Which of the following is used to provide hot standby capabilities using paired routers?

CARP allows a group of hosts (typically routers or firewalls) to share a single virtual IP address for redundancy. If the master router fails, a backup router takes over the virtual IP seamlessly, providing hot standby capability with minimal downtime.

L2TP (Layer 2 Tunneling Protocol) is a VPN tunneling protocol used to encapsulate PPP traffic, not to provide router redundancy.

PPTP (Point-to-Point Tunneling Protocol) is an older VPN protocol for creating encrypted tunnels, not a high-availability or failover mechanism.

ISAKMP (Internet Security Association and Key Management Protocol) is used to negotiate and establish security associations for IPsec VPNs, not for router redundancy.