[c-nsp] mtu issues on 3750

[Johannes Resch]

sthaug at nethelp.no schrieb:
>> Have you tried configuring IP MTU on SVI/L3 interface?
> 
> Won't work. This is a known limitation of using the 3750 for L3. It
> works fine with large MTUs for L2, but not for L3.

with recent IOS, you can set "system mtu routing <x>" to set the L3 MTU 
for all routed ports/SVIs. particularly useful if you need L2 MTU > 
1500, but want to keep L3 MTU at 1500 byte.

-jr


> Steinar Haug, Nethelp consulting, sthaug at nethelp.no
> 
>> Tassos Chatzithomaoglou wrote:
>>> 3750 switches are said to support mtu > 1500 (1500-9000) on all GE ports 
>>> according to this:
>>>
>>> http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_example09186a008010edab.shtml#c3
>>>
>>> 3750#sh system mtu
>>>
>>> System MTU size is 1500 bytes
>>> System Jumbo MTU size is 1600 bytes
>>>
>>> Routed port
>>> -----------
>>> 3750#sh int g1/0/10
>>> GigabitEthernet1/0/10 is up, line protocol is up (connected)
>>>    MTU 1600 bytes, BW 1000000 Kbit, DLY 10 usec,
>>>
>>> 3750#sh ip int gi1/0/10
>>> GigabitEthernet1/0/10 is up, line protocol is up
>>>    MTU is 1500 bytes
>>>
>>> SVI
>>> ---
>>> 3750#sh int g1/0/10
>>> GigabitEthernet1/0/10 is up, line protocol is up (connected)
>>>    MTU 1600 bytes, BW 1000000 Kbit, DLY 10 usec,
>>>
>>> 3750#sh ip int vlan 99
>>> Vlan99 is up, line protocol is up
>>>    MTU is 1500 bytes
>>>
>>>
>>> So you can't have L3 mtu > 1546 (= system mtu) if the GE ports are configured as 
>>> L3 (Routed/SVI) ports. Any idea how to overcome this?
>>>
>>> --
>>> Tassos
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