BUIP018: Bitnodes Seeding and User-Configurable DNS Seeds
Proposer: Simon Liu
Submitted: 2016-04-02
Status: passed


Improve seeding so that a client can quickly and reliably find peers
when trying to connect to the network. Currently Bitcoin relies on
hard-coded DNS seed addresses and hard-coded IP addresses of nodes. It
is not possible for users to change the DNS seeds unless they can
compile the software themselves. Relying on hard-coded IP addresses is


This BUIP intends to:

  1. Obtain peer addresses from the public Bitnodes API [1] operated by
    21.co. The Bitnodes software itself is open-source [2]. Active peers
    are obtained from the Bitnodes Leaderboard [3].

  2. Improve DNS seeding by:
    (a) Enabling users to specify custom DNS seed hosts in bitcoin.conf and
    via command-line options. New options are ‘bitnodes’, ‘forcebitnodes’,
    (b) Update the default DNS seed addresses to represent a variety of
    community sources with reliable uptime (using data from

  3. Remove mainnet usage of hard-coded node IP addresses as they are
    likely to be stale and no longer active.


Code is available for review:

Pull request against BU 0.12:

The hard-coded DNS seeds have been updated to reflect a cross-section of
the Bitcoin community, so that the client is no longer relying on just
volunteer seeds (with variable uptime based on recent data from
bitcoinstats.com): BTCC, Bitnodes, Pieter Wuille . More can be added
over time, with a preference for individuals and institutions with the
resources to maintain uptime of their Bitcoin related infrastructure

By default, accessing the public API at bitnodes.21.co is enabled - just
like DNS seeding which also remains enabled. Thus a client will
bootstrap onto the network by obtaining peers from these two different

’Example usage:

To disable Bitnodes:

bitcoind -bitnodes=0

To always query for peer addresses via Bitnodes API, even if many peers
already known:

bitcoind -forcebitnodes=1

Use custom DNS seeds and over-ride client defaults:

bitcoind -usednsseed=seed.bitnodes.io -usednsseed=seed.btcc.com

To verify that hard-coded node addresses are no longer used, disable
Bitnodes and DNS seeding. When launching Bitcoin for the first time
(i.e. peers.dat does not exist) the client will never connect to the

bitcoind -dnsseed=0 -bitnodes=0


[1] https://bitnodes.21.co/api/
“Refactor hard-coded DNS seeds into configuration file” (Jan 2016) -