Trying to understand router slot/port designation and slot/port.subinterface designation

I understand slots and port designations.
but I don't understand slot/port.subinterface designations.
What are they for?
brothertruffle880Asked:
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naderzCommented:
A sub-interface allows you to make one interface (Ethernet, Serial, Etc.) look and behave like multiple independent interfaces.

So, when you have Interface FastEthernet 0/1.1 and FastEthernet 0/1.2 you have essentially created two interfaces out of one. Each interface can have its own IP address, Access Lists, etc.
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naderzCommented:
It's best to explain using an example. Do you have an example that you would like to review?
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kevinhsiehCommented:
Sub interface would normally be for a vlan on a trunk port. Each vlan would have its own sub interface.
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brothertruffle880Author Commented:
I'm drawing a visio diagram for someone and I see notations for sub interfaces.  I know nothing about them whatsoever.  The reason for my posting the question was:  I wanted to educate myself about them.  I know about routers and switches but my knowledge is quite dated (back to the 1990's)
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AkinsdNetwork AdministratorCommented:
A common terminology for this is "Router-On-A-Stick"
This has multiple advantages but all are centered on apparently making 1 "port" appear as many "ports".
Popular with WAN links, ISPs etc
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brothertruffle880Author Commented:
naderz:  So how do you address each of the interfaces?  If one interface can create multiple interfaces out of one, how do you differentiate or address the two different interfaces?
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kevinhsiehCommented:
Say you have interface FastEthernet0/1. A sub interface would then be FastEthernet0/1.1, FastEthernet0/1.2, FastEthernet0/1.3, etc.
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