I am running a bitcoin core (v0.15.01) full node according to https://bitcoin.org/en/full-node. They say
"To support the Bitcoin network, you also need to allow incoming connections."
I hesitate opening ports because having a port open for incoming connection allows for anyone to connect. So is this really necessary for bitcoin to work? They to not explicitly state what kind of support this enables.
I see that the client already makes connections to various domains like
x9.dnsseed.bluematt.me x9.seed.bitcoinstats.com dnsseed.bitcoin.dashjr.org x9.seed.bitcoin.sipa.be x9.seed.btc.petertodd.org x9.seed.bitcoin.jonasschnelli.ch
Do these represent the "distributed" properties of Bitcoin? Why are there not more of them? Or is this completely unrelated?