What is the largest TCP IP network port number allowable for IPv4

Question

What is the highest port number one can use

User · Accepted Answer

The port number is an unsigned 16-bit integer  so 65535

User · Answer

It should be 65535

User · Answer

The largest port number is an unsigned short 2 16-1  65535  A registered port is one assigned by the Internet Corporation for Assigned Names and Numbers  ICANN  to a certain use  Each registered port is in the range 1024   49151   Since 21 March 2001 the registry agency is ICANN  before that time it was IANA   Ports with numbers lower than those of the registered ports are called well known ports  port with numbers greater than those of the registered ports are called dynamic and or private ports   Wikipedia   Registered Ports

User · Answer

It depends on which range you re talking about  but the dynamic range goes up to 65535 or 2 16-1  16 bits    http   en wikipedia org wiki List of TCP and UDP port numbers

User · Answer

Valid numbers for ports are  0 to 2 16-1   0 to 65535  That is because a port number is 16 bit length   However ports are divided into  Well-known ports  0 to 1023  used for system services e g  HTTP  FTP  SSH  DHCP      Registered user ports  1024 to 49151  you can use it for your server  but be careful some famous applications  like Microsoft SQL Server database management system  MSSQL  server or Apache Derby Network Server are already taking from this range i e  it is not recommended to assign the port of MSSQL to your server otherwise if MSSQL is running then your server most probably will not run because of port conflict   Dynamic private ports  49152 to 65535   not used for the servers rather the clients e g  in NATing service   In programming you can use any numbers 0 to 65535 for your server  however you should stick to the ranges mentioned above  otherwise some system services or some applications will not run because of port conflict  Check the list of most ports here  https   en wikipedia org wiki List of TCP and UDP port numbers

User · Answer

Just a followup to smashery s answer  The ephemeral port range  on Linux at least  and I suspect other Unices as well  is not a fixed  This can be controlled by writing to   proc sys net ipv4 ip local port range  The only restriction  as far as IANA is concerned  is that ports below 1024 are designated to be well-known ports  Ports above that are free for use  Often you ll find that ports below 1024 are restricted to superuser access  I believe for this very reason

User · Answer

As I understand it  you should only use up to 49151  as from 49152 up to 65535 are reserved for Ephemeral ports

User · Answer

According to RFC 793  the port is a 16 bit unsigned int   This means the range is 0 - 65535   However  within that range  ports 0 - 1023 are generally reserved for specific purposes  I say generally because  apart from port 0  there is usually no enforcement of the 0-1023 reservation  TCP UDP implementations usually don t enforce reservations apart from 0  You can  if you want to  run up a web server s TLS port on port 80  or 25  or 65535 instead of the standard 443  Likewise  even tho it is the standard that SMTP servers listen on port 25  you can run it on 80  443  or others   Most implementations reserve 0 for a specific purpose - random port assignment  So in most implementations  saying  listen on port 0  actually means  I don t care what port I use  just give me some random unassigned port to listen on    So any limitation on using a port in the 0-65535 range  including 0  ephemeral reservation range etc  is implementation  i e  OS driver  specific  however all  including 0  are valid ports in the RFC 793

[tcp] What is the largest TCP/IP network port number allowable for IPv4?

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