OVH and Proxmox Network Setup

Question

I have the following Debian Network Konfiguration

Main IP: 1.2.3.4 Subnet 1: 8.1.2.248/29 Subnet 2: 15.1.2.0/29

Main Host Network Configuration:

    # network interface settings; autogenerated
    # Please do NOT modify this file directly, unless you know what
    # you're doing.
    #
    # If you want to manage part of the network configuration manually,
    # please utilize the 'source' or 'source-directory' directives to do
    # so.
    # PVE will preserve these directives, but will NOT its network
    # configuration from sourced files, so do not attempt to move any of
    # the PVE managed interfaces into external files!

    auto lo
    iface lo inet loopback

    iface eth0 inet manual

    iface eth1 inet manual

    auto vmbr1
    iface vmbr1 inet manual
            bridge_ports dummy0
            bridge_stp off
            bridge_fd 0
            post-up /etc/pve/kvm-networking.sh

    auto vmbr0
    iface vmbr0 inet static
            address  1.2.3.4
            netmask  255.255.255.0
            gateway  1.2.0.254
            broadcast  1.2.0.255
            bridge_ports eth0
            bridge_stp off
            bridge_fd 0
            network 1.2.0.0

I added the first SubNet without any issues. It works and every host is accessible (they have all an equal Setup)

    # This file describes the network interfaces available on your system
    # and how to activate them. For more information, see interfaces(5).

    # The loopback network interface
    auto lo
    iface lo inet loopback

    # The primary network interface
    allow-hotplug eth0
    iface eth0 inet static
            address 8.1.2.248
            netmask 255.255.255.0
            network 8.1.2.0
            broadcast 8.1.2.255
            gateway 8.1.2.254
            # dns-* options are implemented by the resolvconf package, if installed
            dns-nameservers 8.8.8.8
            dns-search host.name

I ordered an additional ip block today to add some additional virtual machines.

    # This file describes the network interfaces available on your system
    # and how to activate them. For more information, see interfaces(5).

    source /etc/network/interfaces.d/*

    # The loopback network interface
    auto lo
    iface lo inet loopback

    # The primary network interface
    allow-hotplug eth0
    iface eth0 inet static
            address 15.1.2.0
            netmask 255.255.255.248
            network 15.1.2.0
            broadcast 15.1.2.7
            gateway 15.1.2.6
            # dns-* options are implemented by the resolvconf package, if installed
            dns-nameservers 8.8.8.8
            dns-search host.name

The first KVM can reach the Ips on the first Subnet without any issues. It can also ping the other Ips on the second subnet. But the others can't.

If I ping the first host I get the message ping 15.1.2.0 Do you want to ping broadcast? Then -b

did I miss something during configuration?

The other vms can reach any host except those on the same subnet.

Please help me, I'm missing something here :)

Answer 1

You're using your subnets wrong. When you have subnet, you cannot use first and last IP address (first one is network address for routing purpose, last one is broadcast IP).

Ie. your subnet 8.1.2.248/29 contains addresses 8.1.2.248 (network one, do not use), 8.1.2.249 - 8.1.2.254 (those IP address you can use for your VM if OVH didn't tell you something) and 8.1.2.255 (broadcast IP for your subnet, do not use). Same rule is for your subnet 15.1.2.0/29 - 15.1.2.0 is network (do not use), 15.1.2.1-15.1.2.6 are usable for VM and 15.1.2.7 is broadcast (do not use).

First subnet works because you have error in configuration of your netmask (you have inserted 255.255.255.0 which is /24, not /29! Or you have your vlan with this subnet shared with another customer of OVH).