I am also interested in this. From what I can tell, the only place this comes in to play (generally) is for Hipersockets and similar private networks. When I asked my network people about it, they said that the function has to be enabled and supported through all the hops in the network (many of which are external network providers in our case), AND that firewalls had to allow the ICMP traffic through. There is also a rumor floating around that PATHMTU results in the "do not fragment' bit always being set on. Which seems very scary and wrong.
________________________________ From: The IBM z/VM Operating System [mailto:ib...@listserv.uark.edu] On Behalf Of Christy Brogan Sent: Friday, December 11, 2009 12:38 PM To: IBMVM@LISTSERV.UARK.EDU Subject: PATHMTU We are currently moving from z/VM 5.3 to z/VM 5.4. We are wondering what to do with TCPIP and the new PATHMTU and PATHMTUAGE . Currently we have left it out so it is disabled and apparently defaults to Path MTU Discovery Aging Interval of 10 minutes (per NETSTAT GATE). In looking at the TCPIP Planning and Admin guide - it happily says what the statements mean, but I am not able to find anything that says what a good value might be, We don't have a lot of IP traffic - is it OK to let it default to 10 minutes? Is there a way to determine what a 'good' value would be....? Is it that important...? Obviously someone thought it important enough to add it to this release... :-) (And we are IPv4). Thanks.
