There are 3 kids of Link Exhange.
1. One way Link Exchange
2. Two way Link Exchange
3. Three way Link Exchange
We can get one way link exchange through Directory Submission, SB, Forum posting etc.
Two way if you offer reciprocal links. A is link to B and B is link to A.
In a three-way link exchange, three different domains must be involved. For example, site A links to site B, but not B to A. So, site B is only receiving a one-way link from site A and NOT linking back to it. Likewise, site C and site A are linked from one site but not linking back. Instead, site C and A are simply reciprocal-linking to different domains.