Re: MTU - wireshark showing length longer than.

[Ant Mitchell <ant () badmagic com>]

> The NICs may be doing segmentation offloading, which reassembles TCP
> Segments before passing it to the computer:

Good idea, maybe so !. Turned it off:
sudo /sbin/ethtool -k eth2
Offload parameters for eth2:
rx-checksumming: on
tx-checksumming: on
scatter-gather: on
tcp segmentation offload: off

But this didn't make any difference on its own. Both wireshark and  
tcpdump still show packet lengths greater than the MTU.

I then played with the receive buffer sizes some more:
net.core.rmem_max = 72000
net.ipv4.tcp_rmem = 4096 9000 9000

The packet length then dropped to always below 9000. Once the default  
and maximum receive buffer sizes went up, so did the wireshark/tcpdump  
lengths.

There must be some setting that I am missing, maybe the myricom card  
is doing something, one of these settings perhaps: lro ?

ls /sys/module/myri10ge/
myri10ge_adapt_big_thresh  myri10ge_dca             
myri10ge_fill_thresh     myri10ge_force_nvidia_msi   
myri10ge_intr_coal_delay  myri10ge_max_irq_loops   
myri10ge_napi_weight    myri10ge_rss_hash      
myri10ge_tx_hash           refcnt
myri10ge_adapt_med_thresh  myri10ge_deassert_wait   
myri10ge_flow_control    myri10ge_fw_name            
myri10ge_lro              myri10ge_max_slices      
myri10ge_pat_idx        myri10ge_small_bytes   
myri10ge_vlan_csum_fixup   sections
myri10ge_bus               myri10ge_ecrc_enable     
myri10ge_force_firmware  myri10ge_initial_mtu        
myri10ge_lro_max_pkts     myri10ge_msi             
myri10ge_reset_recover  myri10ge_tso6         myri10ge_watchdog_timeout

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