nanog mailing list archives
Re: Selection of Appropriate Local SMTP Relay
From: Daniel Senie <dts () senie com>
Date: Mon, 10 Jan 2000 19:36:15 -0500
Joe Abley wrote:
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 in-addr.arpa zone structure as is currently used, but that's all.
Ny using octet boundaries, you're making an inference that the IP addresses are being used in a classful fashion. It's doubtful this will be the case in today's network.
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).
Agree, which is what I said as well.
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.
As others point out, the IP address given out for a particular dialup will NOT be representative of the ISP. For example, I use a national dialup provider for access to the 'net when I'm travelling. This provider rents POPs from PSI.net, Level3.net, and probably plenty of others. The same dialup POPs are rented by a LOT of other ISPs. Having an MX lookup on the INADDR for the IP Address of the dialup port will be quite problematic, since the desired effect is to get the name of the SMTP server for the PROPER ISP, not for the POP vendor.
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.
You didn't comment on my other suggestion, that of doing MX on the assigned name servers. This has all of the advantages you want, without the problems associated with trying to determine which ISP is in use based on IP address. Now I'm not convinced the MX on DNS server approach is a good solution, but it's probably better than doing MX on the IP address assigned. -- ----------------------------------------------------------------- Daniel Senie dts () senie com Amaranth Networks Inc. http://www.amaranthnetworks.com
Current thread:
- Re: Selection of Appropriate Local SMTP Relay D'Arcy J.M. Cain (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Alex P. Rudnev (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Randy Bush (Jan 10)
- <Possible follow-ups>
- Re: Selection of Appropriate Local SMTP Relay Vadim Antonov (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Richard Irving (Jan 10)
- RE: Selection of Appropriate Local SMTP Relay Olivier Gerschel (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Richard Irving (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Joe Abley (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Daniel Senie (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Joe Abley (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Chris Cappuccio (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Andrew Brown (Jan 11)
- Something very odd on an older 2514 . Mr. James W. Laferriere (Jan 10)
- Re: Something very odd on an older 2514 . Chris Cappuccio (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Daniel Senie (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Alex P. Rudnev (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Forrest W. Christian (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Patrick Greenwell (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Forrest W. Christian (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay bmanning (Jan 10)
- Re: Selection of Appropriate Local SMTP Relay Forrest W. Christian (Jan 10)