Authentication

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EIGRP does not have its own authentication method, EIGRP uses Key-chain mechanism and applied on the interface level.

        1. First we need to configure Key-chain, key chain name can be different on both devices
        2. Then we configure Key number that should be same on both end
        3. Finally we configure Key-String and this need to be same on both devices to have successful neighborship.

So here between R1 and R3 we will configure Authentication using Key-Chain

        *R1(config)#key chain r1
        *R1(config-keychain)#key 1
        *R1(config-keychain-key)#key-string ccna
        *R1(config)#int f2/0
        *R1(config-if)#ip authentication mode eigrp 10 md5
        *R1(config-if)#ip authentication key-chain eigrp 10 r1
        *R3(config)#key chain r3
        *R3(config-keychain)#key 1
        *R3(config-keychain-key)# key-string ccna
        *R3(config)#int f2/0
        *R3(config-if)#ip authentication mode eigrp 10 md5
        *R3(config-if)#ip authentication key-chain eigrp 10 r1

In EIGRP Hello packet EIGRP routers exchange this Authentication information

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