Using native AWS constructs, the highest available bandwidth within an IPSEC tunnel is:

The highest available bandwidth within an IPSEC tunnel using native AWS constructs is 1.25Gbps. This maximum throughput is primarily attributed to the limitations of AWS-managed VPN solutions, which are designed to balance performance and security over the internet or AWS Direct Connect connections.

AWS offers specific types of VPN connections, and for Site-to-Site VPN, the bandwidth ceilings are established based on the underlying infrastructure and how it handles encryption and data transmission. For IPSEC tunnels created using AWS's Site-to-Site VPN service, it is important to understand that while they provide encryption for secure data transfer, factors such as latency and the bandwidth of each connection type play a critical role in determining actual performance.

The other available options suggest bandwidths that either exceed or are inconsistent with the limits typically recognized in AWS VPN scenarios. 4Gbps and 10Gbps would likely pertain to dedicated connections such as AWS Direct Connect, which allows for higher throughput without the overhead imposed by IPSEC, while 500Mbps is lower than what AWS deems feasible for IPSEC tunnels. Therefore, 1.25Gbps is established as the maximum bandwidth achievable for IPSEC tunnels, reflecting AWS's infrastructure capabilities while maintaining security protocols.