fragmentation

[lamsf]

I hv done some ping tests with various packet size and with DF set. Below is the results:

C:\>ping google.com -f -l 1452

Pinging google.com [64.233.187.99] with 1452 bytes of data:

Reply from 64.233.187.99: bytes=56 (sent 1452) time=429ms TTL=232
Reply from 64.233.187.99: bytes=56 (sent 1452) time=413ms TTL=232
Reply from 64.233.187.99: bytes=56 (sent 1452) time=410ms TTL=232
Reply from 64.233.187.99: bytes=56 (sent 1452) time=413ms TTL=232

Ping statistics for 64.233.187.99:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 410ms, Maximum = 429ms, Average = 416ms

C:\>ping google.com -f -l 1453

Pinging google.com [64.233.187.99] with 1453 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 64.233.187.99:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

C:\>

My question is, what is actually limiting the size of the packets? What is doing the fragmentation?

Thank you very much.

 

[technome]

My question is, what is actually limiting the size of the packets? What is doing the fragmentation?"
A routing device within the route. Google "black hole router"

If you use the Pathping command such as Pathping yahoo.com, you can see which router is reponsible.

Download TCP Optimizer to test for the optimal MTU size


........................................
Chernobyl disaster..a must see pictorial

http://www.kiddofspeed.com/default.htm

 

[burtsbees]

ADSL MTU size MUST be 1452. I would bet the farm you have dsl. The normal IP packet is 1500 bytes, but for dsl it must be set to 1460, or 1492 MTU and 1452 MTU.

Burt

 

[lamsf]

Thanks for the answers.
Without changing any mtu size anywhere, I noticed that I can access certain web sites but can't access certain web sites. For eg. I can access google.com, tek-tips.com, but cannot access yahoo.com and youtube.com.

What is the reason why I can access to some web sites but cannot access to some web sites?

When google blackhole router, one of the solutions is to enable black hole detection at the registry, as follows:

Method 1
Enable PMTU Black Hole Detection on the Windows-based hosts that will be communicating over a WAN connection. Follow these steps: 1. Start Registry Editor (Regedit.exe).
2. Locate the following key in the registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\tcpip\parameters
3. On the Edit menu, click Add Value, and then add the following registry value:
Value Name: EnablePMTUBHDetect
Data Type: REG_DWORD
Value: 1
4. Quit Registry Editor, and then restart the computer.

Before doing that, I would like to know what do I expect to see, and what test I can do to get more info.

Anyone can help me out here?

Thanks a lot.

 

[burtsbees]

They are likely not blackhole routes. Try the MTU! If not on the router/modem/whatever, then download DrTCP.

Burt

 

[lamsf]

I changed the MTU size of my computer to 1300 and I am able to access to all web sites. Does that mean that one of the router is limiting the access? How can I determine which router is limiting it? Thanks alot.

 

[burtsbees]

Is this your home computer? What is the topology like? That MTU should not have to be that low...

Burt

 

[lamsf]

It's my home computer hooked to the wimax system.

So, home computer -> wimax cpe -> wimax system

Any advice?

Thanks.

 

[burtsbees]

Not sure what wimax is...what is past the computer? A router? Modem?

Burt