Wireshark-users: Re: [Wireshark-users] MTU - wireshark showing length longer than.
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
