How to configure EIGRP Authentication

Hello Oussama

Specifically, the router uses an algorithm based on the routing protocol packet itself, the key, and the key ID to generate the MD5 digest or hash. Now you will find that the digest will be different from packet to packet because the contents of the packet itself are being used to make the hash, and each packet will contain different information, and thus the hash will be different. Using the packet as part of the algorithm ensures the integrity of the packet as well as the correctness of the keys being used.

I hope this has been helpful!