Date: Sat, 29 Jan 2022 23:02:24 +0100 (CET)
From: Prayank <prayank@tutanota.de>
To: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Message-ID: <Mubr4YT--3-2@tutanota.de>
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Subject: [bitcoin-dev] non-default ports for automatic connections in
	Bitcoin P2P network
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## Using non-default ports for automatic connections in Bitcoin P2P network


ISPs can block default port 8333 used by Bitcoin nodes. One example:
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-September/0107=
98.html

While it would still be possible for crawlers and scanners to know about bi=
tcoin nodes listening on non-default ports using other methods, it can be h=
elpful in lot of countries that use basic things to block: domain, port etc=
.

In October 2021 a [pull request][1] was merged in Bitcoin Core in which lot=
 of contributors
agreed to allow non default ports for automatic connections. It did not imp=
lement everything,
was limited to discussing the concept and allow AddrMan to support multiple=
 ports per IP.

It was followed by another [pull request][2] in November 2021 which is stil=
l open and makes most
of the changes required for non-default ports to work with automatic connec=
tions.

I could not find any major issues with the changes however had some nits in=
cluding a discussion on
mailing list which was even requested by a few other reviewers.


=3D=3D=3DThings that I found during my review, research and testing=3D=3D=
=3D

1.One user had posted about issues with default port 8333 on [bitcointalk][=
3] in July 2010. VMWare server
also used port 8333 so an option was requested to change port. This option =
was added in [May 2011][4] by Gavin Andresen. Gavin has discussed this opti=
on and related issues in detail with others on [bitcointalk][5].

2.I tried running signet for 1 hour v22.0 and 1 hour PR branch with debug=
=3Dnet. v22.0 had only 38333 port with different IPs in debug.log for conne=
ctions. PR branch had 2 feeler connections with non-default ports 38331 and=
 13833.

Note: Default ports used in Bitcoin Core are 8333(mainnet), 18333(testnet),=
 18444(regtest) and 38333(signet)

3.Wrote a [PowerShell script][6] and tested it on v22.0 and PR branch which=
 bans all peers every 100 seconds using default port. It works as expected =
and I could see one peer using port 3111 on signet.

4.I am not sure about the 'bad ports' list in Bitcoin Core added in PR #235=
42


8333 in leet becomes 'beee' in plain text. Not sure if this was considered =
by Satoshi to hardcode 8333 for Bitcoin.


=C2=A0 [1]: https://github.com/bitcoin/bitcoin/pull/23306
=C2=A0 [2]: https://github.com/bitcoin/bitcoin/pull/23542
=C2=A0 [3]: https://bitcointalk.org/index.php?topic=3D322.0
=C2=A0 [4]: https://github.com/bitcoin/bitcoin/pull/221
=C2=A0 [5]: https://bitcointalk.org/index.php?topic=3D589.0
=C2=A0 [6]: https://github.com/prayank23/bitcoin-ps-scripts/blob/main/Scrip=
ts/Node/ban_default_peers.ps1

--=20
Prayank

A3B1 E430 2298 178F

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    <meta http-equiv=3D"content-type" content=3D"text/html; charset=3DUTF-8=
">
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  <body>
<div>## Using non-default ports for automatic connections in Bitcoin P2P ne=
twork<br></div><div dir=3D"auto"><br></div><div dir=3D"auto"><br></div><div=
 dir=3D"auto">ISPs can block default port 8333 used by Bitcoin nodes. One e=
xample:<br></div><div dir=3D"auto">https://lists.linuxfoundation.org/piperm=
ail/bitcoin-dev/2015-September/010798.html<br></div><div dir=3D"auto"><br><=
/div><div dir=3D"auto">While it would still be possible for crawlers and sc=
anners to know about bitcoin nodes listening on non-default ports using oth=
er methods, it can be helpful in lot of countries that use basic things to =
block: domain, port etc.<br></div><div dir=3D"auto"><br></div><div dir=3D"a=
uto">In October 2021 a [pull request][1] was merged in Bitcoin Core in whic=
h lot of contributors<br></div><div dir=3D"auto">agreed to allow non defaul=
t ports for automatic connections. It did not implement everything,<br></di=
v><div dir=3D"auto">was limited to discussing the concept and allow AddrMan=
 to support multiple ports per IP.<br></div><div dir=3D"auto"><br></div><di=
v dir=3D"auto">It was followed by another [pull request][2] in November 202=
1 which is still open and makes most<br></div><div dir=3D"auto">of the chan=
ges required for non-default ports to work with automatic connections.<br><=
/div><div dir=3D"auto"><br></div><div dir=3D"auto">I could not find any maj=
or issues with the changes however had some nits including a discussion on<=
br></div><div dir=3D"auto">mailing list which was even requested by a few o=
ther reviewers.<br></div><div dir=3D"auto"><br></div><div dir=3D"auto"><br>=
</div><div dir=3D"auto">=3D=3D=3DThings that I found during my review, rese=
arch and testing=3D=3D=3D<br></div><div dir=3D"auto"><br></div><div dir=3D"=
auto">1.One user had posted about issues with default port 8333 on [bitcoin=
talk][3] in July 2010. VMWare server<br></div><div dir=3D"auto">also used p=
ort 8333 so an option was requested to change port. This option was added i=
n [May 2011][4] by Gavin Andresen. Gavin has discussed this option and rela=
ted issues in detail with others on [bitcointalk][5].<br></div><div dir=3D"=
auto"><br></div><div dir=3D"auto">2.I tried running signet for 1 hour v22.0=
 and 1 hour PR branch with debug=3Dnet. v22.0 had only 38333 port with diff=
erent IPs in debug.log for connections. PR branch had 2 feeler connections =
with non-default ports 38331 and 13833.<br></div><div dir=3D"auto"><br></di=
v><div dir=3D"auto">Note: Default ports used in Bitcoin Core are 8333(mainn=
et), 18333(testnet), 18444(regtest) and 38333(signet)<br></div><div dir=3D"=
auto"><br></div><div dir=3D"auto">3.Wrote a [PowerShell script][6] and test=
ed it on v22.0 and PR branch which bans all peers every 100 seconds using d=
efault port. It works as expected and I could see one peer using port 3111 =
on signet.<br></div><div dir=3D"auto"><br></div><div dir=3D"auto">4.I am no=
t sure about the 'bad ports' list in Bitcoin Core added in PR #23542<br></d=
iv><div dir=3D"auto"><br></div><div dir=3D"auto"><br></div><div dir=3D"auto=
">8333 in leet becomes 'beee' in plain text. Not sure if this was considere=
d by Satoshi to hardcode 8333 for Bitcoin.<br></div><div dir=3D"auto"><br><=
/div><div dir=3D"auto"><br></div><div dir=3D"auto">&nbsp; [1]: https://gith=
ub.com/bitcoin/bitcoin/pull/23306<br></div><div dir=3D"auto">&nbsp; [2]: ht=
tps://github.com/bitcoin/bitcoin/pull/23542<br></div><div dir=3D"auto">&nbs=
p; [3]: https://bitcointalk.org/index.php?topic=3D322.0<br></div><div dir=
=3D"auto">&nbsp; [4]: https://github.com/bitcoin/bitcoin/pull/221<br></div>=
<div dir=3D"auto">&nbsp; [5]: https://bitcointalk.org/index.php?topic=3D589=
.0<br></div><div dir=3D"auto">&nbsp; [6]: https://github.com/prayank23/bitc=
oin-ps-scripts/blob/main/Scripts/Node/ban_default_peers.ps1<br></div><div><=
br></div><div>-- <br></div><div>Prayank<br></div><div><br></div><div dir=3D=
"auto">A3B1 E430 2298 178F<br></div>  </body>
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