Howard,
3750Gs usually do not have any 10/100BaseT ports. They have 10/100/1000BaseT
and SFP ones.
As long as the port is 10/100/1000, the actual speed that is running (10 or 100
or 1000) doesn't have any effect on the MTU.
So you can have it running in 10/100 and use the full mtu.
3750G>sh int gi1/0/22 | i media|MTU
MTU 1600 bytes, BW 100000 Kbit, DLY 100 usec,
Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX
Also, as you can see below, you can go up to 1998 for FastEthernet ports on 3750Gs, which should be more than enough for
most applications:
3750G(config)#system mtu ?
<1500-1998> MTU size in bytes
jumbo Set Jumbo MTU value for GigabitEthernet or TenGigabitEthernet
interfaces
routing Set the Routing MTU for the system
3750G(config)#system mtu jumbo ?
<1500-9000> Jumbo MTU size in bytes
--
Tassos
Howard Jones wrote on 15/10/2008 4:34 μμ:
We're just looking at running QinQ over a network of 3750G switches, and
while I was investigating enabling jumbo frames, I came across this
document:
http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_example09186a008010edab.shtml#c3
which contains:
"*Note: *If Gigabit Ethernet interfaces are configured to accept frames
greater than the 10/100 interfaces, jumbo frames that ingress on a
Gigabit Ethernet interface and egress on a 10/100 interface are dropped."
It seems to me that I want to have jumbo frames enabled on the trunks to
'make room' for the extra dotq header, but if that means that user ports
can't run at 10/100 that seems like a severe limitation. Also, the
document is from 2005, and doesn't mention QinQ at all.
Is this still really the case with a modern 3750G? Is there anything
that can be done?
There's a sort-of middle area where actually the frame that leaves the
10/100 port would have had the extra layer of dotQ stripped off... is
that what I'm missing in the above?
Thanks in advance for any light anyone can shed.
Howie
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