First off, I apologize for posting on a subject I'm sure has been beaten to death -- but reading the Cisco documentation has managed to confuse me entirely. I am not seeming to find an explanation that drives it home for me. So - regarding the following excerpt from a 3rd party I have a question:
(1)Now let’s talk about the “slot#/port#” designation. On the old 2500 series routers, they had fixed ports so there was no slot numbers. Thus, if a 2500 series router had two Ethernet interfaces, they were called Ethernet0 and Ethernet1. It is important to point out that Cisco slots and ports always start with zero first, then one.
(2)On the newer model routers with slots, any interface built onto the router (a fixed port) is considered to be in slot 0 (zero). This is even true for WAN interface cards (WIC) slots that are on the router. Any WIC installed in a router is in slot 0. So, the first WIC installed in the router will always be WIC 0, even if it is in slot 1. This can be confusing sometimes. So if Slot 0 has a 2 port serial WIC and Slot 1 had a BRI interface, you have Serial 0/0, Serial 0/1, and BRI0/0.
(3)Say that you have a Cisco 2610 router. If you put a Serial WIC card in slot zero (called W0 on the router), that module would be called Serial0/0. If there was a two port Serial WIC card in the other slot (slot W1), it would be called Serial0/1 and Serial0/2.
(4)Say that you had a Cisco 3640 router. That router has 4 NM slots and no built in network interfaces. The network module numbering on a 3640 starts with zero and goes to three. This number starts on the bottom right of the router (there are four slots, two and two, each two on top of the other two) with zero. So, the bottom right slot is slot zero. The bottom left slot is one, the top right slot is two, and the top left slot is three. If you put a module with two WIC cards in the top right slot, your WIC cards would be called Ethernet2/0 and Serial2/0.
I was fine all the way up to paragraph 4. I understand the right to left, bottom to top numbering, but I thought all WIC interfaces regardless of slot, based on the previous discussion would start with 0? Any clarification is greatly appreciated.