iperf - MSS

["Mittal Patel" <mp.mpatelp --at-- googlemail.com>]

Hi,

 I would like to ask two question :

 1) I specified the MSS in iperf to 1460 using
 > iperf -s -w 2500000 -M 1460 -m

 It shows the MTU as 1500 after the running iperf as follows:
 WARNING: attempt to set TCP maximum segment size to 1460, but got 536
 ------------------------------------------------------------
 Server listening on TCP port 5001
 TCP window size: 47.7 MByte (WARNING: requested 24.4 MByte)
 ------------------------------------------------------------
 [  4] local 192.1.11.253 port 5001 connected with 192.1.10.253 port 44831
 [  4]  0.0-10.1 sec    871 MBytes    726 Mbits/sec
 [  4] MSS size 1448 bytes (MTU 1500 bytes, Ethernet)

 But when i collect the packet by tcpdump, i found that the MSS is
 around 3000. Could you please give the reason behind this. Also the
 warning says that attempt to set TCP maximum size to 1460 but got 536.
 why?

 2)How i can know which TCP flavor does iperf is using? It is same as
 kernel tcp flavor?

 Thank you,

Mittal