can I ask mtu question

Justin M. Streiner streiner at cluebyfour.org
Fri Jan 30 15:51:00 CST 2009


On Fri, 30 Jan 2009, Ricky Beam wrote:

> On Fri, 30 Jan 2009 12:57:25 -0500, adrian kok <adriankok2000 at yahoo.com.hk> 
> wrote:
>> What is max mtu in jumbo frame?
>
> That depends on the hardware.  I've seen gear running as low as ~8k.  I'd 
> have to consult standard, but I think the max is 10k (10240).
>
> Keep in mind the switch is not the only device on the network with jumbo 
> frame limits.  The NICs in your servers will also have limits.
>
>> Do I need to reboot the switch to take effect after
>> setting up it?
>
> Again, this depends on the system.  Many accept the change immediately, while 
> others have to rebooted or interfaces reset to effect the change.
>
>> if it doesn't need to reboot, How can I know the
>> switch is running fine in this mtu 9000? eg: cisco
>> any tools to check?
>
> "ping" will do.  Set the packet size larger than the normal MTU (1500) and 
> see if it crosses the network intact.  If it's not working, A) the packets 
> will be dropped, and B) the "oversized frame" counter (among others) should 
> be clocking errors.

If you're sourcing the pings from a device that supports it, you can also 
send the large pings with the Do Not Fragment bit set.

jms




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