0

UPDATE 2

Top posting because it is needed to apply the suggested solution.

Found on question - second answer

This has been fixed in the netplan repository on github, and will presumably make its way into Ubuntu at some point.

Two new options have been added, dhcp4-overrides and dhcp6-overrides. To ignore DNS servers from DHCP you would do something like

Anyone knows how to update netplan in Ubuntu 18.04?

Original question

I have an LXD vm with 2 network interfaces. If I use Ubuntu 16.04 (interfaces) I have 1 default gateway. If I use Ubuntu 18.04 (netplan) I have 2 default gateways. How can I get rid of the second gateway?

Ubuntu 16.04 configuration:

root@servizi:/etc/network/interfaces.d# ls -lha
total 3.5K
drwxr-xr-x 2 root root   4 Jul 31  2017 .
drwxr-xr-x 7 root root   8 Jul 12  2017 ..
-rw-r--r-- 1 root root 367 Jul 30  2017 50-cloud-init.cfg
-rw-r--r-- 1 root root  97 Jul 31  2017 60-locale.cfg
root@servizi:/etc/network/interfaces.d# cat 50-cloud-init.cfg 
# This file is generated from information provided by
# the datasource.  Changes to it will not persist across an instance.
# To disable cloud-init's network configuration capabilities, write a file
# /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
# network: {config: disabled}
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp
root@servizi:/etc/network/interfaces.d# cat 60-locale.cfg 
auto eth1
iface eth1 inet dhcp
        up route add -net 192.168.99.0 netmask 255.255.255.0 gw 10.0.1.1
root@servizi:/etc/network/interfaces.d# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         10.220.90.1     0.0.0.0         UG    0      0        0 eth0
10.0.1.0        0.0.0.0         255.255.255.0   U     0      0        0 eth1
10.220.90.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0
192.168.99.0    10.0.1.1        255.255.255.0   UG    0      0        0 eth1
root@servizi:/etc/network/interfaces.d# 

Ubuntu 18.04 configuration

root@servizi2:/etc/netplan# ls -lh
total 2.0K
-rw-r--r-- 1 root root 381 Jan 24 17:30 50-cloud-init.yaml
-rw-r--r-- 1 root root 177 Feb  1 20:25 60-locale.yaml
root@servizi2:/etc/netplan# cat 50-cloud-init.yaml 
# This file is generated from information provided by
# the datasource.  Changes to it will not persist across an instance.
# To disable cloud-init's network configuration capabilities, write a file
# /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
# network: {config: disabled}
network:
    version: 2
    ethernets:
        eth0:
            dhcp4: true
root@servizi2:/etc/netplan# cat 60-locale.yaml 
# seconda scheda
network:
    version: 2
    ethernets:
        eth1:
            dhcp4: true
            routes:
            - to: 192.168.99.0/24
            via: 10.0.1.1

root@servizi2:/etc/netplan# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         10.220.90.1     0.0.0.0         UG    100    0        0 eth0
0.0.0.0         10.0.1.1        0.0.0.0         UG    100    0        0 eth1
10.0.1.0        0.0.0.0         255.255.255.0   U     0      0        0 eth1
10.0.1.1        0.0.0.0         255.255.255.255 UH    100    0        0 eth1
10.220.90.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0
10.220.90.1     0.0.0.0         255.255.255.255 UH    100    0        0 eth0
root@servizi2:/etc/netplan#

UPDATE

Tried what @slangasek suggested and the second file is now:

root@servizi2:/etc/netplan# cat 60-locale.yaml 
# seconda scheda
network:
    version: 2
    ethernets:
        eth1:
            dhcp4: true
            dhcp4-overrides:
                    use-routes: false
            routes:
                - to: 192.168.99.0/24
                  via: 10.0.1.1

But netplan try gives the error "unknown key dhcp4-overrides"

root@servizi2:/etc/netplan# netplan try
Error in network definition /etc/netplan/60-locale.yaml line 5 column 12: unknown key dhcp4-overrides

An error occurred: the configuration could not be generated

Reverting.
root@servizi2:/etc/netplan#

Wha can I do?

0

It appears you have a default route on both eth0 and eth1 that is coming from dhcp; and you want to use only the default route through eth0.

To ignore the default route provided by your dhcp server, you would need to use dhcp4-overrides, like so:

network:
    version: 2
    ethernets:
        eth1:
            dhcp4: true
            dhcp4-overrides:
                use-routes: false
            routes:
                - to: 192.168.99.0/24
                  via: 10.0.1.1

This option is only supported in netplan 0.95 and later, which is currently only available in Ubuntu disco. Until this is backported to Ubuntu 18.04, the only workaround is to use static IP assignment and DNS on eth1 instead of using dhcp.

  • Well, I want a default gateway on eth0 which is generated by cloud-init. On eth1 I want a static route to another lan that is not managed by LXD. Seems that adding this static route generates a default gateway (destination 0.0.0.0) instead the route to 192.168.99.0/24. Hope it is more clear – Mirto Busico Feb 4 at 8:18
  • Sorry, read your route table too quickly without scrolling to check interface names. I've fixed the interface names around in my answer, but the basic answer is the same - your default route appears to be coming from dhcp. – slangasek Feb 5 at 19:01
  • Sorry seems not to work. See question update – Mirto Busico Feb 6 at 11:04
  • As I said, 'dhcp4-overrides' is only supported in netplan 0.95, which is not yet available in any stable Ubuntu releases. In the meantime you should use static IP configuration for eth1 instead of dhcp. – slangasek Feb 6 at 22:32

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