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Article ID: 115388 - Last Review: October 26, 2007 - Revision: 2.4

This article was previously published under Q115388


Windows for Workgroups with TCP/IP-32 and Windows NT utilities can accept Internet Protocol (IP) addresses comprised of decimal, octal, or hexadecimal numbers. This can cause confusion if you unintentionally use a leading zero in a decimal octet. With a leading zero, the number is resolved by these utilities as an octal number, thus specifying the wrong IP address.


Many TCP/IP programs such as Ping and FTP use the inet_addr() sockets function to translate IP address strings into 4-byte addresses. This function accepts an IP address in standard decimal, octal, and hexadecimal notation, such that the following IP address examples are acceptable to Ping and FTP and resolve to the same IP address: (decimal)
   026.0145.037.0231 (octal)
   0x16.0x65.0xF1.0x99 (hexadecimal)
   0x16.101.037.153 (a combination of all three number systems)

If you unintentionally enter a leading zero in an octet, the IP address that Ping and FTP resolve is not the same as you intended, as in the following example (using Ping):

   In Windows NT 3.1:

      Pinging host (unnamed) :
      ICMP Echo Reply:TTL 32
      ICMP Echo Reply:TTL 32
      ICMP Echo Reply:TTL 32
      ICMP Echo Reply:TTL 32
      Host replied to all 4 of the 4 pings

   In Windows NT 3.5:

      Pinging with 32 bytes of data:
      Ping succeeded: 32 bytes time=10ms TTL=32
      Ping succeeded: 32 bytes time=10ms TTL=32
      Ping succeeded: 32 bytes time=10ms TTL=32
      Ping succeeded: 32 bytes time=10ms TTL=32

NOTE: In this example, is resolved by Ping to be decimal, not decimal.

This results in either a successful (shown above) or unsuccessful verification of the wrong IP address, depending on whether the resolved IP address is a valid IP address in your network environment.

Windows NT 4.0 Enterprise Cluster Administrator will give the following error if you specify an ip address to connect to the cluster with leading zeroes on the decimal octet, you may get the following error:

"A connection to the cluster at "" could not be opened. This may be caused by the customer on node "" not being started. Would you like Cluster Administrator to attempt to start the Cluster Service on node ""."

To avoid an address being incorrectly resolved, it is recommended that you check for and remove leading zeros, unless an octal number is intended.

The following utilities also exhibit this behavior:

Internet Explorer (IE)
Microsoft Cluster Adminitrator
Microsoft Cluster Setup Wizard

  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows 2000 Professional Edition
  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Workstation 3.1
  • Microsoft Windows NT Workstation 3.5
  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows NT Server 3.5
  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft TCP/IP-32 for Windows for Workgroups 1.0
  • Microsoft Windows for Workgroups 3.2
  • Microsoft Windows NT Server 4.0 Enterprise Edition
  • Microsoft Cluster Server 1.1
kbproductlink kbclustering kbnetwork KB115388
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