Understanding Router ports and syntax

I'm trying to understand the significance of the numbers before and after the slash.  (See graphic)

The three sets of numbers surrounding the router I'm trying to understand are:
0/0
0/1.100
0/2

What do these combinations of numbers mean?

router
brothertruffle880Asked:
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AkinsdNetwork AdministratorCommented:
Interface identification

My example below includes a third level (module) illustrated with Gi 0/0/0

The picture shows a router with 2 modules.
1 Module has 2 Slots, the 2nd module has 4 slots
Module 1 has a Slot with 4 Ports
1 Port can be subdivided "Virtually" in a method referred to as "Router On A Stick" into Sub-Interfaces. as described above
To create the sub-interface in your diagram. This command was issued

interface Gi 0/0.100
encapsulation dot1q 100 (The encapsulation does not have to match the subinterface but it's good practice to make it match. The encapsulation specifies which vlan that subinterface will operate on)
ip address 172.16.100.254 255.255.255.0 (I used a random IP just for illustration)

Cisco labels interfaces from right to left starting with 0 (See Picture 4 for details)

Picture1Picture2Picture3 Picture4
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Ernie BeekExpertCommented:
Let's see:

0/0 = slot/port
0/1.100 = slot/port.subinterface


Also have a look at: http://www.petri.co.il/csc_how_router_interfaces_get_their_names_on_cisco_routers.htm
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