On Monday, 05/02/2011 at 11:48 EDT, Mark Wheeler <mwheele...@hotmail.com> wrote: > The situation is that the IPs were registered on one VSWITCH, and passed on to > real switches in the external network. Later, another host registered the same > IPs on a different VSWITCH, which failed to pass them on to the external
> network (rejected because they were dups). The 2nd VSWITCH detected this error, > but retained the IPs (for itself) anyway. The question is whether the 2nd > VSWITCH should have retained them given it knew they were dups. There are two cases: 1. Connected VSWITCH. I would argue that this is a bug unless the guest has told the vNIC to suppress the ARP query (which is there specifically to allow almost-hot standby network adapters for IP takeover). When a guest registers an IP in an OSA and does NOT suppress the grat ARP, it has the expectation that the OSA will ensure no one else is actively using the indicated IP. 2. Disconnected VSWITCH. If there is no active connection to the network, CP cannot discover the existence of an in-use IP. If you subsequently connect the VSWITCH to the network, CP will register the guest IPs in the OSA and get a failure. But there is no OSA architecture to warn host of this after it has already successfully done a SETIP in the OSA. There *is* architecture to summarily revoke a host's ownership of an IP in an OSA, but in this case, we have no idea which host is wrong. So in this case, CP should use the no-in-use-IP-addy-detection option when it registers the guest IP addresses in the OSA. The gratuitous ARP *reply* that indicates to others IP ownership and interface activation SHOULD be issued so that any other host using the same IP address can pop-up "Someone else is using my IP address. Here is his MAC address...." I've seen this happen on Windows. Alan Altmark z/VM and Linux on System z Consultant IBM System Lab Services and Training ibm.com/systems/services/labservices office: 607.429.3323 mobile; 607.321.7556 alan_altm...@us.ibm.com IBM Endicott
