[systemd-devel] Missing default route after boot with DHCP on a multi-homed server

[Damir Simunic]

Hi,

I installed CoreOS 298 (with systemd 212) on a multi-homed machine with a public and a private interface. It’s a data-center machine, and the provider assigns both interfaces through DHCP. Stock CoreOS defaults to DHCP settings for all network interfaces.

When I boot the machine, the public interface (eno1) is missing a default route, and the private interface eno2 instead has two (the first two lines in the  routing table below):

Apr 25 12:52:15 garry systemd[1]: Started Network Service.
Apr 25 12:52:17 garry systemd-networkd[3041]: eno2: carrier on
Apr 25 12:52:18 garry systemd-networkd[3041]: eno2: DHCPv4 address 10.60.120.27/26 via 0.0.0.0
Apr 25 12:52:18 garry systemd-networkd[3041]: eno1: carrier on
Apr 25 12:52:18 garry systemd-networkd[3041]: eno2: link configured
Apr 25 12:52:18 garry systemd-networkd[3041]: eno1: DHCPv4 address 33.112.217.84/24 via 33.112.217.1
Apr 25 12:52:18 garry systemd-networkd[3041]: eno1: link configured

# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         0.0.0.0         255.255.255.255 UH    0      0        0 eno2
0.0.0.0         0.0.0.0         0.0.0.0         U     0      0        0 eno2
10.60.120.0     0.0.0.0         255.255.255.192 U     0      0        0 eno2
33.112.217.0    0.0.0.0         255.255.255.0   U     0      0        0 eno1
33.112.217.1    0.0.0.0         255.255.255.255 UH    0      0        0 eno1

Restarting the systemd-networkd.service, correctly assigns the default route for eno1:

# systemctl restart systemd-networkd.service 

Apr 25 12:54:09 garry systemd-networkd[3144]: eno1: DHCPv4 address 33.112.217.84/24 via 33.112.217.1
Apr 25 12:54:09 garry systemd-networkd[3144]: eno1: link configured
Apr 25 12:54:09 garry systemd-networkd[3144]: eno2: DHCPv4 address 10.60.120.27/26 via 0.0.0.0
Apr 25 12:54:10 garry systemd-networkd[3144]: eno2: link configured

# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         0.0.0.0         255.255.255.255 UH    0      0        0 eno2
0.0.0.0         33.112.217.1    0.0.0.0         UG    0      0        0 eno1
10.60.120.0     0.0.0.0         255.255.255.192 U     0      0        0 eno2
33.112.217.0    0.0.0.0         255.255.255.0   U     0      0        0 eno1
33.112.217.1    0.0.0.0         255.255.255.255 UH    0      0        0 eno1

This happens consistently on every boot. I worked around this by assigning a static address to the public interface, but nevertheless wanted to point this out as a possible bug.

Thanks,
Damir

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