Where is /ipfs/id/1.0.0? It is mentioned in a few places, e.g. https://github.com/libp2p/specs/blob/master/7-properties.md#757-protocol-multicodecs, but I can’t find the source. Is it peer ID?
It’s a protocol name. Specifically, it’s the IPFS identify protocol version 1.0.0. IPFS uses the identify protocol when a connection is established to exchange identity information (addresses, protocols we speak, public keys, etc).
Technically, this protocol should be
/libp2p/id/1.0.0 as it’s now a part of libp2p, not IPFS, but this protocol is older than libp2p.