I have 2 public IP addresses given to me by my ISP (a.a.a.8/30 with a.a.a.9 and a.a.a.10 usable IPs). These IPs are routed by the ISP via my DSL connection (ppp0 - b.b.b.b). For example, if I create a tap0 device and assign a.a.a.1 to it, I can ping/access ports on a.a.a.1 from an external host without any additional routes/iptables configuration.

I'd like to create two VMs with libvirt and assign those public IP addresses to the VMs. What would be the right network configuration for the VMs? I was told to create a bridge with ppp0 and VM interfaces but there's no way to bridge ppp0?

Hello and welcome to LQ.

VM's usually have a few ways to connect to either the host, nic card or other vm's. What I think you are suggesting is a public bridge where the ip address of the host's nic is on a vm. One way is to follow this very confusing web page from KVM. https://www.linux-kvm.org/page/Networking

If you tell us your distro there may be more specific steps.

Thank you for your reply. The host distribution is ubuntu 16.04. eth0 on the host is the physical dsl interface. I've tried different KVM network configurations (forward=route, bridge, etc) but there's no way to add ppp0 to the bridge? "can't add ppp0 to bridge br0: Invalid argument". When you say "the ip address of the host's nic is on a vm" which host nic are you referring to? The ppp0 interface? If you could provide an example that would be great.

This is what I have on the host:

eth0 --> ppp0 (assigned b.b.b.b)

The public IP addresses (a.a.a.9 and a.a.a.10) are routed via ppp0 to my host. I can create tap interfaces and assign these public IPs on the host. I'm just looking for a way to assign these IPs to VMs running on the host instead and still route them via ppp0 on the host.

My guess is a gsm doesn't support bridging. Should support nat.

Wonder if there is any way to iptable it?

Was thinking the same thing. According to my ISP, it's a common scenario with public IPs routed via DSL.

Exactly what type of network device are you trying to bridge to?

ppp0 is ppp over ethernet (eth0)
tap[01] are standard tap interfaces

My understanding was to bridge ppp0, tap0 and tap1