Cisco's DLSw+ Ethernet Redundancy feature is a solution for remote DLSw+ router redundancy (ie., multiple DLSw+ routers connected on the same LAN/VLAN bridge segment). DLSw+ ER is NOT a recommended best practice redundancy solution for the core campus data center. The reason this is so is because with DLSw+ ER you have to configure static mac address mappings. When doing this for remote DLSw+ routers you only need one entry for the host mac address and a very limited amount of host mac addresses. However if you were to do this on the core data center side you would need to configure one entry for each remote mac address which is not feasible! This URL on DLSw+ ER configuration should give you appreciation for what's involved here:
http://www.cisco.com/warp/public/697/8.htmlan
A much better approach to SNA transport to the host redundancy you might want to investigate is using DLSw+ for SNA transport over the WAN and combining DLSw+ and Cisco's SNA Switching Services (SNASw) APPN IOS feature in central site data center routers. The Enterprise Extender feature of SNASw would allow you to transport SNA traffic from DLSw+ IP to the host (SNA/LLC traffic uses the DLSw+ VDLC connection in the router to get SNA traffic from DLSw+ to SNASw). This results in LLC traffic being transported IP L3 over the MSFCs instead of L2 bridged. Path redundancy for LLC traffic over IP utilizes dynamic IP routing. There is extensive information on this in the SNASw Design Guide on Cisco CCO:
http://www.cisco.com/warp/public/cc/pd/ibsw/snasw/tech/index.shtml
