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.