Cisco 9400 proper MPLS MTU configuration

[Smurf12345]

What is the proper mtu setting for an MPLS interface on the 9400 to allow full 1500 frame from SVI over the MPLS?  It seems to have changed from older IOS on the 6500/6800  to IOS XE16.6 to 16.9.  Previously with on a 6500/6800 chassis we used "mtu 1580" on the interface, but that is no longer an option on the 9400.  On 16.6 code, using the command "mpls mtu 1580" allowed 1500 byte frame to pass.  However, on 16.9, it seems only 1496 bytes will pass.

Out of the all the mtu commands available which ones/combination need to be used?  

Global:

•  system mtu - increase the whole system mtu?  This seems to work, but it also defaults all the interfaces to the same MTU.  Not sure that is a big deal, but wanted some feed back.

Interface:

•  ip mtu - incease to 1580?
•  mpls mtu override - increase to 1580?

Example interface:

interface TenGigabitEthernet5/0/1
no switchport
ip address 192.168.0.1 255.255.255.252
ip pim sparse-mode
mpls ip
mpls label protocol ldp
mpls mtu 1580

[balaji.bandi]

Please refer below guide for the system mtu settings and per interface can be changed depends on requirement.

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

[Georg Pauwen · Accepted solution]

Hello,

on a side note, looking at the configuration guide linked below, on the 9400 switches you cannot configure the MTU value specifically for MPLS at all:

--> The MPLS MTU value is equivalent to the IP MTU value of the port or switch by default. MTU configuration for MPLS is not supported.

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9400/software/release/16-10/configuration_guide/mpls/b_1610_mpls_9400_cg/multiprotocol_label___switching__mpls_.html#concept_CD9FDFEBE1464E4EAE6DB959945DD6DE

[balaji.bandi]

@Georg Pauwen  - Thanks for the point, since 9400 gear still new. may be missed that reference..thanks again.

[Smurf12345]

Thank you. Just follow up. Cisco confirmed "system mtu <#>" is the proper command.