Linux: 'Neighbour table overflow' on router with static routes

[ATC]

After configuring a Linux router with static routes, traffic on one or more interfaces does not work properly. After a few seconds, the following message appears over and over on the console:
"printk: neighbour table overflow"

When trying to ping, the following error message appears:
"connect: No buffers available"

[ATC]

Check the static routing table entries.

If "x.x.x.x/x" is a directly connected network segment you should normally not have to define a static route manually. The routing table should refer to the local network device like this:
"x.x.x.x/x dev eth0"

If "x.x.x.x/x" is found behind another router you need to specify that gateway address instead:
"x.x.x.x/x via y.y.y.y"
Failure to do so will result in your router trying to locate hosts on the local network segment using ARP. This in turn will fill the local ARP table with requests which have no hope of resolving, which results in the aforementioned error messages.