Joe Landman wrote:
I wonder if the switch could be implicated. We have seen some (cheap)
GbE switches not support (in practice) jumbo frames (irrespective of
literature).
Been there, done that. HP claims to be able to handle packets up to
9000 bytes of payload. (9122 total, IIRC)
Nifty Tom Mitchell wrote:
On Sat, Jan 24, 2009 at 09:36:09AM -0600, Gerry Creager wrote:
Couple of follow-up notes.
MTU=4500: Had one node fall over with the same overflow errors.
MTU=3000: A WRF model is running, but single timesteps are
executing 2.5x slower than MTU=1500
Segment offload? Is TSO on or off?
On.
ethtool -k eth0
will tell you. You might also have one very reluctant machine, in the
sense of being unwilling to switch their mtu. Could you do an
-bash-3.2# ethtool -K rx off
no offload settings changed
-bash-3.2# ethtool -k eth1
Offload parameters for eth1:
rx-checksumming: on
tx-checksumming: on
scatter-gather: on
tcp segmentation offload: on
udp fragmentation offload: off
generic segmentation offload: off
But here's the one I love:
-bash-3.2# ethtool -K tso off
no offload settings changed
I apparently can't control things with ethtool...
ifconfig eth0 | grep MTU
Thought of that. All change appropriately.
on each machine and verify that everyone is using the right MTU?
I'll go snag the new driver and compile it. After all: What can it
hurt!
Thanks, Guy!
Regards, Gerry
Guy Coates wrote:
Hi,
We have also seen problems with the bnx2 drivers.
I got a more recent set of bnx2 drivers from Broadcom:
......
Has the data been snooped for this data to see if all
is as expected.
If you are seeing a natural MTU running faster than a jumbo MTU
then something is fragmenting or causing fragmentation of the data.
Should the MTU=4500 causes overflow errors it might be related to
fragmentation.
Both the sender and receiver have to keep all the bits on a reliable
transfer until the data has been acknowledged. At one time
fragmentation
could only be done once to a minimum MTU in the life of a packet.
In addition to snooping packets try "tracepath" to and from all the
involved boxes to discover what is going on.
--
Gerry Creager -- gerry.crea...@tamu.edu
Texas Mesonet -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983
Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843
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