ipsec open source for linux

Question

What are the open source available for ipsec in linux today.

I came across 1 (strongswan), but I am very new to this. Please suggest me which is the best available one and scalable.

Answer 1

if you look into kernel, you may find it.

For example, there is a ipsec.h under /include/uapi/linux/

I am not an expert of kernel. Just a clue

Answer 2

I think the document of strongswan is a good start point to understand IPSec. but the source code of strongswan is not friendly enough for learning IPsec implementation.

I would recommend you start from the source code of ip, part of iproute2 utility of GNU tools.