No UDP over 2Gb/s

[Steven Carter <scarter --at-- ornl.gov>]

I am unable to get iperf to send a UDP stream at more that 2Gb/s:

[root --at-- cns5 root]# iperf -u -c 192.168.0.2 -w 8m -l 65230 -b 2g
------------------------------------------------------------
Client connecting to 192.168.0.2, UDP port 5001
Sending 65230 byte datagrams
UDP buffer size: 16.0 MByte (WARNING: requested 8.00 MByte)
------------------------------------------------------------
[  5] local 192.168.0.1 port 32768 connected with 192.168.0.2 port 5001
[ ID] Interval       Transfer     Bandwidth
[  5]  0.0-10.0 sec  2.34 GBytes  2.01 Gbits/sec
[  5] Server Report:
[  5]  0.0-10.0 sec  2.34 GBytes  2.01 Gbits/sec  0.007 ms    0/38463 (0%)
[  5]  0.0-10.0 sec  3 datagrams received out-of-order
[  5] Sent 38463 datagrams
[root --at-- cns5 root]# iperf -u -c 192.168.0.2 -w 8m -l 65230 -b 3g
connect failed: Connection refused
[root --at-- cns5 root]#

I can actually send at 2.1g but not 2.2g.  I see similar behavior with 
netperf and other tools.  Has anyone encountered this before?

Thanks,

Steven.

-- 
Steven M. Carter                "A foolish consistency is the hobgoblin of
Oak Ridge National Laboratory    little minds, adored by little statesmen
scarter --at-- ornl.gov                 and philosophers and divines." -- Emerson