SG Broadband Community

I cannot avoid packet fragmentation, unless the packet data is 24 bytes less than MTU.

eg: PPPOe connection, so router is set at 1492 and TCP Optimizer is set to 1492 on my PC behind the router.

Test 1
C:\Windows\system32>ping 8.8.8.8 -f -l 1492

Pinging 8.8.8.8 with 1492 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 8.8.8.8:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss)

Test 2 right after
C:\Windows\system32>ping 8.8.8.8 -f -l 1460

Pinging 8.8.8.8 with 1460 bytes of data:
Reply from 8.8.8.8: bytes=1460 time=13ms TTL=59
Reply from 8.8.8.8: bytes=1460 time=13ms TTL=59
Reply from 8.8.8.8: bytes=1460 time=14ms TTL=59
Reply from 8.8.8.8: bytes=1460 time=13ms TTL=59

Ping statistics for 8.8.8.8:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 13ms, Maximum = 14ms, Average = 13ms

Even if I lower my PCs MTU the problem persists.

eg: Set MTU on PC to 1372 using TCP Optimizer
Fragmentation occurs until
C:\Windows\system32>ping 8.8.8.8 -f -l 1348

Any suggestions on preventing packet fragmentation so C:\Windows\system32>ping 8.8.8.8 -f -l 1492 has no fragmentation? (or whatever MTU is set using TCP Optimizer, my primary concern is to stop fragmentation)

Thanks a bunch

Remember that when pinging, IP and ICMP headers still remain. pings will have 20 bytes of IP header, 8 bytes of ICMP header.

So, actual packets are 28 bytes higher than the non-fragmented packet you get when pinging. Every time you lower MTU to any number, non-fragmented pings will be 28 less than that number.

I'd just use 1492-28 = 1464 bytes to ping if you're on PPPoE. Alternatively, use the tab in the TCP Optimizer.

Thanks for your help, user error as usual

No problem at all, welcome to SG