TCP Analyzer and MTU/MSS results

[xoru]

Hello everyone,

This is my first post on these forums, so please inform me if I'm completely off with the board to post in.

I often use(d) speedguide's TCP Analyzer (https://www.speedguide.net/analyzer.php) to determine the MTU/MSS
for the full route from some location where I'm tweaking network settings. However recently, I've noticed that on
some address where I successfully have configured the MTU/MSS for a PPPoE connection in the past now the tool
reports an MTU of 1492.

When I use the 'ping' trick to determine the MTU to a certain domain, I still get the value of 1500 for known correctly
set network paths.

Did something change about the TCP Analyzer or am I overlooking something?

[Philip]

The Analyzer has not been changed recently, it just reads what your connection to the Analyzer server advertises.
It really depends on the path, most likely some modem/router/node near you may be advertising the smaller max packet size to fit PPPoE encapsulation.

[xoru]

The Analyzer has not been changed recently, it just reads what your connection to the Analyzer server advertises.
It really depends on the path, most likely some modem/router/node near you may be advertising the smaller max packet size to fit PPPoE encapsulation.

I understand, but it seems to only occur on the analyzer tool, not using other tools testing against remote hosts. Even my path to speedguide.net has a 1500 MTU.
My ISP supports baby jumbo specifically for the PPPoE encapsulation.

[Philip]

Not sure exactly.. All I can tell you is the Analyzer reads it from the TCP/IP handshake.

[xoru]

Not sure exactly.. All I can tell you is the Analyzer reads it from the TCP/IP handshake.

Thank you, I might Wireshark this at some point to see what's going on.