DNS seeds

DNS seeds are servers which contains lists of IP addresses. These seeds are custom implementations of Berkeley Internet Name Daemon (BIND) and return random subsets collected by a Bitcoin node. Most of the Bitcoin clients use DNS seeds to connect while trying to establish to first set of connection. It is better to have various seeds present so that a better connection can be established by the client with the peers present over the network. In the Bitcoin core client, the option to use DNS seeds is controlled by the -dnsseed parameter, which is set to 1 by default. Here is how the DNS seeds are represented in the chainparams.cpp file of the Bitcoin source:

 vSeeds.push_back(CDNSSeedData("bitcoin.sipa.be", "seed.bitcoin.sipa.be")); // Pieter Wuille
 vSeeds.push_back(CDNSSeedData("bluematt.me", "dnsseed.bluematt.me")); // Matt Corallo
 vSeeds.push_back(CDNSSeedData("dashjr.org", "dnsseed.bitcoin.dashjr.org")); // Luke Dashjr
 vSeeds.push_back(CDNSSeedData("bitcoinstats.com", "seed.bitcoinstats.com")); // Christian Decker
 vSeeds.push_back(CDNSSeedData("xf2.org", "bitseed.xf2.org")); // Jeff Garzik
 vSeeds.push_back(CDNSSeedData("bitcoin.jonasschnelli.ch", "seed.bitcoin.jonasschnelli.ch")); // Jonas Schnelli

The preceding seeds are currently being used in Bitcoin core, for connecting with the seed client for establishing the connection with the first node.