Can you hard set the MTU on VCS?

[Nick Halbert-Lillyman]

As per the title, is it possible to hard set the MTU on a VCS-C/VCS-E?  I know you can enable RFC4821, but I'm not sure if I can have a hard set limit...

[Dharmesh Nandoria]

Hi,

https://supportforums.cisco.com/docs/DOC-23594

hth

Kind regards,

Dharmmesh

[Nick Halbert-Lillyman]

Thanks Dharmesh - I was aware of that document but I want to know if I can manually set the MTU also.

RFC4821 can be useful for situations where the MTU may drop, but I know none of our traffic will be able to go above 1350, so I would like to set the MTU to a max of 1350 while allowing RFC4821 to automatically adjust for any time it drops below 1350.

[Martin Koch · Accepted solution]

Do you see any issue regards the MTU? Signaling, media, ...?

I mean I would not expect the VCS to re packet RTP anyhow if the receiving MTU is bigger then the sending one,

(never tried though) so you should lower that on your clients anyhow.

On MXP endpoints you could set the RTP packet size, on the TC endpoints I only know about a generic MTU

setting (does anyone know how the RTP packet size is exactly defined?).

[Nick Halbert-Lillyman]

Re - resizing RTP - you are probably right -  we have our internal endpoints set to a lower MTU so that's OK, but we can't control what people outside our organisation send us.

Jabber video sign-in is also very slow over our VPN into VCS-E is also very slow (but can sign in from our DMZ via VCS-E very quickly) so thought it might be an MTU issue.  I thought VCS-E might be able to resize these non-RTP packets.