MTU Change Why ??

[MrIPO]

Hi I have installed many VPNs using different vendors products on xDSL tails of some varant. approx 90% of the time you have to lower the MTU on the routers and the PC's. It order for a reliable stable connection. In regard to throughput and usage.

My question is why do you have to lower the MTU on the PC's as well as the router. Would the Router not fragment a packet if it had to a so resolve the issue. ??

Nobody i speak to seems to be able to answer ??

 

[bytehd]

MTU is the maximum "chunk" size.
You need to play with this command
ping xxx.xxx.xxx.xxx -l 1500 -f
starting at 1500 down to 1200 or so.

If a router,firewall, VPN sees lots of fragmented packets
that taked time to reassemble the chunks.
Slows throughput.

http://www.insyncva.com

 

[MrIPO]

So if you had a more powerful router, you wouldn’t have the problem?

 

[bytehd]

Nope.
Its a matter of how much can you transfer between acknowledgements. Every protocol has phases when data gets setup and data gets transferred. The MTU says "this is how much I can eat at once before I need to swallow".

the IP DF (dont fragment) bit says dont bust this packet up as you pass it. If the firewall is set to reject DF packets, the sender will either fall back to a smaller size or not and lose data.

http://www.insyncva.com