EIGRP notes

• In Named mode per-interface commands are configured under af-interface. Beware of existing eigrp commands in interface configuration that can be misleading
• In Named mode wide metrics are used by default
• It's required to configure authentication mode, otherwise it's considered inactive
• Beware of white space in key-strings within key chains. It is considered a valid key-string character. Always use "show key chain" to verify.
• Uses multicast address 224.0.0.10 for the hello messages but you can configure it to use unicast
• Both routers need to be configured as unicast in order to form an "unicast" adjacency .
• Default route advertisement using a summary address should be avoided. By default it creates a summary route with admin distance 5 pointing to null and can lead to blackholes under certain circumstances
• A summary route is advertised with the lowest metric of it's component routes
• Default hello interval 5 sec. On low speed NBMA networks it's 60 sec. Default hold time 4 x hello interval. Both configured per interface.
• Using "eigrp stub" feature the "connected" and "summary" are default keywords included. 
• EIGRP by default uses up to 50% of configured interface bandwidth. If the bandwidth is configured too low, EIGRP starvation may occur. If you have available bandwidth but you  have intentionally configured a low bandwidth for other reasons, you can increase the interface bandwidth or set the percentage to a value >100%
• The command "distance XXX subnet wildcard ACL" changes the distance of the routes matched by the ACL AND and are learned from specific sources matched by the "subnet wildcard" values. It only affects EIGRP internal routes.
• For redistribution from another protocol to EIGRP you need to set the default metric or specify a metric at the redistribute command. No need to specify that for redistribution from static & connected routes and between EIGRP processes.
• Command "show ip eigrp events" very useful for troubleshooting. Displays ignored ppackets and so on.
• You can filter routes using maximum hop count. It defaults to 100 hops.