IPSec Overhead Calculator

This is a tool to calculate the resulting packet size when it traverses an IPSec tunnel. The options allow you select what encryption settings are used and whether you are using a GRE tunnel.

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

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

This tool was create by Jay Young and Wen Zhang supported by Cisco. Any issues with the site can be reported via the GitHub Repo.