ddp+@ANDREW.CMU.EDU (Drew Daniel Perkins) (10/29/90)
I'm curious about people's opinions on the ISDN provisions of RFC 1183, "New DNS RR Definitions", C. Everhart, L. Mamakos, R. Ullmann, P. Mockapetris. Do people think these RRs are useful? Are they likely to be used? How were they intended to be used? How would these integrate routing protocols? The description in RFC 1183 seems a bit confusing to me. In particular, domains like "Relay.Prime.COM" are used, rather than domains like IN-ADDR.ARPA. I imagine the intended purpose of the ISDN RR is to be able to automatically establishe connections over an ISDN link upon receipt of the first IP packet. I would think that you would want to do lookups by IP address, although I can imagine looking for a PTR record first and then looking for a corresponding ISDN record. I also find it confusing exactly how the RT record is intended to work. Here's one scenario that I think these might be useful in. Imagine two isolated island networks NA and NB, such as might exist in two companies or universities. Each island network has a one or more routers, maybe RC and RD, with ISDN connections which can establish links to other networks. Now let's say I try to telnet from one non-ISDN machine HE on network NA to a non-ISDN machine HR on network NB. One way I could imagine things working is that router RC might advertise a default route to hosts on its network including HE. So, when I telnet, HE would send its packets to RC. Now, when RC received the packet addressed to HF, it might look up RRs for HF and it might find an RT RR for RD. Looking up RD it might find an ISDN RR with RD's number. It could then forward the packet through to RD, which would then forward it to HF. HF's response would hopefully be sent back through RD (due to having corrrect updated routing information) which would then realize that it already has a connection open to RC, and would simply send it through. When we start scaling this simple example up, I see a lot of problems start popping up. Imagine I just have a single host (at home maybe) with an ISDN connection. Now, I want to telnet to a host which is somewhere on the Internet, behind maybe dozens of router hops. It's hard to imagine that every host on the internet will have an RT RR in the DNS. If I were a random site with hosts on the Internet, but no ISDN connections, what RT RR would I want to advertise? There might be thousands of other hosts/routers on the Internet with ISDN connections. Which would I choose, and how? Drew