Network Time Protocol
When I first took over the network responsibilities at my current position, I set up my Internet-facing routers to pull time from trusted servers. Then I attended a SANS class where we talked about an optional strategy to have one key device poll an outside server and the routers then all pull from that controlled device. First advantage is to the outside service, since this changed 57 requests to 1, and I think it makes the routers less visible to the Internet. This is one of those 'IMHO' type choices, but anything that makes my routers less visible (less chatty on the outside interface) makes them less of a target.
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