[c-nsp] mpls mtu of 1492

[Hyunseog Ryu]

Cisco 2950T doesn't support up to baby giants frame size, but you can 
increase "system mtu" to 2018.
In most case for MPLS, you just needs to increase MTU to accomodate MPLS 
SHIM label size you need.
I think 1520 bytes will be enough for most cases unless you use more 
than 5 depths stack of MPLS label.

Most important thing is that you have to maintain same MTU setting in 
all equipments from same physical networks to prevent some issue with 
OSPF routing or others.

I talked to Cisco guys about standardization of ethernet MTU support.
But Cisco uses a lot of OEM manufacturing outsourcing, and they use 
different ethernet chips.
So it is not possible unless Cisco change outsourcing contract to 
mandate those support.

Hyun

tusker keg wrote:
> howdy folks
> 
> I have a test platform of routers connected  to  Cisco 2950T switches.
>  I am testing mpls and mpls based vpns but unfortunately I have ran
> into problems. The 2950T do not support baby giants (frames)
> 
> http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_example09186a008010edab.shtml#subtopic1G
> 
> What will be the effect of setting the mpls mtu to a value lower than 1500.
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