This post explains the interface numbering scheme used in Cisco 1800, Cisco 2800 and Cisco 3800 Series Routers. It also includes line numbering associated with async interfaces.

1. Slots are numbered 0, 1, and 2. The following are the main features of Slot 0: Slot 0 is the motherboard and not removable. It is reserved for integrated ports and NIMs. NIMs are designated by the number of the first slot that they occupy. A double-wide NIM occupies two slots, but its designation is only the left.
2. Note To install double-wide interface cards in Cisco 2811, Cisco 2821, and Cisco 2851 routers, remove the slot divider. When the slot dividers are removed, slot 0 and slot 1 become slot 1, and slot 2 and slot 3 become slot 3. Figure 7 Interface Card Slot Locations on Cisco 2901.

Existing router platforms (earlier than Cisco 1800, Cisco 2800, and Cisco 3800) contain a limitation. In some situations, such as when you insert WIC(s) out of order, the configuration of one WIC interface can be lost or applied to another WIC interface.

Part Number: CISCO2811-DC: Manufacturer: Cisco: Description: Cisco 2811-DC Router AC Power, 2FE 4HWICs 2PVDMs 1NME 2AIMS, IP BASE, 64F/256D: Full Description: Cisco 2811-DC Integrated services router with AC power, 2FE, 1 NME, 4 HWICs, 2 PVDM slots, 2 AIMs: Status: Discontinued by manufacturer.

Example: Assume that you have a serial WIC-2T in WIC slot 1 and WIC slot 0 is empty. The interfaces are named serial 0/0 and serial 0/1. If you insert another WIC-2T into slot 0, the new WIC interfaces are named serial 0/0 and serial 0/1. The old WIC interfaces become serial 0/2 and serial 0/3. Therefore, the old WIC interface configuration moves to the new WIC interfaces.

Refer to How Async Lines are Numbered in Cisco 3600 Series Routers for more information.

In order to overcome this limitation, Cisco 1800, Cisco 2800, and Cisco3800 series platforms now have a three-tiered interface numbering format (slot/subslot/port) for interfaces on WIC slots only.

Note: The slot information for the Cisco 3800 series is the same as the 2800/1800 interface and line numbering. See New Interface and Line Number Conventions for information on interface and line numbering.

New Interface and Line Number Conventions

This section describes the new conventions for interface and line numbering.

Cisco 2811 Slot Numbering Software

1. The interface numbering scheme is the same for async interfaces and non-async interfaces. To configure the line associated with an async interface, use the interface number to specify the async line.For example, line 0/0/0 specifies the line associated with interface serial 0/0/0 on a WIC-2A/S in slot 0. Similarly, line 0/1/1 specifies the line associated with interface async 0/1/1 on a WIC-2AM in slot 1.

   Note: This document uses the following words interchangeably:

   • Network-module-slot and slot.
   • Interface-card-slot and subslot.
2. Ports on network modules are numbered like this:interface-number = network-module-slot/port

   OR

   interface-number = slot/port

3. Ports on interface cards (such as WICs, VWICs and HWICs) installed directly in chassis slots is given here:interface-number = 0/interface-card-slot/port

   OR

   interface-number = 0/subslot/port

4. This numbering convention is used for ports on interface cards that are installed in network module slots:interface-number = network-module-slot/interface-card-slot/port

   OR

   interface-number = slot/subslot/port

   Note: The slot/subslot/port format only applies to WIC interfaces. Interfaces that are native to the network modules still use only the slot/port format. That is:

   • <interface-name> slot/port is used whenever the interfaces are native on the network module.
   • <interface-name> slot/subslot/port is used whenever the interfaces are on the WIC slot of a network module (NM).
5. Here is an example for numbering when the motherboard slot number is always 0. The native interfaces on the motherboard are numbered like this:
   • Fa0/0, Fa0/1 on Cisco 2811.
   • Gi0/0, and Gi0/1 on Cisco 2821 and Cisco 2851.

   The Motherboard WIC slots are numbered from 0 to 3. The number increments from right to left, and from bottom to top.

6. Slot numbers for other slots increase from bottom to top, then right to left. Subslot numbers and port numbers within a slot also increase from bottom to top, then right to left.

Examples

Interfaces native to an extension network module (ENM):

If the ENM carries WIC cards, the WIC slot numbers start from 0:

The extension voice module (EVM) slot analog interfaces are numbered from voice-port 2/0/0 to voice-port 2/0/23, following the NM-HDA convention.

Interface Numbering

This section lists the interface numbering details for Cisco routers.

Table 1 – Interface Numbering on Cisco 1841