3850 and MPLS MTU

[bgp.ripe901]

Hello colleagues !

I plan to test the MPLS functionality (L3VPN/VPLS/EoMPLS) on the 3850 platform, but I have a question about the correct mpls mtu setup.

#mpls mtu ?
<64-1500> MTU (bytes)
override Override mpls mtu maximum of interface mtu

But when i configuration, mpls mtu override i see this error message:

%MFI-30-MPLS_MTU_SET: Setting the mpls mtu to xxxx on Ethernet x/x, which is higher than 
the interface MTU xxxx. This could lead to packet forwarding problems including packet 
drops. 

Most drivers will be able to support baby giants and will gracefully drop packets that are 
too large. Certain drivers will have packet forwarding problems including data corruption. 

Setting the mpls mtu higher than the interface mtu can lead to packet forwarding problems 
and may be blocked in a future release. 

this error scares me

But i read other documentation:

If you have an interface with a default interface MTU value of 1580 or less (such as an Ethernet interface), the mpls mtu command provides an override keyword, which allows you to set the MPLS MTU value higher than the interface MTU value.

Question:

how correctly ?

1) Change system mtu 9198

2) reload

3) after reload MPLS MTU = MTU (9198)

4) i change only ip mtu 1500 (by default) - so that there are no problems with routing ospf/is-is

or using: mpls mtu override 1580 and not reload 3850 ?

[filopeter]

Hello,



Since Cat3850 is an ASIC based platform, I would prefer to change the system mtu (requires reload) and not to configure mpls mtu under interface configuration.



P.

[balaji.bandi]

you need to change the global or system config MTU- before you change on the interface.

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3se/int_hw_components/configuration_guide/b_int_3se_3850_cg/b_int_3se_3850_cg_chapter_0110.html#concept_39E508CDB4DB4C14A44C9B592E2E132E