Some documents (e.g. "EIGRP Message Authentication configuration Example", http://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/82110-eigrp-authentication.html ) seem to indicate time synchronization is generally needed for EIGRP MD5 Authentication to work. Other documents (e.g the "Configuring EIGRP" chapter from the document "IP Routing EIGRP Configuration Guide Cisco IOS Release 12.2SY" http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_eigrp/configuration/12-2sy/eigrp-12-2sy-book/ire-cfg-eigrp.html ) seem to indicate that it's needed primarily to manage key lifetimes. Note that at least some releases on ASA's don't support key chains or key lifetimes.  If that's the environment you're in, do you need need time synchronization for EIGRP adjacencies to work?  Or to turn it around a little bit, to pose it as a technical detail question, rather than a larger design question, what would the impact be on MD5-authenticated EIGRP adjacencies if NTP time synchronization were to fail on one or both routers, assuming the use of infinite key lifetimes and/or devices that did not use key chains? Wireshark traces don't show any evidence of timestamps being sent in MD5-authenticated EIGRP packets.  And in GNS3 simulations, MD5-authenticated adjacencies appear to come up and stay up even when the time on the peers has been set to be years apart. Many thanks. ... View more