Steve Madsen asked:
I am running a Debian Linux server on Lenny. Within it, I am running another Lenny instance using KVM. Both servers are externally available, with public IPs, as well as a second interface with private IPs for the LAN. Everything works fine, except the VM sees all network traffic as originating from the host server. I suspect this might have something to do with the iptables-based firewall I’m running on the host.
What I’d like to figure out is: how to I properly configure the host’s networking such that all of these requirements are met?
- Both host and VMs have 2 network interfaces (public and private).
- Both host and VMs can be independently firewalled.
- Ideally, VM traffic does not have to traverse the host firewall.
- VMs see real remote IP addresses, not the host’s.
Currently, the host’s network interfaces are configured as bridges. eth0 and eth1 do not have IP addresses assigned to them, but br0 and br1 do.
/etc/network/interfaces on the host:
# The primary network interface auto br1 iface br1 inet static address 22.214.171.124 netmask 255.255.255.248 network 126.96.36.199 broadcast 188.8.131.52 gateway 184.108.40.206 bridge_ports eth1 bridge_stp off auto br1:0 iface br1:0 inet static address 220.127.116.11 netmask 255.255.255.248 network 18.104.22.168 broadcast 22.214.171.124 # Internal network auto br0 iface br0 inet static address 192.168.1.1 netmask 255.255.255.0 network 192.168.1.0 broadcast 192.168.1.255 bridge_ports eth0 bridge_stp off
This is the libvirt/qemu configuration file for the VM:
<domain type='kvm'> <name>apps</name> <uuid>636b6620-0949-bc88-3197-37153b88772e</uuid> <memory>393216</memory> <currentMemory>393216</currentMemory> <vcpu>1</vcpu> <os> <type arch='i686' machine='pc'>hvm</type> <boot dev='hd'/> </os> <features> <acpi/> <apic/> <pae/> </features> <clock offset='utc'/> <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>restart</on_crash> <devices> <emulator>/usr/bin/kvm</emulator> <disk type='file' device='cdrom'> <target dev='hdc' bus='ide'/> <readonly/> </disk> <disk type='file' device='disk'> <source file='/raid/kvm-images/apps.qcow2'/> <target dev='vda' bus='virtio'/> </disk> <interface type='bridge'> <mac address='54:52:00:27:5e:02'/> <source bridge='br0'/> <model type='virtio'/> </interface> <interface type='bridge'> <mac address='54:52:00:40:cc:7f'/> <source bridge='br1'/> <model type='virtio'/> </interface> <serial type='pty'> <target port='0'/> </serial> <console type='pty'> <target port='0'/> </console> <input type='mouse' bus='ps2'/> <graphics type='vnc' port='-1' autoport='yes' keymap='en-us'/> </devices> </domain>
Along with the rest of my firewall rules, the firewalling script includes this command to pass packets destined for a KVM guest:
# Allow bridged packets to pass (for KVM guests). iptables -A FORWARD -m physdev --physdev-is-bridged -j ACCEPT
(Not applicable to this question, but a side-effect of my bridging configuration appears to be that I can’t ever shut down cleanly. The kernel eventually tells me “unregister_netdevice: waiting for br1 to become free” and I have to hard reset the system. Maybe a sign I’ve done something dumb?)
You bridged your VMs to the wrong interface. They should be bridged to the network interface that connects to the outside world (
br1 in your case).
Keep in mind that each VM should also have its IP address set in the guest, not on the host.
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