[libvirt-users] Confused setting up a "Virtual Server Hosting" config

[Laine Stump]

On 10/23/19 12:43 AM, Paul O'Rorke wrote:
> Hi list,
> 
> Can anyone advise me on the correct/best set up for Virtual Server Hosting?
> 
> I have a guest in my server room wish to migrate to dedicated server I 
> rented in an offsite in a data centre.  I rented a box with one NIC and 
> one public IP.  I installed KVM on it and a guest. (both Ubuntu 18.04 
> LTS server edition).  I am struggling to get the networking right.
> 
> Essentially I want the "Virtual Server Hosting" config mentioned here:
> https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html-single/virtualization_administration_guide/index#sub-sect-routed-mode 
> <https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html-single/virtualization_administration_guide/index#sect-attch-nic-physdev>
> 
> I have not had any luck setting that up.  It is listed in the "Routed" 
> section but the graphic says the virtual switch should be in bridged mode.
> 
> I also tried using macvtap, and since I have only one guest was 
> expecting to be able to just use the host IP 

No, you will need one IP for the host, and one IP for the guest in 
either bridged mode or for macvtap.

> but it looks like the data 
> centre have restricted packets to the MAC address of the host NIC.

Yes, there is that restriction too. Usually hosting providers will lock 
down the MAC addresses they allow through ports, in order to prevent 
hostile clients from doing MAC spoofing to capture other clients' traffice.

   When
> set up I can ping the public IP (it is both eh host and the guest?)

No. An IP address refers to one entity. It can be the host or the guest, 
but not both.

but
> not their gateway.  Should a macvtap not be presenting the MAC address 
> of the host NIC to the router and thus allowing packets from the guest?

No, that is not what macvtap does. It creates a virtual NIC (macvtap 
device) that is connected directly to the physical NIC, and traffic from 
that device is injected directly into the output queue of the physical 
device, MAC address and all.

> 
> I clearly have a lack of understanding of how this is working and how it 
> is meant to work.  When I tried the same thing on mt hardware/network I 
> can create myltiple guests that all use the macvtap interface and I have 
> no problems getting connectivity to the outside world.

Because on your own network you have no MAC address locking on your 
switch port, and have multiple IP addresses available (one for each 
guest) from the local DHCP server.

> 
> Before I approach the data centre about this I want to be sure I 
> understand what I am doing.   I ultimately want to host a mail server 
> and several different web servers as guests all behind this one host.  I 
> would alias their public IPs to the host NIC and use IPtables to route 
> traffic based on destination IP.

The only reason you would want iptables to be involved is if you were 
limited to only 1 IP address for the host + all the guests. In that case 
you could use *port* forwarding to cause incoming traffic to the host on 
particular TCP ports to be forwarded to different guests:

https://wiki.libvirt.org/page/Networking#Forwarding_Incoming_Connections


> 
> Does that make sense? Can anyone suggest the right way to achieve this?

No, not really :-)

If you can only get a single IP address, then you'll need to look at the 
above link. If you can get the hosting provider to sell you extra IP 
addresses / MAC addresses (usually extra IPs cost money but MAC 
addresses are free, they just want to know what they are - you will need 
one *of each* for each guest), then you should put a bridge on your 
host's ethernet, and connect all the guests to that bridge, configuring 
each with its unique IP address / MAC address / default route info given 
to you by the hosting provider. You can use this as a reference to 
configure the host and guests:

https://wiki.libvirt.org/page/Networking#Debian.2FUbuntu_Bridging

(you could also avoid setting up the bridge and just use macvtap bridge 
mode as you say you've done on your own network. The only limitation of 
that is that it doesn't permit direct communication between the host and 
the guests. If that limitation is okay with you, then that's fine.)