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When do IP's show up in the SHOW ARP command?

Posted on 2008-10-22
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Last Modified: 2008-10-22
I do not fully understand when an IP address will show up in the output of the SHOW ARP command.  For example, I have a VLAN on my CISCO 4006 Switch and I know there 4 dell PC's are connected to it.  I thought that the IP's for those PC's would show up in the output of a SHOW ARP command so I could then get the MAC addresses of those PC's, run a SHOW MAC ADDRESS command, and find the port they are connected to.  However, even though these PC's have been connected for quite some time, their IP addresses do not appear when I run a SHOW ARP command.  
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Question by:frank_nye
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7 Comments
 
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RPPreacher earned 50 total points
ID: 22775831
When something makes an ARP request to them.

Just ping each PC, the switch should populate the ARP table.
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by:knightfox
ID: 22775847
that correct.. you should be able to do a show arp.  Could you please try and ping one of the IP addresses then run:

Router#sh ip arp
Internet  x.x.x.x             -   000b.fc48.xxx  ARPA   Vlanxxx
Internet  x.x.x.x             -   000b.fc48.xxx  ARPA   Vlanxxx
Internet  x.x.x.x             -   000b.fc48.xxxx  ARPA   Vlanxxx
Internet  x.x.x.x             -   000b.fc48.xxx  ARPA   Vlanxxx

/Fox

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Expert Comment

by:knightfox
ID: 22775864
then to show the port do:

Router#sh mac-address table | i xxxx

xxx is the last four chars of the mac address... and you should see

 xxx    0000.0c07.xxx    DYNAMIC    Gi0/1

/Fox
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Author Comment

by:frank_nye
ID: 22775947
If I do a PING command while in ENABLE mode on the switch, does it start a ping and continually run it or does it just send out a few pings and then stop?  On some devices (I think some test equipment like a Fluke Etherscope) I have seen a PING request go out and then it just keeps on running and runing.  I want to make sure I don't start something like that on the Switch.  If I just run the command PING 10.0.4.20 on the switch, will it only send out a few pings?
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Expert Comment

by:RPPreacher
ID: 22775967
5 pings.
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Expert Comment

by:knightfox
ID: 22775990
you can do it either ping.. and enter the number of pings you want.. or just use ping x.x.x.x and use

CTRL + Shift + 6 to escape the ping

/Fox
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Author Comment

by:frank_nye
ID: 22776155
Thanks everyone.  I got it.
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