The basic answer is that device A does not have an ARP entry for C because C has not sent any layer 3 packets to A during the timeout period of ARP on A.
I have seen situations like this when B is configured with A as its default gateway but C is configured with some other device as its default gateway.
The situation could also be caused if C is not configured with a correct IP address on its management interface, or if its management interface is in a VLAN that does not connect to A. Or it might be caused by some interface problem on C (or poossibly on A).
Perhaps you can provide some additional information about your network. Are A and B and C the only devices in the network or are there other devices also?
Can you tell us how B physically connects to A and how C physically connects to A? What is the management VLAN on B and what is the management VLAN on C? Can C ping to A?
Tell us these things and perhaps we will be closer to an answer to your issue.
Hi everyone, I would like to thank you in advance for any help you can provide a newcomer like myself!
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