I am not sure if I totally understand the topology. Let me rephrase it. Please correct me if I misunderstand the topology. In a data centre, there are 4 DLSw routers terminating DLSw peer connections from the remote sites. In the same data centre, there are 4 CIP routers which connects to 2 mainframes. CSNA is configured on all CIP router, which uses the same MAC. You configure transparent bridging on the DLSw routers, which connect to the same ethernet switches as the CIP routers. You configure SR/TLB on the CIP routers; so that all LLC2 circuits coming from the DLSw routers connect through the ethernet interfaces of the CIP routers.
Do you want the LLC2 circuits from a DLSw router load balance across 4 CIP routers? As duplicate MAC address is not allowed, there is no way to connect all 4 DLSw routers and CIP 4 routers on the same VLAN.
I can think of a couple of workarounds.
1. Enable SNASw on the 4 DLSw routers. Create a VDLC port on all 4 DLSw routers. The MAC address of the VDLC interface is the same. The VDLC MAC address is pointed by the remote SNA stations. Each DLSw router uses one of the CIP routers as DLUS.
2. If this is the case, create 4 VLANs on the ethernet switches. Connect a pair of DLSw router and CIP router to each VLAN.
You understand the environment correctly. We decide to use the solution number 2. In this environment fault tolerance is critical, is possible to implement the solution #2 but using 2 VLANs same time (one in each switch, for fault tolerance and load balance) ? This will create a network looping ?
No, it is not possible. The problem is not a network loop. The problem is that the switch cannot learn the same MAC address from 2 different ports on the same VLAN. This is very different than token ring, which uses rif to identify ports for the same MAC address.
If you connect 2 CIP routers on the same VLAN, the ethernet switch will learn the MAC address of the XCA/CSNA from two different port. The switch just flip the CAM table. Eventually, the switch will settle for one CIP. This defect the purpose of load balance 4 CIP routers.
I'm thinking about Ethernet Redundancy feature. It works in this environment ?
Router CIP-1, 2, 3 and 4
One gigabit interface with 4 subinterfaces (one in each VLAN - A, B, C and D) - encapsulation ISL.
One gigabit interface on VLAN A
One gigabit interface on VLAN B
One gigabit interface on VLAN C
One gigabit interface on VLAN D
Router DLSw-1 configured with ethernet redundancy and preference to connect to router CIP 1, 2, 3 and 4.
Router DLSw-2 configured with ethernet redundancy and preference to connect to router CIP 2, 3, 4 and 1.
Router DLSw-3 configured with ethernet redundancy and preference to connect to router CIP 3, 4, 1 and 2.
Router DLSw-4 configured with ethernet redundancy and preference to connect to router CIP 4, 1, 2 and 3.
In a normal operation all circuits are balanced with circuit count. Each DLSw router will use only one CIP router. If a CIP router fail, the DLSw router will redirect the traffic to next CIP router and so on.
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