ALTO S. Kiesel
Internet-Draft University of Stuttgart
Intended status: Standards Track M. Tomsu
Expires: April 28, 2011 Alcatel-Lucent
N. Schwan
M. Scharf
Alcatel-Lucent Bell Labs
M. Stiemerling
NEC Europe Ltd.
October 25, 2010
ALTO Server Discovery Protocol
draft-kiesel-alto-3pdisc-04
Abstract
The goal of Application-Layer Traffic Optimization (ALTO) is to
provide guidance to applications, which have to select one or several
hosts from a set of candidates that are able to provide a desired
resource.
Entities seeking guidance need to discover and possibly select an
ALTO server to ask. This is called ALTO server discovery. This memo
describes an ALTO server discovery mechanism based on several
alternative mechanisms that are applicable in a diverse set of ALTO
deployments.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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 April 28, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
Kiesel, et al. Expires April 28, 2011 [Page 1]
Internet-Draft ALTO Server Discovery Protocol October 2010
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
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Pre-Conditions . . . . . . . . . . . . . . . . . . . . . . 4
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 5
3. Retrieving the URI by DHCP . . . . . . . . . . . . . . . . . . 7
3.1. ALTO Server Domain Name Encoding . . . . . . . . . . . . . 7
3.2. ALTO Server DHCPv4 Option . . . . . . . . . . . . . . . . 7
3.3. ALTO Server DHCPv6 Option . . . . . . . . . . . . . . . . 8
4. Retrieving the URI by U-NAPTR . . . . . . . . . . . . . . . . 10
4.1. U-NAPTR Resolution . . . . . . . . . . . . . . . . . . . . 10
4.2. Retrieving the Domain Name . . . . . . . . . . . . . . . . 10
4.2.1. Option 1: User input . . . . . . . . . . . . . . . . . 11
4.2.2. Option 2: DHCP . . . . . . . . . . . . . . . . . . . . 12
4.2.3. Option 3: Reverse DNS Lookup . . . . . . . . . . . . . 12
5. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1. Applicability for Resource Consumer Server Discovery . . . 13
5.2. Applicability for Third Party Server Discovery . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.2. For U-NAPTR . . . . . . . . . . . . . . . . . . . . . . . 16
8. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 18
9. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 19
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative References . . . . . . . . . . . . . . . . . . . 20
10.2. Informative References . . . . . . . . . . . . . . . . . . 20
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
Kiesel, et al. Expires April 28, 2011 [Page 2]
Internet-Draft ALTO Server Discovery Protocol October 2010
1. Introduction
The goal of Application-Layer Traffic Optimization (ALTO) is to
provide guidance to applications, which have to select one or several
hosts from a set of candidates, that are able to provide a desired
resource [RFC5693]. The requirements for ALTO are itemized in
[I-D.ietf-alto-reqs]. ALTO is realized by a client-server protocol.
ALTO clients send queries to ALTO servers, in order to solicit
guidance.
ALTO clients have to discover suitable ALTO servers. Therefore the
output of the herein defined ALTO discovery procedure tells the ALTO
client which ALTO servers to send the queries to. The ALTO discovery
procedure, as part of the the ALTO client, can be embedded in the
resource consumer, which will eventually access the desired resource.
As an alternative, they can be embedded in a resource directory,
which assists resource consumers in finding appropriate resource
providers. In some specific peer-to-peer application protocols these
resource directories are called "trackers". Finally the ALTO server
discovery procedure can be embedded in the resource consumer, whereas
the ALTO client is embedded in the resource directory. ALTO queries,
which are issued by a resource directory on behalf of a resource
consumer, are referred to as third-party ALTO queries. The various
possibilities to place ALTO servers and the placement of ALTO clients
is discussed in [I-D.stiemerling-alto-deployments].
[I-D.song-alto-server-discovery] compares different protocol options
and identifies DHCP and DNS as two approaches for the ALTO server
discovery without detailing on the exact solution.
No matter where ALTO server and client are located, clients have to
first find out if there is an ALTO server deployed that is in charge
for them, and second they have to get the contact information of that
server, i.e., the IP address, port number, and probably transport
protocol (which defaults to TCP for [I-D.ietf-alto-protocol]).
The goal of this memo is to propose a uniform mechanism for all types
of ALTO client deployments that is implementable and deployable at a
fast pace, i.e., without creating other deployment dependecies for
ALTO. We propose to use a combination of DHCP and DNS to retrieve
the URL of the resposnsible ALTO server.
Comments and discussions about this memo should be directed to the
ALTO working group: alto@ietf.org.
1.1. Requirements
There is other related works on server discovery, for instance
GEOPRIV has rather strong security requirements (for good reasons),
Kiesel, et al. Expires April 28, 2011 [Page 3]
Internet-Draft ALTO Server Discovery Protocol October 2010
which are documented in [I-D.ietf-geopriv-lis-discovery]. However,
these requirements do not apply for the ALTO server discovery, as
ALTO as such has very different requirements (see
[I-D.ietf-alto-reqs]).
The result of the guidance provided to the application via the ALTO
protocol is input to improve the initial peer selection process for
peer-to-peer applications, or any other application applicable. A
missing ALTO server, i.e., no result returned as part of the ALTO
server discovery procedure, does not prevent the application to
operate. A wrong or forged guidance from the ALTO server may only
impact the overall operational result of the peer-to-peer system for
a limited time, as these systems fine-tune their behavior depending
on the experience network behavior.
This means that a wrong, missing, or forged ALTO guidance will not
cause damage to the application or peer-to-peer system. This is in
sharp contrast to the GEOPRIV use case, where a failure may have
severe impact, including loss of human life. This is not the case
for ALTO, as it is intended to be used today and as it is explored
right now from the networking community.
1.2. Pre-Conditions
The whole document assumes certain pre-conditions, such as:
o The ALTO server discovery procedure is executed on a per IP
address base. Multiple IP addresses per interface or multiple IP
addresses assigned to different IP interfaces require to repeat
the procedure for every IP address. It may be fine to group IP
addresses according their domain suffixes and to perfom the
procedure for such a group. However, this is out of scope of this
document.
o The ALTO server discovery procedure is executed on a per IP family
base, i.e., seperate for IPv4 and IPv6. It is up to the ALTO
client to decide which of the possible multiple results of
different IP address families to use. The choice of whether to
use IPv4 or IPv6 is out of scope of this document.
o A change of the IP address at an interface invalidates the result
of the ALTO server discovery procedure. For instance, if the IP
address assigned to a mobile host changes due to host mobility, it
is required to run the ALTO server discovery procedure for the new
IP address without relying on earlier gained information.
Kiesel, et al. Expires April 28, 2011 [Page 4]
Internet-Draft ALTO Server Discovery Protocol October 2010
2. Protocol Overview
We define multiple alternatives to discover the IP address of the
ALTO server, as there are a number of ways possible how such
information can be provided to the ALTO client. The choice of method
is up to the local network deployment. For instance, there can be
deployments where the ALTO server in charge for ALTO client is
provisioned by the network operator and communicated to the ALTO
client's host via a DHCP option, while in other deployments no such
means may exist.
The following figure illustrates the different protocols that are
used to find the URI of a suitable ALTO server.
Descending order of Preference
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~>
-------- -------------- -------- ---------------
| DHCP | | User Input | | DHCP | | Reverse DNS |
-------- -------------- -------- ---------------
| | | |
| \ | /
| Retrieving the DNS suffix
| \ | /
| --------+----------
\ |
\ Determine own IP address
\ |
\ -----------
\ | U-NAPTR |
\ -----------
\ |
Retrieving ALTO Server URI
\ |
---------+----------
|
Final DNS lookup
Figure 1: Protocol Overview
One option to retrieve the URI directly from the access network
provider is DHCP. However for DHCP there are problems with
residential gateways or broadband routers with NAT. If the network
operator gives information about ALTO serves to the residential
gateway via DHCP, the residential gateway would have to forward this
information to the hosts with the (P2P) applications within the local
network. This is not supported by already deployed residential
gateways. Also DHCP poorly supports third-party ALTO server
Kiesel, et al. Expires April 28, 2011 [Page 5]
Internet-Draft ALTO Server Discovery Protocol October 2010
discovery, i.e., in scenarios where the ALTO client is co-located
with a resource directory ("tracker"), which is located in a
different administrative domain than the client which will eventually
access the ressource.
Thus in deployment scenarios where DHCP is not possible, we specify a
U-NAPTR based resolution process as a second option to retrieve the
URL. As a precondition for resolution the U-NAPTR process needs the
right domain name as input. This domain name is determined by the IP
address of the client and the DNS suffix of the access network where
the client is registered in. In order to retrieve the DNS suffix we
specify three options:
User input: a user may manually specify the DNS suffix on its own,
either to access a 3rd party ALTO service provider or as it does
know such information.
DHCP: a network provider provides the DNS suffix through a DHCP
option.
Reverse DNS: the DNS system can be used to retrieve the DNS suffix
through reverse lookup of an FQDN associated with an IP address.
This is the last resort if all other options failed.
Kiesel, et al. Expires April 28, 2011 [Page 6]
Internet-Draft ALTO Server Discovery Protocol October 2010
3. Retrieving the URI by DHCP
One way of directly configuring the ALTO server URI for an access
network provider is the DHCP protocol. The ALTO server URI consists
of a domain name and the protocol the client should use to contact
the server. While the domain name can vary and is configured by
DHCP, the protocol is always HTTP.
For example a client may retrieve the domain name
altoserver.example.com by the DHCP option as described in the
remaining section. The client uses this domain name to contact the
ALTO server under
http://altoserver.example.com/
3.1. ALTO Server Domain Name Encoding
This section describes the encoding of the domain name used in the
DHCPv4 option shown in Section 3.2 and also used in the DHCPv6 option
shown in Section 3.3.
The domain name is encoded according to Section 3.1 of [RFC1035]
whereby each label is represented as a one-octet length field
followed by that number of octets. Since every domain name ends with
the null label of the root, a domain name is terminated by a length
byte of zero. The high-order two bits of every length octet MUST be
zero, and the remaining six bits of the length field limit the label
to 63 octets or less. To simplify implementations, the total length
of a domain name (i.e., label octets and label length octets) is
restricted to 255 octets or less.
3.2. ALTO Server DHCPv4 Option
The ALTO server DHCPv4 option carries a DNS ([RFC1035]) fully-
qualified domain name (FQDN) to be used by the ALTO client to locate
a ALTO server.
The DHCP option for this encoding has the following format:
Code Len ALTO Server Domain Name
+-----+-----+-----+-----+-----+-----+-----+----
| tba | n | s1 | s2 | s3 | s4 | s5 | ...
+-----+-----+-----+-----+-----+-----+-----+----
Figure 2: ALTO FQDN DHCPv4 Option
The values s1, s2, s3, etc. represent the domain name labels in the
domain name encoding. Note that the length field in the DHCPv4
Kiesel, et al. Expires April 28, 2011 [Page 7]
Internet-Draft ALTO Server Discovery Protocol October 2010
option represents the length of the entire domain name encoding,
whereas the length fields in the domain name encoding (see
Section 3.1) is the length of a single domain name label.
Code: to be assigned by IANA
Len: Length of the 'ALTO Server Domain Name' field in octets;
variable.
ALTO Server Domain Name: The domain name of the ALTO server for the
client to use.
A DHCPv4 client MAY request a ALTO server domain name in a Parameter
Request List option, as described in [RFC2131].
The encoding of the domain name is described in Section 3.1.
This option contains a single domain name and, as such, MUST contain
precisely one root label.
3.3. ALTO Server DHCPv6 Option
This section specifies the DHCP option for IPv6 (DHCPv6) to carry the
domain name of the ALTO server. It is similar formatted to the
DHCPv4 option
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBA: OPTION CODE | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ALTO Server Domain Name .
. ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: ALTO Server Domain Name DHCPv4 Option
option-code: to be assigned by IANA
option-length: The length of the 'ALTO Server Domain Name' field in
octets; variable.
ALTO Server Domain Name: The domain name of the ALTO server for the
client to use.
A DHCPv6 client MAY request a ALTO server domain name in an Options
Request Option (ORO), as described in [RFC3315].
Kiesel, et al. Expires April 28, 2011 [Page 8]
Internet-Draft ALTO Server Discovery Protocol October 2010
The encoding of the domain name is described in Section 3.1.
This option contains a single domain name and, as such, MUST contain
precisely one root label.
Kiesel, et al. Expires April 28, 2011 [Page 9]
Internet-Draft ALTO Server Discovery Protocol October 2010
4. Retrieving the URI by U-NAPTR
As already described a direct DHCP configuration may not always be
possible, for example due to deployment restrictions of the access
network. Alternatively the ALTO server URI can be discovered by a
U-NAPTR resolution process, as specified in this section.
The section is devided in two parts: Section 4.1 describes the
U-NAPTR resolution process itself. As a precondition this process
requires the domain name of the access network where the resouce
consumer is registered in. How the client identifies this DNS suffix
is described in Section 4.2.
4.1. U-NAPTR Resolution
ALTO servers are identified by U-NAPTR/DDDS (URI-Enabled NAPTR/
Dynamic Delegation Discovery Service) [RFC4848] application unique
strings, in the form of a DNS name. An example is
'altoserver.example.com'.
Clients need to use the U-NAPTR [RFC4848] specification described
below to obtain a URI (indicating host and protocol) for the
applicable ALTO service. In this document, only the HTTP and HTTPS
URL schemes are defined. Note that the HTTP URL can be any valid
HTTP URL, including those containing path elements.
The following two DNS entries show the U-NAPTR resolution for
"example.com" to the HTTPS URL https://altoserver.example.com/secure
or the HTTP URL http://altoserver.example.com, with the former being
preferred.
example.com.
IN NAPTR 100 10 "u" "ALTO:https"
"!.*!https://altoserver.example.com/secure!" ""
IN NAPTR 200 10 "u" "ALTO:http"
"!.*!http://altoserver.example.com!" ""
4.2. Retrieving the Domain Name
The U-NAPTR resolution process requires a domain name as input. The
algorithm that is applied to determine this domain name is described
in this section. We specify three different options. In option 1
the user manually configures a specific ALTO service instance that he
wants to use. Option 2 defines a DHCP option to allow the network
service provider a remote configuration of the client. In option 3
Kiesel, et al. Expires April 28, 2011 [Page 10]
Internet-Draft ALTO Server Discovery Protocol October 2010
the client tries to get the domain name by performing a reverse DNS
lookup on its IP address.
The resource consumer may have private IP addresses and public IP
addresses and depending on the deployment it might be necessary to
determine for all IP addresses the ALTO server in charge of. To
determine its public IP address the resource consumer may need to use
STUN[RFC5389] or BEP24[bep24]. For the following examples we assume
that the IP address of the resource consumer is a.b.c.d.
4.2.1. Option 1: User input
A user may want to use a third party ALTO service instance.
Therefore we allow the user to specify a DNS suffix on its own, for
example in a config file option. The DNS suffix given by the user is
combined with the IP address of the resource consumer to allow the
third party ALTO service to direct the client to a suitable ALTO
server based on the location of the client. A possible DNS suffix
entered by the user may be:
myaltoprovider.org
This DNS suffix is prepended with the IP address of the resource
consumer in reverse order to compose the domain name used for the
final U-NAPTR lookup Section 4.1. In case there are multiple ALTO
servers deployed, the third party ALTO service instance can direct
the ALTO client to the ALTO server closest to the client based on the
IP address.
Multiple lookups with different domain names might be necessary to
complete the U-NAPTR resolution process. If there is no response for
a lookup the domain name is shortened by one part for the succeeding
lookup, until a lookup is successful, as for example
d.c.b.a.myaltoprovider.org.
c.b.a.myaltoprovider.org.
b.a.myaltoprovider.org.
a.myaltoprovider.org.
myaltoprovider.org.
Kiesel, et al. Expires April 28, 2011 [Page 11]
Internet-Draft ALTO Server Discovery Protocol October 2010
4.2.2. Option 2: DHCP
As a second option network operators can configure the domain name to
be used for service discovery within an access network. RFC
5986[RFC5986] defines DHCP IPv4 and IPv6 access network domain name
options that identify a domain name that is suitable for service
discovery within the access network. The ALTO server discovery
procedure uses these DHCP options to retrieve the domain name as an
input for the U-NAPTR resolution. One example could be:
example.com
4.2.3. Option 3: Reverse DNS Lookup
The last option to get the domain name is to use a DNS PTR query for
the IP address of the resource consumer. The local DNS server
resolves the IP address to the FQDN that also contains the DNS suffix
for the respective IP address. A possible answer for a PTR lookup
for d.c.b.a.in-addr.apra might be, for example:
d-c-b-a.dsl.westcoast.myisp.net
This domain name can be used for the final U-NAPTR lookup
Section 4.1. Again, if there is no response to the lookup the domain
name is shortened by one part for the succeeding lookup. The domain
names used for the example as described above are:
d-c-b-a.dsl.westcoast.myisp.net.
dsl.westcoast.myisp.net.
westcoast.myisp.net.
myisp.net.
Kiesel, et al. Expires April 28, 2011 [Page 12]
Internet-Draft ALTO Server Discovery Protocol October 2010
5. Applicability
This section discusses the applicability of the proposed solution
with respect to the resource consumer server discovery and the third
party deployment scenarios. Each section discusses the proposed
steps that are needed to determine the ALTO Server URI.
5.1. Applicability for Resource Consumer Server Discovery
In this scenario the ALTO server discovery procedure is performed by
the resource consumer, for example a peer in a P2P system. After the
discovery the peer does the ALTO query on its own, or it might share
the ALTO server contact information with a third party, for example a
tracker, which then does the ALTO query on behalf of the peer.
The access network provider has two options based on DHCP to remotely
configure the ALTO client to use its ALTO server. The first option
is to provide the ALTO server URI directly by a DHCP option as
described in Section 3, the second option is to provide the access
network domain name as described in Section 4.2.2. It is up to the
access network provider to choose one of both options.
To complete the ALTO server discovery process the resource consumer
first SHOULD try to retrieve the ALTO server URI by the DHCP option
as described in Section 3. In case this is successful the discovery
process is finished, in case it fails, either as the access network
provider has not configured the specified option or through
deployment restrictions, the resource consumer SHOULD subsequently
check whether the user has provider the domain name through manual
configuration. If this is also not the case the next step SHOULD be
to check for the access network domain name DHCP option
(Section 4.2.2). Finally the client SHOULD try to retrieve the
domain name by the last option, the DNS reverse lookup on its IP
address as described in Section 4.2.3.
In case the ALTO discovery client has determined the domain name
through one of the described options it proceedes with the U-NAPTR
lookup as described in Section 4.1.
If the ALTO server URI could not be retrieved either through direct
configuration by the access network provider through DHCP nor through
the U-NAPTR lookup the discovery process fails.
5.2. Applicability for Third Party Server Discovery
In case of the third party server discovery deployment scenario the
entity performing the ALTO server discovery process is different from
the resource consumer. Typically the resource consumer is a peer
Kiesel, et al. Expires April 28, 2011 [Page 13]
Internet-Draft ALTO Server Discovery Protocol October 2010
whereas the ALTO client is a resource directory which seeks for ALTO
guidance on behalf of the peer. Another use case for the third party
discovery is an application that looks for ALTO guidance
transparently for the resource consumer, for example a CDN.
Here the ALTO server discovery process can also retrieve guidance
through one of the DHCP options or manual user configuration, but
only if the provided discovery information is forwarded by the
resource consumer to the third party entity. In this case,
additional mechanisms for the forwarding of this discovery
information need to be specified. However these mechanisms are out
of scope of this doument.
If the third party entity cannot obtain this discovery information,
the ALTO server discovery process relies on retrieving the domain
name used as input to the U-NAPTR lookup through reverse DNS lookup
of the IP address of the resource consumer as described in
Section 4.2.3. Usually the third party entity already knows the IP
address of the resource consumer which was used to establish the
initial connection. In general this IP address is a public address,
either of the resource consumer or of the last NAT on the path to the
ALTO client. This makes the IP address a good candidate for the DNS
PTR query. Thus, we expect that the DNS query will be successfully
resolved to the FQDN of the domain where the resource consumer is
registered in.
In case the resource consumer needs guidance for a different IP
address, for example one from a private network, we recommend that
the resource consumer discovers the server itself and forwards the
ALTO server contact information directly to the third party entity,
which in turn can then do the third party ALTO query. Again,
forwarding the contact information from the resource consumer to the
third party entity is out of scope of this document.
Kiesel, et al. Expires April 28, 2011 [Page 14]
Internet-Draft ALTO Server Discovery Protocol October 2010
6. IANA Considerations
This document registers the following U-NAPTR application service
tag:
Application Service Tag: ALTO
Defining Publication: The specification contained within this
document.
This document registers the following U-NAPTR application protocol
tags:
o Application Protocol Tag: http
Defining Publication: RFC 2616 [RFC2616]
o Application Protocol Tag: https
Defining Publication: RFC 2818 [RFC2818]
Kiesel, et al. Expires April 28, 2011 [Page 15]
Internet-Draft ALTO Server Discovery Protocol October 2010
7. Security Considerations
7.1. General
This is still to be done in later revision of this draft, as the
draft evolves heavily right now.
7.2. For U-NAPTR
The address of an ALTO server is usually well-known within an access
network; therefore, interception of messages does not introduce any
specific concerns.
The primary attack against the methods described in this document is
one that would lead to impersonation of a ALTO server since a device
does not necessarily have a prior relationship with a ALTO server.
An attacker could attempt to compromise ALTO discovery at any of
three stages:
1. providing a falsified domain name to be used as input to U-NAPTR
2. altering the DNS records used in U-NAPTR resolution
3. impersonation of the ALTO
This document focuses on the U-NAPTR resolution process and hence
this section discusses the security considerations related to the DNS
handling. The security aspects of obtaining the domain name that is
used for input to the U-NAPTR process is described in respective
documents, such as [I-D.ietf-geopriv-lis-discovery].
The domain name that is used to authenticated the ALTO server is the
domain name in the URI that is the result of the U-NAPTR resolution.
Therefore, if an attacker were able to modify or spoof any of the DNS
records used in the DDDS resolution, this URI could be replaced by an
invalid URI. The application of DNS security (DNSSEC) [RFC4033]
provides a means to limit attacks that rely on modification of the
DNS records used in U-NAPTR resolution. Security considerations
specific to U-NAPTR are described in more detail in [RFC4848].
An "https:" URI is authenticated using the method described in
Section 3.1 of [RFC2818]. The domain name used for this
authentication is the domain name in the URI resulting from U-NAPTR
resolution, not the input domain name as in [RFC3958]. Using the
domain name in the URI is more compatible with existing HTTP client
software, which authenticate servers based on the domain name in the
URI.
Kiesel, et al. Expires April 28, 2011 [Page 16]
Internet-Draft ALTO Server Discovery Protocol October 2010
An ALTO server that is identified by an "http:" URI cannot be
authenticated. If an "http:" URI is the product of the ALTO
discovery, this leaves devices vulnerable to several attacks. Lower
layer protections, such as layer 2 traffic separation might be used
to provide some guarantees.
Kiesel, et al. Expires April 28, 2011 [Page 17]
Internet-Draft ALTO Server Discovery Protocol October 2010
8. Open Issues
Here are a few open issues to be clarified:
Handling of reverse DNS lookups for IPv6: Refer to [RFC4472] for a
discussion about the issues.
Missing reverse DNS entries for an IP address: There may be cases
where the reverse DNS lookup does not yield any result. However,
this will leave the ALTO client with no choice, other than giving
up. This needs better documentation.
How to handled multiple results: For instance, a host behind a NAT
that yields an ALTO server in the private IP address domain and
one in the public IP address domain. Whom to ask?
Suffix Issues Document issues with suffix information provided by
DHCP or by other means. For instance, a host behind a NAT may
have a configured DNS suffix ".local". This suffix is not usuable
for the server discovery procedure.
Kiesel, et al. Expires April 28, 2011 [Page 18]
Internet-Draft ALTO Server Discovery Protocol October 2010
9. Conclusion
This document describes a general ALTO server discovery process and
discusses how the process can be applied in different deployment
scenarios, including the resouce consumer discovery as well as the
third party discovery.
Kiesel, et al. Expires April 28, 2011 [Page 19]
Internet-Draft ALTO Server Discovery Protocol October 2010
10. References
10.1. Normative References
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application
Service Location Using SRV RRs and the Dynamic Delegation
Discovery Service (DDDS)", RFC 3958, January 2005.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, March 2005.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008.
10.2. Informative References
[I-D.ietf-alto-protocol]
Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
draft-ietf-alto-protocol-05 (work in progress), July 2010.
[I-D.ietf-alto-reqs]
Kiesel, S., Previdi, S., Stiemerling, M., Woundy, R., and
Y. Yang, "Application-Layer Traffic Optimization (ALTO)
Requirements", draft-ietf-alto-reqs-06 (work in progress),
October 2010.
[I-D.ietf-geopriv-lis-discovery]
Thomson, M. and J. Winterbottom, "Discovering the Local
Location Information Server (LIS)",
draft-ietf-geopriv-lis-discovery-15 (work in progress),
March 2010.
[I-D.song-alto-server-discovery]
Yongchao, S., Tomsu, M., Garcia, G., Wang, Y., and V.
Avila, "ALTO Service Discovery",
draft-song-alto-server-discovery-03 (work in progress),
July 2010.
[I-D.stiemerling-alto-deployments]
Stiemerling, M. and S. Kiesel, "ALTO Deployment
Kiesel, et al. Expires April 28, 2011 [Page 20]
Internet-Draft ALTO Server Discovery Protocol October 2010
Considerations", draft-stiemerling-alto-deployments-05
(work in progress), October 2010.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC4472] Durand, A., Ihren, J., and P. Savola, "Operational
Considerations and Issues with IPv6 DNS", RFC 4472,
April 2006.
[RFC4848] Daigle, L., "Domain-Based Application Service Location
Using URIs and the Dynamic Delegation Discovery Service
(DDDS)", RFC 4848, April 2007.
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693,
October 2009.
[RFC5986] Thomson, M. and J. Winterbottom, "Discovering the Local
Location Information Server (LIS)", RFC 5986,
September 2010.
[bep24] Harrison, D., "Tracker Returns External IP",
BEP http://bittorrent.org/beps/bep_0024.html.
Kiesel, et al. Expires April 28, 2011 [Page 21]
Internet-Draft ALTO Server Discovery Protocol October 2010
Appendix A. Acknowledgments
The authors would like to thank Haibin Song, Richard Alimi, and Roni
Even for fruitful discussions during the 75th IETF meeting.
Hannes Tschofenig provided the initial input to the U-NAPTR solution
part. Hannes and Martin Thomson provided excellent feedback and
input to the server discovery.
Marco Tomsu and Nico Schwan are partially supported by the ENVISION
project (http://www.envision-project.org), a research project
supported by the European Commission under its 7th Framework Program
(contract no. 248565). The views and conclusions contained herein
are those of the authors and should not be interpreted as necessarily
representing the official policies or endorsements, either expressed
or implied, of the ENVISION project or the European Commission.
Michael Scharf is supported by the German-Lab project
(http://www.german-lab.de) funded by the German Federal Ministry of
Education and Research (BMBF).
Martin Stiemerling is partially supported by the COAST project
(COntent Aware Searching, retrieval and sTreaming,
http://www.coast-fp7.eu), a research project supported by the
European Commission under its 7th Framework Program (contract no.
248036). The views and conclusions contained herein are those of the
authors and should not be interpreted as necessarily representing the
official policies or endorsements, either expressed or implied, of
the COAST project or the European Commission.
Kiesel, et al. Expires April 28, 2011 [Page 22]
Internet-Draft ALTO Server Discovery Protocol October 2010
Authors' Addresses
Sebastian Kiesel
University of Stuttgart Computing Center
Allmandring 30
Stuttgart 70550
Germany
Email: ietf-alto@skiesel.de
URI: http://www.rus.uni-stuttgart.de/nks/
Marco Tomsu
Alcatel-Lucent
Lorenzstrasse 10
Stuttgart 70435
Germany
Email: marco.tomsu@alcatel-lucent.com
URI: www.alcatel-lucent.com/bell-labs
Nico Schwan
Alcatel-Lucent Bell Labs
Lorenzstrasse 10
Stuttgart 70435
Germany
Email: nico.schwan@alcatel-lucent.com
URI: www.alcatel-lucent.com/bell-labs
Michael Scharf
Alcatel-Lucent Bell Labs
Lorenzstrasse 10
Stuttgart 70435
Germany
Email: michael.scharf@alcatel-lucent.com
URI: www.alcatel-lucent.com/bell-labs
Kiesel, et al. Expires April 28, 2011 [Page 23]
Internet-Draft ALTO Server Discovery Protocol October 2010
Martin Stiemerling
NEC Laboratories Europe/University of Goettingen
Kurfuerstenanlage 36
Heidelberg 69115
Germany
Phone: +49 6221 4342 113
Email: martin.stiemerling@neclab.eu
URI: http://ietf.stiemerling.org
Kiesel, et al. Expires April 28, 2011 [Page 24]