After upgrading to OS X 10.9 (“Mavericks”), I started getting packet loss on our corporate network. This is apparently a bug in Mavericks relating to ARP, Unicast and GLBP:
A simple temporary workaround appears to work:
sudo sysctl -w net.link.ether.inet.arp_unicast_lim=0
For a permanent fix, place it in /etc/sysctl.conf:
$ grep unicast /etc/sysctl.conf net.link.ether.inet.arp_unicast_lim=0
This is supposedly fixed in OS X 10.9.2.
Update 2014-03-16: seems to be better in 10.9.2, but not gone - I still need the above workaround on my system.