how does light client validate and connect to a full node?
For fast there is no light client.
There is no consensus in IPFS so there is no need of any light client.
You can change
dht-client in the config (
routing part) but that not a light client in the way of other cryptocurrency, your node continue to find by it self thing in the dht (with all fonctionality) but will stop to hosting a small part of the dht (that remove the server part for other node).
IPFS is not a blockchain nor a cryptocurrency, it is a distributed file system so there are no light or full nodes. It is just like Bittorrent: everyone stores and serves what they want. But there is indeed a notion of “client” because IPFS is also a protocol like HTTP, so there are IPFS clients (we should rather say peers because they are both clients and servers) in the same way as for HTTP clients.