Hi, I have created a network bridge in ubuntu and it seems to be working correctly apart from one issue which is holding me back.

I have created the bridge as root like so:

Code:
tunctl -t tap0 -u zombie
ifconfig tap0 0.0.0.0 promisc up
ifconfig eth0 0.0.0.0 promisc up
brctl addbr br0
brctl addif br0 tap0
brctl addif br0 eth0
ifconfig br0 192.168.1.4/24 up
route add default gw 192.168.1.1
route add -net 192.168.100.0 netmask 255.255.255.0 gw 192.168.1.254

My eth0 interface is connected to my physical internet router and the tap0 interface is connected to a GNS3 router. The GNS3 router has a default route to 192.168.1.1 and has internet connectivity. No problem there, the bridge appears to be functioning correctly.

I am encountering difficulty when I add another network in GNS3, in this case, the network 192.168.100.0.

This is my current topology to make things a little clearer:

Physical (Internet) Router -- 192.168.1.1
(eth0)Ubuntu Host(tap0)------ 192.168.1.4
Router1[f0/0](GNS3) --------- 192.168.1.254
Router1[f1/0](GNS3) --------- 192.168.100.254
Ubuntu-Server(Vbox) --------- 192.168.100.1

And this is the routing table from my Ubuntu-Host:

Code:
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         voyager.home    0.0.0.0         UG    0      0        0 br0
192.168.1.0     *               255.255.255.0   U     0      0        0 br0
192.168.100.0   192.168.1.254   255.255.255.0   UG    0      0        0 br0
The Ubuntu Host (192.168.1.4) is able to ping the Ubuntu-Server VM @192.168.100.1 and vice versa.

Why am I unable to achieve internet connectivity on the Ubuntu-Server VM?

I got this working a couple of days ago and I was sure I had entered the commands above to achieve this but I must have missed something or done something slightly different. Is it a firewall issue? I have tried these commands:

Code:
iptables -I INPUT -j ACCEPT -i br0
iptables -I OUTPUT -j ACCEPT -o br0
...which I believe allow ALL traffic through the bridge but I am unsure as I am not familiar with iptables(yet!). I also have no idea of the security issues these could raise for my Host system.

Please, please, help me! Any help or comments at all would be so appreciated even if it is only with one aspect of my problem. Thank you in advance.