dnsext P. Wouters
Internet-Draft Red Hat
Intended status: Standards Track October 15, 2013
Expires: April 18, 2014
TCP chain query requests in DNS
draft-wouters-edns-tcp-chain-query-01
Abstract
This document defines an EDNS0 extension that can be used by a DNSSEC
enabled Recursive Nameserver configured as a forwarder to send a
single query over TCP requesting to receive a complete validation
path along with the regular query answer.
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
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This Internet-Draft will expire on April 18, 2014.
Copyright Notice
Copyright (c) 2013 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
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described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Option Format . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Protocol Description . . . . . . . . . . . . . . . . . . . . 5
5.1. Discovery of Support . . . . . . . . . . . . . . . . . . 5
5.2. Generating a Query . . . . . . . . . . . . . . . . . . . 5
5.3. Generating a Response . . . . . . . . . . . . . . . . . . 6
5.4. Sending the Option . . . . . . . . . . . . . . . . . . . 7
6. Protocol Considerations . . . . . . . . . . . . . . . . . . 7
6.1. DNSSEC Considerations . . . . . . . . . . . . . . . . . . 7
6.2. NS record Considerations . . . . . . . . . . . . . . . . 7
6.3. TCP Session Management . . . . . . . . . . . . . . . . . 8
6.4. Non-Clean Paths . . . . . . . . . . . . . . . . . . . . . 8
6.5. Anycast Considerations . . . . . . . . . . . . . . . . . 8
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8.1. Amplification Attacks . . . . . . . . . . . . . . . . . . 9
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Simple Query for example.com . . . . . . . . . . . . . . 10
9.2. Out-of-path query for example.com . . . . . . . . . . . . 12
9.3. non-existent data . . . . . . . . . . . . . . . . . . . . 12
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
10.1. EDNS0 option code for edns-tcp-chain-query . . . . . . . 13
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
12. Normative References . . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
Traditionally, clients operate in stub-mode for DNS. For each DNS
question the client needs to resolve, it sends a single query to an
upstream DNS resolver to obtain a single DNS answer. When DNSSEC
[RFC4033] is deployed on such clients, validation requires that the
client obtains all the (intermediate) information from the DNS root
down to the queried-for hostname so it can perform DNSSEC validation
on the complete chain of trust.
For example, the validated answer for the question of the A record
for the zone "example.com" requires over a hundred DNS queries. That
many queries adds a significant number of round-trip delays that is
considered unusable by current user expectation. It especially
affects web browsers which usually need to lookup dozens of hostnames
to render a single web page.
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This document specifies an EDNS0 extension that allows a validating
recursive name server running as a forwarder to open a TCP connection
to another recursive name server and request a DNS chain answer using
one DNS query/answer pair. This reduces the number of round-trip
times ("RTT") to two. If combined with [TCP-KEEPALIVE] there is only
1 RTT. While the upstream DNS resolver still needs to perform all
these queries, it usually has a much bigger cache and does not
experience significant slowdown from last-mile latency.
This EDNS0 extension allows the Forwarder to indicate which part of
the DNS hierarchy it already contains in its cache. This reduces the
amount of data required to be transferred and reduces the work the
upstream Resolving Nameserver has to perform.
This EDNS0 extension is only intended for Forwarders. It can (and
should be) ignored by Authoritative Nameservers and by Recursive
Nameservers that do not support this EDNS0 option.
1.1. Requirements Notation
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 [RFC2119].
2. Terminology
Stub Resolver: A simple DNS protocol implementation on the client
side as described in [RFC1034] section 5.3.1.
Authoritative Nameserver: A nameserver that has authority over one
or more DNS zones. These are normally not contacted by clients
directly but by Recursive Resolvers. Described in [RFC1035]
chapter 6.
Recursive Resolver: A nameserver that is responsible for resolving
domain names for clients by following the domain's delegation
chain, starting at the root. Recursive Resolvers frequently use
caches to be able to respond to client queries quickly. Described
in [RFC1035] chapter 7.
Validating Resolver: A recursive nameserver that also performs
DNSSEC [RFC4033] validation.
Forwarder: A Recursive Resolver that is using another (upstream)
Recursive Resolver instead of querying Authoritative Nameservers
directly. It still performs validation.
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3. Overview
When DNSSEC is deployed on the client, it can no longer delegate all
DNS work to the upstream Resolving Nameserer. Obtaining just the DNS
answer itself is not enough to validate that answer using DNSSEC.
For DNSSEC validation, the client requires a locally running
validating DNS server configured as Resolving Nameserver so it can
confirm DNSSEC validation of all intermediary DNS answers. It can
configure itself as a Forwarder if the DHCP server has indicated that
one or more Resolving Nameservers are available. Regardless,
generating the required queries for validation adds a significant
delay in answering the DNS question of the locally running
applications. The application has to wait while the Forwarder on the
client is querying for all the intermediate work. Each round-trip
adds to the total time waiting on DNS resolving to complete. This
makes DNSSEC resolving impractical on networks with a high latency.
The edns-tcp-chain-query option allows the client to request all
intermediate DNS data it requires to resolve and validate a
particular DNS answer in a single round-trip DNS query and answer.
Since this data is most likely larger than the common maximum UDP
packet size, the server must only return the additional data when
using the TCP transport. Requiring TCP furthermore avoid DNS
amplification attacks.
The format of this option is described in Section 4.
As described in Section 5.3, a recursive nameserver could use this
EDNS0 option to include additional data required by the client in the
Authority Section of the DNS answer packet when using the TCP
transport. The Answer Section remains unchanged from a traditional
DNS answer and contains the answer and related DNSSEC entries.
The edns-tcp-chain-query EDNS0 option MAY be sent over UDP as a
discovery method. A DNS server receiving edns-tcp-chain-query over
UDP MAY add an empty edns-tcp-chain-query option in its answer to
indicate that it supports edns-tcp-chain-query when the TCP transport
is used.
The mechanisms provided by edns-tcp-chain-query raise various
security related concerns, related to the additional work and
bandwidth as well as privacy issues with the cache. These concerns
are described in Section 8.
4. Option Format
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This draft uses an EDNS0 ([RFC2671]) option to include client IP
information in DNS messages. The option is structured as follows:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-------------------------------+-------------------------------+
! OPTION-CODE ! OPTION-LENGTH !
+-------------------------------+-------------------------------+
~ Last Known Query Name (FQDN) ~
+---------------------------------------------------------------+
o (Defined in [RFC2671]) OPTION-CODE, 2 octets, for edns-tcp-chain-
query is [TBD].
o (Defined in [RFC2671]) OPTION-LENGTH, 2 octets, contains the
length of the payload (everything after Option-length) in octets.
o Last Known Query Name, a variable length FDQN of the requested
start point of the chain. This entry is the 'lowest' known entry
in the DNS chain known by the recursive server seeking a edns-tcp-
chain-query answer. The end point of the chain is obtained from
the DNS Query Section itself. No compression is allowed for this
value.
o Assigned by IANA in IANA-AFI [1].
5. Protocol Description
5.1. Discovery of Support
A Forwarder may include a zero-length edns-tcp-chain-query option in
queries over UDP or TCP to discover the DNS server capability for
edns-tcp-chain-query. DNS Servers that support and are willing to
accept chain queries over TCP SHOULD respond to a zero-length edns-
tcp-chain-query received over UDP or TCP queries by including a zero-
length edns-tcp-chain-query option in the answer. A Forwarder MAY
then switch to the TCP transport and sent a non-zero edns-tcp-chain-
query value to request a chain-query response from the DNS server.
5.2. Generating a Query
The edns-tcp-chain-query option should generally be deployed by
Forwarders, as described in Section 5.4.
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In this option value, the Forwarder sets the last known entry point
in the chain - furthest from the root - that it already has a DNSSEC
validated (secure or not) answer for in its cache. The upstream
Recursive Resolver does not need to include any part of the chain
from the root down to this option's FQDN. A complete example is
described in Section 9.
5.3. Generating a Response
When a query containing a non-zero edns-tcp-chain-query option is
received over a TCP connection from a Forwarder, the upstream
Recursive Resolver supporting edns-tcp-chain-query MAY respond by
confirming that it is returning a DNS Query Chain. To do so, it MUST
set the edns-tcp-chain-query option with an OPTION-LENGTH of zero to
indicate the DNS answer contains a Chain Query. It extends the
Authority Section for the DNS answer packet with the required DNS
RRSets resulting in an Authority Section that contains a complete
chain of DNS RRsets that start with the first chain element below the
received Last Known Query Name upto and including the NS and DS
RRsets that represent the zone cut (authoritative servers) of the
QNAME. The actual DNS answer to the question in the Query Section is
placed in the DNS Answer Section identical to traditional DNS
answers. If the received query has the DNSSEC OK flag set, all
required DNSSEC related records must be added to their appropriate
sections. This includes records required for proof of non-existence
of regular and/or wildcard records, such as NSEC or NSEC3 records.
Recursive Resolvers that have not implemented or enabled support for
the edns-tcp-chain-query option, or are otherwise unwilling to
perform the additional work for a Chain Query due to work load, may
safely ignore the option in the incoming queries. Such a server MUST
NOT include an edns-tcp-chain-query option when sending DNS answer
replies back, thus indicating it is not able to support Chain Queries
at this time.
Requests with wrongly formatted options (i.e. bogus FQDN) MUST be
rejected and a FORMERR response must be returned to the sender, as
described by [RFC2671], Transport Considerations.
Requests resulting in chains that the receiving resolver is unwilling
to serve can be rejected by sending a REFUSED response to the sender,
as described by [RFC2671], Transport Considerations. This refusal
can be used for chains that would be too big or chains that would
reveal too much information considered private.
At any time, a DNS server that has determined that it is running low
on resources can refuse to acknowledge a Chain Query by omitting the
edns-tcp-chain-query option. It may do so even if it conveyed
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support to a DNS client previously. If [TCP-KEEPALIVE] is used, it
may even change its support for edns-tcp-chain-query within the same
TCP session.
If the DNS request results in an CNAME or DNAME for the Answer
Section, the DNS server MUST return these records in the Answer
Section similar to regular DNS processing. It MUST NOT follow the
CNAME or DNAME. Otherwise, both the CNAME or DNAME and the followed
destination would end up in the Answer Section. [is that actually a
problem? Jelte thought so, but I am not sure]
In any case, the response from the receiving resolver to the client
resolver MUST NOT contain the edns-tcp-chain-query option if none was
present in the client's resolver original request.
5.4. Sending the Option
When edns-tcp-chain-query is available, the downstream Resolving
Nameserver can adjust its query strategy based on the desired queries
and its cache contents.
A Forwarder can request the edns-tcp-chain-query option with every
outgoing DNS query. However, it is RECOMMENDED that Forwarders
remember which upstream Resolving Nameservers did not return the
option (and additional data) with their response. The Forwarder
SHOULD fallback to regular DNS for subsequent queries to those
Recursive Nameservers. It MAY switch to another Resolving Nameserver
that does support the edns-tcp-chain-query option or try again later
to see if the server has become less loaded and is now willing to
answer with Query Chains.
6. Protocol Considerations
6.1. DNSSEC Considerations
The presence or absence of an OPT resource record containing an edns-
tcp-chain-query option in a DNS query does not change the usage of
those resource records and mechanisms used to provide data origin
authentication and data integrity to the DNS, as described in
[RFC4033], [RFC4034] and [RFC4035].
6.2. NS record Considerations
When a DNSSEC chain is supplied via edns-tcp-chain-query, the
Forwarder no longer requires to use the NS RRset, as it can construct
the validation path via the DNSKEY and DS RRsets without using the NS
RRset. However, it is prefered that the Forwarder can populate its
cache with this information regardless, to avoid requiring queries in
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the future just to obtain the missing NS records. Therefor, edns-
tcp-chain-query responses MUST include the NS RRset from the child
zone, which includes DNSSEC RRSIG records required for validation.
6.3. TCP Session Management
It is recommended that TCP Chain Queries are used in combination with
[TCP-KEEPALIVE].
Both DNS clients and servers are subject to resource constraints
which will limit the extent to which TCP Chain Queries can be
executed. Effective limits for the number of active sessions that
can be maintained on individual clients and servers should be
established, either as configuration options or by interrogation of
process limits imposed by the operating system.
In the event that there is greater demand for TCP Chain Queries than
can be accommodated, DNS servers may stop advertising the edns-tcp-
query-chain option in successive DNS messages. This allows, for
example, clients with other candidate servers to query to establish
new TCP sessions with different servers in expectation that those
servers might still allow TCP Chain Queries.
6.4. Non-Clean Paths
Many paths between DNS clients and servers suffer from poor hygiene,
limiting the free flow of DNS messages that include particular EDNS0
options, or messages that exceed a particular size. A fallback
strategy similar to that described in [RFC6891] section 6.2.2 SHOULD
be employed to avoid persistent interference due to non-clean paths.
6.5. Anycast Considerations
DNS servers of various types are commonly deployed using anycast
[RFC4786].
Successive DNS transactions between a client and server using UDP
transport may involve responses generated by different anycast nodes,
and the use of anycast in the implementation of a DNS server is
effectively undetectable by the client. The edns-tcp-chain-query
option SHOULD NOT be included in responses using UDP transport from
servers provisioned using anycast unless all anycast server nodes are
capable of processing the edns-tcp-query-chain option.
Changes in network topology between clients and anycast servers may
cause disruption to TCP sessions making use of edns-tcp-chain-query
more often than with TCP sessions that omit it, since the TCP
sessions are expected to be longer-lived. Anycast servers MAY make
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use of TCP multipath [RFC6824] to anchor the server side of the TCP
connection to an unambiguously-unicast address in order to avoid
disruption due to topology changes.
7. Implementation Status
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC6982].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC6982], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
[While there is some interest, no work has started yet]
8. Security Considerations
8.1. Amplification Attacks
Chain Queries can potentially send very large DNS answers. A
recursive nameserver MUST NOT return Query Chain answers to clients
over UDP. It is allowed to signal support in response to a Query
Chain request over UDP by responding using a zero-length edns-tcp-
chain-query option. This is to prevent a single spoofed UDP packet
from causing extremely large UDP response packets from being sent to
a spoofed IP address. Such Distributed Denial of Service attacks
using other DNS amplification mechanisms are fairly common.
9. Examples
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9.1. Simple Query for example.com
1. A web browser on a client machine asks the Forwarder running on
localhost to resolve the A record of "www.example.com." by
sending a regular DNS UDP query on port 53 to 127.0.0.1.
2. The Forwarder on the client machine checks its cache, and
notices it already has a validated entry of "com." in its cache.
This includes the DNSKEY RRset with its RRSIG records. In other
words, according to its cache, ".com" is DNSSEC validated as
"secure" and can be used to continue a DNSSEC validated chain
on.
3. The Forwarder on the client opens a TCP connection to its
upstream Recursive Resolver on port 53. It adds the edns-tcp-
chain-query option as follows:
* Option-code, set to [TBD]
* Option-length, set to 0x00 0x04
* Last Known Query Name set to "com."
4. The upstream Recursive Resolver receives a DNS query over TCP
with the edns-tcp-chain-query Last Known Query Name set to
"com.". After accepting the query it starts constructing a DNS
reply packet over TCP.
5. The upstream Recursive Resolver performs all the regular work to
ensure it has all the answers to the query for the A record of
"www.example.com.". It does so without using the edns-tcp-
chain-query option - unless it is also configured as a
Forwarder. The answer to the original DNS question could be the
actual A record, the DNSSEC proof of non-existence, or an
insecure NXDOMAIN response.
6. The upstream Recursive Resolver adds the edns-tcp-chain-query
option to the DNS answer reply as follows:
* Option-code, set to [TBD]
* Option-length, set to 0x00 0x00
* The Last Known Query Name is ommited (zero length)
7. The upstream Recursive Resolver constructs the DNS Authority
Section and fills it with:
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* The DS RRset for "example.com." and its corresponding RRSIGs
(made by the "com." DNSKEY(s))
* The DNSKEY RRset for "example.com." and its corresponding
RRSIGs (made by the "example.com" DNSKEY(s))
* The authoritative NS RRset for "example.com." and its
corresponding RRSIGs (from the child zone)
If the answer does not exist, and the zone uses DNSSEC, it also
adds the proof of non-existance, such as NSEC or NSEC3 records,
to the Authority Section.
8. The upstream Recursive Resolver constructs the DNS Answer
Section and fills it with:
* The A record of "www.example.com." and its corresponding
RRSIGs
If the answer does not exist (no-data or NXDOMAIN), the Answer
Section remains empty. For the NXDOMAIN case, the RCode of the
DNS answer packet is set to NXDOMAIN. Otherwise it remains
NOERROR.
9. The upstream Recursive Resolver returns the DNS answer over the
existing TCP connection. When all data is sent, it SHOULD keep
the TCP connection open to allow for additional incoming DNS
queries - provided it has enough resources to do so.
10. The Forwarder receives the DNS answer over TCP. It processes
the Authority Section and the Answer Section and places the
information in its local cache. If it is a DNSSEC validating
resolver, it ensures that no unvalidated data or out of baliwick
data is accepted into the cache without having proper DNSSEC
validation. It MAY do so by looping over the entries in the
Authority and Answer Sections. When an entry is validated for
its cache, it is removed from the processing list. If an entry
cannot be validated it is left in the process list. When the
end of the list is reached, the list is processed again until
either all entries are placed in the cache, or the remaining
items cannot be placed in the cache due to lack of validation.
Those entries are then disgarded.
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11. If the cache contains a valid answer to the application's query,
this answer is returned to the application via a regular DNS
answer packet. This packet MUST NOT contain an edns-tcp-chain-
query option. If no valid answer can be returned, normal error
processing is done. For example, an NXDOMAIN or an empty Answer
Section could be returned depending on the error condition.
9.2. Out-of-path query for example.com
A Recursive Resolver receives a query for the A record for
example.com. It includes the edns-tcp-chain-query option with the
following parameters:
o Option-code, set to [TBD]
o Option-length, set to 0x00 0x0D
o The Last Known Query Name set to 'unrelated.ca.'
As there is no chain that leads from "unrelated.ca." to
"example.com", the Resolving Nameserver answers with RCODE "FormErr".
It includes the edns-tcp-chain-query with the following parameters:
o Option-code, set to [TBD]
o Option-length, set to 0x00 0x00
o The Last Known Query Name is ommited (zero length)
9.3. non-existent data
A Recursive Resolver receives a query for the A record for
"ipv6.toronto.redhat.ca". It includes the edns-tcp-chain-query
option with the following parameters:
o Option-code, set to [TBD]
o Option-length, set to 0x00 0x03
o The Last Known Query Name set to 'ca.'
Using regular UDP queries towards Authoritative Nameservers, it
locates the NS RRset for "toronto.redhat.ca.". When querying for the
A record it receives a reply with RCODE "NoError" and an empty Answer
Section. The Authority Section contains NSEC3 and RRSIG records
proving there is no A RRtype for the QNAME "ipv6.toronto.redhat.ca".
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The Recursive Resolver constructs a DNS reply with the following
edns-tcp-chain-query option parameters:
o Option-code, set to [TBD]
o Option-length, set to 0x00 0x00
o The Last Known Query Name is ommited (zero length)
The RCODE is set to "NoError". The Authority Section is filled in
with:
o The DS RRset for "redhat.ca." plus RRSIGs
o The DNSKEY RRset for "redhat.ca." plus RRSIGs
o The NS RRset for "redhat.ca." plus RRSIGs (eg ns[01].redhat.ca)
o The A RRset for "ns0.redhat.ca." and "ns1.redhat.ca." plus RRSIGs
o The DS RRset for "toronto.redhat.ca." plus RRSIGs
o The NS RRset for "toronto.redhat.ca." plus RRSIGs (eg
ns[01].toronto.redhat.ca)
o The DNSKEY RRset for "toronto.redhat.ca." plus RRSIGs
o The A RRset and/or AAAA RRset for "ns0.toronto.redhat.ca." and
"ns1.toronto.redhat.ca." plus RRSIGs
o The NSEC record for "ipv6.toronto.redhat.ca." (proves what RRTYPEs
do exist, does not include A)
o The NSEC record for "toronto.redhat.ca." (proves no wildcard
exists)
The Answer Section is empty. The RCode is set to NOERROR.
10. IANA Considerations
10.1. EDNS0 option code for edns-tcp-chain-query
IANA has assigned option code [TBD] in the "DNS EDNS0 Option Codes
(OPT)" registry to edns-tcp-chain-query.
11. Acknowledgements
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Andrew Sullivan pointed out that we do not need any new data formats
to support DNS chains. Olafur Gudmundsson ensured the RRsets are
returned in the proper Sections.
12. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC
2671, August 1999.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC
4033, March 2005.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, March 2005.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005.
[RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast
Services", BCP 126, RFC 4786, December 2006.
[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, January 2013.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891, April 2013.
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", RFC 6982, July
2013.
[TCP-KEEPALIVE]
Wouters, P., "The edns-tcp-keepalive EDNS0 Option", draft-
wouters-edns-tcp-keeaplive (work in progress), October
2013.
Wouters Expires April 18, 2014 [Page 14]
Internet-Draft TCP chain query requests in DNS October 2013
Author's Address
Paul Wouters
Red Hat
Email: pwouters@redhat.com
Wouters Expires April 18, 2014 [Page 15]