Subject: Re: [Ecrit] draft-polk-dhc-uri-00

From: Andrew Newton <[email-masked]>
Date: Fri, 16 Sep 2005 14:13:26 -0400

On Sep 16, 2005, at 10:47 AM, John Schnizlein wrote:

> As you know, the caching specification for DNS makes the TTL the  
> upper bound on how long before the client gets a fresh value from  
> an authoritative server.

And a DHCP client can renew its lease before the lease time is up.   
What's your point?  Both are unreliable for the purposes of preemption.

>   The problem with using DHCP is not the duration of an address  
> lease, but that there is no mechanism identified for getting new  
> URIs into the DHCP servers.

Do DHCP servers have such quirky IP connectivity that they cannot use  
the same LCMS as a phone or gateway?

> Why is the comparison of DNS and DHCP relevant?  We have seen no  
> argument that continuing the practice of PSAPs (which might be SIP  
> proxies for VoIP) routing emergency calls among themselves based on  
> location information in the call request.  The unnecessary  
> "optimization" of getting better than default PSAPs into the  
> calling host has unspecified needs for new protocols to distribute  
> information that the PSAPs might not want to share as widely as  
> proposed.

The objection raised was not about call routing based on location,  
but was about call routing based on disaster recovery.
Again... Perhaps we ought to go back to thrust of the objection that  
was raised: a device is given a 24 hour validity duration on a list  
of end points but there is an unforeseen reason for it to be updated  
12 hours after the device was given the information.  My question was  
simply, why is that duration unacceptable when it is a DHCP lease but  
acceptable when it is a DNS TTL?  Both will prevent the information  
from being updated before the end of the duration.

I have no problem with calls being routed be proxies.  Actually, for  
the objection that was raised, that seems to be a pretty good place  
to do it.

On Sep 16, 2005, at 12:28 PM, Marc Linsner wrote:
> Correct me if wrong....in practice, are not DNS TTLs normally much  
> shorter
> than DHCP lease times?

TTLs where? in the roots? in TLDs? in SLDs?  From what Henning has  
said, for this particular case they would be set for a very, very  
long time.  I take that to mean months.

> Of course, beyond the above philosophical argument, the PSAP has no  
> control
> over DHCP lease times, where in the proposed DNS solution, they  
> have control
> over TTLs.

True, but it doesn't disprove my point.

I also wonder, if DHCP lease times are so untrustworthy, then perhaps  
LCI should not be delivered via DHCP either.

-andy

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