On Wednesday, 08/02/2006 at 12:26 EST, Dennis Schaffer <[EMAIL PROTECTED]> wrote: > Our network folks noticed that one of our zLinux systems is driving a lot > of packet retransmissions, caused mainly because packets are being received > out-of-sequence, outside the target workstation's response window (I hope > I'm getting the terminology correct here). > > Going one step further, the network folks say this is happening because the > zLinux system (actually, this is probably VM TCP/IP, as I'll explain in a > moment) is transmitting packets sort of round-robin across both of our OSA > interfaces, rather than picking one interface and transmitting all packets > across that interface. > > They've asked if we can tweak our configuration to send packets across a > single adapter in order to reduce retransmissions. > > VM TCP/IP is involved because the zLinux system is connected to a guest lan > which is connected to VM's TCP/IP stack. The zLinux system has just one > logical ethernet interface but VM TCPIP is connected to both OSA > interfaces, via separate VSWITCH connections. Each of the VSWITCH/OSAs is > attached to a separate IP subnet. > > Does anyone know if there's a TCP/IP or MPROUTE configuration parameter > which can affect this behavior?
If you have AssortedParms EqualCostMultiPath then the stack will merrily round-robin across interfaces. Adjust the cost metric in either MPROUTE CONFIG or in the next-hop routers to prefer one path over the other. > Would this be more easily controlled using a zLinux TCP/IP stack? We've > experimented with connecting a zLinux system to the VSWITCHs directly and > using Zebra/OSPF in zLinux but didn't feel our traffic volume justified the > increased management and automation requirements. But, maybe this would > make it worthwhile? You need to get the Linux guests directly on the VSWITCH and get out of the virtual router business. The VSWITCH will be responsible for managing OSA redundancy at a physical level rather than an IP routing level. <plug> I'll be presenting Guest LAN to VSWITCH Migration at SHARE in Baltimore. </plug> Alan Altmark z/VM Development IBM Endicott
