Path MTU

[Robert Chapin]

I commented yesterday that the Path MTU feature gives unreliable results.  It displays 1500 even when the IPv4 ping from the same app shows 100% packet loss at 1450.

Is it possible that the network I was on yesterday had different MTU values for IPv4 and IPv6?  If so, is it possible to fix this app by forcing or giving an option to use IPv4 only?

[Ulf]

Path MTU uses IPv6 if IPv6 connectivity is available and the IP address/host name contains a colon; otherwise IPv4 is used.

You could help debug this by sending me the output of the log, which contains more detailed information about what Path MTU is doing. In the About dialog, click on the version string. That brings up a window showing the log, which you can share with me via the share menu at the top right. If you choose Email, my address should already be filled in.

Ulf

[Ulf]

I think there may a confusion in the code where to add/subtract 28, and where not. I'll have to check that in more detail, and will post here what I find.

[Ulf]

Was that a publicly accessible server?

[Ping & Net]

No, all is good in this regard. With ping, you need to use a packet size 28 less than what Path MTU reports, due to the overhead that ICMP pings add. So if the Path MTU reports 1500, a ping with 1472 should work. I haven't seen a situation where it doesn't, so unless you can point me to a publicly routable host where I can check this behavior, we're stuck.

[Robert Chapin]

This was definitely a Wi-Fi issue and not a host issue.  I will check the app's log button next time I'm on that hotspot.

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