BUG: Winsock Sends IP Packets with TTL 0 (138268)


The information in this article applies to:

  • Microsoft Win32 Software Development Kit (SDK) 3.5
  • Microsoft Win32 Software Development Kit (SDK) 3.51
  • Microsoft Win32 Software Development Kit (SDK) 4.0
This article was previously published under Q138268

SYMPTOMS

If an application is using IP multicasting on Windows NT version 3.5 or version 3.51 or on Windows 95, then it is possible to send packets with Time to Live (TTL) set to 0.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are reasearching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Please see the following article in the Microsoft Knowledge Base:

131978 Receiving, Sending Multicasts in Windows NT Using WinSock

It is possible to change the TTL for an IP datagram. For example: 

   int ttl  = 0;
   int sock = socket( .... );

   err = setsockopt( sock, IPPROTO_IP, IP_MULTICAST_TTL, (char *)&ttl,
   sizeof(ttl));


However, as per the requirements of RFC 1122, a host must not send an IP datagram with TTL = 0. Here is a quote from the relavent section of RFC 1122: 

   3.2.1.7  Time-to-Live: RFC-791 Section 3.2

   A host must not send a datagram with a Time-to-Live (TTL) value of zero.

   A host must not discard a datagram just because it was received with TTL
   less than 2.

REFERENCES

For more information, please see the following references:
  • \Docs\Misc\Mcast.txt on the Win32 SDK Compact Disc
  • The following article in the Microsoft Knowledge Base:

    131978 Receiving, Sending Multicasts in Windows NT Using WinSock
  • RFCs 791 and 1122
Modification Type:MajorLast Reviewed:10/16/2002
Keywords:kbBug kbIP kbnetwork KB138268
©2002 Microsoft Corporation. All rights reserved.