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End System PMTUD behavior question



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:

 

1.      Send one or two un-fragmented echo requests

2.      Receive the “Packet Too Big” ICMPv6 message from the first interface with the 1280 octet MTU

3.      Begin to send echo requests in two fragments

 

The following questions occurred to us:

 

1.      Should the hosts re-transmit the ICMPv6 echo request(s) in fragments?

2.      If not, should the host that sent two echo requests have waited for a response in support of PMTUD?

 

Any assistance you can provide, especially commercial specification for shipping product or other applications, would be most helpful. Many thanks in advance.

 

Best Regards,
 
Jeffrey Dunn
Info Systems Eng., Lead
 
Center for Enterprise Modernization
MITRE Corp.
 
301-429-5377 (Office)
301-731-8862  (FAX)