How to translate "ip route add local 0.0.0.0/0 dev lo table 100" to systemd-networkd?

I am trying to setup a software router with the goal of routing packets to a proxy server on the router. The tutorial I am reading has the following routing rules:

ip rule add fwmark 1 table 100
ip route add local 0.0.0.0/0 dev lo table 100

and the following iptables rules:

iptables -t mangle -N V2RAY
iptables -t mangle -A V2RAY -d [Private Addresses] -j RETURN
iptables -t mangle -A V2RAY -p udp -j TPROXY --on-port 12345 --tproxy-mark 1
iptables -t mangle -A V2RAY -p tcp -j TPROXY --on-port 12345 --tproxy-mark 1
iptables -t mangle -A PREROUTING -j V2RAY

The whole thing works perfectly. But now I am moving to use systemd-networkd to avoid any startup scripts, and I am having trouble to convert ip route add local 0.0.0.0/0 dev lo table 100 to systemd-networkd language.

My first question is, what does this route do? My understanding so far is:

• iptables add a firewall wall mark 1.
• The rule selects all packets with mark 1 to use routing table 100.
• The route is added to table 100, so it only applies to packets with mark 1.
• The "0.0.0.0/0" part means it is a default route.
• But what does "local" mean here? Why device lo? Why do we need a route here? Can't iptables handle this directly?

My second question is how to do this in systemd-networkd.

For matching packets with mark 1, it seems easy (and worked on my router):

[Match]
Name = *

[RoutingPolicyRule]
FirewallMark = 1
Table = 100

I am not sure if Name = * is required though. Does this make sure that any packet from any device, as long as it has mark 1, will be routed using table 100? Or could I match some particular network device here?

I cannot, however, make the route in systemd-networkd. My attempt so far is:

[Match]
Name = lo

[Route]
Type = local
Destination = 0.0.0.0/0
Table = 100

But it seems that this has no effect: ip route show table 100 actually gives:

Error: ipv4: FIB table does not exist.
Dump terminated

How should I approach this?

Solution 1:

[Match]
Name = lo

[RoutingPolicyRule]
FirewallMark = 1
Table = 100
Priority = 100

[Route]
Table = 100 
Destination = 0.0.0.0/0
Type = local

Combine them into one file