HP has released an advisory saying that with versions of the Emulex Nic driver firmware pre 4.1.450.7 Device Control Channel (DCC) may not work which could cause your blades with NC55x Nics to drop off the network if the upstream network connection fails. This has been an issue which has plagued HP blade networking since the beginning and was a particular problem with the G6 Broadcom Nics so its disconcerting to see similar issues resurface.
4.1.450.7 is older firmware however and my post HP Virtual Connect Flex-10 & VMware ESX(i) pre-requisites recommends Emulex firmware version 4.2.401.605 so if you haven’t updated, now is the time.
HP blade servers have hard wired connections to their immediate upstream Virtual Connect switch via the chassis backplane. This means in normal operation the Nic on the blade will never see a down state unless the physical Virtual Connect switch is powered off or removed. This would still be the case even if the upstream network connection failed if it wasn’t for DCC. DCC is a firmware component where Virtual Connect sees all uplinks for an Ethernet Network are down and then sends a command down to the individual Flex Nics to tell them to mark the port as down so the blade can fail over traffic to another nic in a port group or team. DCC is what SmartLink does and requires coordination between Virtual Connect firmware and the blade Nic firmware which in the past has caused a lot of issues.
Something I noticed in the advisory however was you can actually now see whether DCC/SmartLink is working for each individual network connection. Navigate to the Interconnect Bays in the VCM GUI, then navigate to the server ports and view the DCC state:
This looks like a recent addition to Virtual Connect firmware and will certainly help troubleshooting network connection issues but hopefully the DCC disconnect debacle won’t be repeated.