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Re: Selection of Appropriate Local SMTP Relay

  • From: Joe Abley
  • Date: Mon Jan 10 18:56:12 2000

On Mon, Jan 10, 2000 at 12:16:25PM -0500, Daniel Senie wrote:
> Using DNS, as you propose, has some problems. In your example, you rely
> on the topology of the network, and make assumptions about classful
> structure. This isn't workable in the present network environment.

I'm not convinced that I do.

It's quite possible to specify a different mail relay for every individual
address in an ISP's network. I might be using octet boundaries so that
I can follow the same well-known zone structure as is
currently used, but that's all.

It seems to me that handing out mail relays in IPCP and DHCP are also
very valid approaches, although they arguably require more software changes 
to be useful (e.g. in access-server firmware).

Here are a couple of points:

1. The use of MX records in the manner I suggested allows the SMTP
relays to be used to be changed fairly dynamically -- using IPCP,
for example, a caller would only get one set per call (and calls can
be pretty long-held; I see calls lasting five days here).

2. The use of MX records also allows backup mail relays to be specified,
with an associated priority, in a familiar way.

3. Using a network-layer protocol like PPP or DHCP to collect the data
requires some consistent application-layer interface to retrieve the
specified nameserver info by client software; this, ideally, would
require standardisation across platforms, and practically does not sound
trivial. However, there's already a well-defined mechanism in almost
every platform for applications to perform DNS queries.

Thanks for the feedback,