 cdruGo ColtsPremium,MVM
join:2003-05-14
Fort Wayne, IN
kudos:5
 ·Frontier FiOS
| reply to Da Geek Kid
Re: [Other] MTU quandry! said by Da Geek Kid:When TCP/IP communicates with it needs to set certain things so that the traffic has no issues before it can proceed. example when you want to hit www.google.com your linksys tells your PC that 1492 is the right MTU for communicating with google. However, when the packet is moving to google that MTU may actually change by another device (such as a VPN) and drop the MTU to 1300. the user is not involved in this process and hence does not notice this issue and in reality this is really the case as every where you visit might have a different capability for example if you change your PCs MTU to 1492, than it might effect the local LAN speed. As an example Gigabit Ehernet can handle Jumbo Frames (MTU of 9216).. The issue with MTU is that you want to get the maximum amount of data in each packet to minimize the effect of packet overhead. Each packet has a little bit of overhead. Straight TCP/IP over Ethernet has relatively little. PPPoE adds a little more (hence the 1492 instead of 1500). VPN has quite a bit more, etc. Normally the two machines will try to negotiate a happy number were the sending computer sends data that completely fills what the receiving computer (or some computer inbetween) will accept.
However in some cases there is a chance that a packet needs to get fragmented. For instance if the sending computer sends a 1500 byte packet but the path takes the packet across a PPPoE link in route to the receiving computer, it will get split up into a 1492 byte packet and a 8 byte packet. In the case of the 8 byte packet you are "paying" the overhead for another 1484 bytes of data, but you aren't actually sending it so that slice of bandwidth is gone.
Typically speaking you want to set your MTU as high as possible between you and your ISP and let the rest of everything handle itself automatically. If you are on PPPoE, set it at 1492. Most other DSL and cable connections are 1500. If you have something else, well it could be different.
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