Cisco 2620 Configuration Manual page 30

Understanding Interface Numbering
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Interface (port) numbers begin at 0 for each interface type, and continue from right to left and (if
necessary) from bottom to top.
Figure 1-10
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Figure 1-10 Cisco 3725 Router Rear View
Note
The 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:
Cisco 3745 Router Interface Numbering
The Cisco 3745 router chassis contains the following wide-area network (WAN) and local-area network
(LAN) interface types:
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Software Configuration Guide For Cisco 2600 Series, Cisco 3600 Series, and Cisco 3700 Series Routers
1-10
1 for interfaces in the single-width network module slot
2 for interfaces in the double-width network module slot
below shows an example of interface numbering on a Cisco 3725 router with:
A WIC in each WIC slot (containing interfaces Serial 0/0 and Serial 0/1 in physical slot W0,
interface Serial 0/2 in physical slot W1, and interface BRI 0/0 in physical slot W2)
A 2-port T1 network module in slot 1 (containing the following ports: T1 1/0 and T1 1/1)
A 36-port Etherswitch network module in slot 2 (containing the following ports: FastEthernet 2/0
through 2/35, and GigabitEthernet 2/0 and 2/1)
Two built-in Ethernet 10/100 interfaces—FastEthernet 0/0 and FastEthernet 0/1
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If physical slot W0 is empty and physical slot W1 contains a 1-port serial WIC, the interface in
the WIC is numbered Serial 0/0.
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If slot W0 contains a 2-port serial WIC and slot W1 contains a 1-port serial WIC, the interfaces
in physical slot W0 are numbered Serial 0/0 and Serial 0/1, and the interface in physical slot W1
is numbered Serial 0/2.
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If slot W0 contains a 2-port serial WIC and slot W1 contains a 1-port BRI WIC, the interfaces
in physical slot W0 are numbered Serial 0/0 and Serial 0/1, and the interface in physical slot W1
is numbered BRI 0/0.
2 built-in FastEthernet LAN interfaces
Chapter 1 Understanding Interface Numbering and Cisco IOS Software Basics
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