This tutorial explains the naming convention used in Cisco router and switch for interfaces in details with example.
Cisco makes a large number of products. Among those I will include 1603, 1841, 2500, 2600 series routers and 2960 series switches in this article to explain the nomenclature. As these products are the base lines for CCNA exam.
Router Interface Nomenclature
In entry level series Cisco makes two types of routers :- fixed and modular. In fixed interface series router, all slots and ports are integrated with device. In modular interface series router, we have a choice to install the ports according to requirement.
Router supports several media types of data link layer including ethernet, fastethernet, gigabitethernet, atm, bri, pri, asynch, serial and many more. In fixed interface series router, interface numbers always start with 0 (zero) and goes their way up within specific interface type.
Fixed interface series router
In fixed interface series router, the interface nomenclature is type slot_#/ port_#.
If a fixed interface router has three Ethernet and two Serial interfaces, then they would be named Ethernet 0, Ethernet 1, Ethernet 2, Serial 0 and Serial 1.
For example, 2503 series router has two fixed serial interfaces; so they would be called serial 0 and serial 1.
Let’s take one more example, 1603 Router has one Ethernet port and one BRI port; so it would be called Ethernet 0 and BRI 0.
Modular interface series router
In modular interface series router, the interface nomenclature is type slot_#/port_#.
Modular interface series router has modular slots; we can insert any supportive interface in these slots.
For example, following 2600 series router has two slots. First slot would be slot 0; second slot would be slot 1.
If you install four serial interfaces in first slot, then they would be named 0 - 3.
This naming convention has limitation. When we insert WIC without order, configuration of one modular interface might be lost or applied to other modular interface.
For example, in above router we have two modular slots; slot 0, slot 1 and one modular interface with four serial ports. If we install this modular interface in slot 1, then the interface name would be serial 0/0, serial 0/1, serial 0/2, and serial 0/3. If you install another modular interface with two serial ports in slot 0, then new interface name would be serial 0/0, serial 0/1, serial 0/2, serial 0/3, serial 1/0 and serial 1/1. In this case old WIC interface become serial 1/0, and serial 1/1. Therefore, old interface configuration moves to new interfaces.
To overcome this limitation from Cisco 1800, Cisco 2800, and Cisco 3800 series, routers have three tired interface naming convention for WIC slots only.
New naming convention only for WIC slots is type slot_#/subslot_#/ port_#.
Ports installed directly on chassis still use classic convention that is type slot_#/ port_#.
For example in 1841 series router two Ethernet ports are installed on chassis, they have 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. Modular interface series switch has same nomenclature like router.
Nomenclature of an interface on modular interface series switch is type slot_#/port_#.
In fixed interface series switch all interfaces are installed on chassis. The Catalyst 2960 series switch supports only fixed interfaces.
Nomenclature for interface on fixed interface series switch is type slot_#/port_#.
|type||Type is media type. Media types supported by switch are Ethernet, Fast Ethernet and Gigabit Ethernet.|
|slot_#||This is slot number.|
|port_#||The port number is the number of the port in the specified slot.|
For example on 2960-8TC first Ethernet interface is called ethernet 0/1 and last Ethernet is called Ethernet 0/8.
Catalyst 2960 series switches
|WS-C2960-8TC-S||8 Ethernet 10/100 ports with one dual-purpose uplink|
|WS-C2960-24-S||24 Ethernet 10/100 ports|
|WS-C2960-24TC-S||24 Ethernet 10/100 ports and two dual-purpose uplinks|
|WS-C2960-48TT-S||48 Ethernet 10/100 ports and two copper uplinks|
|WS-C2960-48TC-S||48 Ethernet 10/100 ports and two dual-purpose uplinks|
- For all fixed interfaces on a Cisco switch, the slot number is always 0.
- Port number on switch starts with 1 and goes their way up.
Key difference router and switch nomenclature
On router port number starts with 0( Zero). For example first Fast Ethernet port on router would be fastethernet 0/0.
On switch port number begins with 1. For example first Fast Ethernet port on switch would be fastethernet 0/1.
Cisco IOS commands to find out the name of interface
Interface naming convention may confuse you sometime, especially in exam. Use IOS inbuilt "show ip interface brief" command to turn this confusion in surety.