All, I have a Sun Ultra10 that has been configured with sub interfaces. (hme0 and hme0:1)The two logical interfaces are in different subnets but they utilize the same physical uplink to the switch. I have this machine uplinked to a Summit 48. The only way I have been able to get both interfaces usable is to utilize Extreme multinetting along with vlan tagging. The Extreme documentation does not recommend using this (multinetting)in your design topology but it does not say why or what the problems may be. I would like to know what the limitations are, and what the recommended topology/configuration is in this case. My end goal is to have a host with one physical interface that has multiple logical addresses. Any help will be greatly appreciated.

Extreme recommends multinetting as a transistion strategy only as it makes troubleshooting difficult and bandwidth can become an issue since network isolation is not occuring in this scenario.  May be other reasons but I have never used this so I don't know.  The right way to accomplish what you are doing is to run 802.1q tagging AND have an interface card in your Ultra10 that can do 802.1q tagging as well.  This way you won't see any of the problems possible with multinetting.  In my opinion, if the 802.1q card is not available or is beyond budget, run it like you are doing but be aware that the 2 networks that are involved in multinetting are for all intents a flat network now.