Comment 62 for bug 1573272

Testing on zesty, same e/n/i configuration as artful, same /lib/systemd/system/ifup@.service modification to trigger bug:

$ dpkg -l | grep vlan
ii vlan 1.9-3.2ubuntu2

$ ip r
default via 192.168.122.1 dev ens3
default via 1.2.3.1 dev ens7.100 metric 1000 onlink
default via 4.5.6.1 dev bond0 metric 2000 onlink
1.2.3.0/24 dev ens7.100 proto kernel scope link src 1.2.3.5
4.5.6.0/24 dev bond0 proto kernel scope link src 4.5.6.8
9.8.7.0/24 dev bond0.200 proto kernel scope link src 9.8.7.7
192.168.122.0/24 dev ens3 proto kernel scope link src 192.168.122.131

bond0.200 gateway missing as expected.

After upgrading vlan to -proposed version, bond0.200 gateway is present and ens7.100 vlan is configured correctly:

$ dpkg -l | grep vlan
ii vlan 1.9-3.2ubuntu2.17.04.2

$ ip r
default via 192.168.122.1 dev ens3
default via 1.2.3.1 dev ens7.100 metric 1000 onlink
default via 4.5.6.1 dev bond0 metric 2000 onlink
default via 9.8.7.1 dev bond0.200 metric 3000 onlink
1.2.3.0/24 dev ens7.100 proto kernel scope link src 1.2.3.5
4.5.6.0/24 dev bond0 proto kernel scope link src 4.5.6.8
9.8.7.0/24 dev bond0.200 proto kernel scope link src 9.8.7.7
192.168.122.0/24 dev ens3 proto kernel scope link src 192.168.122.131