My inquire is I am trying to understand why this works.
I have 4 internal routers (2620) connecting directly to a switch (2900XL) the switch is directly connected to a server running OpenBSD 3.9. The server has 2 NICs it is setup as a bridge. The NIC_1 on the server is directly connected to Switch 2900XL. NIC_2 is directly connected to a router the outer_router. The network between the routers, Switch, and NIC_1 on the server is 10.10.100.0/24. NIC_2 and the outer_router are using 10.10.200.0/24.
The internal routers default gateway is set to the switch 2900XL
The switch 2900XL default gateway is set to NIC_1 on the server OpenBSD
The server's default gateway is set to the outer_router
There is no blocking or security setup on this test network. The Bridge is setup to look at all traffic coming from NIC_1 and NIC_2
Now my question is this, when the routers are set to use the switch as the default gateway, I am unable to ping the outer_router. I am thinking the switch that the routers are in should know where the outer_router is because the switches gateway is NIC_1 on the server and the server knows where the outer_router is.
When I set the default gateway of the internal routers to NIC_1 on the server, I am able to ping the outer_router just fine. The traffic must pass thru the switch, the only thing I changed is the default gatway of the inner routers. If I use the switch as the default gateway on the inner routers I cannot ping the outer_router. If I use NIC_1 on the server as the default gateway on the inner_routers I can ping the outer_router. I am puzzled as there is no routing protocol being used just a straight static IP setup.