I was playing around with some routed networks and in order to allow one of them access to the internet, I added a static route to its gateway and added a source nat rule for that network.
Like this:
I was surprised to find that the packets where leaving on RED with 0.0.0.0 as a source. This is what I found in IpTables:
So I manually changed it and then it worked fine.
So then I changed RED from DHCP to STATIC and that was better:
It makes sense that it did not work the first time, when RED was set to DHCP. A MASQUERADE would have been required. But it is misleading that the NAT rule shows the new source IP address as RED (192.168.100.251). That suggest that it will indeed be 192.168.100.251, not 0.0.0.0.
So maybe RED should not be available for NAT if it is set to DHCP? Or better yet, it should add a MASQUERADE instead of SNAT?