Extending a VXLAN across nodes with Wireguard

Virtualizing environments is something I do quite often in a day-to-day basis, usually, these environments live in different hypervisors. While I don’t always need these environments to talk to each other, from time to time I need some sort of connectivity between them.

Getting the VMs running on these hypervisors routed through the lab network is one of the solutions I have been using for a long time. For the last few days, I have been thinking of extending a virtual network across two hypervisors. This allows me to run VMs on this virtual network and get VMs to talk to each other without having to run these VMs in a routed lab network.

For this solution to work, we will be using Wireguard to create a tunnel between the two hypervisors using a routed lab network and VXLAN to encapsulate our virtual network in the Wireguard tunnel.

The instructions in this blog were tested on RHEL 9. This focuses on IPv4 VXLAN network, but the same should be doable with IPv6.

Warning

I’m far (like really far) from being a Networking expert, take the information in this post with a grain of salt since it may not be 100% accurate (but it works though).

Solution Overview

VXLAN over Wireguard

In the diagram above we can see we have two hypervisors which are connected to a routed lab network via their eth0 interface. We will configure a Wireguard tunnel using this interface, the Wireguard interface will be named wg0. On top of that, we will configure a VXLAN interface that we will connect to the bridge named br0 which will be configured to send traffic via the wg0 tunnel.

Both hypervisors will follow this setup. When we create a VM on these hypervisors, we will connect the VM’s eth0 interface to the bridge br0 and that will place the VM in the VXLAN network. If everything goes according to the plan, we will be able to connect from VM1 in Hypervisor 1 to VM1 in Hypervisor 2 and vice versa.

Installing Wireguard

Attention

Steps below must be done on every hypervisor node.

  1. Install epel-release repository by following the instructions here.

  2. Install elrepo repository by following the instructions here.

  3. Install the required packages:

    sudo dnf install -y kmod-wireguard wireguard-tools bridge-utils
    
  4. Make sure the wireguard kernel module is loaded (if you get an error when trying to load the module, you may need to reboot into a newer kernel):

    sudo modprobe wireguard
    

    Attention

    If you get the following error when trying to load the module: modprobe: ERROR: could not insert 'wireguard': Required key not available.

    This means that you are trying to use ELRepo’s kernel modules (kmod packages) on a system with Secure Boot enabled, therefore this must import the ELRepo Secure Boot public key into their Machine Owner Key (MOK) list.

    sudo curl -L https://elrepo.org/SECURE-BOOT-KEY-elrepo.org.der -o /etc/pki/elrepo/SECURE-BOOT-KEY-elrepo.org.der
    

    Install the downloaded key:

    sudo mokutil --import /etc/pki/elrepo/SECURE-BOOT-KEY-elrepo.org.der
    

    When prompted, enter a password of your choice. This password will be used when enrolling the key into the MOK list. Reboot the system and follow-up the BMC interface for entrolling the MOK key. Once the boot finished:

    sudo modprobe wireguard
    
    sudo lsmod | grep wireguard
    wireguard             212992  0
    ip6_udp_tunnel         16384  1 wireguard
    udp_tunnel             20480  1 wireguard
    

Configuring Wireguard Tunnel (wg0)

  1. First we need to enable IPv4 forwarding in both hypervisors.

    cat <<EOF | sudo tee /etc/sysctl.d/wireguard.conf
    net.ipv4.ip_forward=1
    EOF
    sudo sysctl -p /etc/sysctl.d/wireguard.conf
    
  2. Generate Wireguard keys in both hypervisors.

    sudo mkdir -p /etc/wireguard/certs/
    sudo wg genkey > /etc/wireguard/certs/private_key
    sudo wg pubkey < /etc/wireguard/certs/private_key > /etc/wireguard/certs/public_key
    sudo chmod 600 /etc/wireguard/certs/private_key
    sudo chmod 644 /etc/wireguard/certs/public_key
    

Configuring Wireguard in Hypervisor 1

  • Hypervisor 1 has its eth0 interface connected to the lab network and configured with the 10.19.3.4/26 IP. Hypervisor 1 can reach Hypervisor 2 at 10.19.3.5/26.
  • Hypervisor 1 will configure 172.16.0.1/16 IP for wg0 and will NAT traffic through its eth0 which is connected to the routed lab network.
  • Hypervisor 1 Priv Key in this example is: QP1LNvlaejugxgHj+DtDOX20DvBilOCn1RPRBQFakFs=
  • Hypervisor 1 Pub Key in this example is: 3TxNmlyWmNeL4EavtHi9dRfsqPHcEeiexKzMDF7n7nU=
  • Hypervisor 2 Priv Key in this example is: sIWrsVAvFm/VIHQhHRPaCzBOTWK/jmM6NkGYEwd/oXk=
  • Hypervisor 2 Pub Key in this example is: GmG2HkjvV8OebDy9ezHPG/+ODb6CMv51oSEKz4StdHQ=
  1. Configure wg0:

    HYPERVISOR_EXT_NIC=eth0
    cat <<EOF | sudo tee /etc/wireguard/wg0.conf
    [Interface]
    PrivateKey = QP1LNvlaejugxgHj+DtDOX20DvBilOCn1RPRBQFakFs=
    Address = 172.16.0.1/16
    ListenPort = 51820
    PostUp   = iptables -A FORWARD -i %i -j ACCEPT; iptables -A FORWARD -o %i -j ACCEPT; iptables -t nat -A POSTROUTING -o ${HYPERVISOR_EXT_NIC} -j MASQUERADE
    PostDown = iptables -D FORWARD -i %i -j ACCEPT; iptables -D FORWARD -o %i -j ACCEPT; iptables -t nat -D POSTROUTING -o ${HYPERVISOR_EXT_NIC} -j MASQUERADE
    
    [Peer]
    PublicKey = GmG2HkjvV8OebDy9ezHPG/+ODb6CMv51oSEKz4StdHQ=
    Endpoint = 10.19.3.5:51820
    AllowedIPs = 172.16.0.0/16
    PersistentKeepalive = 25
    EOF
    

Configuring Wireguard in Hypervisor 2

  • Hypervisor 2 has its eth0 interface connected to the lab network and configured with the 10.19.3.5/26 IP. Hypervisor 1 can reach Hypervisor 1 at 10.19.3.4/26.
  • Hypervisor 2 will configure 172.16.0.2/16 IP for wg0 and will NAT traffic through its eth0 which is connected to the routed lab network.
  • Hypervisor 1 Priv Key in this example is: QP1LNvlaejugxgHj+DtDOX20DvBilOCn1RPRBQFakFs=
  • Hypervisor 1 Pub Key in this example is: 3TxNmlyWmNeL4EavtHi9dRfsqPHcEeiexKzMDF7n7nU=
  • Hypervisor 2 Priv Key in this example is: sIWrsVAvFm/VIHQhHRPaCzBOTWK/jmM6NkGYEwd/oXk=
  • Hypervisor 2 Pub Key in this example is: GmG2HkjvV8OebDy9ezHPG/+ODb6CMv51oSEKz4StdHQ=
  1. Configure wg0:

    HYPERVISOR_EXT_NIC=eth0
    cat <<EOF | sudo tee /etc/wireguard/wg0.conf
    [Interface]
    PrivateKey = sIWrsVAvFm/VIHQhHRPaCzBOTWK/jmM6NkGYEwd/oXk=
    Address = 172.16.0.2/16
    ListenPort = 51820
    PostUp   = iptables -A FORWARD -i %i -j ACCEPT; iptables -A FORWARD -o %i -j ACCEPT; iptables -t nat -A POSTROUTING -o ${HYPERVISOR_EXT_NIC} -j MASQUERADE
    PostDown = iptables -D FORWARD -i %i -j ACCEPT; iptables -D FORWARD -o %i -j ACCEPT; iptables -t nat -D POSTROUTING -o ${HYPERVISOR_EXT_NIC} -j MASQUERADE
    
    [Peer]
    PublicKey = 3TxNmlyWmNeL4EavtHi9dRfsqPHcEeiexKzMDF7n7nU=
    Endpoint = 10.19.3.4:51820
    AllowedIPs = 172.16.0.0/16
    PersistentKeepalive = 25
    EOF
    

Starting and verifying Wireguard Tunnel

In both hypervisors run the following command:

sudo systemctl enable wg-quick@wg0.service --now

If everything went well, Hypervisors should be able to reach each other over the 172.16.0.0/16 network.

  1. We can check wg0 state in Hypervisor 1:

    wg show wg0
    
    interface: wg0
      public key: 3TxNmlyWmNeL4EavtHi9dRfsqPHcEeiexKzMDF7n7nU=
      private key: (hidden)
      listening port: 51820
    
    peer: GmG2HkjvV8OebDy9ezHPG/+ODb6CMv51oSEKz4StdHQ=
      endpoint: 10.19.3.5:51820
      allowed ips: 172.16.0.0/16
      latest handshake: 1 minute, 15 seconds ago
      transfer: 1.56 MiB received, 105.65 MiB sent
    
  2. Same in Hypervisor 2:

    wg show wg0
    
    interface: wg0
      public key: GmG2HkjvV8OebDy9ezHPG/+ODb6CMv51oSEKz4StdHQ=
      private key: (hidden)
      listening port: 51820
    
    peer: 3TxNmlyWmNeL4EavtHi9dRfsqPHcEeiexKzMDF7n7nU=
      endpoint: 10.19.3.4:51820
      allowed ips: 172.16.0.0/16
      latest handshake: 1 minute, 21 seconds ago
      transfer: 105.76 MiB received, 1.82 MiB sent
    
  3. Hypervisor 1 pings Hypervisor 2:

    ping -I wg0 -c 1 172.16.0.2
    
    PING 172.16.0.2 (172.16.0.2) from 172.16.0.1 wg0: 56(84) bytes of data.
    64 bytes from 172.16.0.2: icmp_seq=1 ttl=64 time=0.523 ms
    
    --- 172.16.0.2 ping statistics ---
    1 packets transmitted, 1 received, 0% packet loss, time 0ms
    rtt min/avg/max/mdev = 0.523/0.523/0.523/0.000 ms
    

Configuring VXLAN (br0)

Now that we have the Wireguard tunnel up and running, next step is defining the VXLAN interface, plug it to a bridge interface and get the traffic encapsulated in the Wireguard tunnel.

In this example the VXLAN has a CIDR 172.16.30.0/24.

Configuring VXLAN in Hypervisor 1

  • Hypervisor 1 has its wg0 interface configured with the 172.16.0.1 IP and can reach the Hypervisor 2 at 172.16.0.2 through the Wireguard tunnel.
  • Hypervisor 1 will configure 172.16.30.1/16 IP for br0. to-node2 VXLAN interface will be configured with the 172.16.0.2 remote and plugged into the br0 interface.

Below commands rely on the nmcli tool, if your environment do not have it, you can refer to alternative commands to nmcli section.

  1. Create the bridge interface:

    Attention

    I’m creating the bridge with spanning tree protocol disabled, you may want to enable it depending on your lab needs.

    sudo nmcli con add ifname br0 type bridge con-name br0 stp no ipv4.addresses 172.16.30.1/24 ipv4.method manual
    
  2. Create the VXLAN interface:

    sudo nmcli con add ifname to-node2 type vxlan con-name to-node2 remote 172.16.0.2 id 1 destination-port 4789 ipv4.method disabled
    
  3. Add the VXLAN interface to the bridge:

    sudo nmcli con modify to-node2 master br0
    
  4. Bring up the bridge interface:

    Warning

    Be patient, the bridge may take a few seconds to be up.

    sudo nmcli con up br0
    

Configuring VXLAN in Hypervisor 2

  • Hypervisor 2 has its wg0 interface configured with the 172.16.0.2 IP and can reach the Hypervisor 1 at 172.16.0.1 through the Wireguard tunnel.
  • Hypervisor 2 will configure 172.16.30.2/16 IP for br0. to-node1 VXLAN interface will be configured with the 172.16.0.1 remote and plugged into the br0 interface.
  1. Create the bridge interface:

    Attention

    I’m creating the bridge with spanning tree protocol disabled, you may want to enable it depending on your lab needs.

    sudo nmcli con add ifname br0 type bridge con-name br0 stp no ipv4.addresses 172.16.30.2/24 ipv4.method manual
    
  2. Create the VXLAN interface:

    sudo nmcli con add ifname to-node1 type vxlan con-name to-node1 remote 172.16.0.1 id 1 destination-port 4789 ipv4.method disabled
    
  3. Add the VXLAN interface to the bridge:

    sudo nmcli con modify to-node1 master br0
    
  4. Bring up the bridge interface:

    Warning

    Be patient, the bridge may take a few seconds to be up.

    sudo nmcli con up br0
    

Verifying VXLAN configuration

If everything went well, Hypervisors should be able to reach each other over the 172.16.30.0/24 network.

  1. Hypervisor 1 pings Hypervisor 2:

    ping -I br0 -c 1 172.16.30.2
    
    PING 172.16.30.2 (172.16.30.2) from 172.16.30.1 br0: 56(84) bytes of data.
    64 bytes from 172.16.30.2: icmp_seq=1 ttl=64 time=1.38 ms
    
    --- 172.16.30.2 ping statistics ---
    1 packets transmitted, 1 received, 0% packet loss, time 0ms
    rtt min/avg/max/mdev = 1.381/1.381/1.381/0.000 ms
    

Configuring VMs on VXLAN network

For this part I’ll be using the kcli tool to interact with my KVM Hypervisors.

  1. If we check in our hypervisors we will have a new network available for our VMs, the br0 network of type bridged:

    kcli list networks
    
    Listing Networks...
    +-----------------+---------+---------------------+-------+-------------------+----------+
    | Network         |   Type  |         Cidr        |  Dhcp |       Domain      |   Mode   |
    +-----------------+---------+---------------------+-------+-------------------+----------+
    | eth0            | bridged |     10.19.3.0/26    |  N/A  |        N/A        |   N/A    |
    | br0             | bridged |    172.16.30.0/24   |  N/A  |        N/A        |   N/A    |
    | default         |  routed |   192.168.122.0/24  |  True |      default      |   nat    |
    +-----------------+---------+---------------------+-------+-------------------+----------+
    
  2. I configured a DHCP server in the VXLAN network with DNSMasq, the relevant configuration can be found below:

    Attention

    I’m running this DNSMasq in one of my hypervisors, node1 to be exact. Note that this node will act as router for the VXLAN network as well.

    dhcp-range=br0,172.16.30.50,172.16.30.200,255.255.255.0,24h
    dhcp-option=br0,option:dns-server,172.16.30.1
    dhcp-option=br0,option:ntp-server,172.16.30.1
    dhcp-option=br0,option:router,172.16.30.1
    
  3. We can plug a new VM into this network, I’ll run the command below in both hypervisors:

    kcli download image centos9stream
    kcli create vm -i centos9stream -P nets=[br0] -P name=vm-hypervisorX
    
  4. If I list the VMs in both hypervisors this is what I see:

    1. Hypervisor 1:

      kcli list vm
      
      +------------------+--------+---------------+
      |       Name       | Status |       Ip      |
      +------------------+--------+---------------+
      |  vm-hypervisor1  |   up   |  172.16.30.59 |
      +------------------+--------+---------------+
      
    2. Hypervisor 2:

      kcli list vm
      
      +------------------+--------+----------------+
      |       Name       | Status |       Ip       |
      +------------------+--------+----------------+
      |  vm-hypervisor2  |   up   |  172.16.30.143 |
      +------------------+--------+----------------+
      
  5. As you can see both VMs got their IP via DHCP, we could have used static addressing as well. We can access one of the VMs and ping the other one.

    kcli ssh vm-hypervisor1
    
    [cloud-user@vm-hypervisor1 ~]$ ping -c1 172.16.30.143
    PING 172.16.30.143 (172.16.30.143) 56(84) bytes of data.
    64 bytes from 172.16.30.143: icmp_seq=1 ttl=64 time=1.94 ms
    
    --- 172.16.30.143 ping statistics ---
    1 packets transmitted, 1 received, 0% packet loss, time 0ms
    rtt min/avg/max/mdev = 1.935/1.935/1.935/0.000 ms
    
  6. We were able to reach the other VM, if we try now to access internet or any other network not directly connected to our hypervisor node doing the routing this is what happens:

    [cloud-user@vm-hypervisor1 ~]$ ping -c1 1.1.1.1
    
    PING 1.1.1.1 (1.1.1.1) 56(84) bytes of data.
    From 172.16.30.1 icmp_seq=1 Time to live exceeded
    
    --- 1.1.1.1 ping statistics ---
    1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms
    
  7. If we want this VXLAN to access other networks we need to NAT the traffic, we can do that by running the following command in the hypervisor node doing the routing. Hypervisor 1 in my case:

    sudo iptables -t nat -A POSTROUTING -s 172.16.30.0/24 -j MASQUERADE
    
  8. If we try the ping again:

    [cloud-user@vm-hypervisor1 ~]$ ping -c1 1.1.1.1
    
    PING 1.1.1.1 (1.1.1.1) 56(84) bytes of data.
    64 bytes from 1.1.1.1: icmp_seq=1 ttl=41 time=27.2 ms
    
    --- 1.1.1.1 ping statistics ---
    1 packets transmitted, 1 received, 0% packet loss, time 0ms
    rtt min/avg/max/mdev = 27.175/27.175/27.175/0.000 ms
    

Cleaning up the environment

In case we want to get rid of this setup we can run the following commands.

  1. Make sure all VMs using the VXLAN network are stopped and removed from the network.

  2. In Hypervisor 1 run:

    sudo nmcli con del br0
    sudo nmcli con del to-node2
    sudo systemctl stop wg-quick@wg0.service
    sudo systemctl disable wg-quick@wg0.service
    sudo iptables -t nat -D POSTROUTING -s 172.16.30.0/24 -j MASQUERADE
    
  3. In Hypervisor 2 run:

    sudo nmcli con del br0
    sudo nmcli con del to-node1
    sudo systemctl stop wg-quick@wg0.service
    sudo systemctl disable wg-quick@wg0.service
    

Alternative commands to nmcli

In case you don’t have nmcli in your environment you can use the following IP commands instead:

  1. Hypervisor 1

    sudo ip link add name br0 type bridge stp_state 0
    sudo ip address add dev br0 172.16.30.1/24
    sudo ip link add to-node2 type vxlan remote 172.16.0.2 id 1 dstport 4789
    sudo ip link set up dev br0
    sudo ip link set up to-node2
    sudo ip link set to-node2 master br0
    
  2. Hypervisor 2

    sudo ip link add name br0 type bridge stp_state 0
    sudo ip address add dev br0 172.16.30.2/24
    sudo ip link add to-node1 type vxlan remote 172.16.0.1 id 1 dstport 4789
    sudo ip link set up dev br0
    sudo ip link set up to-node1
    sudo ip link set to-node1 master br0
    
  3. Cleanup

    sudo ip link del br0
    sudo ip link del to-node1
    sudo ip link del to-node2
    

References

In order to achieve the work described here I used several resources from different places. I want to thank these wonderful people that created such awesome content I could make this work.