With the increasing popularity of IPSec VPN deployments on the Internet, there is often a need to understand the exact IPSec and other tunnel encapsulation overhead in order to determine the fragmentation boundary conditions for optimal MTU/MSS tuning, or to perform bandwidth budgeting on low-bandwidth links. Given these overheads vary depending on the specific IPSec protocols and algorithms used, we have developed a tool to make this task easier, and it can be found here:
This tool was just recently updated with an improved user interface and IPv6 support. Check it out and feel free to provide feedback or improvement ideas by clicking on the Feedback icon on the top right corner of the page.
Note, even though most of the overhead calculation for this tool is standard RFC based, some can be implementation specific, such as ESP padding. For those calculations, the tool is based on the Cisco IOS/IOS-XE implementation.