George Bonser wrote:
I am saying that MTU probing works just fine, even with a link in between that has a shorter MTU and doesn't pass ICMP.
And I have been saying your statement is unfounded.
I actually have one of those.
I can't see any.
It actively probes with packets of varying sizes and learns what the path MTU is.
First, it sets eff_pmtu to 1400B. OK?
It does not rely on ICMP. Again, it actively probes with varying sizes of packets until it believes it has "converged".
The initial value for search_high SHOULD be the largest possible packet that might be supported by the flow. This may be limited by the local interface MTU, by an explicit protocol mechanism such as the TCP MSS option,
OK, so, even with local MTU of 7500B and without ICMP PTB, if local MTU of your peer is 1500B, TCP MSS makes search_high 1500B. As eff_pmtu of 1400B is close enough to search_high, you are done. Eff_pmtu of 1400B will be used forever with no probe packets sent.
The timer for Linux is 5 minute by default but you can change it.
Timer timeouts do not affect TCP MSS. Masataka Ohta PS Your lengthy quotation means you don't see the point.