This got tossed on my lap and I am rushing to try and figure out how (or if even possible) to do this. I'm a far cry from adapt at this.
Basically, we have two T1's that are connected to an 1841. They are setup on the serial interfaces using PPP encapsulation and connected via Multilink (they are confirmed working). What I'd like to do is simply pass that connection on to our main router which currently does all the routing via one of the 1841 Ethernet ports. In essence letting the 1841 act as a bridge or pass through for the connection.
An engineer from the T1 provider has told us that we'll need to use two Ethernet connections, a host of routing rules (for this portion of our network) and one of the connections will require a cross-over cable so that incoming traffic comes on one interface and outgoing on another. We have a router that handles our firewalls, other internet connections and WAN traffic already, I'd rather it handle the routing so we have one last place to worry about updating things.
Can the 1841 just act like a bridge or Ethernet hand off with the multilink? Is this possible?
Are you physically able to terminate the T1 connections currently going into your 1841 router to your other main router instead? If so, there's your solution right here.
If for cabling distance/hardware reasons you can't terminate the MLPPP on your "main" router and it needs to remain terminated on your 1841 router, then either configure static routing between your main router & 1841 router, or establish a dynamic routing protocol (RIP, EIGRP, OSPF, etc.) between them.
If dynamic, advertise the networks between the 1841 and main router and connectivity will be able to pass.
This is not a bridge, simply routing from one network to another.