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New Member

IOS "interface" command

Greetings. I am attempting to configure my Cisco 831 router to VPN connect to another server. I have been given IOS commands in order to create the connection, however there is one command that does not seem to be valid with my router and I was hoping someone could help me interpret it. The command is:

interface fa0/0

the comment beside this command says: "Assumed as inside interface" and this appears later as:

interface fa0/1

with the description "Assumed as Public Internet interface"

however, when I look at the available commands in interface mode, none resemble "fa0", here are the commands for interface:

router(config)#interface ?

Async Async interface

BVI Bridge-Group Virtual Interface

CDMA-Ix CDMA Ix interface

CTunnel CTunnel interface

Dialer Dialer interface

Ethernet IEEE 802.3

FastEthernet FastEthernet IEEE 802.3

Group-Async Async Group interface

Lex Lex interface

Loopback Loopback interface

MFR Multilink Frame Relay bundle interface

Multilink Multilink-group interface

Null Null interface

Tunnel Tunnel interface

Vif PGM Multicast Host interface

Virtual-PPP Virtual PPP interface

Virtual-Template Virtual Template interface

Virtual-TokenRing Virtual TokenRing

range interface range command

any ideas?


Re: IOS "interface" command

"fa0' is short for "FastEthernet0" ... IOS is smart enough to recognise this and will work even if you just use that abbreviation...

IOS also has a command completion utility which you can invoke by using the TAB key. So try the following:

router(config)#interface fa

and you will see that the fa will be expanded to FastEthernet.

Hope that helps - pls rate the post if it does.



New Member

Re: IOS "interface" command

Paresh, thanks, however it seems "0" is an invalid fastEthernet choice (even though typing "?" says:

<0-4> FastEthernet interface number

Why is 0 invalid?

Also, the command I was told to use is the following:

interface fa0/1 # Assumed as Public Internet interface

ip address ##.##.###.### 255.255.255.x #Customer public interface

I removed the ip address numbers in this post for my own security, however the .x was exactly as the instructions said to use. I replaced this with (as that is my subnet mask, and that's what I figured they were asking for), however I get the following message:

IP addresses may not be configured on L2 links.

what does that mean? (and thanks again for the help).


Re: IOS "interface" command


Can you first determine what interfaces are installed on your router by getting the output of the following:

'sh ip int brief' ?

Hope that helps - pls rate posts that help



New Member

Re: IOS "interface" command

Interface IP-Address OK? Method Status Prot


Ethernet0 YES NVRAM up up

Ethernet1 YES DHCP up up

FastEthernet1 unassigned YES unset down down

FastEthernet2 unassigned YES unset down down

FastEthernet3 unassigned YES unset down down

FastEthernet4 unassigned YES unset up up

Re: IOS "interface" command


You dont have ethernet interfaces numbered based slot,port numbers.Thats the reason you are getting the error when you enter fastethernet 0/1..

As far as the error message which you have mentioned up in ur earlier post i feel you are trying to configure the High Speed Etherswitch module card.

Also you can post out the o/p of show version command to confirm the hardware type being used out there (which you are trying to configure).