Routed subnets cannot use snat

Hi,

We have the following network configuration:
- Subnet A: 10.20.0.0/24
- Subnet B: 10.20.10.0/24
- Router Ext:
    > With a external gateway
    > linked to Subnet A (10.20.0.1)
    > Route to 10.20.10.0/24 via 10.20.0.254
- Router Lan: Linked to both networks (10.20.0.254 and 10.20.10.1)
    > linked to Subnet A (10.20.0.254)
    > linked to Subnet B (10.20.10.1)
    > Route to 0.0.0.0/0 via 10.20.0.1

While instances in the Subnet A can access Internet, instances in Subnet B cannot.
I got an error: From 10.20.0.1 icmp_seq=1 Destination Net Unreachable.

It looks like there is an ip rule in the namespace of the qrouter-RouterExt which route only requests from 10.20.0.1/24 through the Snat.

[root@host ns: qrouter-e17d62be-deea-4317-948c-b1c9eedc93fa ~] ip route
10.20.0.0/24 dev qr-3a2a89c7-53 proto kernel scope link src 10.20.0.1
10.20.10.0/24 via 10.20.0.254 dev qr-3a2a89c7-53
169.254.110.154/31 dev rfp-e17d62be-d proto kernel scope link src 169.254.110.154
192.168.1.0/24 dev qr-0b3f2d0d-8b proto kernel scope link src 192.168.1.1
[root@host ns: qrouter-e17d62be-deea-4317-948c-b1c9eedc93fa ~] ip rule list
0: from all lookup local
32766: from all lookup main
32767: from all lookup default
169082881: from 10.20.0.1/24 lookup 169082881
[root@host ns: qrouter-e17d62be-deea-4317-948c-b1c9eedc93fa ~] ip route show table 169082881
default via 10.20.0.173 dev qr-3a2a89c7-53

Is there a reason why we only route directly attached networks through the snat ?

I've come up with a fix that adds an ip rule for each network specified in the router's routes. Can you give me some feedback on this ? I'm mainly concerned about the reasons why this was this way in the first place and about the cleanup of the unused rules.

Best regards,