MTU for IDNet (using vista)

[Gary]

Hi what should I set my routers MTU at for IDNet? My stats are Sync rate 8128 down 448 up profile, profile 7150 throughput is a about 6250 (I think, did not write that down) just wondering what MTU I should use. Since there are no tweaks for Vista should I set it at 1500 in my router?

[Simon]

Mine is, Gary, but that doesn't mean it's right. 

[Gary]

Mine is, Gary, but that doesn't mean it's right. 

I'll leave it at that then Simon

[Sebby]

Yep, definitely set the router to 1500, Gary. As I understand it, Vista adjusts the MTU dynamically.

[Rik]

Thirded.

[Gary]

Cheers 

[LesD]

I have my MTU set at 1500 and have done the ping tests to prove it's OK but in the "BBMax Myths & Legends Document" Rik posted the link to the other day, at Section 14.2 it says different!

Code Select Expand

14.2 What is the "MTU" and how does it affect throughput?

The MTU is the Maximum Transmission Unit. This determines the maximum size packet that can be sent over a network.
For ADSL the MTU should be less than 1488 kilobytes to ensure that fragmentation does not occur on Ethernet segments of the network.

I  what do you make of this paradox? 

[Rik]

I ignore it.

Do a series of pings with the -f flag set, and use the -l flag to set the size of the packet. Start with ping www.idnet.net -f -l 1500 and you'll get something like this:

ping www.idnet.net -f -l 1500

Pinging www.idnet.net [212.69.36.10] with 1500 bytes of data:

Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.

Ping statistics for 212.69.36.10:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),


Now, reduce that to 1472 (ie allow for the 28 byte packet overhead), and you'll see something like this:

ping www.idnet.net -f -l 1472

Pinging www.idnet.net [212.69.36.10] with 1472 bytes of data:

Reply from 212.69.36.10: bytes=1472 time=47ms TTL=59
Reply from 212.69.36.10: bytes=1472 time=45ms TTL=59
Reply from 212.69.36.10: bytes=1472 time=46ms TTL=59
Reply from 212.69.36.10: bytes=1472 time=44ms TTL=59

Ping statistics for 212.69.36.10:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 44ms, Maximum = 47ms, Average = 45ms


Providing you do, then the MTU should be 1500, because that will be the total data sent.

[LesD]

I have done the ping test many times before but for the hell of it I have just done it again with this result: 

C:\>ping www.idnet.net -f -l 1500

Pinging www.idnet.net [212.69.36.10] with 1500 bytes of data:
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.

Ping statistics for 212.69.36.10:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

C:\>ping www.idnet.net -f -l 1472

Pinging www.idnet.net [212.69.36.10] with 1472 bytes of data:
Reply from 212.69.36.10: bytes=1472 time=63ms TTL=59
Reply from 212.69.36.10: bytes=1472 time=62ms TTL=59
Reply from 212.69.36.10: bytes=1472 time=61ms TTL=59
Reply from 212.69.36.10: bytes=1472 time=62ms TTL=59

Ping statistics for 212.69.36.10:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 61ms, Maximum = 63ms, Average = 62ms

C:\>

My pings are not as quick as the one you posted Rik but typical of what I get! 
My MTU at 1500 passes the ping test once again. 

[Rik]

Actually, those pings were untypically high for me, Les. These are more typical:

ping www.idnet.net

Pinging www.idnet.net [212.69.36.10] with 32 bytes of data:

Reply from 212.69.36.10: bytes=32 time=21ms TTL=59
Reply from 212.69.36.10: bytes=32 time=21ms TTL=59
Reply from 212.69.36.10: bytes=32 time=20ms TTL=59
Reply from 212.69.36.10: bytes=32 time=23ms TTL=59

Ping statistics for 212.69.36.10:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 20ms, Maximum = 23ms, Average = 21ms

Not bad for an interleaved line.

[LesD]

Actually, those pings were untypically high for me, Les. These are more typical:

ping www.idnet.net

Pinging www.idnet.net [212.69.36.10] with 32 bytes of data:

Reply from 212.69.36.10: bytes=32 time=21ms TTL=59
Reply from 212.69.36.10: bytes=32 time=21ms TTL=59
Reply from 212.69.36.10: bytes=32 time=20ms TTL=59
Reply from 212.69.36.10: bytes=32 time=23ms TTL=59

Ping statistics for 212.69.36.10:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 20ms, Maximum = 23ms, Average = 21ms

Not bad for an interleaved line.

Well not to be completely outdone with my iffy interleaved line I have just had another go and got this this evening:

C:\Users\Les>ping www.idnet.net

Pinging www.idnet.net [212.69.36.10] with 32 bytes of data:
Reply from 212.69.36.10: bytes=32 time=29ms TTL=59
Reply from 212.69.36.10: bytes=32 time=25ms TTL=59
Reply from 212.69.36.10: bytes=32 time=26ms TTL=59
Reply from 212.69.36.10: bytes=32 time=27ms TTL=59

Ping statistics for 212.69.36.10:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 25ms, Maximum = 29ms, Average = 26ms

C:\Users\Les>

Better than last night but still a few milliseconds down on yours!

It must be the 

[Lance]

You can't beat a bit of !

[Simon]

Or even... 

[Rik]

Or, perhaps, being nearer to London?