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Beginner

CUCM IP Phones MTU settinsg

Hi All,

I'd like to ask your valuable help for the following question:

- is there a way to change the MTU size of the CUCM endpoints (Dx650, 7841, etc...) packets ?

Customer indeed has an environment in which some recently added crypto device asks the phones to lower their MTU or fragment but they seems to not care of this and RTP is dropped resulting in no media flowing.

Thanks,

Andrea

3 REPLIES 3
Cisco Employee

Hi Andrea,

Hi Andrea,

I am not aware of such a setting on the endpoints. It can be changed from CUCM CLI though using the following command :

set network mtu size < value >

You should do it on all servers and doing it will cause a temporary network connectivity loss on the servers.

Manish

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Beginner

Hi Manish,

Hi Manish,

thanks for your kind reply ;-)

I'm almost sure the MTU size you select under CUCM (either during install or later on using the command you mentioned) affects only CUCM own signaling traffic :-/

... I'm afraid endpoints RTP traffic MTU stays untouched.

Cheers,

Andrea

Cisco Employee

Hello Andrea, IP phones doesn

Hello Andrea, IP phones doesn't allow the administrators to change the MTU settings, the only setting which is allowed is to turn ON and Off the DF bit setting via CUCM.

And as you rightly mentioned, the change of MTU on the CUCM is for the signaling or the media ( via MTP) which is traversing via CUCM.

Hope it helps.

Thank you.
Aashish

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