On Thursday, 02/28/2002 at 02:36 PST, Todd Booher <[EMAIL PROTECTED]> wrote: > Being a S390/VM newbie, please excuse my ignorance.... > > Is it a hard and fast rule that the Linux guest OS cannot be in the > same subnet as z/VM? In using other VM products (like vmware) this > doesn't seem to be a problem.
Apples and oranges, Todd. On vmware, the hosts are sharing the adapter. They *are* on the LAN and are entitled to IP address in the LAN's subnet. The same is true on z/VM -- if you share the network adapter with the Linux guests, they get IP addresses in the LAN's subnet. But the situation being described here is different. In this case, the Linux guests (virtual machines) are one network hop away from the LAN. Another virtual machine (whether VM TCP/IP, Linux, z/OS, VSE, whoever) is acting as a router; the adapter is not being shared. To use IP addresses that are in the same subnet as the LAN, you must enable VM's proxy ARP support so that VM will answer ARPs on behalf of guests on the other end of those point-to-point links. As a side note, I've been telling everyone that proxy ARP is a stop-gap measure to get things going until you get your network *properly* defined. Now that guest LANs have arrived with z/VM Version 4 Release 2, I should point out that Proxy ARP does NOT apply to LAN interfaces. I.e. VM TCP/IP will not perform Proxy ARP for guests that are on a guest LAN (since VM TCP/IP doesn't know or care who is connected to the LAN). Guest LANs need their own routable subnets. And THAT means that if you are using a shared OSA, the host that is performing the routing function MUST be defined as Primary Router. You can get around it for LCS by manually updating the OAT, but that doesn't work for QDIO. Regards, Alan IBM Senior Software Engineer z/VM Development, Endicott, NY Phone 607.752.6027 fax 607.752.1497 t/l 852
