[c-nsp] mtu issues on 3750

[Tassos Chatzithomaoglou]

Johannes Resch wrote on 19/4/2006 16:54:

> 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.

Does such an IOS exist for 3750s? If yes which one?

--
Tassos

> 
> -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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>>>
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>>
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> 
> 
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