I would like to know how do we connect the blockchain to the network when there is no IP? Indeed we all use bitcoin core (for bitcoin) to connect and retrieve information and update. However the source code of bitcoin core (I have never read it) does not redirect us to an IP address, but people still manage to find themselves, without ever saving the IP. How can people know or find the information, when the source code of the software does not have IP, they do not know address (IP) which has the information? Knowing that the IP is the basis of the connection ...
The bitcoin client has many means to discover other ip in the bitcoin network, in the case of DNS request, which will return many ip address each times, here are the diferent DNS used as in 2017:
seed.bitcoin.sipa.be dnsseed.bluematt.me dnsseed.bitcoin.dashjr.org seed.bitcoinstats.com seed.bitcoin.jonasschnelli.ch seed.btc.petertodd.org
You can see all the methods used by the bitcoin client to discover nodes here: https://en.bitcoin.it/wiki/Satoshi_Client_Node_Discovery