Arp timeout without any traffic

[from88]

                   Hello, i have a simple question.

If I set for example ARP timeout for 10mins and no traffic is received or transmited for 10hours. So questions do ARP timeout after 10mins will refresh it's ARP table with ARP request or no  even with no traffic ? Can't find clear documentation on that... thanks.

[handoko wiyanto]

hi there,

may i know what device are you working on and the ios version?

and what do you mean by no traffic? are you unplugging the cable?

regards,

[from88]

it's just theoretical question.

Just imagine two standard cisco Routers connected to each other. And all the features like CDP is turned off. The ARP will renew or not ?

[John Blakley]

ARP times out after 4 hours by default and dynamic entries will go away.

HTH,

John

[from88]

but will it renew after timeout even if no traffic is received or transmited ?

[John Blakley]

It  will not renew automatically without an arp request. Local addresses should still show up in the arp table though. Once the dynamically learned address hits the 1440 minute threshold, it will drop from the table. Addresses that are set with static arp and local addresses will always stay in the table and will not drop out.

[handoko wiyanto]

hi,

im reading a good chapter abour ARP here:

http://www.tcpipguide.com/free/t_AddressResolutionandtheTCPIPAddressResolutionProto.htm

what interest me the most is the way the writer use the simple analogy:

"The alternative to direct mapping  is a technique called dynamic address resolution. To understand  how this works, we can consider a simple analogy. I'm sure you've seen  limousine drivers waiting to pick up a person at the airport they do  not know personally. (Well, you've seen it in a movie, haven't you?)  This is similar to our problem: they know the name of the person they  must transport, but not the person's face (a type of “local address”  in a manner of speaking!) To find the person, they hold up a card bearing  that person's name. Everyone other than that person ignores the card,  but hopefully the individual being sought will recognize it and approach  the driver.
"

so, theoritically, based on my understanding, if there is no traffic that needs to be transmitted, the arp protocol must not start itself.

but nowadays, in the real world, even if you only connects two cisco routers without having any client and disabling cdp, there are some protocols that depends on ARP, such as dhcp, dynamic routing protocol, or multicast routing, etc.

regards,