This is the Winsock Programmer's FAQ. See the Introduction section for history, a list of mirrors, and information about the maintainer.

This FAQ answers the most commonly-asked questions on the alt.winsock.programming and comp.os.ms-windows.programmer.tools.winsock newsgroups. The FAQ also contains a growing repository of Winsock programming information and links useful for all levels of programmers. Please email me if you have any corrections or additions for the list.

If you would like to view this FAQ off-line, you can download a ZIPped version (405 KB, last packaged 2001.01.06) of these pages.

What's New?

2001.02.06

Did a minor re-write on the I/O strategies article. I clarified some my advice on non-blocking sockets (Heuristic 2), split some information out of the old Heuristic 2 into its own item (Heuristic 3, now), and removed some redundant and misleading advice about asynchronous sockets from Heuristic 4. I also added Heuristic 12, on designing your program around the protocol.

2001.01.23

Made several clarifications to the BSD sockets compatibility article.

2000.12.18

Added an item that has a link that will get you off the Winsock 2 Mailing List.

Previous "What's New" Entries...

the FAQ

Contents

Section 0 - Introduction

0.1 The Original Introduction
0.2 A Bit About the Maintainer
0.3 Legal Stuff
0.4 Mirrors
0.5 What if your question is not in the FAQ?
0.6 Is there a mailing list for FAQ updates?
0.7 Language Bias
0.8 Protocol Bias
0.9 Acknowledgements

Section 1 - General Winsock Information

1.1 What is Winsock?
1.2 What's the difference between Winsock and TCP/IP?
1.3 What newsgroups and mailing lists exist for Winsock and TCP/IP?
1.4 How do I get off the Winsock 2 Mailing List?
1.5 What versions of Winsock are available?
1.6 What does Winsock 2 have that Winsock 1.1 doesn't?
1.7 When is the next rev of the specification due out?
1.8 Can Winsock speak { DECNet, IPX/SPX, etc. }?

Section 2 - Issues for New Winsock Programmers

2.1 Are there any sample apps on the Net?
2.2 Do I need to initialize the WSAData structure before calling WSAStartup?
2.3 I'm getting link errors when compiling Winsock programs. What's wrong?
2.4 If I write a Winsock program, will I be able to communicate with a Unix Sockets program?
2.5 Can I use Winsock with { My Favorite Language }?
2.6 Are there any tools available for debugging Winsock programs?
2.7 How do I get a readable error message from a Winsock error number?
2.8 Winsock keeps returning the error WSAEWOULDBLOCK. What's wrong with my program?
2.9 How can I test my Winsock application without setting up a network?
2.10 What's the proper way to close a TCP socket?
2.11 Is it possible to close the connection "abnormally"?
2.12 How do I detect when my TCP connection is closed?
2.13 How do I detect an abnormal network disconnect?
2.14 How can I change the timeout for a Winsock function?
2.15 What is peeking (MSG_PEEK), and why is it bad?
2.16 What is out-of-band data (MSG_OOB), and why is it bad?
2.17 If MSG_PEEK and MSG_OOB are bad, what do I pass for send() and recv()'s flags parameter?

Section 3 - Intermediate Winsock Issues

3.1 How do I speak { HTTP, POP3, SMTP, FTP, Telnet, NNTP, etc. } with Winsock?
3.2 How can I encrypt my TCP stream with SSL/TLS?
3.3 How do I get my IP address from within a Winsock program?
3.4 What's the proper way to impose a packet scheme on a stream protocol like TCP?
3.5 I'm writing a server. What's a good network port to use?
3.6 What is UDP? What are its limitations?
3.7 What is UDP good for?
3.8 How do I send a broadcast packet?
3.9 Is Winsock thread-safe?
3.10 If two threads in an application call recv() on a socket, will they each get the same data?
3.11 Is there any way for two threads to be notified when something happens on a socket?
3.12 How do I detect if the modem is connected?
3.13 How can I get the local username?
3.14 Windows 9x's Dial Up Networking keeps popping up an automatic dial window, even when it isn't necessary. Can I make it stop?
3.15 I've heard that asynchronous sockets are unreliable. Is this true?
3.16 What is the Nagle algorithm?
3.17 When should I turn off the Nagle algorithm?
3.18 What is TCP's sliding window?
3.19 What is the silly window syndrome?
3.20 What is the delayed ACK algorithm?
3.21 What platform should I deploy my server on?

Section 4 - Advanced Winsock Issues

4.1 How can I open a raw data socket?
4.2 How can I capture packets on a LAN with Winsock?
4.3 How can I change the IP or TCP header of a packet?
4.4 How can I "ping" another machine with Winsock?
4.5 Is it possible to create sockets that map to a DLL rather than an application?
4.6 How can I get access to the {route, ARP, interface, etc.} table?
4.7 How do I get the MAC (a.k.a. hardware) address of the local Ethernet adapter?
4.8 How many simultaneous sockets can I have open with Winsock?
4.9 What are the "64 sockets" limitations?
4.10 How do I make Winsock use a specific network interface?
4.11 What do the FIN_WAIT_x, TIME_WAIT, CLOSE_WAIT and other states mean?
4.12 What is the { SYN, ACK, FIN, RST } bit?
4.13 Is it a bad idea to bind() to a particular port in a client program?
4.14 What is the TCP window size?
4.15 What is the connection backlog?

Section 5 - Resources

5.1 Winsock Libraries and Controls
5.2 Samples: Tutorial Code
5.3 Samples: Useful Code
5.4 Debugging Tools (packet sniffers and shims)
5.5 Useful Web Pages
5.6 Other FAQs
5.7 MS Knowledge Base Articles
5.8 Winsock SDKs and Specifications
5.9 Miscellaneous

Section 6 - Examples

6.1 Several Basic Winsock Programs
6.2 Pinging a Host Using Microsoft's ICMP.DLL
6.3 Pinging a Host Using Raw Sockets
6.4 How to Pass a Socket Handle in Win32
6.5 Getting the Local IP Address
6.6 Getting the Network Interface List
6.7 How to Get the MAC (a.k.a. "hardware") Address, NetBIOS method
6.8 How to Get the MAC (a.k.a. "hardware") Address, SNMP method
6.9 How to Get the MAC (a.k.a. "hardware") Address, RPC method
6.10 Finding the Maximum Number of Open Sockets
6.11 How to Get the Local User Name

Section 7 - Articles

Winsock for the Impatient by Warren Young
Which I/O Strategy Should I Use? by Warren Young
How to Use TCP Effectively by Warren Young
The Lame List by the Winsock Vendor Community
Debugging TCP by Warren Young
Winsock's Compatibility With BSD Sockets by Warren Young
WsControl() Revealed by Tom Sanfilippo
CSocket Considered Harmful by Warren Young
Passing Sockets Between Processes by Warren Young and Frank Schmied
Dealing with Firewalls by Warren Young
Winsock for Non-Windows Systems by Warren Young

Section 8 - Book and Software Reviews

Section 9 - Glossary

the FAQ