SSH rekeying is the process of replacing the encryption keys used by an existing SSH session while the connection stays open. SSH does this periodically to limit how much data is protected by one key and to reduce the impact of key exposure over long-lived sessions. It is part of normal SSH operation and is handled automatically by clients and servers.
From a security perspective, rekeying matters because it sits inside the protocol logic that protects remote administration. If rekeying is implemented incorrectly, attackers may be able to desynchronize the session, bypass checks, or trigger memory and state errors that lead to authentication failures or unauthorized access. Defenders look for unusual rekey behavior, such as repeated renegotiation, failed handshakes, or session drops, because those can signal protocol abuse, implementation bugs, or active exploitation attempts.