Specifications

1-7
Software Configuration Guide For Cisco 2600 Series, Cisco 3600 Series, and Cisco 3700 Series Routers
OL-1957-03
Chapter 1 Understanding Interface Numbering and Cisco IOS Software Basics
Understanding Interface Numbering
Figure 1-7 Example of the Cisco 3631 Router Interface Numbering
Figure 1-7 shows an example of the interface numbering where the following interfaces are installed:
• A WIC in each WIC slot (containing interfaces serial 0/0 and serial 0/1 in physical slot W0, and
interface serial 0/2 in physical slot W1)
• A 32-port asynchronous network module in slot 1 (containing interfaces serial 1/0 through serial
1/31)
• An alarm interface controller network module in slot 2 (internally connected to interface serial 2/0)
• One built-in Ethernet 10/100 interface—FastEthernet 0/0
Note The logical slot number for all WIC interfaces is always 0. (The W0 and W1 slot designations are for
physical slot identification only.) Interfaces in the WICs are numbered from right to left, starting with
0/0 for each interface type, regardless of which physical slot the WICs are installed in. Some
examples are:
– If physical slot W0 is empty and physical slot W1 contains a 1-port serial WIC, then the logical
interface in the WIC is numbered serial 0/0.
– If physical slot W0 contains a 2-port serial WIC and slot W1 contains a 1-port serial WIC, then
the logical interfaces in physical slot W0 are numbered serial 0/0 and serial 0/1 and the logical
interface in physical slot W1 is numbered Serial 0/2.
– If physical slot W0 contains a 2-port serial WIC and slot W1 contains a 1-port BRI WIC, then
the logical interfaces in physical slot W0 are numbered serial 0/0 and serial 0/1, and the logical
interface in physical slot W1 is numbered BRI 0/0.
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Serial 0/2
Serial 1/0 to 1/7
Serial 1/16 to 1/23
Serial 1/8 to 1/15
Serial 1/24 to 1/31
Internal connections to serial 2/0
Console/AUX
ports
FastEthernet 0/0
Serial 0/0
Serial 0/1