EDNS X-Proxied-For
draft-bellis-dnsop-xpf-01
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This is an older version of an Internet-Draft whose latest revision state is "Expired".
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| Author | Ray Bellis | ||
| Last updated | 2017-01-09 | ||
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draft-bellis-dnsop-xpf-01
DNSOP Working Group R. Bellis
Internet-Draft ISC
Intended status: Standards Track January 09, 2017
Expires: July 13, 2017
EDNS X-Proxied-For
draft-bellis-dnsop-xpf-01
Abstract
It is becoming more commonplace to install front end proxy devices in
front of DNS servers to provide (for example) load balancing or to
perform transport layer conversions.
This document defines an option within the EDNS(0) Extension
Mechanism for DNS that allows a DNS server to receive the original
client source IP address when supplied by trusted proxies.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 13, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Description . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. EDNS Option Format . . . . . . . . . . . . . . . . . . . 3
3.2. Proxy Processing . . . . . . . . . . . . . . . . . . . . 4
3.3. Server Processing . . . . . . . . . . . . . . . . . . . . 4
3.4. Secret Key Transaction Authentication for DNS (TSIG) . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
It is becoming more commonplace to install front end proxy devices in
front of DNS servers [RFC1035] to provide load balancing or to
perform transport layer conversions (e.g. to add DNS over TLS
[RFC7858] to a DNS server that lacks native support).
This has the unfortunate side effect of hiding the clients' source IP
addresses from the server, making it harder to employ server-side
technologies that rely on knowing those address (e.g. ACLs, DNS
Response Rate Limiting, etc).
This document defines an option within the EDNS(0) Extension
Mechanism for DNS [RFC6891] that allows a DNS server to receive the
original client source IP address when supplied by trusted proxies.
Whilst in some circumstances it would be possible to re-use the
Client Subnet EDNS Option [RFC7871] to carry this information, a new
option is defined to allow both this option and the Client Subnet
option to co-exist in the same packet.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
"Key words for use in RFCs to Indicate Requirement Levels" [RFC2119].
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The word "proxy" in this document means a network component that sits
on the inbound query path in front of a recursive or authoritative
DNS server, receiving DNS queries from clients and dispatching them
to local servers. This is to distinguish these from a "forwarder"
since that term is usually understood to describe a network component
that sits on the oubound query path of a client.
3. Description
3.1. EDNS Option Format
The overall format of an EDNS option is shown for reference below,
per [RFC6891], followed by the option specific data:
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | |
/ OPTION-DATA /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
OPTION-CODE: TBD, with mnemonic "XPF".
OPTION-LENGTH: Size (in octets) of OPTION-DATA.
OPTION-DATA: Option specific, as below:
+0 (MSB) +1 (LSB)
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | Unused | IP Version | Address Octet 0 |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | Address Octet 1 | ... |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| ... /// |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Unused: Currently reserved. These MUST be zero unless redefined in a
subsequent specification.
IP Version: The IP protocol version number used by the client, as
defined in the IANA IP Version Number Registry [IANA-IP].
Implementations MUST support IPv4 (4) and IPv6 (6).
Address: The source IP address of the client.
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3.2. Proxy Processing
Proxies MUST append this option to each request packet received
before sending it to the intended DNS server.
If this option is already present in an incoming request it MUST be
stripped from the request unless the request was received from an
upstream proxy that is itself white-listed by the receiving proxy
(i.e. if the proxies are configured in a multi-tier architecture),
in which case the original value of the option MUST be preserved.
If the proxy has to create a new OPT RR (because none was present in
the original request) it MUST strip any OPT RR subsequently seen in
the response for conformance with Section 7 of [RFC6891].
3.3. Server Processing
When this option is received from a white-listed client the DNS
server MUST (SHOULD?) use the address from the option contained
therein in preference to the client's source IP address for any data
processing logic that would otherwise depend on the latter.
If this option is received from a non-white-listed client the server
MUST return a REFUSED response.
If the IP version is not understood by the server it MUST return a
REFUSED response.
If the length of the client IP address contained in the OPTION-DATA
is not consistent with that expected for the given IP version then
the server MUST return a FORMERR response.
Servers MUST NOT send this option in DNS responses.
3.4. Secret Key Transaction Authentication for DNS (TSIG)
The considerations for TSIG [RFC2845] from Section 4.5 of "DNS Proxy
Implementation Guidelines" [RFC5625] apply here.
A TSIG-signed request MUST either:
1. be forwarded according to RFC 5625 without addition of this
option, or
2. be verified using a secret shared between client and proxy,
updated with this option, and then re-signed with a (potentially
different) shared secret before sending to the server.
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In the case of option 1, the server might still be able to uniquely
identify and authenticate the client through its shared key, but not
by its IP address.
If option 2 is used, there is an operational trade-off to be
considered as to whether the two secrets (between client and proxy,
and between proxy and server) are actually the same secret. A
potential advantage of three-way sharing of the secret is that if the
server response requires no modifications it may be returned directly
to the client without any further TSIG operations.
Author's note: A third alternative exists, which is to append an
additional TSIG signature to the packet based on a secret shared only
between the proxy and server. If end-to-end TSIG validation is
required alongside TSIG validation between proxy and server, the
server would have to 1) validate that second signature, 2) strip it,
and then 3) perform further validation on the original signature.
Feedback is sought on whether this is worth pursuing.
4. Security Considerations
If the white-list of trusted proxies is implemented as a list of IP
addresses, the server administrator MUST have the ability to
selectively disable this feature for any transport where there is a
possibility of the proxy's source address being spoofed.
This does not mean to imply that use over UDP is impossible - if for
example the network architecture keeps all proxy-to-server traffic on
a dedicated network and clients have no direct access to the servers
then the proxies' source addresses can be considered unspoofable.
5. Privacy Considerations
Used incorrectly, this option could expose internal network
information, however it is not intended for use on proxy / forwarder
devices that sit on the client-side of a DNS request.
This specification is only intended for use on server-side proxy
devices that are under the same administrative control as the DNS
servers themselves. As such there is no change in the scope within
which any private information might be shared.
6. IANA Considerations
IANA are directed to assign the value TBD for the XPF option in the
DNS EDNS0 Option Codes Registry.
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7. Acknowledgements
8. References
8.1. Normative References
[IANA-IP] IANA, "IANA IP Version Registry", November 2016,
<http://www.iana.org/assignments/version-numbers/>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
Wellington, "Secret Key Transaction Authentication for DNS
(TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,
<http://www.rfc-editor.org/info/rfc2845>.
[RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines", BCP
152, RFC 5625, DOI 10.17487/RFC5625, August 2009,
<http://www.rfc-editor.org/info/rfc5625>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891, DOI 10.17487/
RFC6891, April 2013,
<http://www.rfc-editor.org/info/rfc6891>.
8.2. Informative References
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <http://www.rfc-editor.org/info/rfc7858>.
[RFC7871] Contavalli, C., van der Gaast, W., Lawrence, D., and W.
Kumari, "Client Subnet in DNS Queries", RFC 7871, DOI
10.17487/RFC7871, May 2016,
<http://www.rfc-editor.org/info/rfc7871>.
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Author's Address
Ray Bellis
Internet Systems Consortium, Inc.
950 Charter Street
Redwood City CA 94063
USA
Phone: +1 650 423 1200
Email: ray@isc.org
Bellis Expires July 13, 2017 [Page 7]