PCP Working Group M. Boucadair
Internet-Draft France Telecom
Updates: 6887 (if approved) R. Penno
Intended status: Standards Track D. Wing
Expires: July 10, 2014 P. Patil
T. Reddy
Cisco
January 06, 2014
PCP Server Selection
draft-ietf-pcp-server-selection-02
Abstract
Multiple IP addresses may be configured on a PCP client in some
deployment contexts such as multi-homing. This document specifies
the behavior to be followed by the PCP client to contact its PCP
server(s) when one or several PCP server IP addresses are configured.
This document updates RFC6887.
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.
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 10, 2014.
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Copyright Notice
Copyright (c) 2014 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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. IP Address Selection . . . . . . . . . . . . . . . . . . . . 3
4. Multiple Interfaces . . . . . . . . . . . . . . . . . . . . . 4
5. Example: Multiple PCP servers on a Single Interface . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Multi-homing . . . . . . . . . . . . . . . . . . . . 8
A.1. IPv6 Multi-homing . . . . . . . . . . . . . . . . . . . . 8
A.2. IPv4 Multi-homing . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Multiple IP addresses may be configured on a PCP client in some
deployment contexts such as multi-homing (see Appendix A). A PCP
server may also have multiple IP addresses associated with it. This
document specifies the behavior to be followed by the PCP client
[RFC6887] to contact its PCP server(s) [RFC6887] when it receives one
or several PCP server IP addresses (e.g., using DHCP
[I-D.ietf-pcp-dhcp]).
This document is not specific to DHCP; any other mechanism can be
used to configure PCP server IP addresses.
It is out of scope of this document to enumerate all deployment
scenarios that require multiple IP addresses to be configured.
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2. Terminology
This document makes use of the following terms:
o PCP server denotes a functional element that 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., Network
Address Translation (NAT), firewall) it controls. Refer to
[RFC6887].
o PCP client denotes a PCP software instance responsible for issuing
PCP requests to a PCP server. Refer to [RFC6887].
3. IP Address Selection
These steps specify the behavior to be followed by the PCP client to
contact a PCP server when the PCP client has multiple IP addresses
for a single PCP server. Additional considerations to be taken into
account when the PCP client is multi-interfaced are specified in
Section 4:
1. If the PCP client can use both address families when
communicating to a particular PCP server, the PCP client SHOULD
select the source address of the PCP request to be of the same IP
address family as its requested PCP mapping (i.e., the address
family of the Requested External IP Address).
2. Whenever communicating with a PCP server, the rules of Section 6
of [RFC6724] SHOULD be followed by using the source address
selected in the previous step as input to the destination address
selection algorithm.
3. The PCP client initializes its Maximum Retransmission Count (MRC)
to 4.
4. The PCP client sends its PCP message to the PCP server's IP
address following the retransmission procedure specified in
Section 8.1.1 of [RFC6887]. If no response is received after MRC
attempts, the PCP client re-tries the procedure excluding the
destination addresses which did not respond. The PCP client
SHOULD ignore any response received from an IP address after
exhausting MRC attempts for that particular IP address. If, when
sending PCP requests, the PCP client receives a hard ICMP error
[RFC1122] it SHOULD immediately try the next IP address from the
list of PCP server' IP addresses.
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5. If the PCP client has exhausted all IP addresses configured for a
given PCP server, the procedure is repeated every fifteen minutes
until the PCP request is successfully answered.
6. Once the PCP client has successfully received a response from a
PCP server's IP address, it sends subsequent PCP requests to the
same server's IP address until that IP address becomes non-
responsive, which causes the PCP client to follow the steps above
to contact its PCP server.
For efficiency, the PCP client should use the same Mapping Nonce for
requests sent to all PCP server' IP addresses.
If several PCP servers are configured, each with multiple IP
addresses, the PCP client contacts all PCP servers in parallel
following the steps described above. This 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 implementation-specific and only the PCP client can decide
whether all mappings are needed or only a subset of them.
4. Multiple Interfaces
When an end host has multiple interfaces concurrently active (e.g.,
IEEE 802.11 and 3G), a PCP client would discover different PCP
servers over different interfaces. A host may have multiple network
interfaces (e.g, 3G, IEEE 802.11, etc.); each configured differently.
Each PCP server learned MUST be associated with the interface via
which it was learned. Particularly, the PCP client relies on the
source IP address of an outgoing PCP request to select which PCP
server(s) to use.
Although multiple interfaces may be available, a PCP client 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.
Generic multi-interfaces considerations are documented in Section 8.4
of [RFC6887]
5. Example: Multiple PCP servers on a Single Interface
Figure 1 depicts an example that is used to illustrate the server
selection procedure specified in Section 3.
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ISP Network
| |
.........................................................
| | Subscriber Network
+-------+------+ +----+---------+
| PCP-Server-A | | PCP-Server-B |
| | | |
+-------+------+ +----+---------+
192.0.2.1 | | 198.51.100.1
2001:db8:2222::1 | | 2001:db8:3333::1
| |
| |
-------+--------------+-----------
|
| 203.0.113.0
| 2001:db8:1111::1
+---+---+
| Host |
+-------+
Figure 1
The example shows the experienced behavior when a single IP address
for one PCP server is not responsive. The PCP client is configured
with two PCP servers, PCP-Server-A and PCP-Server-B each having two
IP addresses, an IPv4 address and an IPv6 address. The PCP client
wants an IPv4 mapping so it orders the addresses as follows:
o PCP-Server-A:
* 192.0.2.1
* 2001:db8:1111::1
o PCP-Server-B:
* 198.51.100.1
* 2001:db8:2222::1
Suppose that:
o The path to reach 192.0.2.1 is broken
o The path to reach 2001:db8:1111::1 is working
o The path to reach 198.51.100.1 is working
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o The path to reach 2001:db8:2222::1 is working
The PCP client sends two PCP requests at the same time, the first to
192.0.2.1 (corresponding to PCP-Server-A) and the second to
198.51.100.1 (corresponding to PCP-Server-B). The path to
198.51.100.1 is working so a PCP response is received. Because the
path to 192.0.2.1 is broken, no PCP response is received. The PCP
client retries 4 times to elicit a response from 192.0.2.1 and
finally gives up on that address and sends a PCP message to
2001::db8:1111:1. That path is working, and a response is received.
Thereafter, the PCP client should continue using that responsive IP
address for PCP-Server-A (2001:db8:1111::1). In this particular
case, it will have to use THIRD_PARTY option for IPv4 mappings.
6. Security Considerations
PCP-related security considerations are discussed in [RFC6887].
This document does not specify how PCP server addresses are
provisioned to the PCP client. It is the responsibility of any PCP
server provisioning document(s) to elaborate on the security
considerations to discover a legitimate PCP server.
7. IANA Considerations
This document does not request any action from IANA.
8. Acknowledgements
Many thanks to Dave Thaler for the review and comments.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, September 2012.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
2013.
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9.2. Informative References
[I-D.ietf-pcp-dhcp]
Boucadair, M., Penno, R., and D. Wing, "DHCP Options for
the Port Control Protocol (PCP)", draft-ietf-pcp-dhcp-09
(work in progress), November 2013.
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[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.
[RFC4116] Abley, J., Lindqvist, K., Davies, E., Black, B., and V.
Gill, "IPv4 Multihoming Practices and Limitations", RFC
4116, July 2005.
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Appendix A. Multi-homing
The main problem of a PCP multi-homing situation can be succinctly
described as 'one PCP client, multiple PCP servers'. As described in
Section 3, if a PCP client discovers multiple PCP servers, 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 multi-homing examples to
illustrate the PCP client behavior.
A.1. IPv6 Multi-homing
In this example of an IPv6 multi-homed 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 servers. Consider a
scenario in which firewalls within an IPv6 multi-homing environment
also implement a PCP server. The PCP client learns the available PCP
servers using DHCP [I-D.ietf-pcp-dhcp] or any other provisioning
mechanism. In reference to Figure 2, a typical model is to embed
DHCP servers in rtr1 and rtr2. A host located behind rtr1 and rtr2
can contact these two DHCP server and retrieves from each server the
IP address of the corresponding PCP server.
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 |
+-------+---+ +----+------+
| |
| |
-------+----------+------
|
+---+---+
| Host |
+-------+
Figure 2: IPv6 Multihoming
A.2. IPv4 Multi-homing
In this example an IPv4 multi-homed network described in 'NAT- or
RFC2260-based multi-homing' (Section 3.3 of [RFC4116]), the gateway
router is connected to different service provider networks. This
method uses Provider-Aggregatable (PA) addresses assigned by each
transit provider to which the site is connected. The site uses 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. The PCP client learns the available PCP servers using
DHCP [I-D.ietf-pcp-dhcp] or any other provisioning mechanism. In
reference to Figure 3, a typical model is to embed the DHCP server
and the PCP servers in rtr1. A host located behind rtr1 can contact
the DHCP server to obtain IP addresses of the PCP servers. 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
| |
+----+-------------------+
|rtr1: NAT & PCP servers |
| GW Router |
+----+-------------------+
|
|
|
-----+--------------
|
+-+-----+
| Host | (private address space)
+-------+
Figure 3: IPv4 Multihoming
Authors' Addresses
Mohamed Boucadair
France Telecom
Rennes 35000
France
EMail: mohamed.boucadair@orange.com
Reinaldo Penno
Cisco
USA
EMail: repenno@cisco.com
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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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