I)
I have following configuration:

/etc/systemd/network/enp0s3.network:
----------------------------------------------------
[Match]
Name=enp0s3

[Network]
Description="xxx"
DHCP=yes
Domains=softsystem.pl

[Route]
Gateway=172.29.24.1
Destination=10.0.0.0/8
Metric=1
----------------------------------------------------

/etc/systemd/network/enp0s11u1.network:
----------------------------------------------------
[Match]
Name=enp0s11u1

[Network]
Description="yyy"
DHCP=yes
# Resolver1.OpenDNS.com Resolver2.OpenDNS.com Resolver3.OpenDNS.com Resolver4.OpenDNS.com google google
DNS=208.67.222.222 208.67.220.220 208.67.222.220 208.67.220.222 8.8.8.8 8.8.4.4

[DHCP]
UseDNS=false
----------------------------------------------------


II)
ip route:
----------------------------------------------------
default via 172.29.24.1 dev enp0s3 proto dhcp src 172.29.2.123 metric 1024
default via 192.168.8.1 dev enp0s11u1 proto dhcp src 192.168.8.100 metric 1024
172.29.0.0/19 dev enp0s3 proto kernel scope link src 172.29.2.123
172.29.24.1 dev enp0s3 proto dhcp scope link src 172.29.2.123 metric 1024
192.168.8.0/24 dev enp0s11u1 proto kernel scope link src 192.168.8.100
192.168.8.1 dev enp0s11u1 proto dhcp scope link src 192.168.8.100 metric 1024
----------------------------------------------------


III)

1)
How to tell systemd-networkd not to add:
default via 172.29.24.1 dev enp0s3 proto dhcp src 172.29.2.123 metric 1024
to routing table ?

2)
Why:

[Route]
Gateway=172.29.24.1
Destination=10.0.0.0/8
Metric=1

is not in routing table ?

3)
Is there way to tell systemd-networkd to do something like:
ip route add 10.0.0.0/8 dev enp0s3


???

Please help.

What's your Linux distribution, Fedora and so on?

Fedora release 21 (Twenty One)
Linux 4.1.13-100.fc21.x86_64

systemd.x86_64 216-25.fc21

The interface init script is under /etc/sysconfig/network-scripts/ifcfg-ifname. You can set DEFROUTE to no.

As far as I know /etc/sysconfig/network-scripts/ifcfg-ifname are only for ifup/ifdown scripts and/or NetworkManager but systemd-networkd.service does not use those files because it has its own configuration files.
Am I wrong ?

Yes, that is for Network Manager. Are you disable network manager?

Ofcourse I did - I do not want it..

In /etc/systemd/network/enp0s3.network, create DHCP section to control route that is from DHCP server.

[DHCP]
UseRoutes=false

It does not work.
(I think this option is for different purpose: https://www.freedesktop.org/software...d.network.html)

Should be this. It could be a issue.