sh ip arp 2

[Almin]

HI

I was wondering if someone could explain the output of "sh ip arp" command. I understand some part of that output but im not sure about the Age (min) colum.

Here is an output from my router. it says that ip address 192.168.2.6 has 1 min

Primary-Router#sh ip arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 75.***.**.** - 0017.59bf.2143 ARPA FastEthernet0/1
Internet 192.168.2.6 1 904c.e52d.072c ARPA FastEthernet0/0.2
Internet 192.168.7.1 - 0017.59bf.2142 ARPA FastEthernet0/0.24
Internet 75.**.**.* 0 001d.a2e8.0ad9 ARPA FastEthernet0/1

and I got this output bellow about 3 minutes later. as you see that under Age (min)
it now shows 0. shouldnt it be 4 since that is 3 min after the first output. I
thought that, the Age colum is for how long that perticular device has been
connected to the router.

Primary-Router#sh ip arp
Protocol Address Age (min) Hardware Addr Type Interface
Internet 75.132.9.225 - 0017.59bf.2143 ARPA FastEthernet0/1
Internet 192.168.2.6 0 904c.e52d.072c ARPA FastEthernet0/0.2
Internet 192.168.7.1 - 0017.59bf.2142 ARPA FastEthernet0/0.24
Internet 75.**.**.* 0 001d.a2e8.0ad9 ARPA FastEthernet0/1
Primary-Router#

the 192.168.2.6 address is the address that I used to SSh to the router.

Can someone explain the Age (min) colum.

I appriciate any help
Thanks

 

[Lemon13]

it´s the time there was no request for that entry, after a specified amount of time the entry gets flushed.

"By default, Cisco routers use an ARP cache timeout period of four hours. This means that if the router hasn't sent or received any packets with a particular address for the last four hours, it will flush the ARP entry from its cache"

from here

http://www.ciscoarticles.com/Cisco-IOS/925.html

M. Knorr

MCSE, MCTS, MCSA, CCNA

 

[Quadratic]

Another thing to note is that, while the default timeout is 4 hours, it's recommended in most circumstances to lower that to a period of less than 5 minutes. That way, the arp traffic makes sure that downstream switch CAM tables (mac address tables) are current, preventing any flooding of unicast traffic to hosts that just aged out for lack of regular bi-directional traffic through the network. The default has mac entries aging out much faster (5 minutes).

CCNP, CCDP