I recently upgraded from ubuntu 18.04 to 20.04 and now I'm unable to get KVM bridges to work.
For testing purposes I'm using a bone stock 20.04lts install with only the required KVM, bridge utils etc packages installed. No firewall configured or anything.
I can create the bridge and the host has network access etc. but if I assign the bridge to a VM it does not get a IP assigned from the DHCP server. I tried setting static IPs but the problem doesn't change, no internet access.
I seems that something is going wrong with the bridge/routing part but I have no clue as to what.
Host settings:
ip link
ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master br0 state UP mode DEFAULT group default qlen 1000
link/ether 1c:69:7a:a9:b3:f0 brd ff:ff:ff:ff:ff:ff
3: wlo1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 14:85:7f:46:94:ed brd ff:ff:ff:ff:ff:ff
4: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
link/ether 1c:69:7a:a9:b3:f0 brd ff:ff:ff:ff:ff:ff
5: vnet0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel master br0 state UNKNOWN mode DEFAULT group default qlen 1000
link/ether fe:54:00:77:53:d9 brd ff:ff:ff:ff:ff:ff
ip addr show
ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master br0 state UP group default qlen 1000
link/ether 1c:69:7a:a9:b3:f0 brd ff:ff:ff:ff:ff:ff
3: wlo1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
link/ether 14:85:7f:46:94:ed brd ff:ff:ff:ff:ff:ff
4: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 1c:69:7a:a9:b3:f0 brd ff:ff:ff:ff:ff:ff
inet 192.168.0.59/24 brd 192.168.0.255 scope global dynamic br0
valid_lft 6655sec preferred_lft 6655sec
inet6 fe80::5cf0:6eff:feec:6394/64 scope link
valid_lft forever preferred_lft forever
5: vnet0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel master br0 state UNKNOWN group default qlen 1000
link/ether fe:54:00:77:53:d9 brd ff:ff:ff:ff:ff:ff
inet6 fe80::fc54:ff:fe77:53d9/64 scope link
valid_lft forever preferred_lft forever
brctl
brctl show
bridge name bridge id STP enabled interfaces
br0 8000.1c697aa9b3f0 no enp1s0
vnet0
netplan
network:
ethernets:
enp1s0:
dhcp4: yes
dhcp6: no
version: 2
bridges:
br0:
interfaces: [enp1s0]
dhcp4: yes
dhcp6: no
parameters:
stp: false
forward-delay: 0
iptables
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
virsh
virsh net-list --all
Name State Autostart Persistent
---------------------------------------------
host-bridge active yes yes
virsh net-edit host-bridge
<network>
<name>host-bridge</name>
<uuid>5c83bc93-624f-47fe-908e-be22cee755ea</uuid>
<forward mode='bridge'/>
<bridge name='br0'/>
</network>
ip v4 forwarding
sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 1
route
route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.0.210 0.0.0.0 UG 100 0 0 br0
192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 br0
192.168.0.210 0.0.0.0 255.255.255.255 UH 100 0 0 br0
The VM is just a basic ubuntu 18.04 install with networking set to DHCP but no IP is obtained. If I set a static IP I can ping the host ip but not the gateway or any other ip on the same subnet which again leads me to believe there is something wrong with the bridge.
