Is there a recommeded MTU for voice/video traffic?

[carl_townshend]

Hi All

Can anyone tell me if there is a recommended ip mtu for voice and video?

We seem to be having some issues with video over one of our tunnels and was wondering if increasing the mtu would make it any better?

cheers

[Deepak Kumar]

Hi,

Which type of tunnel? What is current MTU size? 

[carl_townshend]

GRE tunnel protected with IPSEC, current MTU is 1400

[Deepak Kumar]

Hi,

I am not aware of any recommendation in your case but let we work on your case as:

If your ISP supported MTU is: 1500

MTU on GRE Tunnel: 1500 (ISP) - 58 (IPsec) - 24 (GRE) = 1418

Ethernet interface facing to ISP: MTU should be 1500

On our Tunnel MSS: 1418-40B (TCP Header)=1378

We also recommended configuring command on the GRE tunnel "tunnel path-MTU-discovery".

More details: https://www.cisco.com/c/en/us/support/docs/ip/generic-routing-encapsulation-gre/25885-pmtud-ipfrag.html

[paul driver]

Hello Carl

Incorrect mtu would be a problem but that looks okay so are you sure this  isn't due to traffic congestion on the line, are you implementing any quality of service?

Can you post details of your current topology is applicable?

[Georg Pauwen]

Hello,

actually, Cisco recommends an MTU of 1400 (and a subsequent MSS of 1360), according to the document below:

--> The MTU value of 1400 is recommended because it covers the most common GRE + IPv4sec mode combinations. Also, there is no discernable downside to allowing for an extra 20 or 40 bytes overhead. It is easier to remember and set one value and this value covers almost all scenarios.

https://www.cisco.com/c/en/us/support/docs/ip/generic-routing-encapsulation-gre/25885-pmtud-ipfrag.html#anc6