Layer 3 Etherchannel and MPLS MTU

[alaertevidale]

Greetings,

If two 7609 are connected through layer 3 giga etherchannel and 7609-1 sends a frame with 1514 bytes plus two MPLS header to 7609-2, does the command “mpls mtu 1522” under the giga etherchannel interface on both routers is enough?

Or it is necessary to add the global command “system jumbomtu 1522” and the interface command “mtu 1522” under physical gigainterfaces participating on the channel?

Cisco docs say many platforms will accept frames higher than 1500 bytes (up to 24 bytes) to accommodate control flags; that is why I am considering just “mpls mtu xxx” is enough.

Also, reading Cisco doc I understood that “system jumbomtu xxxx” and “mtu xxxx” should be used together. I tested sending frames higher than 1514 bytes (without MPLS tags) and “system jumbomtu xxxx” alone was not enough, ping failed; it was necessary to add “mtu xxxx” under the interface. Do you have a different experience?

Thanks,

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Alaerte Gladston Vidali

IBM Global Services - SO

Tel.55+11+2121-2879 Fax:55+11+2121-2449

[spremkumar]

Hi

We had some peculiar exp with 7600 (7609/7606) boxes in which we did change the physical mtu of the interface instead of mpls mtu.

Again that did the trick for us even in 7200 where we monitored the same kinda behaviour..

regds

[alaertevidale]

Thanks,

Do you configured just the interface command?

or it was necessary to configure global jumbo command?

[spremkumar]

hi

We have them under the interface mode only not specific to the global mode config.

regs