arp table: How to cause entries to stay forever

zvivered · 09-09-2011, 02:15 AM

Hello,

I'm using the ARP table in a RedHat PC to inspect all IPs that are connected to a specified ethernet card.

All switches and PCs connected to this card get their IP address using DHCP so the arp table contains those IPs.

But after 5 minutes, the entries from the ARP table are deleted.

How can I cause the entries to stay forever, till I delete them ?

Thanks,
Zvika.

acid_kewpie · 09-09-2011, 02:58 AM

you would add them yourself as a static entry. "arp -i eth0 -s 192.168.1.1 00:00:00:00:00:01" etc.

eSelix · 09-09-2011, 03:52 AM

If I properly understood your goal, if you add this information statically, forever you will not be able to check if another device wasn't connected or disconnected, or already added device doesn't changed their MAC or IP. Also your communication with these devices can be disturbed. It must be dynamic.

The solution can be reading this table with 5 or 4 minutes interval and storing it somewhere. And after finding inconsistency do what you want.