Sub interfaces on a interface

[John Cheetley]

Hi Techs,

Am aware that you can have up to so many sub interfaces on a interface based on link below

https://learningnetwork.cisco.com/thread/65242

What is the purpose of this when for access list purposes, you must have 2 separate interfaces.

One for internal for devices(whether computer or IP phones) and one external for internet access

I am confused..

As I have configured FA0/0 to 192.168.0.1

This has 2 sub interfaces of FA0/0.1 (192.168.1.2 ) and FA0/0.2 to (192.168.2.2) with phones off this address and router ip of 192.168.0.12

I was going to use 192.168.1.2 as outside LAN and 192.168.2.2 as inside LAN for access list purpose

Thanks again :) :)

[iMedxSGower]

If you are using Gigabit Ethernet, you can apply an ACL directly to a sub-interface.  Unfortunately, in your example, you're using Fast Ethernet, which does not support this usage, so any ACL has to be applied at the physical level and thus affects all the sub-interfaces equally.   Your plan will need revision.