We are on OEL 5. And I am trying to run some network throughput test between to machines connected over OC-48. When I try to run the test I get the following:

iperf -M 2M -c 10.144.21.100 -p 1526 -n 8G -i 2
WARNING: attempt to set TCP maxmimum segment size to 2097152 failed.
Setting the MSS may not be implemented on this OS.

My sysctl setting are:

net.core.rmem_default = 4194304
net.core.rmem_max = 4194304
net.core.wmem_default = 262144
net.core.wmem_max = 4194304
vm.nr_hugepages = 10752

Could someone please tell me why that might be happening? On the other hand if the remote machine becomes the client it works fine and that machine has similar settings to.