Subject: [dhcwg] Re: Last Call: DHCP Domain Search Option to Proposed Standard

From: Thomas Narten <[email-masked]>
Date: Fri, 28 Sep 2001 14:34:51 -0400

Keith Moore <[email-masked]> writes:

(in a message sent to the iesg)

> The problem I have with this option is that it invites implementors
> and network administrators to presume that a host's domain should be 
> tied to a host's location in the network - when these are intentionally, 
> and by design, entirely separate.  For instance, a mobile computer user 
> who wishes DNS lookups to be performed relative to a particular domain 
> should not have this choice overridden by each POP to which he connects.

> (The fact that protocol designers often try to use DNS lookups as a 
> means to discover topologically close services does not change this.
> There is an inherent conflict between using DNS as a way to discover
> services relative to a domain and using it as a way to discover
> services relative to a network location, but the intent of DNS 
> clearly favors the former.)

> Host DHCP implementations therefore should not blindly accept Domain 
> Search information from a DHCP server.  Local configuration of any 
> DNS information (including not just search domains, but also DNS servers) 
> should override anything supplied by DHCP.

> Keith

I am sympathetic with your general point. I'll also note that this
arguably applies to a number of other existing DHCP options. I don't
believe right off that this point is explicitely addressed in the
other cases either.

There is a general issue of when should (and shouldn't) a DHCP-learned
option override a manually configured one. My guess is that
DHCP-learned options generally do not override manually configured
ones. But I suspect that this is all considered implementation
specific. Can other DHC WG members comment? What do existing RFCs say
about this point?

Finally, what do you propose? I.e., "send text" :-) Would it suffice
to add some language stating that in the case of this option, it
should not override a manually configured search list?

Thomas

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---

From: John Schnizlein <[email-masked]>
Date: Fri, 28 Sep 2001 15:52:57 -0400

At 02:34 PM 9/28/2001, Thomas Narten wrote:
>..
>specific. Can other DHC WG members comment? 

Since there is at least one widespread case in which DHCP-learned 
options MUST override manually configured ones, it would be wrong to
prohibit it. The case is acquiring (through DCHP) the addresses of 
DNS servers when connecting to a VPN. The DNS servers able to resolve
private names are often not available to the general Internet, but
necessary once the host's traffic tunnels behind the firewall. Using
DHCP both before and after establishing the tunnel does not work with
cable-access that requires an enterprise-incompatible host-name to
validate DHCP requests.

>What do existing RFCs say about this point?
>
>Would it suffice to add some language stating that 
>*** in the case of this option, *** [emphasis added]
>it should not override a manually configured search list?

Separate from the case above (and possibly the general case),
the order in which domain suffixes are applied is not critical to
operation, but could lead to wasteful time-outs.

John