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Here is a good document that describes the naming conventions for 800 series routers; this also helps answer the above question.http://www.cisco.com/en/US/prod/collateral/routers/ps10906/ps380/qa_c67-716652.html
"LX4 is only made for Multimode fiber and it is not going to work on single mode fiber no matter what you try (as you are saying link is not comming up)."Not entirely true.In the link below:http://www.cisco.com/en/US/prod/collateral/modules/ps5455/...