Dynamic DNS

[HIBBS, BARR (PB)]

Irina--

thanks for your comments and suggestions.

For several reasons, the population of docking stations that are in cubicle
"hotels" cannot be placed into a separate domain.  I'm not actually seeking
a solution for how to configure my client population -- instead, I'm trying
to identify real-world situations where DNS updates need to be done very
carefully.

Docking stations present particular difficulties because the Microsoft DHCP
client software will use the NIC address of the docking station to form a
client identifier, making EVERY mobile client that uses a particular docking
station IDENTICAL from the perspective of dhcpd.

But, clearly, the clients are NOT identical.  They may use the same chaddr
and client-identifier, but their hostnames differ!  So, if the DHCP-DNS
dynamic update causes an RR for the prior client docked in a particular
station to be removed as part of instantiating the current client with both
forward and reverse address mappings, the process MUST ensure that only the
appropriate RR's are removed.  After all, the prior client may have moved to
a different docking station or begun to use, for example, a PCMCIA Ethernet
adapter and caused a DNS update before the current client docks their
laptop.

I read some of the dialogue between yourself and Brian in such a way that I
thought that the proposed process for the DHCP server would be to
intentionally remove all resource records for the prior client -- this would
break my roaming clients!  The DHCP server should be more restrictive when
requesting DNS updates:   an existing RR should be deleted/updated only if
doing so is likely to be harmless.  It's probably always okay for a DHCP
server to update the PTR record with a new hostname, but probably never okay
to update an A record unless the existing PTR record shows, for example,
host "T" AND the A record for host "T" shows the address of the PTR record.

--Barr


> From: 	Irina Goble[SMTP:irinag at ims.com]
> Sent: 	Monday, August 09, 1999 11:01 AM
> To: 	dhcp-hackers at isc.org
> Subject: 	RE: Dynamic DNS
> 
> > 
> > I basically have two types of static hosts:  the truly static client
> > workstation which for various reasons must have a static IP address (and
> an
> > invariant forward and reverse address mapping in DNS), and docking
> stations,
> > which are assigned a static address, but the forward and reverse
> mappings
> > between IP address and fully-qualified domain name are *not* invariant.
> > 
> 	It is just logical to do dynamic DNS updates for dynamic IP
> addresses
> and have static IP - domain name mappings for static IP addresses.
> 
> 	If it is possible to separate these docking stations in a group 
> with a special domain for this group, on a DNS server allow dynamic DNS
> updates for this zone. Then it can work with a patch (sorry, it is rough)
> I sent last week to Ted and Brian, when the DHCP server can keep a status
> of updates and will stop sending update requests if DNS server rejects 
> them.
> 
>