Block brute force login attempts while maintaining access for legitimate source addresses. This is in theory unnecessary if VTY ACLs are in place, yet things happen and this adds the "belt" to the VTY ACL "suspenders." Note carefully the use of ACL 100 in the login quiet-mode statement. This ensures our legitimate administrator addresses can still reach the router even after a vigorous bruteforce or attack attempt.

access-list 100 remark VTY Access ACL
access-list 100 permit tcp host 192.168.0.34 host 0.0.0.0 range 22 23 log-input
access-list 100 permit tcp host 192.168.0.30 host 0.0.0.0 range 22 23 log-input
access-list 100 deny ip any any log-input
!
login block-for 100 attempts 15 within 100
login quiet-mode access-class 100
login on-failure log
login on-success log

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