial 1.

Examples

A 2503 series router has two fixed serial interfaces, so they are called serial 0 and serial 1.

A 1603 Router has one Ethernet port and one BRI port, so they are called Ethernet 0 and BRI 0.

Modular routers

A modular router has modular slots. You can install interfaces in these slots. It uses the following interface nomenclature.

Type Slot_#/ Port_#

Numbers for each slot and port within each slot begin at 0 and increase. For example, if you had a modular router with four slots, the first slot would be 0, the second 1, the third 2, and the fourth 3. If the first slot had two FastEthernet interfaces, the interface numbers would be 0 and 1. If the second slot had four serial interfaces, the interface numbers would be 0 -3. If slots 2 and 3 have interfaces, their numbers would also follow the same nomenclature.

Example

A 2600 series router has two slots. These slots would be called Slot 0 and Slot 1.

If you install four serial interfaces in the first slot, they would be named Serial0/0, Serial0/1, Serial0/2, and Serial0/3.

Three-tier interface naming convention

Newer Cisco devices use the following three-tier interface naming convention.

Type Device_Index Slot_ID Interface_ID

Device_Index is an index number referencing the device. You can stack devices to work as a single unit. In this case, the first device will use device index 0, while the second device will use device index 1. After identifying the device, it uses the slot and interface numbers as before.

Ports installed directly on the chassis still use the classic convention: type slot_#/port_#.

For example, in the 1841 series router, two Ethernet ports are installed on the chassis; they are named Fast Ethernet 0/0 and Fast Ethernet 0/1.

Switch Interface Nomenclature

Entry-level switches have only fixed interfaces. Higher-end switches support modular slots. The modular interface series switch has the same nomenclature as a router. The nomenclature for an interface on a modular interface series switch is slot_#/port_#.

A fixed-interface series switch has all interfaces on the chassis. The Catalyst 2960 series switch supports only fixed interfaces. The nomenclature for the fixed interface series switch is type slot_#/port_#. On a switch with all fixed interfaces, the slot number is always 0.

For example, on a 2960-8TC, the first Ethernet interface is Ethernet 0/1, and the last Ethernet interface is Ethernet 0/8.

• For all fixed interfaces on a Cisco switch, the slot number is always 0.
• Port numbers on the switch start with 1 and go up from there.

Key difference between router and switch nomenclature

• The router port number starts with 0( Zero). For example, the first Fast Ethernet port on the router would be Fast Ethernet 0/0.
• The switch port number begins with 1. For example, the first Fast Ethernet port on the switch would be Fast Ethernet 0/1.

Viewing interface name

You can use the "show ip interface brief" command to view the names of all active interfaces. The following image the output of this command on a 2960 switch.

The following image the output of this command on a 1800 series router.

The following image the output of this command on a 2600 series router.

Conclusion

Understanding the Cisco device naming convention and interface nomenclature is essential for effective network management and configuration. This guide highlights the distinctions between fixed and modular interfaces for routers and switches. By familiarizing yourself with these naming conventions, you can more efficiently configure and manage your network devices, ensuring seamless communication and performance across your Cisco infrastructure.