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Ubuntu VM cannot grab an IP address in when in Bridige mode with Default adapter.

APPLIES TO:
  • Parallels Desktop for Mac Business Edition

Symptoms

The Ubuntu VM cannot grab an IP and its DHCP requests timeout when trying to grab an IP, Please see log output below from the VM /var/log/syslog

Resolution

When setting up network in Linux, you may need to configure the DHCP client to send the virtual machine's ID in DHCP requests. For information on how to configure your DHCP client, refer to the DHCP client documentation.

For example, in Red Hat Linux guest OSs, you need to edit the DHCP client configuration file.

Open the dhclient.conf file and make sure that the following lines are present

    interface "eth0" {
    send dhcp-client-identifier 1:<MAC address>; 
    }

If there are no such lines, add them manually to the file and save it.

When the dhclient.conf file contains these lines, DHCP client sends the virtual machine's ID to the DHCP server. The DHCP server sends an IP address in response.

Tip: To locate the dhclient.conf file, in a Terminal, enter:

    strings /sbin/dhclient | grep etc | grep dhclient.conf

or:

    rpm -ql dhclient

Additional informationregarding the cause of the issue

  1. WiFi due to its nature requires that all outgoing network frames have authenticated MAC-address. So, Parallels have to use the MAC-address of the Host Mac Os.

  2. Cisco by default blocks DHCP requests in which Dhcp-Client-Mac-Address doesn't match the field SORCE_ADDR in the ethernet header.

  3. So, we provide a setting to configure the option to whether send host MAC-address in the DHCP-header. By default this option is "Auto", which means that we first try to send MAC-address from virtual machine and if we don't receive a reply from DHCP-Server, we do send of host's MAC-address in the DHCP-header. Please refer to documentation.

  4. When you are trying to connect to the Internet via Wi-Fi, and the Wi-Fi Access Point has the Validate DHCP packets option enabled, you may experience problems connecting to the Internet. In this case, enable the Send the host's MAC address to DHCP server option to ensure that your virtual machine gets an IP address for accessing the Internet.

    Note Enabling the Send the host's MAC address to DHCP server option will not work with some DHCP servers - your virtual machine may get the same IP address as the physical computer.

  5. By default, correct DHCP-server uses the field DHCP-Client-ID in the DHCP-request to identify client and provide him an IP-address. It uses the Dhcp-Client-Mac-Address field only if client didn't fill the CliendID field.

The problem is that the earlier Linuxes doesn't fill ClientID (modern linuxes fill it correctly). So, if due to the previous point we have sent the field Dhcp-Client-Mac-Address equal to Host's MAC-address, DHCP-server will reply with the same IP-address as for Mac-host. This replies are of course blocked by Parallels, since otherwise there will be IP-address conflict between Mac-host and Linux VM.

The solution is to configure Linux to send correctly filled ClientID, as described above.




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