Updated: 2013-09-22

If you are working with Citrix Provisioning services you might have seen a small difference in the MTU size value from previous releases of the product? If not, it is time you take a look in the GUI.

The older version of the product (5.1), had a MTU size of 1464 bytes set in the GUI, compared to the newer  releases (5.6/6.0/6.1) of the product, which has 1506 bytes set in the GUI.

Now, that is interesting, isn’t it? And we all know that UDP is unreliable, and most network guys would typically recommend a smaller size (especially something that is smaller than the default 1500 bytes for Ethernet).

So, we raised this topic internally, and got the feedback that the default value (1506) is correct.  And trust me, it is, but it is also very confusing.

One of my team members (thank you Martin Latteier) decided to “Wireshark” the truth and came up with the following information:

Pvs 5.1 MTU setting: payload size (default GUI Value: 1464)

Pvs 5.6/6.0/6.1 MTU setting: payload size + UDP header (L4) + IP header (L3) + Ethernet header (L2) (default GUI Value: 1464 + 8 + 20 + 14 = 1506)

Right or wrong, this tells us that the GUI is a bit different from the two versions, and hence a bit confusing.

What does it mean for you? If it ain’t broken don’t touch it. And that you should use the default value 1506 bytes, for a “normal” network. A normal network means, no Jumbo packages. If you decrease the MTU Size (in the GUI) to something less than 1506 bytes (version 5.6 and above) you will most likely get a lower throughput than normal.

Regards Dimitrios