just to add to leos advice: If the 2921 is too big (you say small office, but not the needed bandwidth), you could save much money if you buy a smaller router with only RJ45 (800 or 1900 series) and a switch with an SFP-uplink-port.
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Don't stop after you've improved your network! Improve the world by lending money to the working poor:
http://www.kiva.org/invitedby/karsteni
