Tag Archives: Mac

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.

Verizon tips for Mac security and anti-virus

Some handy tips to keep your Mac safe on the Internet:

Our most critical recommendations for OS X security have not changed much since its release ten years ago:

  • Uncheck the “Open ’safe’ files after download” box in Safari’s General Preferences.
  • Utilize your browser’s security features (anti-popup, anti-phishing, etc.).
  • Run Software Update on a weekly basis, and install security updates as they are made available.
  • In the Security System Preference, be sure the firewall is on.
  • Do not download, run, or share software from unknown sources.
  • Do not open or share unexpected attachments received via email or instant messenger.
  • Only connect to trusted wireless networks.
  • In an enterprise environment, an anti-spam solution should be in place.

via Verizon Business Security Blog » Blog Archive » It’s time to consider Mac AV.