Dan Stromberg <dstromberglists@gmail.com> wrote:

> 1) Enable jumbo frames on your gigabit NIC's and all network
> equipment between them, if you haven't already.
> http://stromberg.dnsalias.org/ ~strombrg/jumbo.html

Keeping in mind there are still switches out there (older ones at
least) which do not support JF, and since JF is not a de jure
standard, there can be NICs (and switches) for which the definition of
"JumboFrame" is something other than the 9000 byte MTU "de facto"
standard initiated (IIRC) by Alteon.

If the switch does not support JF, enabling JF on the NICs will result
in odd losses of connectivity, with stuff like telnet/ssh _mostly_
working and stuff like FTP and perhaps HTTP not working well at all.

Even if the switch supports JF, unless one enables it across the
_entire_ broadcast domain, UDP traffic for stuff like NFS can be
fubared - the NIC with JF support will fragment to JF sizes, which
will arrive at the NIC without JF and be dropped. Don't assume that
just because something like an FTP or netperf TCP_STREAM works that
all is OK - the TCP MSS exchange at the beginning of a TCP connection
will result in the smaller MSS being used, masking the MTU mismatch.

I _like_ JF, but it isn't a pancea. Also, as more and more NICs
support LRO (Large Receive Offload) in addition to TSO (Transport
Segmentation Offload) the benefit to JF becomes reduced.

rick jones
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