When you upgrade your VMware environment to version 5.5. remember to upgrade your distributed vSwitch as well; it will not be done automatically. In this way, you can utilize new features in dvSwitch 5.5, including:

• Multiple LAGs and Enhanced LACP (Link Aggregation capability for high performance VMs which need high bandwidth)
• Traffic Filtering and packet classification (based on MAC, IP, Port number)
• Quality of Service Tagging and Marking
• Enhanced Packet Capturing

The upgrade process is fairly easy and the good thing is that according to VMware documentation, it is non-disruptive which means there is no outage and no host and VM will get down or experience issues. Find your distributed vSwitch either in vSphere Client or Web client, right click and do upgrade.