A simplistic explanation of EIGRP offset-list configuration command you might see every now and then is “it adjusts the RD/FD to influence route selection”. If that would be the case, the adjustment would not be propagated to upstream routers (remember: only the EIGRP vector metric is sent in the routing updates, not RD or FD) resulting in potential routing loops (it’s never a good idea to use one set of metrics and propagate another set of metrics to your neighbors).
In reality, the EIGRP offset lists adjust the delay portion of the EIGRP vector metric (which linearly influences the RD/FD value). You can increase
or decrease the value of the delay metric for EIGRP updates received or sent through a specific interface (or all interfaces). You can also use an access list in the offset-list command, applying changes only to specific IP prefixes (very similar to what I described in the Scalable policy routing IP corner article). For more details, please read this technology note on Cisco’s web site.