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

David L. Mills mills at udel.edu
Thu Aug 18 18:24:22 UTC 2005


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.


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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