[CentOS] Neighbour table overflow

Just started getting this.  I tried the following by adding it to my
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

That pretty much locked things up.  

Then I tried another googled solution:

echo 256 > /proc/sys/net/ipv4/neigh/default/gc_thresh1

echo 512 > /proc/sys/net/ipv4/neigh/default/gc_thresh2

echo 1024 > /proc/sys/net/ipv4/neigh/default/gc_thresh3

And adding it also to etc/sysctl.conf:

net.ipv4.neigh.default.gc_thresh1 = 256
net.ipv4.neigh.default.gc_thresh2 = 512
net.ipv4.neigh.default.gc_thresh3 = 1024

Still not working.

Any ideas?

TIA