bitcoin-seeder

Bitcoin-seeder is a crawler for the Bitcoin network, which exposes a list of reliable nodes via a built-in DNS server.

Features:

regularly revisits known nodes to check their availability
bans nodes after enough failures, or bad behaviour
accepts nodes down to v0.3.19 to request new IP addresses from, but only reports good post-v0.3.24 nodes.
keeps statistics over (exponential) windows of 2 hours, 8 hours, 1 day and 1 week, to base decisions on.
very low memory (a few tens of megabytes) and cpu requirements.
crawlers run in parallel (by default 24 threads simultaneously).

REQUIREMENTS

$ sudo apt-get install build-essential libboost-all-dev libssl-dev

USAGE

Assuming you want to run a dns seed on dnsseed.example.com, you will need an authorative NS record in example.com's domain record, pointing to for example vps.example.com:

$ dig -t NS dnsseed.example.com

;; ANSWER SECTION dnsseed.example.com. 86400 IN NS vps.example.com.

On the system vps.example.com, you can now run dnsseed:

./dnsseed -h dnsseed.example.com -n vps.example.com

If you want the DNS server to report SOA records, please provide an e-mail address (with the @ part replaced by .) using -m.

COMPILING

Compiling will require boost and ssl. On debian systems, these are provided by libboost-dev and libssl-dev respectively.

$ make

This will produce the dnsseed binary.

TESTING

It's sometimes useful to test dnsseed locally to ensure it's giving good output (either as part of development or sanity checking). You can inspect dnsseed.dump to inspect all nodes being tracked for crawling, or you can issue DNS requests directly. Example:

$ dig @:: -p 15353 dnsseed.example.com ^ ^ ^			__ Should match the host (-h) argument supplied to dnsseed
	___ Port number (example uses the user space port; see below)
___ Explicitly call the DNS server on localhost

RUNNING AS NON-ROOT

Typically, you'll need root privileges to listen to port 53 (name service).

One solution is using an iptables rule (Linux only) to redirect it to a non-privileged port:

$ iptables -t nat -A PREROUTING -p udp --dport 53 -j REDIRECT --to-port 15353

If properly configured, this will allow you to run dnsseed in userspace, using the -p 15353 option.

Another solution is allowing a binary to bind to ports < 1024 with setcap (IPv6 access-safe)

$ setcap 'cap_net_bind_service=+ep' /path/to/dnsseed