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Updated Frequently Asked Questions (markdown)

dswd 2016-08-25 09:39:16 +02:00
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Frequently-Asked-Questions.md

@ -17,7 +17,7 @@ Most likely this is because of a slightly too high (or missing) MTU setting on t
#### What happens when I increase the MTU above 1400? #### What happens when I increase the MTU above 1400?
Setting the MTU higher than the physical medium causes IP to fragment each inner packet into several outer packets and reassemble them at the receiving side. This has the advantage that VpnCloud has to process less packets and therefore uses less CPU (most of it will be memcpy) and has less context switches. It will also save some bytes on the wire as less bytes are used for VpnCloud headers and UDP headers and only a small additional IP fragmentation header is added. I think in total that is the 2% you are seeing. Setting the MTU higher than the physical medium causes IP to fragment each inner packet into several outer packets and reassemble them at the receiving side. This has the advantage that VpnCloud has to process less packets and therefore uses less CPU (most of it will be memcpy) and has less context switches. It will also save some bytes on the wire as less bytes are used for VpnCloud headers and UDP headers and only a small additional IP fragmentation header is added.
The downside is that if one of the outer packets gets lost on the wire the whole inner packet is lost. If your MTU is is 40 times higher than normal, 40 outer packets will be sent for one inner packet. So your packet loss rate will be about 40 times higher than normal (e.g. 4.1% instead of 0.1%). It will also influence your delay distribution negatively. The downside is that if one of the outer packets gets lost on the wire the whole inner packet is lost. If your MTU is is 40 times higher than normal, 40 outer packets will be sent for one inner packet. So your packet loss rate will be about 40 times higher than normal (e.g. 4.1% instead of 0.1%). It will also influence your delay distribution negatively.