> I don't know any thing about VM and very little about IP. > However I can > share one OSA card with multiple LPARS each with its own IP > address and > possibly a VIPA address. All IP addresses are in the same > network, and all > have the same physical MAC address of the OSA card.
Yeah. There's a lot of seriously unusual magic going on to make that work -- this part is one of the hardest things for network weenies to grasp: that there can be more than one system with the same physical MAC *iff* there is a separation of layer 2 MAC frame processing from layer 3 IP processing, and a single entity (your OSA) controls the mapping between layer 2 and layer 3 address mappings in a consistent way. ARP and MAC addresses are layer 2 things -- below the IP layer (at layer 3). At layer 2, the MAC address IS unique -- there's only one physical card with that MAC attached within the collision domain. In the shared environment you mention, the OSA is acting as a "layer 2.75" device -- it's aware of some layer 3 addressing, but is not a full layer 3 router. The OSA ucode is handling mapping the single layer 2 MAC to multiple layer 3 addresses (which is why the stacks behind the OSA don't do ARP processing, because to make all this work, the card has to do it to keep all the ducks lined up while sharing a single physical MAC). If you load the layer 2 microcode, or you're dealing with combinations of internal and external systems on VLANs, then you have to have unique MACs, because that OSA ucode mapping magic is no longer active for that conenction -- you gotta play with the real world scenario, where everything has to have a unique MAC. ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
