PCP Working Group M. Boucadair
Internet-Draft France Telecom
Intended status: Standards Track R. Penno
Expires: May 24, 2013 D. Wing
P. Patil
T. Reddy
Cisco
November 20, 2012
PCP Server Selection
draft-ietf-pcp-server-selection-00
Abstract
This document specifies the behavior to be followed by the PCP Client
to contact its PCP Server(s) when one or several PCP Names are
configured. Multiple Names may be configured to a PCP Client in some
deployment contexts such as multi-homing.
Requirements Language
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].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 24, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Name Resolution . . . . . . . . . . . . . . . . . . . . . . . . 3
4. IP Address Selection . . . . . . . . . . . . . . . . . . . . . 4
4.1. Serial Queries . . . . . . . . . . . . . . . . . . . . . . 4
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . . 6
Appendix A. Multihoming . . . . . . . . . . . . . . . . . . . . . 7
A.1. IPv6 Multihoming . . . . . . . . . . . . . . . . . . . . . 7
A.2. IPv4 Multihoming . . . . . . . . . . . . . . . . . . . . . 8
A.3. Multiple interfaces and Servers . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
This document specifies the behavior to be followed by the PCP Client
[I-D.ietf-pcp-base] to contact its PCP Server(s) [I-D.ietf-pcp-base]
when receiving one or several PCP Names (e.g., DHCP
[I-D.ietf-pcp-dhcp]). This document is not specific to DHCP; it is
applicable to any mechanism that configures server names.
Multiple Names may be configured to a PCP Client in some deployment
contexts such as multi-homing (see Appendix A). It is out of scope
of this document to enumerate all deployment scenarios which require
multiple Names to be configured.
This document assumes appropriate name resolution means (e.g.,
Section 6.1.1 of [RFC1123]) are available on the host client.
2. Terminology
This document makes use of the following terms:
o PCP Server denotes a functional element which receives and
processes PCP requests from a PCP Client. A PCP Server can be co-
located with or be separated from the function (e.g., NAT,
Firewall) it controls. Refer to [I-D.ietf-pcp-base].
o PCP Client denotes a PCP software instance responsible for issuing
PCP requests to a PCP Server. Refer to [I-D.ietf-pcp-base].
o Name is a string that can be passed to getaddrinfo (Section 6.1 of
[RFC3493]), such as a DNS name, address literals, etc. A name may
be a fully qualified domain name (e.g., "myservice.example.com."),
IPv4 address in dotted-decimal form (e.g., 192.0.2.33) or textual
representation of an IPv6 address (e.g., 2001:db8::1). Refer to
[I-D.ietf-pcp-dhcp].
3. Name Resolution
Each configured Name is passed to the name resolution library (e.g.,
Section 6.1.1 of [RFC1123] or [RFC6055]) to retrieve the
corresponding IP address(es) (IPv4 or IPv6). Then, the PCP Client
MUST follow the procedure specified in Section 4 to contact its PCP
Server(s).
A host may have multiple network interfaces (e.g, 3G, WiFi, etc.);
each configured differently. Each PCP Server learned MUST be
associated with the interface via which it was learned.
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4. IP Address Selection
This section specifies the behavior to be followed by the PCP Client
to contact its PCP Server(s) when receiving one or several PCP Names:
1. If only one PCP Name is configured: if a list of IP addresses is
returned as a result of resolving the PCP Server Name, the PCP
Client follows the procedure specified in Section 4.1.
2. If several PCP Names are configured: each Name is treated as a
separate PCP Server. Moreover, each Name may be resolved into
one IP address or a list of IP addresses. The PCP Client
contacts in parallel the first IP address of each Name and
follows the procedure specified in Section 4.1 for the list of IP
addresses returned for each Name. Section 5 provides some
examples to illustrate this procedure.
The discovery procedure may result in a PCP Client instantiating
multiple mappings maintained by distinct PCP Servers. The decision
to use all these mappings or delete some of them is deployment-
specific. Only the client can decide whether all the mappings are
needed or only a subset of them.
4.1. Serial Queries
The PCP Client initializes its Maximum Retransmission Count (MRC) to
4.
The PCP Client sends its PCP message to the PCP Server following the
retransmission procedure specified in Section 8.1.1 of
[I-D.ietf-pcp-base]. If no response is received after MRC attempts,
the PCP Client tries with the next IP address in its list of PCP
Server addresses. If it has exhausted its list, the procedure is
repeated every fifteen minutes until the PCP request is successfully
answered. If, when sending PCP requests the PCP Client receives an
ICMP error (e.g., port unreachable, network unreachable) it SHOULD
immediately try the next IP address in the list. Once the PCP Client
has successfully received a response from a PCP Server address on
that interface, it sends subsequent PCP requests to that same server
address until that PCP Server becomes non-responsive, which causes
the PCP client to attempt to re-iterate the procedure starting with
the first PCP Server address on its list.
5. Examples
The following sub-sections provide three examples to illustrate the
procedure.
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For all these examples, let's suppose pcpserver-x, pcpserver-y and
pcpserver-z are configured as PCP Names.
5.1. Example 1
Let's also suppose:
* IPx1 and IPx2 are returned for pcpserver-x; IPx1 is not reachable.
* IPy1 and IPy2 are returned for pcpserver-y; IPy1 is reachable
* IPz1 and IPz2 are returned for pcpserver-z; IPz1 is reachable
The procedure to contact the PCP Servers is as follows:
* Send PCP requests to all servers: IPx1, IPy1 and IPz1
* Responses are received from IPy1 and IPz1 but not from IPx1
- The request is re-sent to IPx1
- If no response is received after four attempts, the request
is sent to IPx2
5.2. Example 2
Now, if the following conditions are made:
* IPx1 and IPx2 are returned for pcpserver-x; IPx1 is not reachable.
* IPy1 and IPy2 are returned for pcpserver-y; IPy1 is reachable
* IPz1 and IPz2 are returned for pcpserver-z; IPz1 is not reachable
The procedure to contact the PCP Servers lead to the following:
* Send PCP requests to all servers: IPx1, IPy1 and IPz1
* A response is received from IPy1 but not from IPx1 and IPz1
- the requests are re-sent to IPx1 and IPz1
- If no response is received after four attempts, the request
is then sent to IPx2 and IPz2
5.3. Example 3
Let's suppose now that:
* IPx1 and IPx2 are returned for pcpserver-x; IPx1 is not reachable.
* IPy1 and IPy2 are returned for pcpserver-y; IPy1 is not reachable
* IPz1 and IPz2 are returned for pcpserver-z; IPz1 is not reachable
The procedure to contact the PCP Servers is as follows:
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* Send PCP requests to all servers: IPx1, IPy1 and IPz1
* No answer is received for all requests
- the requests are re-sent to IPx1, IPy1 and IPz1
- If no response is received after four attempts, the request
is then sent to IPx2, IPy2 and IPz2
6. Security Considerations
The security considerations in [I-D.ietf-pcp-base] are to be
considered.
7. IANA Considerations
This document does not request any action from IANA.
8. Acknowledgements
Many thanks to D. Thaler for the review and comments.
9. References
9.1. Normative References
[I-D.ietf-pcp-base]
Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)",
draft-ietf-pcp-base-29 (work in progress), November 2012.
[I-D.ietf-pcp-dhcp]
Boucadair, M., Penno, R., and D. Wing, "DHCP Options for
the Port Control Protocol (PCP)", draft-ietf-pcp-dhcp-05
(work in progress), September 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6",
RFC 3493, February 2003.
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[RFC4116] Abley, J., Lindqvist, K., Davies, E., Black, B., and V.
Gill, "IPv4 Multihoming Practices and Limitations",
RFC 4116, July 2005.
[RFC6055] Thaler, D., Klensin, J., and S. Cheshire, "IAB Thoughts on
Encodings for Internationalized Domain Names", RFC 6055,
February 2011.
Appendix A. Multihoming
The main problem of a PCP multihoming situation can be succintly
described as 'one PCP client, multiple PCP servers'. As described in
Section 4, if a PCP Client discovers multiple PCP Server names, it
should send requests to all of them in parallel with the following
assumptions:
o There is no requirement that multiple PCP Servers have the same
capabilities.
o PCP requests to different servers are independent, the result of a
PCP request to one server does not influence another.
o If PCP Servers provide NAT, it is out of scope how the client
manages ports across PCP Servers. For example, whether PCP Client
requires all external ports to be the same or whether there are
ports available at all.
The following sub-sections describe multihoming examples to
illustrate PCP client behavior.
A.1. IPv6 Multihoming
In this example of an IPv6 multihomed network, two or more routers
co-located with firewalls are present on a single link shared with
the host(s). Each router is in turn connected to a different service
provider network and the host in this environment would be offered
multiple prefixes and advertised multiple DNS/NTP servers. Consider
a scenario in which firewalls within an IPv6 multihoming environment
also implement a PCP Server. PCP client learns of the available PCP
servers using DHCP [I-D.ietf-pcp-dhcp] or any other PCP server
discovery technique defined in future specifications. The PCP client
will send PCP requests in parallel to each of the PCP Servers.
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==================
| Internet |
==================
| |
| |
+----+-+ +-+----+
| ISP1 | | ISP2 |
+----+-+ +-+----+ ISP Network
| |
.........................................................
| |
| | Subscriber Network
+-------+---+ +----+------+
| rtr1 with | | rtr2 with |
| FW1 | | FW2 |
+-------+---+ +----+------+
| |
| |
| |
-----+-+-----+------
|
+-+-----+
| Hosts |
+-------+
Figure 1: IPv6 Multihoming
A.2. IPv4 Multihoming
In this example an IPv4 multihomed network described in 'NAT- or
RFC2260-based Multihoming' (Section 3.3 of[RFC4116]), the gateway
router is connected to different service provider networks. This
method uses PA addresses assigned by each transit provider to which
the site is connected. The site uses Network Address Translation
(NAT) to translate the various provider addresses into a single set
of private-use addresses within the site. In such a case, two PCP
servers have to be present to control NAT to each of the transit
providers. PCP client learns of the available PCP servers using DHCP
[I-D.ietf-pcp-dhcp] or any other PCP server discovery technique
defined in future specifications. The PCP client will send PCP
requests in parallel to each of the PCP Servers.
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====================
| Internet |
=====================
| |
| |
+----+--------+ +-+------------+
| ISP1 | | ISP2 |
| | | |
+----+--------+ +-+------------+ ISP Network
| |
| |
..............................................................
| |
| Port1 | Port2 Subscriber Network
| |
+----+-----------------+
| NAT & PCP Servers |
| GW Router |
+----+-----------------+
|
|
|
-----+-+-----+------
|
+-+-----+
| Hosts | (private address space)
+-------+
Figure 2: IPv4 Multihoming
A.3. Multiple interfaces and Servers
In case for Multihoming when an end host such as a mobile terminal
has multiple interfaces concurrently active, for example, Wi-Fi and
3G, a PCP client would discover different PCP Servers over different
interfaces. Although multiple interfaces are available, an
application might choose to use just one based on, for example, cost
and bandwidth requirements, and therefore would need to send PCP
requests to just one PCP Server.
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Authors' Addresses
Mohamed Boucadair
France Telecom
Rennes, 35000
France
Email: mohamed.boucadair@orange.com
Reinaldo Penno
Cisco
USA
Email: repenno@cisco.com
Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, California 95134
USA
Email: dwing@cisco.com
Prashanth Patil
Cisco Systems, Inc.
Bangalore
India
Email: praspati@cisco.com
Tirumaleswar Reddy
Cisco Systems, Inc.
Cessna Business Park, Varthur Hobli
Sarjapur Marathalli Outer Ring Road
Bangalore, Karnataka 560103
India
Email: tireddy@cisco.com
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