Linux: arp cache timeout for non existent hosts

arplinuxnetworking

In Linux, is there a different arp cache timeout for non existent hosts?

At my router, 192.168.0.1, i'm seeing aprox. 8 new entries every 10 seconds for an IP that has been down for a long time.

Sample output from tcpdump -n -i eth1 broadcast:

18:54:21.107848 arp who-has 192.168.0.45 tell 192.168.0.1
18:54:21.607919 arp who-has 192.168.0.45 tell 192.168.0.1
18:54:22.107922 arp who-has 192.168.0.45 tell 192.168.0.1

gc_stale_time is set to 200:

# cat /proc/sys/net/ipv4/neigh/eth1/gc_stale_time 
200

And yes, this ip is on my arp table:

arp -an | grep 192.168.0.45
? (192.168.0.45) at <incomplete> on eth1

Why it keeps sending so many requests every 10 seconds?

Best Answer

This is probably not your router which do the requests by itself. Another computer want to contact 192.168.0.45 using your router. So the router just try to do its job.

This should help you to find which computer is faulty: 

    tcpdump -n -i dst 192.168.0.45
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