Jump to content


Register a free account to unlock additional features at BleepingComputer.com
Welcome to BleepingComputer, a free community where people like yourself come together to discuss and learn how to use their computers. Using the site is easy and fun. As a guest, you can browse and view the various discussions in the forums, but can not create a new topic or reply to an existing one unless you are logged in. Other benefits of registering an account are subscribing to topics and forums, creating a blog, and having no ads shown anywhere on the site.

Click here to Register a free account now! or read our Welcome Guide to learn how to use this site.


TCPIP Loopback Address

  • Please log in to reply
1 reply to this topic

#1 scotty_ncc1701


  • Members
  • 520 posts
  • Gender:Male
  • Local time:12:08 PM

Posted 17 August 2014 - 08:04 AM

Normally, when a TCP/IP application wants to send information, that information travels down the protocol layers to IP where it is encapsulated in an IP datagram. That datagram then passes down to the data link layer of the device's physical network for transmission to the next hop, on the way to the IP destination.

However, one special range of addresses is set aside for loopback functionality. This is the range to IP datagrams sent by a host to a 127.x.x.x loopback address are not passed down to the data link layer for transmission. Instead, they “loop back” to the source device at the IP level. In essence, this represents a “short-circuiting” of the normal protocol stack; data is sent by a device's layer three IP implementation and then immediately received by it.

The purpose of the loopback range is testing of the TCP/IP protocol implementation on a host. Since the lower layers are short-circuited, sending to a loopback address allows the higher layers (IP and above) to be effectively tested without the chance of problems at the lower layers manifesting themselves. is the address most commonly used for testing purposes.


127.*.*.* never accesses the Internet.

Have a great day!
:bananas: :bounce:

BC AdBot (Login to Remove)


#2 Wand3r3r


  • Members
  • 2,027 posts
  • Local time:09:08 AM

Posted 19 August 2014 - 12:22 PM

Best of luck!

Edited by Wand3r3r, 19 August 2014 - 08:35 PM.

0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users