ifupdown and inet6 gateways for inet interfaces

[Andy Smith <andy@strugglers.net>]

Hi,

Here is a manual network setup I have created by use of the "ip"
command:

$ ip address show dev enX0
2: enX0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether 00:16:5e:00:02:39 brd ff:ff:ff:ff:ff:ff
    inet 85.119.82.225/32 scope global enX0
       valid_lft forever preferred_lft forever
    inet6 2001:ba8:1f1:f1d7::2/64 scope global 
       valid_lft forever preferred_lft forever
    inet6 fe80::216:5eff:fe00:239/64 scope link 
       valid_lft forever preferred_lft forever
$ ip route show
default via inet6 fe80::1 dev enX0 src 85.119.82.225 
$ ip -6 route show
2001:ba8:1f1:f1d7::/64 dev enX0 proto kernel metric 256 pref medium
fe80::/64 dev enX0 proto kernel metric 256 pref medium
default via fe80::1 dev enX0 metric 1024 pref medium

Note that it has a single global scope IPv4 address which is a /32, and
its IPv4 default route is via an IPv6 link-local address.

This works fine, however I had to configure it using the "ip" command:

# ip address add 85.119.82.225/32 dev enX0
# ip -4 route add default via inet6 fe80::1 src 85.119.82.225

Is it possible to configure that using ifupdown's
/etc/network/interfaces syntax?

If there's no actual syntax for this (particularly, the "gateway" option
says it expects a dotted quad) possibly it can be done with pre-up
commands?

Is it doable with any of the other network configuration frameworks
(systemd-networkd, NetworkManager, netplan, …)?

Thanks,
Andy

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