Re: Changing MTU size on the fly

Paul Landay <landay@xxxxxxxxxxxxx> wrote:
I've never done this on an oracle box, but I would be suprised if
the listener process or database needed to be restarted. When the
'ifconfig ... down' was done any existing socket connections would
have been closed. After the 'chdev ... state=up' any new socket
connections would use the new MTU value.

Indeed - a plain listen socket shouldn't care about interface state.
It might care if it were bound to a specific IP and that IP was no
longer known to the stack. But it shouldn't care if that interface
with the IP was up or down. Particularly since, unless the system
employs a "strong end system model" traffic for that destination IP
address could in theory be received via other interfaces.

I'd think that existing socket connections using that interface
wouldn't close immediately - they would probably retransmit a bit, but
if the interface came back up "in time" they should survice the
cycling.

Keep in mind that the interface mtu is just a 'starting' value for
negotiating the actual mtu to be used. The actual mtu could be
different for different concurrent socket connections depending on
the path taken (i.e. different routers) for the different partners.
So the listener should not need to know or care what the interface
mtu is.

Terminology nit - what TCP exchanges at least is "MSS" or Maximum
Segment Size which will indeed be based in part on the interface MTU.

Paul Landay

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