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Environment

I rent a dedicated server from OVH and installed Proxmox 3.3 (which is based on Debian 6 Wheezy) in order to create and manage multiple Virtual Machines on it.

Each VM is configured to use a public IP (given by OVH), configured as IP aliases on the host - one virtual network device for each IP : eth0:0, eth0:1 and so on - as recommended by OVH's guide :http://help.ovh.co.uk/IpAlias#link7

And they are bridged to the different guests, through the vmbr0 bridge and with use of the virtual MAC addresses created for each IP - as recommended by these OVH guides : http://help.ovh.com/Proxmox and /BridgeClient [sorry cannot post more than 2 links]

The VMs are CentOS 7 installations, and the configuration works perfectly for access to the VMs and communication between the Virtual Machines, using the public IPs.

I also have SSH access to the host machine and the guests.

Use case

I am trying to setup backups of the different VMs using BackupPC installed on the host, for easier access to the physical machine's storage and the "backup storage" offered by OVH.

BackupPC has been installed on the host and configured to use rsync, and the goal is to connect to the VMs through ssh.

Issue

I cannot connect to the VMs from the host using SSH. This is because the public IPs I am trying to access the VMs through are in fact (from a host's perspective) assigned to the host itself as IP aliases.

This means, that when I connect to a VM's IP through SSH, I actually connect in loop to the host itself.

Question

How can I resolve this issue to get my backups working ?

1. Of course I could create one more VM and handle the backups from there, but this isn't an optimal solution since I will have to dedicate ressources for backups, and I want to avoid storing the backups in a VM.

2. I thought of adding a second network device to the VMs to handle 'local' communications but can't figure out how to do so. Since my "public-IP-configuration-bridge" already uses my host's eth0 device, I suppose I must create another bridge for this use case. But shall I bridge it to my host's eth0 without causing trouble with the "public IP configuration" ?

NB: If my reasoning behind my backup concept is wrong, please let me know. I welcome any other solution offering incremental and full backups of my different VMs.

Thanks a lot for you help !

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You are not supposed to configure the failover IP addresses on the host in this scenario. They must be configured only in the guests.

Better yet, use your IPv6 addresses to access your VMs from the host. This is going to be more reliable anyway.

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  • Thanks a lot. I didn't realise I could just configure the VMs directly with the virtual MACs without adding it as failover IP on the host. IPv6 didn't work though, but that most probably comes from my host's IPv6's configuration.
    – Danyright
    Mar 20, 2015 at 13:33
  • @Danyright That's probably an artifact of OVH's network. They don't do SLAAC so you have to manually configure IPv6 addresses and routes on all your VMs.
    – Michael Hampton
    Mar 20, 2015 at 13:34
  • Yes, most probably indeed. Anyway, I removed all the failover IPs so the public IP addresses reach directly to the VMs. Thanks for your help :-)
    – Danyright
    Mar 20, 2015 at 14:14

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