systemd network interface configuration (was "Re: systemd woes continue")

[Bob Tracy <rct@gherkin.frus.com>]

On Wed, Sep 18, 2019 at 11:46:06AM +0200, John Paul Adrian Glaubitz wrote:
> Your permanent bashing of systemd makes answering your mails stressful
> for me.

Adrian -- please accept my apology for my rantings...  They contribute
nothing to the conversation, and as you note, irritate the very people
in the best position to render needed assistance.  

Going back to a previous message you sent, you suggested looking at a
few systemd network-related services:

(1) systemd-networkd: this is currently showing "disabled" on my system
    (vendor preset: enabled).

(2) resolver-related systemd services such as "resolvconf" and "systemd-resolved":
    "resolvconf" is "enabled", but "systemd-resolved" is "disabled"
    (vendor preset: enabled).

None of the services mentioned above have any configuration files other
than the defaults.

So, I guess the main question on the table is, what's the best path
forward to ensure network interfaces are brought up and configured
automatically at boot time?  Related to that question: is the use of
"/etc/network/interfaces" deprecated?  That's where my network
configuration details currently exist, and that used to be sufficient,
even after the migration from the old-style init program/scripts to
"systemd".  A sanitized copy of my current "interfaces" file is
attached.

Thanks in advance for the assist.

--Bob

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
allow-hotplug eth0
iface eth0 inet static
	address (masked)
	netmask 255.255.255.240
	network (masked)
	broadcast (masked)
	gateway (masked)
	# dns-* options are implemented by the resolvconf package, if installed
	dns-nameservers (masked)
	dns-search (my registered domain)

# /64 prefix assigned by Hurricane Electric 
iface eth0 inet6 static
	address (masked)
	netmask 64
	scope global

# Wireless settings for D-Link DWA-131 (r8712u driver from staging -- sigh)
# The initial interface name is wlan0, but that gets remapped to the name
# below by systemd+udev.
allow-hotplug wlx1c7ee513fb7b
iface wlx1c7ee513fb7b inet dhcp
	wireless-mode Managed
	wpa-driver wext
	wpa-ssid (masked)
	wpa-psk (masked)

# USB RTL8153 Gigabit Ethernet Adapter
allow-hotplug enx00e04c6881f7
iface enx00e04c6881f7 inet static
	address (masked)
	netmask 255.255.255.0
	network (masked)
	broadcast (masked)
	gateway (masked)

# Hurricane Electric tunnel: ID# (masked) est. 01 May 2016
auto he-ipv6
iface he-ipv6 inet6 v4tunnel
	address (masked)
        netmask 64
	endpoint (masked)
	local (masked, but IPv4 address of eth0)
	ttl 255
	gateway (masked)