ping test.com
connect: No buffer space available

/var/log/messages

Oct 18 12:21:03 vps kernel: printk: 177 messages suppressed.
Oct 18 12:21:03 vps kernel: Neighbour table overflow.

Solution in /etc/sysctl.conf:

net.ipv4.neigh.default.gc_thresh1 = 4096
net.ipv4.neigh.default.gc_thresh2 = 8192
net.ipv4.neigh.default.gc_thresh3 = 8192
net.ipv4.neigh.default.base_reachable_time = 86400
net.ipv4.neigh.default.gc_stale_time = 86400
 

Edit the thresh1,2,3 to higher values if it keeps happening, usually heavy network traffic/torrents will cause this to happen.