dns and software, was Re: Reliable Cloud host ?
bill at herrin.us
Tue Feb 28 13:11:54 UTC 2012
On Tue, Feb 28, 2012 at 12:45 AM, Mark Andrews <marka at isc.org> wrote:
> getaddrinfo was designed to be extensible as was struct
> addrinfo. Part of the problem with TTL is not [all] data sources
> used by getaddrinfo have TTL information.
By the time getaddrinfo replaced gethostbyname, NIS and similar
systems were on their way out. It was reasonably well understood that
many if not most of the calls would return information gained from the
DNS. Depending on how you look at it, choosing not to propagate TTL
knowledge was either a belligerent choice to continue disrespecting
the DNS Time To Live or it was fatalistic acceptance that the DNS TTL
isn't and would not become functional at the application level.
Still works fine deeper in the query system, timing out which server
holds the records though.
> Additionally for
> many uses you want to reconnect to the same server rather
> than the same name.
The SRV record was designed to solve that whole class of problems
without damaging the operation of the TTL. No one uses it.
It's all really very unfortunate. The recipe for SOHO multihoming, the
end of routing table bloat and IP roaming without pivoting off a home
base all boils down to two technologies: (1) a layer 4 protocol that
can dynamically rebind to the layer 3 IP address the same way IP uses
ARP to rebind to a changing ethernet MAC and (2) a DNS TTL that
actually works so that the DNS supports finding a connection's current
William D. Herrin ................ herrin at dirtside.com bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004
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