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

Danny Mayer mayer at gis.net
Fri Aug 19 02:28:40 UTC 2005

David L. Mills wrote:
> Danny,
> Conflict. Once upon a time the administrative boundaries for multicast 
> were set by TTLs where the hop increment was artificially set at the 
> boundaries of each domain, for instance, local, campus, regional. 
> Whether this is good or bad or whether modern practice has outrun the 
> idea is unknown to me. I just did what the RFC said. Now, the intent was 
> to provide a command where the TTL vector could be set arbitrarily, but 
> I never got around to implementing that command. Tell me whether this is 
> a good or bad idea. I would just as soon return to the simple increment. 
> However, somebody might get mad at me, claiming historic 
> incompatibility. Tell me what to do.

Dave, I'm only addressing current practice rather than what the original 
design looked like. It's sounds like you were involved in the initial 
designs. I'm not sure what the conflict is that you mention.


> Dave
> Danny Mayer wrote:
>> David L. Mills wrote:
>>> Roger,
>>> There is a mapping table which converts integers to actual TTL 
>>> values. See at or near line 2954 of ntp_proto.c. This is intended to 
>>> follow guidelines for administrative scoping. I don't remember which 
>>> RFC and the implementation has never been tested for conformance to 
>>> my knowledge. What to do in IPv6 is even of more murk. I am happy to 
>>> listen to suggestions.
>>> Dave
>> In IPv6 it's known as a hop count which is what happens in effect 
>> anyway even with IPv4. Each hop decrements the number until it reaches 
>> 0 and then it stops forwarding. Currently the ttl/hop count shouldn't 
>> be more than about 2.
>> Danny
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