Tag Archives: Hyper-V

Hyper-V VM loses network connectivity intermittently

I just resolved an issue where a Hyper-V virtual machine was running fine for a few weeks, then it suddenly dropped off the network and connectivity went unpredictably intermittent.

Couldn’t remote desktop to it, pings drop most of the time but not all of the time; they looked like this:

Reply from 172.24.255.153: Destination host unreachable.
Reply from 172.24.255.153: Destination host unreachable.
Reply from 172.24.255.237: bytes=32 time=1098ms TTL=126
Reply from 172.24.255.237: bytes=32 time=1ms TTL=126
Reply from 172.24.255.153: Destination host unreachable.
Reply from 172.24.255.153: Destination host unreachable.
Reply from 172.24.255.153: Destination host unreachable.
Reply from 172.24.255.237: bytes=32 time<1ms TTL=126
Reply from 172.24.255.153: Destination host unreachable.
Reply from 172.24.255.153: Destination host unreachable.
Reply from 172.24.255.153: Destination host unreachable.
Reply from 172.24.255.237: bytes=32 time<1ms TTL=126
Reply from 172.24.255.237: bytes=32 time<1ms TTL=126

Live replies from the correct address, unreachable response from a different address (but another Hyper-V virtual machine).

The Hyper-V environment is composed of five Windows Server 2012 R2 Standard server loaded on top of a five-blade Cisco UCS B200 M3 with Nimble SAN.

Google found lots of wrong answers involving disabling VMQ on the host and guest, but my new hero Joel Coel mentioned some of his Hyper-V guests had been given duplicate MAC addresses.

Sure enough, I checked the guests with those two IP addresses and they had the same MAC:

These two Hyper-V guests have the same MAC address.

I solved the conflict by turning off the VM, removing the Network Adapter with the duplicate MAC, Applying the change, then adding a new NIC.

Technet’s Gilson Banin wrote how  to solve the root cause – Hyper-V servers with duplicate MAC pools.

First look: Hyper-V 2012 targets VMware’s air supply

This looks pretty interesting:

With the release of Windows Server 2012 yesterday, Microsoft significantly updated its Hyper-V virtualization platform. Available both as part of Server 2012 and as a free as in beer standalone installation, the third generation of Hyper-V brings with it a collection of features that largely commoditize the sorts of things you’ve gotten used to having to pay extra for. There are even a few features you couldn’t do at all with other hypervisors like live migration of a server from one server to another with no shared storage between the two.

Hyper-V supports a host of high-availability and “resiliency” features, such as off-site replication of servers. And it does many of those things as well or better than offerings from VMware and Citrix—regardless of whether you’re virtualizing Windows servers, Windows desktops, or Linux. And then there’s the free part: while the licenses for Windows Server itself are tied to a specific set of hardware, other operating systems can be hosted on the standalone Hyper-V server and managed as part of the same environment. All with the same sort of manageability.

Big boost in capacity, too:

Hyper-V 2012 can now handle significantly more substantial virtual hosts than its predecessor, making it possible to virtualize even some of the biggest workloads you may have running on physical servers. Hyper-V 2012, both on Windows Server 2012 and in standalone, can manage up to 320 logical processors and 4 terabytes of RAM; the virtual hosts running within the hypervisor can be configured with up to 64 virtual processors and a terabyte of RAM, and virtual disks can be configured to sizes ranging up to 64 terabytes (thanks to the new VHXD format for virtual drives, introduced in Server 2012). A single instance of Hyper-V can run up to 1,024 active virtual machines.

Pics and story at: First look: Hyper-V 2012 targets VMware’s air supply | Ars Technica.