Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!sdd.hp.com!mips!apple!agate!ucbvax!UCDAVIS.EDU!rdhobby From: rdhobby@UCDAVIS.EDU (Russ Hobby) Newsgroups: comp.protocols.tcp-ip.domains Subject: Experimental DNS RFC (Re: MX Records) Message-ID: <9104082253.AA26014@aggie.ucdavis.edu> Date: 8 Apr 91 22:53:59 GMT Sender: daemon@ucbvax.BERKELEY.EDU Distribution: inet Organization: The Internet Lines: 194 The following document has been sent to the RFC Editor to be an Experimental RFC (as opposed to being on the standards tract). It is along the lines of the MX Record discussion that has been going on. The RFC Editor has given one week (until Apr 15) to reveiw the document and to say if it is a "good thing". As an experimental RFC the specs are there for people to try it and get some experience with the "experiment". Since there is a Working Group for DNS, the WG has the opportunity to review the document before publication and say if it fits into the plans of the WG. If the WG thinks that experiemental experience will be good, then fine. If the WG has suggestions to the author before making it an experimental RFC, that can be done as well. If the WG thinks that this is something that should be put on the standards tract now, the experimental RFC can be redirected to the WG for review and on to becoming an Proposed Standard RFC in a timely manner. If it goes on to be an experimental RFC now, it can be put into the standards tract by the WG at a later date. (whew, made it though all that ;-) Send your comments to me and Greg Vaudreuil (gvaudre@nri.reston.va.us> (since I will be on vacation starting Saturday) and, of course, the WG mail list. Russ Hobby INTERNET: rdhobby@ucdavis.edu IETF Area Director - Applications BITNET: RDHOBBY@UCDAVIS UUCP: ...!ucbvax!ucdavis!rdhobby -------------------------------------------------------------------------- Network Working Group T. P. Brisco Request for Comments: 12XX Rutgers University Updates: RFCs 1034, 1035 April 1991 LMX DNS Resource Record Status of This Memo This memo defines an additional Domain Name Specification Resource Record. This RFC specifies a Experimental Protocol and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited. 1. Overview This memo is intended to standardize a method for the determination of local mail addresses for use within an organization only. The Domain Name System Resource Record detailed herein is designed for use from a mail gateway to client machines only. 2. Introduction This memo proposes an extension of RFC1035 [Domain Names - Implementation and Specification]. The extension provides a Domain Name System ("DNS") Resource Record ("RR") for the addressing of local systems for mail redistribution. With increased levels of security for networks becoming commonplace, it is not unusual to find that mail destined for a particular domain (or set of domains) to be routed through a single addressable machine (sometimes known as "mail gateways"). With the increased level of security, it may be impossible for hosts on a subnet to communicate with the rest of the Internet Community at all. This DNS RR provides a fashion for these systems on restricted subnets to be able to exchange mail with hosts external to the addressable networks. 3. The LMX RR The LMX resource record became necessary in order to support the concept of "restricted networks". This networks typically contain hosts that present minor security problems, usually because no user authentication is necessary or possible. This may be public-access microcomputer laboratories in a typical computing center. Hosts in Brisco [Page 1] RFC 12XX LMX DNS Resource Record April 1991 these laboratories may not be able to send packets to networks outside of the autonomous system, effectively rendering these systems incapable of establishing connections to the "outside world". However, users may wish to originate or receive mail from hosts on this restricted network. Typically, an organization may have a designated "mail gateway" through which all mail, inbound and outbound, passes. For mail passing from within the organizational network to external networks, there is typically no problem. All hosts (except the gateway) forward mail to a particular machine. The gateway, in turn, re-sends the mail to the indicated user on the specified host. However, for inbound mail, the gateway will be unable to resolve any additional Mail Exchanger for the destined system. For instance, assume that some host "public.rutgers.edu" exists on a publically accessible network, and may not establish connections to machines outside of the autonomous system. To the external world, an MX record is announced for "public.rutgers.edu" as "gateway.rutgers.edu". Inbound mail will arrive at "gateway.rutgers.edu" for redelivery to "public.rutgers.edu". However, since the MX record is already in use to advertise the MX of "gateway", the host has no way of resolving an address for the local system. In effect, a private, "local" MX is necessary in order to resolve an address. The LMX ("Local Mail eXchanger") record is for use within the organization's autonomous system (since the address specified by the LMX will probably not be addressable from external networks). It is the mechanism by which the mail gateway may determine an address for a host on local network. The mail gateway, which receives a message bound for a host for which it is the mail exchanger (i.e., the gateway's own host name is specified in the MX record) may attempt to retrieve an LMX record to determine the local address accepting mail for this host. 4. Format of the LMX RR The LMX is a DNS resource record, the data specified in it is case insensitive, it has type code XX (to be assigned by the IANA). The LMX has the following format: LMX Both RDATA fields are required in all LMX RRs. The is the domain name of the external name by which the host is known. The is the domain name of the internal name by which the host is known. LMX records cause type A additional section processing for . Brisco [Page 2] RFC 12XX LMX DNS Resource Record April 1991 Note that the format and handling (by the DNS) of the LMX is exactly identical to that of the MX record. LMX RRs should be exported by the DNS, in order for secondary nameservers to back up a site properly. 5. Security Considerations Security issues are not discussed in this memo. 6. Author's Address Thomas P. Brisco Rutgers University Computing Services Hill Center for the Mathmatical Sciences Busch Campus P.O. Box 879 Piscataway, New Jersey 08855-0879 Phone: 908-932-2351 EMail: brisco@RUTGERS.EDU Brisco [Page 3]