Use IPv4-encoded IPv6 address to get IPv4 node address with port number from DNS seeds

1440000bytes commented at 5:35 pm on September 13, 2024: none

Please describe the feature you’d like to see added.

Use the IPv4-encoded IPv6 addresses that start with a reserved prefix to support nodes with non-default ports in bootstrapping process.

There are 7k IPv4 reachable nodes and some of them use non-default ports:

Example: Port 39388 is used by more than 1000 nodes

The scripts used in this testing guide can be helpful to discover more nodes with non-default ports: https://web.archive.org/web/20230129111013/https://github.com/bitcoin-core/bitcoin-devwiki/wiki/23.0-Release-Candidate-Testing-Guide

Non-default ports are supported in automatic connections since v23.0: #23542. However, DNS seeds cannot return port numbers in DNS queries. So, the nodes with non-default port will never be a part of bootstrapping.

Related discussion:

#23542 (comment)

https://delvingbitcoin.org/t/hardcoded-seeds-dns-seeds-and-darknet-nodes/1123/8

https://njump.me/nevent1qqst405e4jwg9fwufrqrmjczxdc6desc8xsqlhzsvk7w5wk3lrlmqlczyq9288j6a7v6qq98hkctfxg43jftcj4zp7m9jvd995z4kh4kmlmns9h6j6q

Describe the solution you’d like

IPv4 address and port number can be encoded in an IPv6 address by DNS seeds. IPv6 address format:

0| 80 bits                          | 32 bits         | 16 bits |
1|----------------------------------|-----------------|---------|
2| 0000 0000 0000 0000 abcd (prefix)| IPv4 Address    | Port    |

Python script to encode and decode: https://gitlab.com/-/snippets/3746764

 01. Encode
 12. Decode
 23. Exit
 3Enter your choice: 1
 4Enter IPv4 address: 127.0.0.1
 5Enter port number: 8080
 6Encoded IPv6: 0000:0000:0000:0000:abcd:7f00:0001:1f90
 71. Encode
 82. Decode
 93. Exit
10Enter your choice: 2
11Enter the encoded IPv6 address: ::abcd:7f00:1:1f90
12Decoded Data (IPv4, Port): 127.0.0.1, 8080

I am using clouflare for DNS and tested this on a domain:

IPv6 addresses are valid, AAAA for domain is resolved successfully by getaddrinfo and Google DNS: https://dns.google/resolve?name=test.joinstr.xyz&type=AAAA&cd=true

Describe any alternatives you’ve considered

IPv4 mapped IPv6 addresses are supported based on RFC 4291 and I tested it on Cloudflare. However, you cannot add anything more than IPv4 address.

https://datatracker.ietf.org/doc/html/rfc4291#section-2.5.5.2
NULL and TXT records

Related issues:

https://delvingbitcoin.org/t/hardcoded-seeds-dns-seeds-and-darknet-nodes/1123/6

https://njump.me/nevent1qqsp9v4jxynf8k93erdl2ku3nh92ng7fwr695lvwmh0tek8k2r6fvscpp4mhxue69uhkummn9ekx7mqpz3mhxue69uhhyetvv9ujuerpd46hxtnfdupzqz4rnedwlxdqqznmmv95ny2cey4uf23qldjexxjj6p2mt6mdlaeceaxu3t

1440000bytes added the label Feature on Sep 13, 2024

petertodd commented at 8:52 pm on September 16, 2024: contributor

NACK

The purpose of the DNS seeds is just to find some bootstrap nodes. More addresses are then learned from those bootstrap nodes, and additional connections are made to them. There’s no need for the initial bootstrap nodes to be sampled from the entire set of possible nodes.

1440000bytes commented at 9:29 pm on September 16, 2024: none

The purpose of the DNS seeds is just to find some bootstrap nodes. There’s no need for the initial bootstrap nodes to be sampled from the entire set of possible nodes.

I disagree. @cdecker’s DNS seed was recently removed from bitcoin core because it did not return enough nodes for bootstrapping. It was noticed that @luke-jr’s DNS seed returned only nodes with older version and now it only returns newer versions.

Such results violate 1 and 2 mentioned in DNS seed policy and even if the policy is useless, they do affect the bootstrapping process used for a decentralized network.

If most nodes start using non-default ports for various reasons, including government censorship, DNS seeds may become irrelevant.

petertodd commented at 10:08 pm on September 16, 2024: contributor

@1440000bytes As you can see by clicking through to the removal pull-req, the problem wasn’t “insufficient nodes”, it was failing to implement filtering properly: #29911

Re: censorship, that’s just nonsense. If government is blanket censoring specific ports they can pretty much just as easily censor the DNS seeding mechanism itself. There’s no need to include complex new code for such a niche use-case - you can easily bootstrap a node by getting the IP address of any other working node and connecting to it.

1440000bytes commented at 1:52 pm on September 18, 2024: none

@1440000bytes As you can see by clicking through to the removal pull-req, the problem wasn’t “insufficient nodes”, it was failing to implement filtering properly: #29911

Sharing the PR rationale/description below with people who ACKed it:

0This seeder no longer appears to be serving sufficient addresses.
1
2Fixes [#29911](/bitcoin-bitcoin/29911/)

0ACKs for top commit:
1  1440000bytes:
2    ACK https://github.com/bitcoin/bitcoin/commit/c88a7dc53e3be7489605c3326cf768df5437393a
3  virtu:
4    ACK https://github.com/bitcoin/bitcoin/commit/c88a7dc53e3be7489605c3326cf768df5437393a
5  mzumsande:
6    ACK https://github.com/bitcoin/bitcoin/commit/c88a7dc53e3be7489605c3326cf768df5437393a
7  BrandonOdiwuor:
8    ACK https://github.com/bitcoin/bitcoin/commit/c88a7dc53e3be7489605c3326cf768df5437393a

Re: censorship, that’s just nonsense.

Governments dont act rationally and sometimes block ports: https://x.com/SimpleXChat/status/1835072004921475219

Non-default ports were supported in v23.0 and p2p v2 is used for a reason even if ISP can identify a bitcoin node.

Use IPv4-encoded IPv6 address to get IPv4 node address with port number from DNS seeds #30900

Please describe the feature you’d like to see added.

Is your feature related to a problem, if so please describe it.

Describe the solution you’d like

Describe any alternatives you’ve considered