In the
example, however, Router D would never be a feasible successor no matter what the variance is.
This decision is because the advertised distance of Router D is 25, which is greater than the Router
E feasible distance of 20; therefore, to avoid a potential routing loop, Router D is not considered
a feasible successor.
EIGRP Authentication
You can con?¬?gure EIGRP neighbor authentication, also known as neighbor router authentication
or route authentication, such that routers can participate in routing based on prede?¬?ned passwords.
By default, no authentication is used for EIGRP packets. EIGRP can be con?¬?gured to use Message
Digest Algorithm 5 (MD5) authentication.
When you con?¬?gure neighbor authentication on a router, the router authenticates the source of
each routing update packet that it receives. For EIGRP MD5 authentication, you must con?¬?gure
an authenticating key and a key ID on both the sending and the receiving router. The key is
sometimes referred to as a password.
The MD5 keyed digest in each EIGRP packet prevents the introduction of unauthorized or false
routing messages from unapproved sources.
Each key has its own key ID, which the router stores locally.
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