6x6 Deck post repair, Joining two 6x6 posts
Dry rot doesn't really exist but I'll imagine you said brown rot.
https://en.wikipedia.org/wiki/Dry_rot
It sounds like your post is not 6&quot; above grade.
I'd probably just put a 6x6 sonotube into the ground and have it extend up to where the wood is still good.  Add a Simpson CB66PC and bolt the post back into it.
https://www.strongtie.com/classiccollection_architecturalproductsgroup/cbpc_base/p/cbpc