On 03/13/12 12:11, Christopher J. Walker wrote:
> Must have a look at jumbo frames.
>
> Any hints and tips?
Keep Jumbo and non-Jumbo separate (so it pretty much necessitates
dual-homing unless you can easily switch your whole network). They can
mix but we've found it's a recipe for Weird Effects. Other than making
sure everything in the path has Jumbo support enabled (Jumbo on and MTUs
set to 9000byte or higher on switches) there's not a great deal to
setting it up on an internal network. We have found some gigabit
chipsets don't support it but they're pretty rare these days.
You can get packet fragmentation or failed MTU discovery at the boundary
between Jumbo/non-Jumbo networks. None of our Jumbo systems talk to the
outside directly, they're all NATed so we maybe haven't seen as many
problems here as we might have done otherwise. All our public addresses
use standard frames.
> Did it make much difference.
It did when we first moved to it (substantial improvement to throughput
and CPU load on older machines) but times have moved on. How much
difference it will make in real life on our new 10G kit and with modern
packet offloading support is yet to be seen. I expect there is still an
improvement but it has to be weighed against the hassles of enabling it.
>> The topology will certainly change with the new kit (to a two tier mesh)
>> the rest will probably stay pretty similar but we'll be doing lots of
>> testing before switching.
>>
> Interesting.
Probably sounds more interesting than it is (and the interesting stuff
may rely on TRILL support) but while the new topology will be more
complicated it's certainly far more flexible, expandable and affordable
than large scale chassis switches like ours.
If only Dell would hurry up and deliver our switches we could start to
find out...
John
--
John Bland [log in to unmask]
System Administrator office: 220
High Energy Physics Division tel (int): 42911
Oliver Lodge Laboratory tel (ext): +44 (0)151 794 2911
University of Liverpool http://www.liv.ac.uk/physics/hep/
"I canna change the laws of physics, Captain!"
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