Hi Jeffrey,I have attached a picture which shows one of the topologies we use for our PMTUD tests.
In this test case we transmit an Echo Request from REF-Host2 to TAR- Host1 with a packet size of 1500 bytes. REF-Host2 fragments the Echo Request it transmits. TAR-Host1 replies to this Echo Request with an Echo Reply to REF-Host2 with a size of 1500 bytes that is not fragmented. TAR-Router1 sends a Packet Too Big message in response as this Echo Reply is too large to forward onto Network 2.
In all of the cases we have seen TAR-Host1 does fragment future Echo Replies to REF-Host2, however, it does not retransmit any Echo Replies for Echo Requests received prior to receiving the Packet Too Big message from TAR-Router1.
Additionally from the tests we have performed in our lab if TAR-Host1 were to send an Echo Request with a packet size of 1500 bytes TAR- Router1 would send a Packet Too Big message in response. In all cases we have seen TAR-Host1 would not re-transmit this Echo Request and this would be counted as packet loss in the ping command results.
If this does not ideally match your test scenario we'd be happy to work together off-line to replicate your scenario.
Thanks, Tom
<<inline: MTU_Interoperability_Topology.png>>
On Jan 21, 2009, at 5:24 PM, Dunn, Jeffrey H. wrote:
Thomas,We would be happy to see any results you may have concerning application behavior during PMTUD.Best Regards, Jeffrey Dunn Info Systems Eng., Lead MITRE Corporation. (301) 448-6965 (mobile) -----Original Message----- From: Thomas Peterson [mailto:thom...@iol.unh.edu] Sent: Wednesday, January 21, 2009 3:00 PM To: Dunn, Jeffrey H.Cc: Rémi Denis-Courmont; ipv6@ietf.org; Huang, Frank; Sherman, Kurt T.; Liou, Chern; steve_eiser...@uscourts.gov; ipv6-boun...@ietf.org; v6...@ops.ietf.org ; Grayeli, ParisaSubject: Re: End System PMTUD behavior question Hi Jeffrey, This is Thomas Peterson from the InterOperability Laboratory at UNH. We have done extensive testing in this area and would be happy to work with you off line to examine this scenario. If you would like we can even set up your test topology in our lab. Thanks, Tom On Jan 21, 2009, at 2:44 PM, Dunn, Jeffrey H. wrote:Rémi, I agree with you assertions concerning "ping" versus TCP; however, I am looking for some concrete documentation or experiences. Best Regards, Jeffrey Dunn Info Systems Eng., Lead MITRE Corporation. (301) 448-6965 (mobile) -----Original Message----- From: Rémi Denis-Courmont [mailto:rde...@simphalempin.com] Sent: Wednesday, January 21, 2009 2:33 PM To: ipv6@ietf.org Cc: Dunn, Jeffrey H.; ipv6-boun...@ietf.org; v6...@ops.ietf.org; Sherman, Kurt T.; Liou, Chern; steve_eiser...@uscourts.gov; Huang, Frank; Grayeli, Parisa Subject: Re: End System PMTUD behavior question Le mercredi 21 janvier 2009 20:56:23 Dunn, Jeffrey H., vous avez écrit :Colleagues, We have been performing some PMTUD tests and have found that different operating systems handle PMTUD differently. Specifically, we found that the "ping" application behaves in the following way when the PMTU is set to 1280 and a 1500 octet ICMPv6 echo request is sent to that routed path. The hosts we tested:I'm afraid ping applications are not representative of what the operating system IP stacks do. Besides, there are no standards regarding the behavior of "ping" in case of Path MTU problems; it's really up to the implementor of each "ping" whether to report an error or to transparently fragment. The behavior of real transport protocols, such as TCP, DCCP and SCTP is moreinteresting when it comes to evaluating operating systems and their IPstacks. -- Rémi Denis-Courmont http://www.remlab.net/ -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
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