Why does geth -light start importing block headers from 3297471

Question

I've been using geth to download the blockchain (on full) and one of the requirements for my research involves the use of light clients. I used 2 computers to download the blockchain on the -light argument and both computers (one clean and another with an existing chain) start downloading headers from block 3297471.

Is there any explanation on why geth downloads from this block and not from 0? (screenshot of geth -light running attached)

Answer 1

A light client doesn't download the entire chain. It uses a Merkle hash which mathematically represents the entire chain in a small fraction of the space. Transactions can be verified with it. The protocol then only transfers a small portion of the chain over the wire to your device, which looks for events that it is interested in and requires access to a full node.

Check this out for more, in-depth information.

https://github.com/ethereum/wiki/wiki/Light-client-protocol