ntp.h ISBADADR(srcadr) macro - NTP

This is a discussion on ntp.h ISBADADR(srcadr) macro - NTP ; Hi all, I currently need to use ntp where the server for several internal clients is a 127.x.x.x address, not 127.127.x.x. I noticed it is fairly easy for me to modify the ISBADADR macro in ntp.h to allow these types ...

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Thread: ntp.h ISBADADR(srcadr) macro

  1. ntp.h ISBADADR(srcadr) macro

    Hi all,

    I currently need to use ntp where the server for several internal clients is a 127.x.x.x address, not 127.127.x.x.
    I noticed it is fairly easy for me to modify the ISBADADR macro in ntp.h to allow these types of addresses. Is this the only change required?
    Also, what reservations do you guys have about changing this?

    Thanks,
    Andrew

  2. Re: ntp.h ISBADADR(srcadr) macro

    Hi Andrew !

    Andrew Stone wrote:
    > Hi all,
    >
    > I currently need to use ntp where the server for several internal clients is a 127.x.x.x address, not 127.127.x.x.

    This is a pretty unusual setup.

    > I noticed it is fairly easy for me to modify the ISBADADR macro in ntp.h to allow these types of addresses. Is this the only change required?

    ISBADADR() is only used to prohibit exactly that configuration. Thus it
    would be the only change required. But attempting to use 127.0.0.0/8 for
    real network communication will most likely bring you into all sorts of
    trouble. ISBADADR() would be the least of your problems. See below:

    > Also, what reservations do you guys have about changing this?


    First reservation would be RFC 3330 (http://tools.ietf.org/html/rfc3330).

    To quote RFC3330:

    ...
    127.0.0.0/8 - This block is assigned for use as the Internet host
    loopback address. A datagram sent by a higher level protocol to an
    address anywhere within this block should loop back inside the host.
    This is ordinarily implemented using only 127.0.0.1/32 for loopback,
    but no addresses within this block should ever appear on any network
    anywhere [RFC1700, page 5].
    ...

    This wisdom (even older than RFC3330) is put into many configurations
    (e. g. interface/routing setups on hosts). Attempting to ignore age old
    practice might burn you.
    As I said - it looks like a pretty unusual setup.

    There may be more reservations... :-)

    You may be better off with RFC1918 if you are trying to find a private
    address space.

    >
    > Thanks,
    > Andrew


    Frank

  3. Re: ntp.h ISBADADR(srcadr) macro

    Andrew Stone wrote:
    > Hi all,
    >
    > I currently need to use ntp where the server for several internal

    clients is a 127.x.x.x address, not 127.127.x.x.

    I think you misunderstand NTP's use of the 127.127.x.x space. It is only
    used for refclocks and nothing else. If you don't have a refclock
    attached to the server, you don't need to know about these addresses.
    You must *NOT* use them in any other way. 127.x.x.x is not allowed to be
    used for any other purpose. You should use other private address space.
    See Frank's message.

    > I noticed it is fairly easy for me to modify the ISBADADR macro in

    ntp.h to allow these types of addresses. Is this the only change required?

    This is not allowed. See Frank's message on this.

    > Also, what reservations do you guys have about changing this?


    We won't be changing this.

    Danny

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