SDN/SDDC Retreat in Miami, Florida (November 4th-6th)
Separate SDN hype from real life!

CLNS and CLNP

Yap Chin Hoong has been looking at the OSI protocol stack I’ve published in the CT3 wiki and asked an interesting question: “where is CLNS in that protocol stack?”

The OSI protocol stack has a major advantage over the TCP/IP stack: it defines both the protocols and the APIs between the layers. CLNS (Connection-less network Service) is the API (the function calls that allow transport layers to exchange datagrams across the network) while CLNP (Connection-less network Protocol) is the layer-3 protocol that implements CLNS. In my diagram, CLNS would be a thin line above CLNP between L3 and L4 boxes.

IOS developers did not escape the confusion between CLNS and CLNP. The clns routing command does not make sense; you cannot route an API. The command should have been called clnp routing.

5 comments:

  1. It means CLNS is like device driver.

    ReplyDelete
  2. Yap Chin Hoong23 March, 2010 02:36

    Hi Ivan, thanks for answering my question. :-)
    Kindly address me in full name, cuz my first name should be Chin Hoong instead, Yap is the surname. :-)
    I am still in the midst of studying the theory of IS-IS (yes it is obsolete in CCNP syllabus but I studying for my own good), I haven't spend many times in labbing IS-IS stuffs, I believe I will have better visualization when I capture the packets upon the "ping clns" command. :-)

    thanks and have a nice day... expect more questions from me in the future. 8-)

    ReplyDelete
  3. Ivan Pepelnjak23 March, 2010 07:20

    Oh, my ... I apologize for the blunder. I'm used to the surname being last; another one of those culture-specific things that I'm totally unaware of. Thank you!

    When you do a capture on a LAN segment between two routers, you should see ES-IS packets (routers advertising themselves to non-existent hosts), IS-IS packets (obvious) as well as CLNP packets (when you do ping).

    ReplyDelete
  4. Yap Chin Hoong23 March, 2010 15:18

    Really thanks for the info, I spent quite some times today trying to figure out how to capture ES-IS packets, even thought of running OpenVMS and configuring DECnet. =-X

    ReplyDelete
  5. Hey Guys,

    I was wondering if you could help me...
    I've been studying IS-IS because I'll be participating in a intense course in the mid August and I'm trying to be a bit proactive.

    Anyways...

    I'm really trying to figure out CLNS's role with IS-IS and it seems like this topic is ambiguous and no one can give me a straight answer.

    I've read a book that says "OSI suite is also referred to as the CLNS suite", that "CLNS + CLNP = IP (in the TCP/IP stack)..

    You wrote: "In my diagram, CLNS would be a thin line above CLNP between L3 and L4 boxes."

    However, this site shows: http://www.cellsoft.de/telecom/dcn.htm
    that it's a thin line between layer 2 and 3.

    I need some help and if you guys could reply, that would be fantastic..


    ReplyDelete

You don't have to log in to post a comment, but please do provide your real name/URL. Anonymous comments might get deleted.

Ivan Pepelnjak, CCIE#1354 Emeritus, is an independent network architect. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.