[libvirt-users] set a different default gateway in an isolated network

[Laine Stump]

On 02/06/2016 04:16 PM, pichon wrote:
> Hello,
>
> I would like to set a specify default gateway for my VMs. However I’m not succeeding
>
> Here after is the isolated lan, where I added the statement   <route address='10.0.0.0' prefix='8' gateway='10.10.0.7’/> where my aim is to route to the 10.10.0.7
>
> What should I do , to make it works ?

You've misunderstood the purpose of the <route> element in a network. 
That element is used to setup a route that will be added *to the host* 
when the network is started; guest routing tables are not affected (that 
would require a dhcp option, which you allude to in your later message 
on the same subject, and which isn't currently supported by libvirt).

If you look on the host after starting this network, you'll find that it 
has a route that looks like this:

Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.0.0.0        10.10.0.7       255.0.0.0       ?     ?      ?      ?   virbr3

This feature was added with the idea in mind of automatically setting up 
routes from the host to networks that are behind guests connected to a 
virtual network; the idea of automatically adding routes to guests who 
use DHCP to acquire their config is also a good one, but not what this 
feature does.

(btw, what you're trying to set isn't a "default gateway" either, it is 
just a route for traffic to 10.0.0.0/8. A default gateway is for traffic 
with a destination of 0.0.0.0/0, i.e. anything that doesn't match any 
other route in the routing table.)

>
> Thanks
>
> <network>
>   <name>prd-private-lan</name>
>   <uuid>255083f4-05a1-4a24-bc66-d3a3a9ab0724</uuid>
>   <bridge name='virbr3' stp='off' delay='0'/>
>   <mac address='52:54:00:08:1e:d8'/>
>   <domain name='prd.pipiche.net'/>
>   <dns>
>     <forwarder addr='8.8.4.4'/>
>     <forwarder addr='8.8.8.8'/>
>   </dns>
>   <ip address='10.10.0.1' netmask='255.255.255.0'>
>     <dhcp>
>       <range start='10.10.0.128' end='10.10.0.254'/>
>       <host mac='52:54:10:b6:35:ca'  ip='10.10.0.3'/>
>       <host mac='52:54:10:5f:92:05'  ip='10.10.0.7'/>
>       <host mac='52:54:10:7d:3a:3f'  ip='10.10.0.10'/>
>       <host mac='52:54:10:30:93:56'  ip='10.10.0.21'/>
>       <host mac='52:54:10:78:c1:c2'  ip='10.10.0.22'/>
>       <host mac='52:54:10:64:00:21'  ip='10.10.0.25'/>
>       <host mac='52:54:10:5a:5f:63'  ip='10.10.0.26'/>
>       <host mac='52:54:10:4c:b2:61'  ip='10.10.0.27'/>
>       <host mac='52:54:10:62:de:5f' ' ip='10.10.0.62'/>
>     </dhcp>
>   </ip>
>   <route address='10.0.0.0' prefix='8' gateway='10.10.0.7'/>
> </network>
>
> When looking on the VM (guest) the route is not correctly set
>
> route
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
> 10.10.0.0       0.0.0.0         255.255.255.0   U     100    0        0 ens4
>
> arp -a
> ? (10.10.0.1) at 52:54:00:08:1e:d8 [ether] on ensue
>
>
> ifconfig
> ens4: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
>         inet 10.10.0.27  netmask 255.255.255.0  broadcast 10.10.0.255
>         inet6 fe80::5054:10ff:fe4c:b261  prefixlen 64  scopeid 0x20<link>
>         ether 52:54:10:4c:b2:61  txqueuelen 1000  (Ethernet)
>         RX packets 1805  bytes 153644 (150.0 KiB)
>         RX errors 0  dropped 0  overruns 0  frame 0
>         TX packets 1745  bytes 136075 (132.8 KiB)
>         TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
>
>
>
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