setting bridge for VMs IP assignment by router's DHCP server
I am running a libvirt hostmachine (Fedora 40) which has 192.168.1.6 IP address, assigned by router's DHCP server. I want the libvirt VMs IPs to be assigned by router's DHCP server, so I tried to setup a bridge via # virsh net-define foo.xml and trying the following files as xml file, but they all failed to achieve the task. Here I list the two XML variants I tried to use 1) <network> <name>bridge-no-nat</name> <bridge name='virbr1_no-nat' stp='on' delay='0'/> <forward mode='open'/> </network> RETURNS: open forwarding requested, but no IP address provided for network 'bridge-no-nat' 2) I created in nmtui the bridge virbr1_no_nat then I used following XML for virsh net-define <network> <name>br1_no_nat</name> <forward mode='bridge'/> <bridge name='virbr1_no_nat'/> <virtualport type='openvswitch'/> <portgroup name='default'/> </network> then I configure the VM network to use but when I start the VM I get error: internal error: Unable to add port vnet1 to OVS bridge virbr1_no_nat: <null> Do you know how I can solve this? Thank you
On Fri, Aug 2, 2024 at 11:44 AM Germano Massullo <germano.massullo@gmail.com> wrote:
I am running a libvirt hostmachine (Fedora 40) which has 192.168.1.6 IP address, assigned by router's DHCP server. I want the libvirt VMs IPs to be assigned by router's DHCP server, so I tried to setup a bridge via # virsh net-define foo.xml and trying the following files as xml file, but they all failed to achieve the task. Here I list the two XML variants I tried to use
1) <network> <name>bridge-no-nat</name> <bridge name='virbr1_no-nat' stp='on' delay='0'/> <forward mode='open'/> </network> RETURNS: open forwarding requested, but no IP address provided for network 'bridge-no-nat'
2) I created in nmtui the bridge virbr1_no_nat then I used following XML for virsh net-define <network> <name>br1_no_nat</name> <forward mode='bridge'/> <bridge name='virbr1_no_nat'/> <virtualport type='openvswitch'/> <portgroup name='default'/> </network> then I configure the VM network to use but when I start the VM I get error: internal error: Unable to add port vnet1 to OVS bridge virbr1_no_nat: <null>
Do you know how I can solve this?
Here are the rough steps I perform to bridge VMs to my home network so the VMs receive a DHCP address from my DHCP server. It also allows you to SSH into your VMs like any other host on your network. The steps are for a modern install on Fedora with Systemd and Network Manager (and not systemd-network). 1. Ignore anything from `sudo -E virsh net-edit default`. You don't use the default NAT. You use virbr0 instead. 2. Install nmtui. 3. `sudo nmtui`, then 'Edit a connection." Select bridge virbr0. * Under slaves, add Ethernet Connection 1. Check Automatically Connect and Available to All Users. * Under IPv4, select Automatic. Remove addresses and friends. * Under IPv6, select Disabled. I don't run IPv6 internally. 4. Reboot the machine. 5. After reboot and login, you should see ethernet UP, vbridge UP, and the host has a DHCP address via the bridge. $ ip link show 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: enp0s20f0u3c2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel mast er virbr0 state UP mode DEFAULT group default qlen 1000 link/ether 20:7b:d2:8c:55:d4 brd ff:ff:ff:ff:ff:ff 3: wlo1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN m ode DORMANT group default qlen 1000 link/ether 9a:28:0e:bd:f4:ee brd ff:ff:ff:ff:ff:ff permaddr 00:41:0e:67:0e:7 b altname wlp87s0 4: virbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mod e DEFAULT group default qlen 1000 link/ether 20:7b:d2:8c:55:d4 brd ff:ff:ff:ff:ff:ff And: $ ip addr 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group defaul t 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 2: enp0s20f0u3c2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel mast er virbr0 state UP group default qlen 1000 link/ether 20:7b:d2:8c:55:d4 brd ff:ff:ff:ff:ff:ff 3: wlo1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN g roup default qlen 1000 link/ether 9e:8e:8a:6f:35:5e brd ff:ff:ff:ff:ff:ff permaddr 00:41:0e:67:0e:7 b altname wlp87s0 4: virbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP gro up default qlen 1000 link/ether 20:7b:d2:8c:55:d4 brd ff:ff:ff:ff:ff:ff inet 172.16.2.15/12 brd 172.31.255.255 scope global dynamic noprefixroute vi rbr0 valid_lft 6293sec preferred_lft 6293sec 6. In Virtual Machine Manager, select a VM, select NIC, choose Bridge device... and select virbr0. 7. Start the VM. The VM will get an IP address from your local DHCP server. You might find these commands useful if you don't (yet) have a bridge: <https://wiki.archlinux.org/title/Network_bridge> and maybe this discussion: <https://bbs.archlinux.org/viewtopic.php?id=253232>. Jeff
On 8/2/24 11:44 AM, Germano Massullo wrote:
I am running a libvirt hostmachine (Fedora 40) which has 192.168.1.6 IP address, assigned by router's DHCP server. I want the libvirt VMs IPs to be assigned by router's DHCP server, so I tried to setup a bridge via # virsh net-define foo.xml and trying the following files as xml file, but they all failed to achieve the task. Here I list the two XML variants I tried to use
1) <network> <name>bridge-no-nat</name> <bridge name='virbr1_no-nat' stp='on' delay='0'/> <forward mode='open'/> </network> RETURNS: open forwarding requested, but no IP address provided for network 'bridge-no-nat'
This method doesn't provide at all what you want - it will give you a bridge device that isn't directly connected to any physical interface, so any traffic between the guests connected to the bridge and the physical network must be *routed* vi the host's IP stack, i.e. it is on a different segment from the physical network and so no broadcast traffic will pass between the bridge and the physical network. This means that the bridge device must have a separate subnet, while you've given it no network at all. Basically the only thing such a network would be useful for would be to connect multiple guests that have statically configured IP addresses (on the same subnet) but isolate them from the outside network *and* the host itself (the host could still monitor traffic on the bridge, but none of that traffic would be sent up to the host IP stack for routing or forwarding - that would only be done if the bridge device was given an IP address (on the same subnet as the guests).
2) I created in nmtui the bridge virbr1_no_nat then I used following XML for virsh net-define <network> <name>br1_no_nat</name> <forward mode='bridge'/> <bridge name='virbr1_no_nat'/> <virtualport type='openvswitch'/>
Since you've used nmtui to create the bridge device, I'm guessing that it must be a standard Linux host bridge, and *not* an openvswitch bridge (OVS has its own commandline tools to create an OVS bridge. That being the case, you do *not* want the "<virtualport type='openvswitch'/>" element in your network config. Aside from that, when you create the bridge device, you need to make sure that you host ethernet is attached to the bridge, and that any IP configuration that was previously on the ethernet device is now on the bridge. (you'll be able to verify this by running "ip link show dev $name" for the ethernet and bridge devices, the ethernet device should say "master virbr1_no_nat" and have no IP addresses associated with it, and the bridge device should have the IP address that was previously (before you created the bridge) assigned to the ethernet. Once you've done both of these things, do a "virsh net-destroy br1_no_nat; virsh net-start br1_no_nat" and you should be able to start up your guest and have it connected directly to the physical network. (BTW, I would call the bridge device some shorter name BTW, most people just call it "br0" - not only is it easier to type, but the maximum length of a network device name is IFNAMSIZ-1 == 15, and you could easily run into some program that used IFNAMSIZ for the length of a buffer used to store some variation of the if name that was a few characters longer, and your name is already just 2 shy of the limit!)
<portgroup name='default'/> </network> then I configure the VM network to use but when I start the VM I get error: internal error: Unable to add port vnet1 to OVS bridge virbr1_no_nat: <null>
Do you know how I can solve this? Thank you
participants (3)
-
Germano Massullo -
Jeffrey Walton -
Laine Stump