The /proc/sys/net/ipv4/neigh/unres_qlen value is 0 instead of 3 in RHEL 6.5.

Issue

• We are experiencing connectivity problems under high network load that seem to be dependent on kernel version and sysctl configuration. When using an earlier kernel version (2.6.32-358.23.2.el6.x86_64) we don't see these problems, but using a newer version (2.6.32-431.3.1.el6.x86_64) the problems occur. When we diff the output of sysctl -a on systems running the two kernel versions, one thing that stands out is that on the "working" earlier version, the contents of net.ipv4.neigh.<interface_name>.unres_qlen is 3. On the systems we are having issues with, the same sysctl entries show up with 0, as in:

$ net.ipv4.neigh.bond1/xxxx.unres_qlen = 3
---
$ net.ipv4.neigh.bond1/yyyy.unres_qlen = 0

$ net.ipv4.neigh.bond1/pppp.unres_qlen = 3
---
$ net.ipv4.neigh.bond1/qqqq.unres_qlen = 0

Could the setting of unres_qlen to 0 on the problematic systems be the cause of the connectivity problems? We plan to test this, but this is an urgent problem that is holding up a release, so we'd like to hear from the experts on this.

Is it expected that on kernels running 2.6.32-431.3.1.el6.x86_64 that these unres_qlen entries would end up with 0s in them solely because of the kernel change?