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READ THE CODE

Inside Bitcoin

The code behind the network, with room to understand it.

Stable release v32.1bitcoin/bitcoin · f0de87f04062 ↗3,020 source files · 47.5 MB stored on the server440 file guides

Release published 2026-10-28 · Snapshot fetched 2026-11-01. Latest stable release at fetch time; development branches and Git history are excluded. Only the selected code window and visible folders load here.

bitcoin / bitcoinstable

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bitcoin / doc / p2p-bad-ports.md

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3,360 bytes · SHA-256 808dc6485a7956cf… · View upstream ↗

1When Bitcoin Core automatically opens outgoing P2P connections, it chooses
2a peer (address and port) from its list of potential peers. This list is
3populated with unchecked data gossiped over the P2P network by other peers.
4
5A malicious actor may gossip an address:port where no Bitcoin node is listening,
6or one where a service is listening that is not related to the Bitcoin network.
7As a result, this service may occasionally get connection attempts from Bitcoin
8nodes.
9
10"Bad" ports are ones used by services which are usually not open to the public
11and usually require authentication. A connection attempt (by Bitcoin Core,
12trying to connect because it thinks there is a Bitcoin node on that
13address:port) to such service may be considered a malicious action by an
14ultra-paranoid administrator. An example for such a port is 22 (ssh). On the
15other hand, connection attempts to public services that usually do not require
16authentication are unlikely to be considered a malicious action,
17e.g. port 80 (http).
18
19Below is a list of "bad" ports which Bitcoin Core avoids when choosing a peer to
20connect to. If a node is listening on such a port, it will likely receive fewer
21incoming connections.
22
23    1:     tcpmux
24    7:     echo
25    9:     discard
26    11:    systat
27    13:    daytime
28    15:    netstat
29    17:    qotd
30    19:    chargen
31    20:    ftp data
32    21:    ftp access
33    22:    ssh
34    23:    telnet
35    25:    smtp
36    37:    time
37    42:    name
38    43:    nicname
39    53:    domain
40    69:    tftp
41    77:    priv-rjs
42    79:    finger
43    87:    ttylink
44    95:    supdup
45    101:   hostname
46    102:   iso-tsap
47    103:   gppitnp
48    104:   acr-nema
49    109:   pop2
50    110:   pop3
51    111:   sunrpc
52    113:   auth
53    115:   sftp
54    117:   uucp-path
55    119:   nntp
56    123:   NTP
57    135:   loc-srv /epmap
58    137:   netbios
59    139:   netbios
60    143:   imap2
61    161:   snmp
62    179:   BGP
63    389:   ldap
64    427:   SLP (Also used by Apple Filing Protocol)
65    465:   smtp+ssl
66    512:   print / exec
67    513:   login
68    514:   shell
69    515:   printer
70    526:   tempo
71    530:   courier
72    531:   chat
73    532:   netnews
74    540:   uucp
75    548:   AFP (Apple Filing Protocol)
76    554:   rtsp
77    556:   remotefs
78    563:   nntp+ssl
79    587:   smtp (rfc6409)
80    601:   syslog-conn (rfc3195)
81    636:   ldap+ssl
82    989:   ftps-data
83    990:   ftps
84    993:   ldap+ssl
85    995:   pop3+ssl
86    1719:  h323gatestat
87    1720:  h323hostcall
88    1723:  pptp
89    2049:  nfs
90    3306:  MySQL
91    3389:  RDP / Windows Remote Desktop
92    3659:  apple-sasl / PasswordServer
93    4045:  lockd
94    5060:  sip
95    5061:  sips
96    5432:  PostgreSQL
97    5900:  VNC
98    6000:  X11
99    6566:  sane-port
100    6665:  Alternate IRC
101    6666:  Alternate IRC
102    6667:  Standard IRC
103    6668:  Alternate IRC
104    6669:  Alternate IRC
105    6697:  IRC + TLS
106    10080: Amanda
107    27017: MongoDB
108
109For further information see:
110
111[pull/23306](https://github.com/bitcoin/bitcoin/pull/23306#issuecomment-947516736)
112
113[pull/23542](https://github.com/bitcoin/bitcoin/pull/23542)
114
115[fetch.spec.whatwg.org](https://fetch.spec.whatwg.org/#port-blocking)
116
117[chromium.googlesource.com](https://chromium.googlesource.com/chromium/src.git/+/refs/heads/main/net/base/port_util.cc)
118
119[hg.mozilla.org](https://hg.mozilla.org/mozilla-central/file/tip/netwerk/base/nsIOService.cpp)
120

A READING COMPANION

Source available. Guide coming next.

This file is included in the stable source snapshot. A file-specific guide has not been published yet.

440 guided files · 2,580 pending. Guides cover key sections, not every line.

cmake/bitcoin-build-config.h.in src/consensus/amount.h src/consensus/consensus.h src/primitives/block.h src/primitives/transaction.h src/crypto/sha256.h src/util/moneystr.h src/clientversion.h src/uint256.h src/script/script.h src/policy/policy.h CMakeLists.txt README.md COPYING src/consensus/tx_check.cpp src/consensus/tx_verify.cpp src/consensus/merkle.cpp src/pow.cpp src/validation.cpp src/script/interpreter.cpp src/script/solver.cpp src/script/sign.cpp src/key_io.cpp src/net.cpp src/net_processing.cpp src/netaddress.cpp src/protocol.h src/wallet/wallet.cpp src/wallet/spend.cpp

Code page 1

src/wallet/receive.cpp

src/wallet/coinselection.cpp

src/wallet/fees.cpp

src/wallet/load.cpp

src/txmempool.cpp

src/node/miner.cpp

src/chainparams.cpp

src/consensus/validation.h

src/primitives/transaction.cpp

src/script/descriptor.cpp

src/bitcoin-cli.cpp

src/rpc/blockchain.cpp

src/rpc/rawtransaction.cpp

src/crypto/sha256.cpp

src/serialize.h

src/consensus/merkle.h

src/consensus/tx_check.h

src/consensus/tx_verify.h

src/policy/feerate.h

src/policy/feerate.cpp

src/primitives/transaction_identifier.h

src/chainparamsbase.h

src/chainparamsbase.cpp

src/util/moneystr.cpp

src/crypto/ripemd160.h

src/crypto/sha1.h

src/crypto/sha512.h

src/crypto/hmac_sha256.h

src/crypto/hmac_sha512.h

src/crypto/hmac_sha256.cpp

src/crypto/hmac_sha512.cpp

src/crypto/hkdf_sha256_32.h

src/crypto/hkdf_sha256_32.cpp

src/support/cleanse.h

src/support/cleanse.cpp

src/arith_uint256.h

src/blockencodings.h

src/blockfilter.h

src/crypto/siphash.h

src/crypto/siphash.cpp

src/crypto/muhash.h

src/crypto/chacha20.h

src/crypto/poly1305.h

src/crypto/chacha20poly1305.h

src/crypto/chacha20poly1305.cpp

src/compressor.h

src/compressor.cpp

src/flatfile.cpp

src/dbwrapper.h

src/util/chaintype.h

src/util/chaintype.cpp

src/scheduler.h

src/scheduler.cpp

src/checkqueue.h

src/threadsafety.h

src/util/obfuscation.h

src/util/byte_units.h

src/util/overflow.h

src/blockencodings.cpp

src/blockfilter.cpp

src/merkleblock.cpp

src/merkleblock.h

src/addrman.cpp

src/netgroup.cpp

src/net_permissions.cpp

src/netbase.cpp

src/torcontrol.cpp

src/net_types.h

src/net_types.cpp

src/policy/packages.cpp

src/policy/rbf.cpp

src/policy/truc_policy.cpp

src/policy/ephemeral_policy.cpp

src/policy/settings.cpp

src/policy/policy.cpp

src/node/transaction.cpp

src/node/coin.cpp

src/rpc/client.cpp

src/rpc/external_signer.cpp

src/rpc/request.cpp

src/rpc/server_util.cpp

src/rpc/fees.cpp

src/rpc/output_script.cpp

src/rpc/rawtransaction_util.cpp

src/rpc/server.cpp

src/rpc/mempool.cpp

src/rpc/mining.cpp

src/rpc/net.cpp

src/rpc/node.cpp

src/rpc/blockchain.h

src/rpc/client.h

src/rpc/mempool.h

src/rpc/mining.h

src/rpc/rawtransaction_util.h

src/rpc/register.h

src/rpc/request.h

src/rpc/server_util.h

src/rpc/protocol.h

src/rpc/server.h

src/rpc/signmessage.cpp

src/rpc/txoutproof.cpp

src/rpc/util.cpp

src/wallet/rpc/addresses.cpp

src/wallet/rpc/backup.cpp

src/wallet/rpc/coins.cpp

src/wallet/rpc/encrypt.cpp

src/wallet/rpc/signmessage.cpp

src/wallet/rpc/util.cpp

src/wallet/rpc/util.h

src/wallet/coincontrol.cpp

src/wallet/coincontrol.h

src/wallet/context.cpp

src/wallet/context.h

src/wallet/crypter.cpp

src/wallet/crypter.h

src/wallet/db.cpp

src/wallet/export.cpp

src/wallet/external_signer_scriptpubkeyman.cpp

src/wallet/rpc/spend.cpp

src/wallet/rpc/transactions.cpp

src/wallet/rpc/wallet.cpp

src/wallet/feebumper.cpp

src/wallet/feebumper.h

src/index/base.h

src/index/base.cpp

src/index/txindex.h

src/index/txindex.cpp

src/index/txindex_key.h

src/index/txospenderindex.h

src/index/txospenderindex.cpp

src/index/blockfilterindex.h

src/index/blockfilterindex.cpp

src/index/coinstatsindex.h

src/index/coinstatsindex.cpp

src/index/db_key.h

src/index/disktxpos.h

src/kernel/chain.cpp

src/kernel/chain.h

src/kernel/checks.cpp

src/kernel/checks.h

src/kernel/context.cpp

src/kernel/context.h

src/kernel/cs_main.cpp

src/kernel/cs_main.h

src/kernel/disconnected_transactions.cpp

src/kernel/disconnected_transactions.h

src/kernel/mempool_removal_reason.cpp

src/kernel/mempool_removal_reason.h

src/kernel/coinstats.cpp

src/kernel/coinstats.h

src/kernel/chainparams.cpp

src/kernel/chainparams.h

src/wallet/sqlite.cpp

src/wallet/sqlite.h

src/wallet/transaction.cpp

src/wallet/transaction.h

src/wallet/dump.cpp

src/wallet/dump.h

src/wallet/init.cpp

src/wallet/walletutil.cpp

src/wallet/walletutil.h

src/wallet/wallettool.cpp

src/wallet/wallettool.h

src/wallet/export.h

src/wallet/migrate.cpp

src/wallet/migrate.h

src/wallet/db.h

src/wallet/walletdb.cpp

src/wallet/interfaces.cpp

src/wallet/scriptpubkeyman.cpp

src/wallet/scriptpubkeyman.h

src/kernel/bitcoinkernel.cpp

src/kernel/bitcoinkernel.h

src/kernel/bitcoinkernel_wrapper.h

src/node/abort.cpp

src/node/abort.h

src/node/caches.cpp

src/node/caches.h

src/kernel/caches.h

src/node/chainstate.cpp

src/node/chainstate.h

src/node/blockstorage.cpp

src/node/blockstorage.h

src/node/mempool_persist.cpp

src/node/mempool_persist.h

src/node/utxo_snapshot.cpp

src/node/utxo_snapshot.h

src/node/kernel_notifications.cpp

src/node/kernel_notifications.h

src/node/blockmanager_args.cpp

src/kernel/blockmanager_opts.h

src/util/expected.cpp

src/policy/settings.h

src/util/types.h

src/kernel/messagestartchars.h

src/kernel/warning.h

src/util/exception.h

src/common/license_info.h

src/node/coins_view_args.h

src/node/database_args.h

src/util/batchpriority.h

src/util/ui_change_type.h

src/node/coins_view_args.cpp

src/node/peerman_args.h

src/util/serfloat.h

src/node/blockmanager_args.h

src/node/database_args.cpp

src/util/overloaded.h

src/util/rbf.cpp

src/util/thread.h

src/common/netif.h

src/common/url.h

src/interfaces/types.h

src/node/chainstatemanager_args.h

src/node/minisketchwrapper.h

src/util/macros.h

src/util/syserror.h

src/common/run_command.h

src/util/bytevectorhash.cpp

src/node/mempool_persist_args.cpp

src/util/exec.h

src/crypto/hex_base.h

src/node/mempool_persist_args.h

src/interfaces/echo.h

src/util/batchpriority.cpp

src/util/threadnames.h

src/node/coin.h

src/node/mempool_args.h

src/util/asmap.h

src/util/bytevectorhash.h

src/node/context.cpp

src/util/insert.h

src/util/readwritefile.h

src/util/thread.cpp

src/kernel/types.h

src/interfaces/rpc.h

src/util/fees.cpp

src/node/peerman_args.cpp

src/node/interface_ui.cpp

src/interfaces/handler.h

src/node/mining_args.h

src/util/hasher.cpp

src/common/init.h

src/kernel/mempool_limits.h

src/common/system.h

src/crypto/sha3.h

src/util/threadinterrupt.cpp

src/node/protocol_version.h

src/util/exception.cpp

src/common/messages.h

src/node/connection_types.cpp

src/util/bip32.h

src/common/license_info.cpp

src/util/stdmutex.h

src/common/run_command.cpp

src/util/check.cpp

src/util/golombrice.h

src/node/types.h

src/node/timeoffsets.h

src/util/readwritefile.cpp

src/util/fastrange.h

src/util/signalinterrupt.h

src/util/task_runner.h

src/util/syserror.cpp

src/common/interfaces.cpp

src/common/types.h

src/util/threadinterrupt.h

src/kernel/chainstatemanager_opts.h

src/node/psbt.h

src/policy/ephemeral_policy.h

src/util/trace.h

src/common/url.cpp

src/kernel/mempool_options.h

src/util/serfloat.cpp

src/kernel/notifications_interface.h

src/node/timeoffsets.cpp

src/node/warnings.cpp

src/util/hash_type.h

src/crypto/hex_base.cpp

src/node/eviction.h

src/util/tokenbucket.h

src/crypto/aes.h

src/common/pcp.h

src/util/feefrac.cpp

src/node/transaction.h

src/util/threadnames.cpp

src/common/signmessage.h

src/util/exec.cpp

src/util/signalinterrupt.cpp

src/attributes.h

src/chainparams.h

src/clientversion.cpp

src/common/signmessage.cpp

src/compat/assumptions.h

src/compat/byteswap.h

src/compat/cpuid.h

src/compat/endian.h

src/compat/stdin.cpp

src/compat/stdin.h

src/core_memusage.h

src/crypto/common.h

src/deploymentinfo.cpp

src/deploymentinfo.h

src/deploymentstatus.cpp

src/deploymentstatus.h

src/dummywallet.cpp

src/external_signer.h

src/indirectmap.h

src/init/basic.cpp

src/init/bitcoin-gui.cpp

src/init/bitcoin-node.cpp

src/init/bitcoin-qt.cpp

src/init/bitcoin-wallet.cpp

src/init/bitcoind.cpp

src/init/common.h

src/interfaces/init.h

src/interfaces/ipc.h

src/logging/categories.h

src/logging/timer.h

src/net_permissions.h

src/netmessagemaker.h

src/node/chainstatemanager_args.cpp

src/node/connection_types.h

src/node/context.h

src/node/interface_ui.h

src/node/mempool_args.cpp

src/node/mining_args.cpp

src/node/minisketchwrapper.cpp

src/node/txreconciliation.h

src/node/warnings.h

src/outputtype.cpp

src/outputtype.h

src/policy/fees/estimator_args.cpp

src/policy/fees/estimator_args.h

src/policy/fees/estimator_man.cpp

src/policy/fees/estimator_man.h

src/policy/packages.h

src/policy/rbf.h

src/policy/truc_policy.h

src/primitives/block.cpp

src/randomenv.h

src/script/keyorigin.h

src/script/parsing.cpp

src/script/parsing.h

src/script/script_error.h

src/script/sigcache.cpp

src/script/sigcache.h

src/script/solver.h

src/script/verify_flags.h

src/semaphore_grant.h

src/support/allocators/secure.h

src/support/allocators/zeroafterfree.h

src/uint256.cpp

src/util/bip32.cpp

src/util/fees.h

src/util/fs.cpp

src/util/result.h

src/util/string.cpp

src/util/tokenpipe.cpp

src/util/translation.h

src/util/vector.h

src/versionbits.h

src/versionbits_impl.h

src/wallet/external_signer_scriptpubkeyman.h

src/wallet/fees.h

src/wallet/load.h

src/wallet/receive.h

src/wallet/rpc/wallet.h

src/wallet/types.h

src/walletinitinterface.h

src/zmq/zmqabstractnotifier.cpp

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