I've seen references to both strewn around. Specifically, is there a bitcoin client running at the DNS seeds or seed nodes?

There is two types of seeds DNS seeds and seed nodes as you have identified. DNS seeds are stored in chainparams.cpp As of today (April 2017) the following nodes are listed in this file.

  • seed.bitcoin.sipa.be
  • dnsseed.bluematt.me
  • dnsseed.bitcoin.dashjr.org
  • seed.bitcoinstats.com
  • seed.bitcoin.jonasschnelli.ch
  • seed.btc.petertodd.org

I performed nslookups on these DNS names and they return a list of IP (14-26) addresses that all seemed to be running bitcoin nodes.

There is also the concept of seed nodes which are hardcoded IP addresses in the event that someone is experiencing a DNS failure or other issue. These nodes are only contacted if no other discovery mechanism works.

No, the DNS seeds are not running a Bitcoin client. The DNS seed nodes only give you a list of IP addresses that are running (or were recently running) a Bitcoin client. In the source code you can see that the DNS seed nodes are contacted only to get a list of addresses.

Source: https://github.com/bitcoin/bitcoin/blob/master/src/net.cpp#L1210

  • 2
    I'm having trouble seeing that from the code you linked to. Reading the source my impression is that the DNS records point to nodes understanding a bitcoin-specific protocol that allows them to be queried for (addresses of) peers, in the same way a proper bitcoin client could be queried. So why isn't it fair to say these nodes run (at least) a partial, and likely a full, bitcoin node (client, service, or whatever one might wish to call it)? – pyramids Nov 28 '13 at 15:50
  • DNS records are what the DNS returns, that is a list of addresses corresponding to nodes running the Bitcoin client. The DNS itself is not required to run Bitcoin. However, the current standard for Bitcoin DNS (github.com/sipa/bitcoin-seeder) also implement a 'crawler' function, which search the web for running nodes to add to the list. To that purpose, DNS seeders implement some small Bitcoin functions to communicate with active nodes. Still they are not considered as active nodes unless they also run a Bitcoin client on the same server. – FedFranz Nov 23 '17 at 13:41

2017 values are:

  • seed.bitcoin.sipa.be
  • dnsseed.bluematt.me
  • dnsseed.bitcoin.dashjr.org
  • seed.bitcoinstats.com
  • seed.bitcoin.jonasschnelli.ch
  • seed.btc.petertodd.org
  • Thanks for the update, although I'd say it would have been a great suggested edit for the accepted answer on this question. – Murch Apr 10 '17 at 11:58
  • For sure, will do that next time. – Tearo Dactyl Apr 10 '17 at 20:47

Yes, all "seed nodes" refer to bitcoin clients known (or suspected) to be more or less permanently available. The DNS seed nodes are those reached via DNS lookup; the others via their IP address. A more thorough answer (including other initial "bootstrapping" connection methods than these hardcoded seeds) has been given to another question.

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