wdiff rfc7314.original rfc7314.txt

Network Working Group
Independent Submission M. Andrews
Internet-Draft
Request for Comments: 7314 ISC
Intended status:
Category: Experimental March 28, July 2014
Expires: September 29, 2014

EDNS
ISSN: 2070-1721

Extension Mechanisms for DNS (EDNS) EXPIRE OPTION
draft-andrews-dnsext-expire-04 Option

Abstract

This document specifies a method for secondary DNS servers to honour
the SOA EXPIRE field as if they were always transferring from the
primary, even when using other secondaries to perform indirect
transfers and refresh queries.

Status of this This Memo

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provisions of BCP 78 not an Internet Standards Track specification; it is
published for examination, experimental implementation, and BCP 79.

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This Internet-Draft will expire on September 29, 2014.
http://www.rfc-editor.org/info/rfc7314.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2
1.1. Reserved Words . . . . . . . . . . . . . . . . . . . . . . 3 2
2. Expire EDNS option Option (Query) . . . . . . . . . . . . . . . . . . 3
3. Expire EDNS option Option (Response) . . . . . . . . . . . . . . . . . 3
3.1. Primary Server . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Secondary Server . . . . . . . . . . . . . . . . . . . . . 4 3
3.3. Non-Authoritative Non-authoritative Server . . . . . . . . . . . . . . . . . 4 3
4. Secondary Behaviour . . . . . . . . . . . . . . . . . . . . . . 4 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 4
7. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 5 4

1. Introduction

The expire field of a DNS zone's SOA record [RFC 1035] [RFC1035] is supposed to
indicate when a secondary server shall discard the contents of the
zone when it has been unable to contact the primary [RFC 1034]. [RFC1034].
Current practice only works when all the secondaries contact the
primary directly to perform refresh queries and zone transfers.

While secondaries are expected to be able to, and often are
configured to, transfer from other secondaries for robustness reasons
as well as reachability constraints, there was is no mechanism provided
to preserve the expiry behaviour when using a secondary. Secondaries
instead Instead,
secondaries have to know whether they were are talking directly to the
primary or another secondary, secondary and use that to decide whether or not to
update the expire timer or not. This however timer. This, however, fails to take into account
delays in transferring from one secondary to another.

There are also zone transfer zone-transfer graphs in which the secondary never
talks to the primary, so the effective expiry period becomes
multiplied by the length of the zone transfer graph--which zone-transfer graph, which is
infinite when it contains loops is infinite. loops.

This document provides a mechanism to preserve the expiry behaviour
regardless of what zone transfer zone-transfer graph is constructed and whether the
secondary is talking to the primary or another secondary.

1.1. Reserved Words

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119]. [RFC2119].

2. Expire EDNS option Option (Query)

The EDNS [RFC 6891] [RFC6891] EXPIRE option has the value <TBA>. <9>. The EDNS EXPIRE
option MAY be included set on any QUERY, though usually this is only done
on SOA, AXFR AXFR, and IXFR queries involved in zone maintenance. This is
done by adding a zero length zero-length EDNS EXPIRE option to the options field
of the OPT record when the query is made.

3. Expire EDNS option Option (Response)

3.1. Primary Server

When the query is directed to the primary server for the zone, the
response will be a an EDNS EXPIRE option of length 4 containing the
value of the SOA EXPIRE field, in seconds and network byte order.

3.2. Secondary Server

When the query is directed to a secondary server for the zone, then
the response will be an EDNS EXPIRE option of length 4 containing the
value of the expire timer on that server, in seconds and network byte
order.

3.3. Non-Authoritative Non-authoritative Server

If an EDNS EXPIRE option is sent to a server that is not
authoritative for the zone zone, it MUST NOT add an EDNS EXPIRE option to
the response.

4. Secondary Behaviour

When a secondary server performs a zone transfer zone-transfer request or performs a zone zone-
refresh query query, it SHALL add an EDNS EXPIRE option to the query
message.

If a secondary receives an EDNS EXPIRE option in a response to a an SOA
query, it SHALL update its expire timer to be the maximum of the
value returned in the EDNS EXPIRE option and the current timer value.
Similarly, if a secondary receives an EDNS EXPIRE option in its
response to an IXFR query which that indicated the secondary is up to date
(serial matches current serial) serial), the secondary SHALL update the
expire timer to be the maximum of the value returned in the EXPIRE EDNS
EXPIRE option and the current timer value.

If the zone is transferred or updated as the result of an AXFR or
IXFR query and there is an EDNS EXPIRE option with the response response, then
the value of the EDNS EXPIRE option SHOULD be used instead of that the
value of the SOA EXPIRE field to initialise the expire timer.

In all cases, if the value of the SOA EXPIRE field is less than the
value of the EDNS EXPIRE option, then the value of the SOA EXPIRE
field MUST be used and MUST be treated as a maximum when updating or
initialising the expire timer.

5. IANA Considerations

IANA is requested to assign a has assigned an EDNS option code point (Registry Name:
DNS EDNS0 Options) for the EDNS EXPIRE
option specified in Section 2 with "Optional" status. status in the "DNS
EDNS0 Option Codes (OPT)" registry.

6. Security Considerations

This

The method described in this document ensures that servers that no
longer have a connection to the primary server, direct or indirectly,
cease serving the zone content when SOA EXPIRE timer is reached.
This prevent prevents stale data from being served indefinitely.

The EDNS EXPIRE option exposes how long the secondaries have been out
of communication with the primary server. This is not believed to be
a problem and may provide some benefit to monitoring systems.

7. Normative References

[RFC 1034]

[RFC1034] Mockapetris, P., "DOMAIN NAMES "Domain names - CONCEPTS AND FACILITIES", concepts and facilities",
STD 13, RFC 1034, November 1987.

[RFC 1035]

[RFC1035] Mockapetris, P., "DOMAIN NAMES "Domain names - IMPLEMENTATION AND
SPECIFICATION", implementation and
specification", STD 13, RFC 1035, November 1987.

[RFC 2119]

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC 6891]

[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891, April 2013.

Author's Address

Mark P. Andrews
Internet Systems Consortium
950 Charter Street
Redwood City, CA 94063
US

Email:

EMail: marka@isc.org