More important is too large an MSS which can cause fragmentation. You can test your network route from z/OS with this ping: ping 192.168.20.54 (PMTU yes LENGTH 1472 Verbose
'PMTU yes' says 'do not fragment'. On my host 1472 is max value that does not fragment. 1473 will need fragmentation. Going over a VPN will have larger TCP/IP headers giving a smaller MSS. For dynamic detection to work, your routers must pass the necessary ICMP packets. By default, some do not. Good article here: http://www.networkworld.com/article/2224654/cisco-subnet/mtu-size-issues.html -- Donald J. dona...@4email.net On Fri, Jan 29, 2016, at 07:35 AM, Cohen, Sam wrote: > Chris, > > If you look in the hardware documentation for the Open Systems Adapter (OSA), > it has a "normal" MTU of 1492, so your Linux is matching the hardware > settings. The OSA does support jumbo frames (8992) if your network is > configured to use them. > > Thanks, > > > Sam Cohen > Levi, Ray & Shoup, Inc. > > > > -----Original Message----- > From: Linux on 390 Port [mailto:LINUX-390@VM.MARIST.EDU] On Behalf Of > Christer Solskogen > Sent: Friday, January 29, 2016 1:56 AM > To: LINUX-390@VM.MARIST.EDU > Subject: MTU size > > Hi! > > On all of my x86_64 Linux boxes the default MTU is 1500. But with SuSE (both > 11 and 12) on s390 they seems to be 1492. How come? > > ---------------------------------------------------------------------- > For LINUX-390 subscribe / signoff / archive access instructions, send email > to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit > http://www.marist.edu/htbin/wlvindex?LINUX-390 > ---------------------------------------------------------------------- > For more information on Linux on System z, visit http://wiki.linuxvm.org/ -- http://www.fastmail.com - Or how I learned to stop worrying and love email again ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
