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the command ARP ?

Posted on 2004-09-10
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Last Modified: 2008-07-03
hello ,,
whats this command mean and and what the output mean ?


C:\>arp /a

Interface: 147.159.123.159 on Interface 0x1000003
  Internet Address      Physical Address      Type
  147.159.123.1         00-03-99-88-96-8b     dynamic
  147.159.123.248       00-01-2e-05-90-0c     dynamic

147.159.123.159 is my ip , my server ip is 147.159.123.1 , 147.159.123.248 is another computer ! ..
thank you v much

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Question by:3ezz
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by:PsiCop
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ID: 12031792
The ARP command shows you the entries in the TCP/IP Address Resolution Protocol table. ARP provides translation of IP addresses into local-subnet MAC addresses. What you are seeing is all the MAC addresses of the IP addresses on the local subnet.
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by:3ezz
ID: 12031819
but there are 4 PC's in the same subnet too ... where they are ?
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by:dis1931
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ID: 12031991
These are most likely the ones that you have used recently...aka in the last 2 minutes.  I believe the ARP table keeps entries for two minutes and then they are cleared assuming that you are not accessing anything on these devices constantly.  So say you access a share on 147.159.123.1 and then close the window and don't communicate with it for 2 minutes or so it will be wiped from arp cache.  I believe pinging devices causes it to enter arp cache.  So if you ping another pc on the subnet it will appear in the list.  It doesn't necessarily go out and attempt to find all devices on the network it is simply a cache of MAC addresses that the computer has had to resolve on the local subnet.....

This is all from memory so might be a little off....i was trying to find a site that had a good explanation but couldn't find one....if i do i will post it.

Dis
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Expert Comment

by:cyrnel
ID: 12032033
It can be configured since NT4 sp3 but otherwise 2 minutes is right for the initial value. If used the timer resets to 10 minutes. Controllable by:

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\ArpCacheLife and ArpCacheMinReferencedLife
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by:dis1931
ID: 12032056
Thanks cyrnel..i knew i wasn't going crazy about the 2 minute thing.

Dis
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by:cyrnel
cyrnel earned 400 total points
ID: 12032190
Yep, not a limit you have to fight too often.

The control keys don't exist by default so changing defaults means adding the pairs & restarting.

Also, I recall old experiments where the win stack cache expands automatically once you get past the initial table of 50 entries. But it doesn't shrink gracefully, or didn't in old stacks. Setting the default timers too high would worsen the small mess in memory on wires with lots of interfaces.
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by:valicon
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iwontleaveyou earned 400 total points
ID: 12033206
the command arp /a  or arp -a are the same commands and this command shows the current arp table entries. I have answered to this question and want you to refer it.

http://www.experts-exchange.com/Networking/Q_21125477.html#12023921

there is a link in the accepted answer view that link also.
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