Resolve invalid elastic network interface configurations

Symptoms

The network configuration of an elastic network interface on a Windows instance can become invalid. Symptoms include disconnected or failed network connections, invalid IP addresses, invalid subnet configurations such as the subnet mask and default gateway, unusual traffic routing, and invalid VLAN configurations.

These failures typically occur in the following scenarios:

• You attach multiple disks when creating an ECS instance. After the instance is created, you alternately hot-swap disks and elastic network interfaces, and then restart the instance.

• You attach a secondary elastic network interface when creating an ECS instance. After the instance is created, you alternately hot-swap disks and elastic network interfaces, and then restart the instance.

For example, you create a Windows instance with three disks attached. After the instance is created, you detach the disks, attach a new elastic network interface to the instance, and configure a secondary private IP address. The configuration is as follows:

In the Network Connections window (Control Panel > Network and Internet > Network Connections), you can see two Red Hat VirtIO Ethernet Adapters, Ethernet and Ethernet 2, both in a connected state.

C:\Users\Administrator>ipconfig
Windows IP Configuration
Ethernet adapter Ethernet:
   Connection-specific DNS Suffix  . :
   Link-local IPv6 Address . . . . . : fe80::a915:a252:4124:aae6%3
   IPv4 Address. . . . . . . . . . . : 192.168.1.166
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   IPv4 Address. . . . . . . . . . . : 192.168.1.167
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 192.168.1.253
Ethernet adapter Ethernet 2:
   Connection-specific DNS Suffix  . :
   Link-local IPv6 Address . . . . . : fe80::f3b3:c68:e912:216c%10
   IPv4 Address. . . . . . . . . . . : 192.168.1.148
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 192.168.1.253

After you restart the ECS instance, the network configuration of the attached elastic network interface becomes invalid. For example, Ethernet 3 becomes an unidentified network.

C:\Users\Administrator>ipconfig
Windows IP Configuration
Ethernet adapter Ethernet:
   Connection-specific DNS Suffix  . :
   Link-local IPv6 Address . . . . . : fe80::e9d9:70a7:70ea:cda4%3
   IPv4 Address. . . . . . . . . . . : 192.168.1.166
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   IPv4 Address. . . . . . . . . . . : 192.168.1.167
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 192.168.1.253
Ethernet adapter Ethernet 3:
   Connection-specific DNS Suffix  . :
   Link-local IPv6 Address . . . . . : fe80::f12c:fc6:9a63:e40f%11
   Autoconfiguration IPv4 Address. . . : 169.254.214.80
   Subnet Mask . . . . . . . . . . . : 255.255.0.0
   Default Gateway . . . . . . . . . :

Cause

Windows names elastic network interfaces based on the scan order. Alternately hot-swapping disks and elastic network interfaces changes the device detection order and causes device numbers to change. As a result, Windows cannot apply the network configuration to the correct elastic network interface, and the configuration becomes invalid.

Solution

Choose a solution based on whether your elastic network interface requires a secondary private IP address or IPv6 addresses.