Using a gateway for a private network interface on Ubuntu

Question

I have a private network interface, as follows, on a Ubuntu 16.04 VM:

# Private network
auto ens19
iface ens19 inet static
    address 10.10.10.179
    netmask 255.255.255.0
    mtu 1450

My vLAN requires a gateway to be specified in order for it to work, so I append it as follows:

# Private network
auto ens19
iface ens19 inet static
    address 10.10.10.179
    netmask 255.255.255.0
    mtu 1450
    gateway 10.10.10.1

However, whenever I add that gateway and restart the networking service, it won't start with the following error:

Dec 15 10:50:08 postfix0 ifup[1968]: RTNETLINK answers: File exists
Dec 15 10:50:08 postfix0 ifup[1968]: Failed to bring up ens19.

Executing ip addr flush dev xxx does not help.

So, how do I fix this?

Possible duplicate of Using ip addr instead of ifconfig reports "RTNETLINK answers: File exists" on Debian — GAD3R
– GAD3R, Commented Dec 16, 2017 at 19:58
@GAD3R The answer in that question does not solve my problem. — William
– William, Commented Dec 16, 2017 at 21:18
@WilliamD.Edwards – Did you try this?: serverfault.com/a/724090/375458 — Travis Clarke
– Travis Clarke, Commented Dec 17, 2017 at 3:11
@TravisClarke Yes. Doesn't work: RTNETLINK answers: File exists — William
– William, Commented Dec 18, 2017 at 17:30

Christopher · Accepted Answer · 2017-12-19 20:00:12Z

1

+150

Create a named routing table. The name, pvtnet, is arbitrary. This will not work if DHCP is handing out addresses on the 10.10.10 network.

echo '200 pvtnet' >> /etc/iproute2/rt_tables

Modify the file, /etc/network/interfaces.

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
# DHCP hands out the DEFAULT gateway.
auto eth0 # use the real device name on your system
allow-hotplug eth0
iface eth0 inet dhcp

# The private network interface
auto ens19
allow-hotplug ens19
iface ens19 inet static
address 10.10.10.179
netmask 255.255.255.0
mtu 1450
post-up ip route add 10.10.10.0/24 dev ens19 src 10.10.10.179 table pvtnet
post-up ip route add default via 10.10.10.1 dev ens19 table pvtnet
post-up ip rule add from 10.10.10.179/32 table pvtnet
post-up ip rule add to 10.10.10.179/32 table pvtnet

edited Dec 19, 2017 at 20:00

answered Dec 19, 2017 at 19:54

Christopher

16.4k7 gold badges56 silver badges66 bronze badges

That did the trick. Thank you! I tried many variations of that. Will award bounty in 23 hours when allowed.

William
– William

2017-12-19 20:22:11 +00:00
Commented Dec 19, 2017 at 20:22

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