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16.3. Configuring externally visible virtual machines

In many scenarios, the default VM networking configuration is sufficient. However, if you need to adjust the configuration, you can use the command line (CLI) or the RHEL 10 web console to do so.

By default, a newly created VM connects to a NAT-type network that uses virbr0, the default virtual bridge on the host. This ensures that the VM can use the host’s network interface controller (NIC) for connecting to outside networks, but the VM is not reachable from external systems.

If you require a VM to appear on the same external network as the hypervisor, you must use bridged mode instead. To do so, attach the VM to a bridge device connected to the hypervisor’s physical network device.

Prerequisites

  • A shut-down existing VM with the default NAT setup.

  • The IP configuration of the hypervisor. This varies depending on the network connection of the host. As an example, this procedure uses a scenario where the host is connected to the network by using an ethernet cable, and the hosts' physical NIC MAC address is assigned to a static IP on a DHCP server. Therefore, the ethernet interface is treated as the hypervisor IP.

    To obtain the IP configuration of the ethernet interface, use the ip addr utility: 

    # ip addr
[...]
enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 54:ee:75:49:dc:46 brd ff:ff:ff:ff:ff:ff
    inet 192.0.2.1/24 brd 192.0.2.255 scope global dynamic noprefixroute enp0s25

Procedure

  1. Create and set up a bridge connection for the physical interface on the host. For instructions, see the Configuring a network bridge.

    Note that in a scenario where static IP assignment is used, you must move the IPv4 setting of the physical ethernet interface to the bridge interface.

  2. Modify the VM’s network to use the created bridged interface. For example, the following sets testguest to use bridge0. 

    # virt-xml testguest --edit --network bridge=bridge0
Domain 'testguest' defined successfully.

  3. Start the VM. 

    # virsh start testguest

  4. In the guest operating system, adjust the IP and DHCP settings of the system’s network interface as if the VM was another physical system in the same network as the hypervisor.

    The specific steps for this differ depending on the guest operating system used by the VM. For example, if the guest operating system is RHEL 10, see Configuring an Ethernet connection.

Verification

  1. Ensure the newly created bridge is running and contains both the host’s physical interface and the interface of the VM. 

    # ip link show master bridge0
2: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel master bridge0 state UP mode DEFAULT group default qlen 1000
    link/ether 54:ee:75:49:dc:46 brd ff:ff:ff:ff:ff:ff
10: vnet0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel master bridge0 state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether fe:54:00:89:15:40 brd ff:ff:ff:ff:ff:ff

  2. Ensure the VM is displayed on the same external network as the hypervisor:

    1. In the guest operating system, obtain the network ID of the system. For example, if it is a Linux guest: 

      # ip addr
[...]
enp0s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 52:54:00:09:15:46 brd ff:ff:ff:ff:ff:ff
    inet 192.0.2.1/24 brd 192.0.2.255 scope global dynamic noprefixroute enp0s0

    2. From an external system connected to the local network, connect to the VM by using the obtained ID. 

      # ssh root@192.0.2.1
root@192.0.2.1's password:
Last login: Mon Sep 24 12:05:36 2019
root~#*

      If the connection works, the network has been configured successfully.

Troubleshooting

  • In certain situations, such as when using a client-to-site VPN while the VM is hosted on the client, using bridged mode for making your VMs available to external locations is not possible.

    To work around this problem, you can set destination NAT by using nftables for the VM.

By default, a newly created VM connects to a NAT-type network that uses virbr0, the default virtual bridge on the host. This ensures that the VM can use the host’s network interface controller (NIC) for connecting to outside networks, but the VM is not reachable from external systems.

If you require a VM to appear on the same external network as the hypervisor, you must use bridged mode instead. To do so, attach the VM to a bridge device connected to the hypervisor’s physical network device. To use the RHEL 10 web console for this, follow the instructions below.

Prerequisites

  • You have installed the RHEL 10 web console.

    For instructions, see Installing and enabling the web console.

  • The web console VM plugin is installed on your system.
  • A shut-down existing VM with the default NAT setup.

  • The IP configuration of the hypervisor. This varies depending on the network connection of the host. As an example, this procedure uses a scenario where the host is connected to the network by using an ethernet cable, and the hosts' physical NIC MAC address is assigned to a static IP on a DHCP server. Therefore, the ethernet interface is treated as the hypervisor IP.

    To obtain the IP configuration of the ethernet interface, go to the Networking tab in the web console, and see the Interfaces section.

Procedure

  1. Create and set up a bridge connection for the physical interface on the host. For instructions, see Configuring network bridges in the web console.

    Note that in a scenario where static IP assignment is used, you must move the IPv4 setting of the physical ethernet interface to the bridge interface.

  2. Modify the VM’s network to use the bridged interface. In the Network Interfaces tab of the VM:

    1. Click Add Network Interface

    2. In the Add Virtual Network Interface dialog, set:

      • Interface Type to Bridge to LAN
      • Source to the newly created bridge, for example bridge0
    3. Click Add
    4. Optional: Click Unplug for all the other interfaces connected to the VM.
  3. Click Run to start the VM.

  4. In the guest operating system, adjust the IP and DHCP settings of the system’s network interface as if the VM was another physical system in the same network as the hypervisor.

    The specific steps for this will differ depending on the guest operating system used by the VM. For example, if the guest operating system is RHEL 10, see Configuring an Ethernet connection.

Verification

  1. In the Networking tab of the host’s web console, click the row with the newly created bridge to ensure it is running and contains both the host’s physical interface and the interface of the VM.

  2. Ensure the VM is displayed on the same external network as the hypervisor.

    1. In the guest operating system, obtain the network ID of the system. For example, if it is a Linux guest: 

      # ip addr
[...]
enp0s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 52:54:00:09:15:46 brd ff:ff:ff:ff:ff:ff
    inet 192.0.2.1/24 brd 192.0.2.255 scope global dynamic noprefixroute enp0s0

    2. From an external system connected to the local network, connect to the VM by using the obtained ID. 

      # ssh root@192.0.2.1
root@192.0.2.1's password:
Last login: Mon Sep 24 12:05:36 2019
root~#*

      If the connection works, the network has been configured successfully.

Troubleshooting

  • In certain situations, such as when using a client-to-site VPN while the VM is hosted on the client, using bridged mode for making your VMs available to external locations is not possible.

16.3.3. Replacing macvtap connections
复制链接

macvtap is a Linux networking device driver that creates a virtual network interface, through which virtual machines have direct access to the physical network interface on the host machine. Using macvtap connections is supported in RHEL 10.

However, in comparison to other available virtual machine (VM) networking configurations, macvtap has suboptimal performance and is more difficult to set up correctly. Therefore, if your use case does not explicitly require macvtap, use a different supported networking configuration.

If you are using a macvtap mode in your VM, consider instead using the following network configurations:

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