KVM bridge only assiging ipv6 adresses on VM

Question

I use KVM in bridged network mode so I can have a VM that has an IP from the host LAN network. My host (Ubuntu 18.04 server) networking is configured as below :

network:
  ethernets:
    enp0s31f6:
      dhcp4: true
    enp5s0:
      dhcp4: true
  bridges:
    br0:
      interfaces: [enp0s31f6]
      macaddress: EX:DX:5X:X0:X0:XO
      dhcp4: yes
  version: 2

I have created a bridged connection using virtsh for my VM.

<network>
  <name>host-bridge</name>
  <uuid>0fe3b67b-5155-4581-92f2-2510d864ed65</uuid>
  <forward mode='bridge'/>
  <bridge name='br0'/>
</network>

However, when i do an ifconfig on the VM, I only see an ipv6 address assigned.

enp1s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet6 2a01:cb00:c3c:e500:9949:de93:1df3:c13c  prefixlen 64  scopeid 0x0<global>
        inet6 2a01:cb00:c3c:e500:ae16:cee:c3a6:c493  prefixlen 64  scopeid 0x0<global>
        inet6 fe80::ff22:79d5:c7fe:884f  prefixlen 64  scopeid 0x20<link>
        ether XX:XX:XX:XX:XX:XX  txqueuelen 1000  (Ethernet)
        RX packets 5990  bytes 560495 (560.4 KB)
        RX errors 0  dropped 2778  overruns 0  frame 0
        TX packets 702  bytes 89008 (89.0 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

How can i force KVM or change the host/guest network to only assign IPV4?

I thought about turning ipV6 on the guest grub, but this seems to cause issues on VMs. My server is a remote one,and I don't want to lose ssh connectivity.

score 0 · Accepted Answer · answered Jun 21 '22 at 15:42

I had to explicitly disable dhcp4 and dhcp4 in the enp0s31f6 interface and restart both the host and the VM. This is the final netplan config i used:

network:
  ethernets:
    enp0s31f6:
      dhcp4: false
      dhcp6: false
    enp5s0:
      dhcp4: false
      dhcp6: false
  bridges:
    br0:
      interfaces: [enp0s31f6]
      macaddress: XX:XX:XX:XX:XX:X
      dhcp4: yes
      dhcp6: true
  version: 2

Everything worked fine after that. It is also important to note that I had to explicitly set the mac address of the bridge on the config to avoid the router not updating the bridge as a seprate device.

KVM bridge only assiging ipv6 adresses on VM

1 Answers1