[ntp:questions] Re: Multicast TTL and FreeBSD trouble

Per Hedeland per at hedeland.org
Sun Aug 21 13:28:22 UTC 2005

In article <4304155B.6080704 at udel.edu> mills at udel.edu (David L. Mills) writes:
>No. See the RFC for IPv4 on administrative distance. I make no 
>judgemenst here, just tell me what to do.

Hm, searching the RFCs for "administrative distance" turns up only RFC
966 (anno 1985), which says e.g.

      The existing Time to Live field in the IP header can be used for
      crude control over the delivery radius of multicast datagrams.  To
      provide finer-grain control, a new IP option is defined to specify
      the maximum delivery distance in "administrative units", such as
      "this network", "this department", "this company", "this country",
      etc.  The set of units and their encoding is to be determined.

However no such option has been defined (or at least deployed) AFAIK,
RFC 966 has "status UNKNOWN", and has been obsoleted several times over
ending with RFC 1112 (anno 1989), which is the official (IPv4) multicast
standard, and which doesn't mention anything other than the standard IP
ttl for this purpose. (The typical socket interface does allow for
setting the "multicast ttl" independently from the normal IP ttl, but
the settings end up doing the same thing.)

Either way, introducing a change in ntpd somewhere between 4.1.1 and
4.2.0 (i.e. 2002-2003 timeframe), such that the single integer specified
with the ttl option to the broadcast command gets mapped to another
integer, hardly seems to be motivated.

--Per Hedeland
per at hedeland.org

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