Subnetting/Routing

Discussion in 'Linux Networking' started by Chris Rennert, May 10, 2005.

  1. Yeou can[*].

    ^^^^ ^^^^^^
    1 2

    1) => Classless Inter-Domain Routing
    It's not primary about 'continuos Bits'

    2) Of course you asume _continuos_ bits when using "/prefix"-Notation...


    May be.

    Nobody said that 'discontinous Maks' are fun :)
    But nobody _proofed_ that they are *formally* *forbidden*


    If you seek for "netmask 255.255.0.255" in groups.google.de, you'll
    get a lot ( fourteen :) of answers.

    One of them states, that "an old AIX" might use them.
    [ Message-ID: <> ]



    Greetings, Holger

    [*] A "Zungenbrecher" from my old english-textbook:

    a canner can can
    everything he can can
    but can a canner can a can?
     
    Holger Petersen, May 14, 2005
    #41
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  2. Chris Rennert

    Wolf Guest

    The one good thing about not only being involved in networking as long as I
    have but having taken advanced classes in the subject matter is you know the
    theory and understand how things work. The one thing I hated the most were
    the subnet problems. Two tests a week 3-4 subnet problems per test for a
    year-plus the labs! It was drummed into me. When I took the BSCI course
    it was even worse when you have to build a network of a bunch of routers all
    running differing protocols (some classful), one IP range and you have to
    subnet and make them all work and play or you don't pass. After you know
    the rules and practice a while you start seeing patterns and the numbers
    jump into your head. Then you just double check it with an IP calculator
    (see a previous post with a link and try using .253 netmask). I have on my
    PDA/phone that goes everywhere with me.

    Say what you want about Cisco but subnetting is subnetting and you either
    know it or you just think you do. I know it and have proven it in both
    school and in industry.

    As for the problem, the good news is that it seems the problem was an
    exercise. There were some really doable answers including using a router.
    The solution I gave will work, does not require a router and is simple-I
    love siimple. And does not rely on an invalid netmask. But others had
    different approaches to solutions like the guy who offered a /23 but you had
    to start a 0.x. But he will have to wade through the chaff to get at the
    kernels of wheat.
     
    Wolf, May 14, 2005
    #42
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  3. Chris Rennert

    Guest Guest

    That explains it .. Schooled to death!
    Years of schooling to learn a few simple rules.. all of which were in
    one rfc.

    Nothing worse that a paper engineer
    And You've proved which You are and which You think You are.
     
    Guest, May 14, 2005
    #43
  4. Chris Rennert

    Moe Trin Guest

    You are not bothering to read the documents that were pointed out for you
    that refute your incorrect interpretations. Please read the official
    standards. Start here:

    2026 The Internet Standards Process -- Revision 3. S. Bradner. October
    1996. (Format: TXT=86731 bytes) (Obsoletes RFC1602) (Updated by
    RFC3667, RFC3668, RFC3932, RFC3979, RFC3978) (Also BCP0009) (Status:
    BEST CURRENT PRACTICE)

    particularly sections 3 and 4 of that document. Then read the two standards
    applicable to subnet masks:

    0950 Internet Standard Subnetting Procedure. J.C. Mogul, J. Postel.
    Aug-01-1985. (Format: TXT=37985 bytes) (Updates RFC0792) (Also
    STD0005) (Status: STANDARD)

    1122 Requirements for Internet Hosts - Communication Layers. R.
    Braden, Ed.. October 1989. (Format: TXT=295992 bytes) (Updated by
    RFC1349) (Also STD0003) (Status: STANDARD)

    Look up thread if you want to learn the specific sections to read if you
    are in a hurry. Then read the _proposed_ standard for CIDR (can you guess
    why that word is underlined?)

    1519 Classless Inter-Domain Routing (CIDR): an Address Assignment and
    Aggregation Strategy. V. Fuller, T. Li, J. Yu, K. Varadhan. September
    1993. (Format: TXT=59998 bytes) (Obsoletes RFC1338) (Status: PROPOSED
    STANDARD)

    and read section 4.1 of that document.
    and fix your browser (or use a real news client) so that you are not
    using a proportional font when trying to show tables. I know it may come
    as a surprise to you, but those of us who have been network admins for more
    that five or ten years really do have that table memorized - in CIDR form,
    decimal and hex masks, and the number of hosts in the block.
    Your opinion is unimportant, but they are also not recommended by RFC1219,

    1219 On the assignment of subnet numbers. P.F. Tsuchiya. Apr-01-1991.
    (Format: TXT=30609 bytes) (Status: INFORMATIONAL)

    but if you read RFC2026 you would discover that the _standard_ does permit
    them. Also, if you read the post you replied to, you would discover I am
    quite aware that few O/S will tolerate such masks. I don't know anyone still
    using MIT's concept (RFC0932), but that is one example of a working setup
    where they _required_ non-contiguous bits in the subnet mask. Jon Postal's
    version (RFC0925) didn't _care_ about the mask.

    If you think that the whole world must use the slash notation to express
    network masks, how do you explain the assignments by the five RIR
    (AFRINIC|APNIC|ARIN|LACNIC|RIPE) and why they use CIDR notation as a
    secondary means of indicating network size. Could it be because they
    are not assigning netblocks in binary sizes??? Hmmm, what is the mask for
    a network of 768 hosts? There are 3 such assignments in AFRINIC, 416 in
    ARIN, and 52 in RIPE. How about one for 1536 hosts? There are 2 such
    assignments in AFRINIC, 210 in ARIN, and 27 in RIPE. In fact, the latest
    copy of the RIR zone files I have has 201 different sizes of allocations.
    I started in IP network administration in the spring of 1986, but had
    access back when most of the net that spoke TCP was using a ARPA address
    in the 10.0.0.0/8 range. You?

    Old guy
     
    Moe Trin, May 15, 2005
    #44
  5. Chris Rennert

    Wolf Guest

    For those of you who are actually interested and want to know how it really
    works, please check out the following links as a starting point. It will
    show you the proper way to subnet/supernet and what netmasks you can use.

    "Subnetting for Beginners"
    http://www.raiden.net/techhelp/SubnettingForNewbies.html

    "Introduction to Supernetting"
    http://www.red.net/support/resourcecentre/leasedline/intro.php

    "Supernetting": Classless Inter-Domain Routeing (CIDR) Hierachical
    Addressing and Notation"
    http://www.tcpipguide.com/free/t_IPSupernettingClasslessInterDomainRoutingCIDRHiera.htm


    CIDR: Classless Inter-Domain Routing Cheat Sheet"
    http://nukecops.com/article548.html

    "Subnt Cheat Sheet" http://rdweb.cns.vt.edu/~benchoff/subnet.html

    "Exam Hints: Subnetting"
    http://www.mcmcse.com/win2k/guides/subnettinghints.shtml
     
    Wolf, May 17, 2005
    #45
  6. Will any of these references provide a definitive answer to what
    is or is not a *valid* netmask though? Or will they indicate
    which are *useful* or *reasonable* or *functional* netmasks.
    Nobody has said that a discontinuous mask is any of those other
    than valid. It may not even be workable...
     
    Floyd L. Davidson, May 17, 2005
    #46
  7. Chris Rennert

    Wolf Guest

    *sigh* Have you bothered to even look?

    I know the answre to that question. The cheat sheets show you what the
    netmask available bit-by-bit position. .
    It is all there if you ever bother to read it. But I would start with
    learning about subnetting first it I were you.
     
    Wolf, May 17, 2005
    #47
  8. "Reading" words and *understanding* them are distinct.

    Tutorials are meant to teach what works. Standards are
    intended to define what is valid.

    The question is what is valid; hence, your tutorials are
    meaningless. The Standards that others have posted are in
    fact definitive.
    You should start with the Standards documents that have been
    previously posted. (Of course, if you were me you'd have done
    that long ago...)
     
    Floyd L. Davidson, May 17, 2005
    #48
  9. Chris Rennert

    k.mukkamala Guest

    You can add the following line in /etc/sysctl.conf

    net.ipv4.ip_forward=1

    which enables the ipforwarding between interfaces at boot time.

    regards,

    KIRAN
     
    k.mukkamala, May 23, 2005
    #49
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