Routed network can't reach outside network

[Daniel P. Berrange]

On Sun, Jul 19, 2020 at 11:54:06AM +0100, Rui Correia wrote:
> Greetings folks.
> I've setup libvirtd on my manjaro linux laptop.
> Got a couple of VM's running (Win10 and Debian10) through NAT without any
> issues.
> 
> This is what the current network diagram looks like and it works fine:
> 
>                            +-----------------------------------+
>                            |           +---------------------+ |
>                            |           |     +----------+    | |
>                            |           |     |Win 10 VM |    | |
>                            |           |     |10.1.1.10 |    | |
>                            |           |     +----------+    | |
>                            | Laptop    |                     | |
>                            | Manjaro   |     +-------------+ | |
>                            | 10.0.0.10 |     |Debian 10 VM | | |
>                  +-------->+           |     |10.1.1.11    | | |
>                  |         |           |     +-------------+ | |
>                  |         |           |NAT                  | |
>                  |         |           |10.1.1.0/24          | |
>                  |         |           +---------------------+ |
> +------------+   |         +-----------------------------------+
> |router      |   |
> |switch      +---+
> |10.0.0.0/24 |   |         +---------+
> +------------+   |         |Desktop  |
>                  +-------->+Manjaro  |
>                            |10.0.0.11|
>                            +---------+
> 
> But now I need the debian machine to be accessible from another host on the
> lan 10.0.0.0/24 which of course is outside the host.
> That network diagram would look like this:
> 
>                            +-----------------------------------------+
>                            |              +------------------+       |
>                            |              |     +----------+ |       |
>                            |              |     |Win 10 VM | |       |
>                            |              |     |10.1.1.10 | |       |
>                            |              | NAT +----------+ |       |
>                            |              | 10.1.1.0/24      |       |
>                            |              +------------------+       |
>                            |  Laptop                                 |
>                  +-------->+  Manjaro     +------------------------+ |
>                  |         |  10.0.0.10   |        +-------------+ | |
>                  |         |              |        |Debian 10 VM | | |
>                  |         |              |        |10.2.2.10    | | |
>                  |         |              | Routed +-------------+ | |
> +------------+   |         |              | 10.2.2.0/24            | |
> |router      |   |         |              +------------------------+ |
> |switch      +---+         +-----------------------------------------+
> |10.0.0.0/24 |   |
> +------------+   |
>                  |
>                  |         +---------+
>                  |         |Desktop  |
>                  +-------->+Manjaro  |
>                            |10.0.0.11|
>                            +---------+
> 
> 
> So, I've setup a 'routed network' for the Debian 10 VM but it's not working
> as I would expect.
> The host can ping the Debian VM and the Debian VM can ping the host but the
> Debian VM cannot ping the router 10.0.0.1 or any ip address on the internet.
> I've been using Virtual Machine Manager to set everything up.
> And this is how the routed network is configured
> <network connections="1">
>   <name>routed</name>
>   <uuid>970a25f7-29b6-4a6b-b890-f593eae4fc15</uuid>
>   <forward dev="wlo1" mode="route">
>     <interface dev="wlo1"/>
>   </forward>
>   <bridge name="virbr2" stp="on" delay="0"/>
>   <mac address="52:54:00:bf:35:42"/>
>   <domain name="routed"/>
>   <ip address="10.2.2.1" netmask="255.255.255.0">
>     <dhcp>
>       <range start="10.2.2.2" end="10.2.2.254"/>
>     </dhcp>
>   </ip>
> </network>
> 
> Any idea on what i might be doing wrong?

Is net.ipv4.ip_forward  set to 0 ? 


Also, for this to work fully, your router switch needs to know where to 
send traffic for the 10.2.2.1/24 network. IOW, you need to configure
static routes on your router switch for 10.2.2.1

I've covered a similar setup to yours here:

https://www.berrange.com/posts/2009/12/13/routed-subnets-without-nat-for-libvirt-managed-virtual-machines-in-fedora/



Regards,
Daniel
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