# Sunday, August 25, 2013

After replacing a Hyper-V (windows Server 2012) host, DHCP started to have issues. Unpredictable results so to say.

The old host had a teamed dual-port Intel PT1000. At the network side, a Link Aggregation Group was defined on the Cisco SG300 switch.The new host is equipped with an on-board Broadcom NetXtreme controller and an additional dual-port NetXtreme II adapter. The onboard controller was configured as IP-interface for the host, for the dual-port adapter I installed the Broadcom Advanced Control Suite 4 (BACS4, Version and an additional LAG was defined on the SG300. Well, it wasn’t a clear victory! When pinging between hosts, packets between physical and virtual hosts seemed to be dropped, DHCP wasn’t renewing and RDP-sessions to virtual systems were having response issues (can happen when packets are dropped). The main difference to me was the Hyper-V host, where in the old situation the Intel PT1000 was shared between the host OS and the guests (as external virtual switch). In the new situation the dual port Broadcom was dedicated for the virtual switch.I must admit knowing little more than the basics on Hyper-V thus one Googles in all directions. And thus I stumbled upon SR-IOV. It’s late, SR-IOV made sense to my new situation thus I gave it a try by replacing the old virtual switch with a new SR-IOV based virtual switch. Hurrah, everything seemed to work now; ping, stable RDP sessions and DHCP renewals.

However after a couple of days, I wanted to use my Android tablet, but it did not receive an IP-address. Pressed for time, I switched to my laptop. A few days later, I turned on a Windows 8 system that had been unused for the last couple of weeks and it too did not get an IP-address… so I still did have a DHCP issue! I blamed the switch configuration for a while, as well as the firewalls on the Windows systems. Wireshark showed the DHCP Discover leave at Windows 8 hosts and never arrive at the virtual DHCP server. But other DHCP packets (renewals) were observed, both at the unwilling client and at the server. When I put a static IP on the Windows 8 host, it still couldn’t ping the DHCP Server (or any other virtual system). The MAC of the Windows 8 host did however show up in the MAC table of the switch (but so did the MAC addresses of the virtual servers). I must have reconfigured the switch 13 times, disabled the firewalls and still no result. Oh my… do I now have one of those nasty interoperability issues between switches of different vendors (Cisco and Microsoft)… I needed to learn more about virtual switches in Hyper-V and luckily one of the first links I hit was Hyper-V and VLAN’s by Aidan Finn. I especially want to quote him on:

“I must warn anyone reading this that I’ve worked with a Cisco CCIE while working on Hyper-V and previously with another senior Cisco guy while working on VMware ESX and neither of them could really get their heads around this stuff.  Is it too complicated for them?  Hardly.  I think the problem was that it was too simple!  Seriously!”

That was comforting, it must therefore be that the solution should be simple. At the bottom of Aidan’s post was yet another link that seemed useful Windows Server 2012 NIC Teaming Part 6 – NIC Teaming In The Virtual Machine, and it was! The final part of a series useful articles, which led me to the Microsoft un-support statement of third party NIC teaming: Microsoft Support Policy for NIC Teaming with Hyper-V

Bottom line: the Broadcom Advanced Control Suite could be the source of my problem. I uninstalled it from the Hyper-V host and then configured NIC Teaming from Hyper-V. And the result of ipconfig /renew on the Windows 8 computer: Discover, Offer, Request, ACK. Just the way it should be.

Sunday, August 25, 2013 10:08:07 PM (W. Europe Daylight Time, UTC+02:00)