Packet Errors?

Question

I just signed-up for ClearWire. So far, it's working great and much faster than my regular DSL (I had 768Mbps but now have 1.5Gbps). Because I live in an Apartment building where I can see eight other wireless networks, I have a WPA2 (Personal) password on my AirPort Express. I have the light enabled to display network activity and previously with the regular DSL, I used see some activity that I couldn't explain. Now with the ClearWire modem attached the activity light is going absolutely bonkers. It appears that I'm downloading constantly even if I turn AirPort off all the computers here. I can check with the AirPort Management Utility and it appears that only my computers are connected (when turned on). I called ClearWire support and they said I'd have to check my router's manufacturer to explain the local network activity and could not confirm that the ClearWire modem was kind of "chatty" on the local network. In fact, they had no way to tell if any outside activity (leaving the LAN) was happening through my modem.
While I'm not overly concerned about the activity light now, while checking the AirPort Management Utility just now, I noticed that under my Monitor tab, the Rx Packets errors on my MacBook are approximately 15 times greater than the actual normal packets. For example, if I have 100,000 normal packets, my (errors) are (1,500,000). Should I be concerned about this? Anyone know why this might be happening or how to fix it? Any advice before I call ClearWire support back? I will admit, I never noticed the errors with my regular DSL, but I did check in the AirPort Management Utility every once in a while and I think they would have stood out.
-Doug

Answer 1

I would definately agree with you that the number of error packets you're experiencing is way too high. Might it be the Maximum Transmission Unit (MTU) setting is not optimized with your new ISP?
To do so, you can use a utility, like Cocktail or via OS X's Terminal.
As you probably already know, MTU will vary with connection type. Cable and non-PPPoE, can use up to 1500, whereas PPPoE connections (WinPoet, RASPPPOE, Enternet, etc.) can only use up to 1492.
The best value for MTU is that value just before the packets get fragmented. To test, use the Ping utility.
OS X: ping -D -s 1472 www.dslreports.com
WinXP: ping -f -l 1472 www.dslreports.com
Reduce 1472 by 10 until you no longer get the “packet needs to be fragmented” error message. Then increase by 1 until you are 1 less from getting the same error message. Add 28 more to this (since your ping packet size, not including IP/ICMP header is 28 bytes). This will be your MaxMTU. (Note: If you can ping thru at 1472, stop, you’re done! Add 28 and your MaxMTU is 1500.)