I have a routing problem with IP forwarding on my ubuntu server.
On my ubuntu server (an old laptop) I have VirtualBox installed with a number of virtual machines. Each VM has it's virtual NIC bridged to the physical wlan0 adaptor on the server, and if set to use DHCP they will happily get an IP address from my home wireless router. So bridging seems to be working fine.
The wireless router operates on the subnet 172.17.17.0/24.
Some VMs have static IPs set up on different subnets which are awkward to change due to the applications running on them. I have two VM subnets:
I thought I could get them all happily talking by giving my host laptop an IP address on each subnet, pointing the VMs to the appropriate IP as their gateway and then enable IP forwarding on the host. So the host has the following IPs assigned to wlan0:
172.17.17.100 172.19.40.1 192.168.195.1
With this set up, VMs on the subnet 172.19.40.0 can ping those on the 192.168.195.0 subnet and vice versa. The host happily IP forwards between those two subnets. The VMs on those subnets can also ping the server on 172.17.17.100.
However, none of the VMs on either subnet 172.19.40.0 or 192.168.195.0 can ping the wireless router on 172.17.17.254.
I guess the config on the host is lacking something, but i can't see what the difference is between VMs in each subnet pinging each other, and VMs on either subnet pinging the router on a third subnet - other than that it's a physical device - i'm still just asking the host to IP forward from one subnet to another. What's the difference that i'm missing?!
Appreciate any help offered.