Just noticed that PPPoE is limited to 1492 in my Speedstream
5100b modem (SBC Yahoo DSL service). My router and OS are set for 1500 and I wonder if they should be changed to 1492 (or some other number) to optimize the connection?No. The WAN side should be 1492 because there is an 8byte overhead in tunneling IP with PPPoE. MTU should remain 1500 on the LAN side as this is the "standard" for Ethernet.
However, it has been noted in the past that "IF" you have problems retrieving/sending email or posting to UseNet you *may* have to set the LAN nodes MTU setting to 1492. However, it should only be done if there is a problem.
Thanks for both replies. I'm getting good throughput, and I use WindowsXP with Path MTU Discovery ON so I think all is well.
Yes. Otherwise you (in some circumstances) cause the speedsteam to have to fragment the packets. This would only happen with packets between the size of 1492 and 1500.
T. Sean Weintz
I tested my setup (SS 5360, Siemens 2602 router, Linux) and found a small (4%) advantage for 1492 (data below).
Since the fragmentation happens on the fast 10baseT network between my router & modem (or perhaps within the modem itself), it doesn't make much difference.
-- Robert
$ for i in `seq 1440 8 1500` ; do ping -qc 10 -s $i gw2 ; done
PING gw2 (70.240.223.254) 1440(1468) bytes of data.
10 packets transmitted, 10 received, 0% packet loss, time 9011ms rtt min/avg/max/mdev = 56.755/57.230/57.635/0.261 msPING gw2 (70.240.223.254) 1448(1476) bytes of data.
10 packets transmitted, 10 received, 0% packet loss, time 9011ms rtt min/avg/max/mdev = 56.623/57.146/57.469/0.416 msPING gw2 (70.240.223.254) 1456(1484) bytes of data.
10 packets transmitted, 10 received, 0% packet loss, time 9011ms rtt min/avg/max/mdev = 56.770/57.284/58.066/0.416 msPING gw2 (70.240.223.254) 1464(1492) bytes of data.
10 packets transmitted, 10 received, 0% packet loss, time 9011ms rtt min/avg/max/mdev = 56.900/57.380/57.788/0.440 msPING gw2 (70.240.223.254) 1472(1500) bytes of data.
10 packets transmitted, 10 received, 0% packet loss, time 9012ms rtt min/avg/max/mdev = 59.047/59.766/60.740/0.496 msPING gw2 (70.240.223.254) 1480(1508) bytes of data.
10 packets transmitted, 10 received, 0% packet loss, time 9013ms rtt min/avg/max/mdev = 59.881/60.153/60.432/0.318 msPING gw2 (70.240.223.254) 1488(1516) bytes of data.
10 packets transmitted, 10 received, 0% packet loss, time 9002ms rtt min/avg/max/mdev = 59.388/59.984/60.494/0.452 msPING gw2 (70.240.223.254) 1496(1524) bytes of data.
10 packets transmitted, 10 received, 0% packet loss, time 9010ms rtt min/avg/max/mdev = 59.273/59.911/60.636/0.423 msand normally:
$ ping -qc 10 gw2 PING gw2 (70.240.223.254) 56(84) bytes of data.
10 packets transmitted, 10 received, 0% packet loss, time 9011ms rtt min/avg/max/mdev = 10.702/11.322/12.552/0.555 msCabling-Design.com Forums website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.