RSS

Category Archives: Network Adapters

Second network adapter and TCP Offload

I have been having all fun and games trying to get a second NIC to work correctly using Microsoft Hyper V (core and full install). I could see the NIC and configure but the VM would not see the network.

I first thought that Hyper V didn’t like the brand of network card, so I ordered some others. But in the meantime, I have found a solution.

It comes down to an advanced NIC option – TCP Offload. This option is normally on by default on the NIC’s that I have seen. The TCP Offload is an option which was first used way-back-when PC’s were not as powerful as they are now. It would give the CPU a break from digesting network traffic and send it straight to the NIC. In this modern era, we do not need to do this any more. Also, disabling this option is supposed to assist in quicker network transfer speeds – we will see.

So how do you disable it? Open up your network card properties and click on the ADVANCED tab. The screen will look similar to this:

The 3 options that I disable are “IPv4 Checksum Offload”, “TCP Checksum Offload (IPv4)” and “TCP Checksum Offload (IPv6)”. Please note, the screen shot above has lumped in TCP and UDP together – that’s OK. Your network card driver may do a similar thing or separate them. Just disable TCP when you can.

Your VM’s will work like magic now.

 

 
 

Failed to join domain

I was setting up a new Hyper-V Core server with 3 network cards – 2 x LAN and 1 x WAN. I configured all cards with static IP Addresses. But when I attempted to join the domain, I received a very unhelpful error message:

Failed to join domain

And that’s it! No event log, nothing! Great. Now where do I go?

After searching all the corners of the internet, I found a solution. The problem was in the way the Hyper-V box ordered the network cards. It made the WAN card the first in the queue, so of course, when I attempted to connect it to the domain, it was going out into the Internet to find our domain. Doh!

To change the “order” of the network cards, you need to change the “Interface Metric”. In a normal Windows GUI, you can change each NIC interface metric by going into the properties of the NIC’s IP address, choosing advanced, and then manually changing the metric that way. NOTE: lower numbered metrics go first – but don’t choose ‘0’ as this signals an automatic metric which will put you back to where you are now. After you have changed the values, reboot for good measure.

But, if you have a server core machine without a GUI, then you need to perform some command line work.

Open a command prompt and do the following:

To display all of the adapters in the computer with their current IP addresses to determine the correct adapter name, type the following command:

netsh interface ip show config

To change to a static address, type the following command:

netsh interface ip set address “Local Area Connection” static ipaddr subnetmask gateway metric

For example, I need to change my Local Area Connection #7 to a metric of 5, I would do this:

netsh interface ip set address “Local Area Connection 7” static 172.16.1.10 255.255.0.0 172.16.1.1 5

And after a reboot, you will be able to join your server / PC to the domain without a problem.

 

Hidden or phantom network adapters

After converting a server from a physical machine to a virtual machine, my network adapters did not find the network. A message appeared like this:

The IP address you have entered for this network adapter is already assigned to another adapter “<network card name>”. “<network card name>” is hidden from the Network Connections folder because it is not physically in the computer. If the same address is assigned to both adapters and they both become active,
only one of them will use this address. This may result in incorrect system configuration. Do you want to enter a different IP address for this adapter in the list of IP addresses in the Advanced dialog box? Yes/No

What the???

I thought that the NIC was hidden so I opened device manager and selected “Show hidden devices” from the menu. I expanded the network cards section but I could still not see the phantom network cards.

After a quick search on Google, I found a solution. Do the following:

  • Open a command prompt
  • Type the following: set DEVMGR_SHOW_NONPRESENT_DEVICES=1
  • Press enter
  • Type the following: devmgmt.msc

Your mystery network adapters will now be visible so you can right click and uninstall them.