Default 60 seconds

$ cat /proc/sys/net/ipv4/neigh/eth1/gc_stale_time 
60

References

http://www.linuxquestions.org/questions/linux-networking-3/default-arp-cache-timeout-on-linux-866048/

http://www.networkers-online.com/blog/2009/02/arp-caching-and-timeout/

Category:Linux