Thus spake "Francois Baligant" <francois@ops.be.wanadoo.com>
>
> The output analyzer on the Cisco web site stress out
> that the default MTU on ATM interface and subinterface
> should be changed from the default to a much smaller
> value (1500 sounds like a good candidate) because
> smaller MTU allows for more MEMD buffers and so
> better performance.
>
> Can anyone comment on this ? Is there a real performance
> gain ? Is this true for 7200 and VIP4 or only older
> 4500 with ATM NPM ?
On older architectures (2500, 4x00, 7000, 7500), lowering MTUs to 1500 can
have significant gains in buffer space. I'm not sure I'd call it "better
performance", but having more buffers available (by lowering MTU) on 7500's
can significantly reduce dropped packets, particularly if you have many
high-speed (100mb+) interfaces.
Beware that changing MTUs on a 7500 can cause a 30+ second outage for the
entire box. On other platforms it should be benign.
Newer architectures (2600, 3600, 7200) use a more complex buffering
technique (particles), so it makes no difference what the MTU is.
S
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