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Port Numbers
Newer Versions
Older Versions

Port Numbers

A port number allows a computer program to listen to, or connect to, a particular network channel. Think of it like TV channels - you have BBC1 on channel 1, ITV on channel 3; on your computer you have HTTP on port 80, and SimSig on port 50505 (this varies).

Note that if you're behind a router, rather than dial-up access, then you'll need to tell your router to forward the required port numbers to your PC.

Newer Versions

Since June 2008, the simulations use a system that allows the user to select two pre-defined ports (50505 and 50507) or custom ports to use. Servers publish the port number upon which they're hosting, which clients need to connect to the server. Chaining simulations also need this port number.

Older Versions

In a multiplay the connections between the host and the client(s) usually use port 4321 for older simulations.


  • this is the port used by the host (that is the server listens for connection(s) from the client on this port), while client(s) usually listen and talk on a different port. Usually in a multiplay it is enough that the firewall is opened only on the server side at this port (the client(s) will receive answer(s) on the same connection they have initiated).


This section has largely been superseded by newer versions which use the port numbering at the top of this page. It is kept here for historical reasons until all simulations use the newer method. Didcot and Swindon aren't available for download as a newer (scrolly) version.

When chaining the port numbers are listed in the following table. Note that a port may have been allocated now for future use, so the existence of an entry in this table doesn't mean that the relevant chaining is possible.

Chaining sim
Chained sim
Bristol Exeter 4902
Bristol Swindon 4601
Bristol Westbury 4803
Cambridge King's Cross 6251
Cambridge Peterborough 6255
Didcot Swindon 4600
Doncaster Peterborough 6253
Exeter Bristol 5003
Exeter Westbury 4804
Gloucester Swindon 4603
King's Cross Cambridge 6250
King's Cross North London Line 5600
King's Cross Peterborough 5800
North London Line King's Cross 5700
Peterborough Cambridge 6254
Peterborough Doncaster 6252
Peterborough King's Cross 5900
Swindon Bristol 4701
Swindon Didcot 4502
Swindon Gloucester 5400
Swindon Westbury 4801
Westbury Bristol 4702
Westbury Exeter 4901
Westbury Swindon 4602

Last edited by GeoffM on 15/09/2016 at 03:01