Internet DRAFT - draft-ietf-pcp-proxy
draft-ietf-pcp-proxy
Network Working Group S. Perreault
Internet-Draft Jive Communications
Intended status: Standards Track M. Boucadair
Expires: January 15, 2016 France Telecom
R. Penno
D. Wing
Cisco
S. Cheshire
Apple
July 14, 2015
Port Control Protocol (PCP) Proxy Function
draft-ietf-pcp-proxy-09
Abstract
This document specifies a new PCP functional element denoted as a PCP
Proxy. The PCP Proxy relays PCP requests received from PCP clients
to upstream PCP server(s). A typical deployment usage of this
function is to help establish successful PCP communications for PCP
clients that can not be configured with the address of a PCP server
located more than one hop away.
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 January 15, 2016.
Copyright Notice
Copyright (c) 2015 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
Perreault, et al. Expires January 15, 2016 [Page 1]
Internet-Draft PCP Proxy July 2015
(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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Use Case: the NAT Cascade . . . . . . . . . . . . . . . . 3
1.2. Use Case: the PCP Relay . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Operation of the PCP Proxy . . . . . . . . . . . . . . . . . 5
3.1. Optimized Hairpin Routing . . . . . . . . . . . . . . . . 8
3.2. Termination of Recursion . . . . . . . . . . . . . . . . 8
3.3. Source Address for PCP Requests Sent Upstream . . . . . . 9
3.4. Unknown OpCodes and Options . . . . . . . . . . . . . . . 9
3.4.1. No NAT is Co-located with the PCP Proxy . . . . . . . 9
3.4.2. PCP Proxy Co-located with a NAT Function . . . . . . 10
3.5. Mapping Repair . . . . . . . . . . . . . . . . . . . . . 10
3.6. Multiple PCP Servers . . . . . . . . . . . . . . . . . . 11
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
This document defines a new PCP [RFC6887] functional element: the PCP
Proxy. As shown in Figure 1, the PCP proxy is logically equivalent
to a PCP client back-to-back with a PCP server. The "glue" between
the two is what is specified in this document. Other than that
"glue", the server and the client behave exactly like their regular
counterparts.
The PCP Proxy is responsible for relaying PCP messages received from
PCP clients to upstream PCP servers and vice versa.
Whether the PCP Proxy is co-located with a flow-aware function (e.g.,
NAT, firewall) is deployment-specific.
Perreault, et al. Expires January 15, 2016 [Page 2]
Internet-Draft PCP Proxy July 2015
.................
+------+ : +------+------+ : +------+
|Client|-------:-|Server|Client|-:----|Server|
+------+ : +------+------+ : +------+
: Proxy :
.................
Figure 1: Reference Architecture
This document assumes a hop-by-hop PCP authentication scheme. That
is, in reference to Figure 1, the left-most PCP client authenticates
with the PCP Proxy, while the PCP Proxy authenticates with the
upstream server. Note that in some deployments, PCP authentication
may only be enabled between the PCP Proxy and an upstream PCP server
(e.g., a customer premises host may not authenticate with the PCP
Proxy but the PCP Proxy may authenticate with the PCP server). The
hop-by-hop authentication scheme is more suitable from a deployment
standpoint. Furthermore, it allows to easily support a PCP Proxy
that alters PCP messages (e.g., strip a PCP option, modify a PCP
field, etc.).
1.1. Use Case: the NAT Cascade
In today's world, with public routable IPv4 addresses becoming less
readily available, it is increasingly common for customers to receive
a private address from their Internet Service Provider (ISP), and the
ISP uses a NAT gateway of its own to translate those packets before
sending them out onto the public Internet. This means that there is
likely to be more than one NAT on the path between client machines
and the public Internet:
o If a residential customer receives a translated address from their
ISP, and then installs their own residential NAT gateway to share
that address between multiple client devices in their home, then
there are at least two NAT gateways on the path between client
devices and the public Internet.
o If a mobile phone customer receives a translated address from
their mobile phone carrier, and uses "Personal Hotspot" or
"Internet Sharing" software on their mobile phone to make Wireless
LAN (WLAN) Internet access available to other client devices, then
there are at least two NAT gateways on the path between those
client devices and the public Internet.
o If a hotel guest connects a portable WLAN gateway to their hotel
room Ethernet port to share their room's Internet connection
between their phone and their laptop computer, then packets from
the client devices may traverse the hotel guest's portable NAT,
Perreault, et al. Expires January 15, 2016 [Page 3]
Internet-Draft PCP Proxy July 2015
the hotel network's NAT, and the ISP's NAT before reaching the
public Internet.
While it is possible, in theory, that client devices could somehow
discover all the NATs on the path, and communicate with each one
separately using Port Control Protocol [RFC6887], in practice it's
not clear how client devices would reliably learn this information.
Since the NAT gateways are installed and operated by different
individuals and organizations, no single entity has knowledge of all
the NATs on the path. Also, even if a client device could somehow
know all the NATs on the path, requiring a client device to
communicate separately with all of them imposes unreasonable
complexity on PCP clients, many of which are expected to be simple
low-cost devices.
In addition, this goes against the spirit of NAT gateways. The main
purpose of a NAT gateway is to make multiple downstream client
devices to appear, from the point of view of everything upstream of
the NAT gateway, to be a single client device. In the same spirit,
it makes sense for a PCP-capable NAT gateway to make multiple
downstream client devices requesting port mappings to appear, from
the point of view of everything upstream of the NAT gateway, to be a
single client device requesting port mappings.
1.2. Use Case: the PCP Relay
Another envisioned use case of the PCP Proxy is to help establish
successful PCP communications for PCP clients that can not be
configured with the address of a PCP server located more than one hop
away. A PCP Proxy can be for instance embedded in a CPE (Customer
Premises Equipment) while the PCP server is located in a network
operated by an ISP. This is illustrated in Figure 2.
|
+------+ |
|Client|--+
+------+ | +-----+ +------+
+--|Proxy|--------<ISP network>----------|Server|
+------+ | +-----+ +------+
|Client|--+ CPE
+------+ |
|
LAN
Figure 2: PCP Relay Use Case
This works because the proxy's server side is listening on the
address used as a default gateway by the clients. The clients use
Perreault, et al. Expires January 15, 2016 [Page 4]
Internet-Draft PCP Proxy July 2015
that address as a fallback when discovering the PCP server's address.
The proxy picks up the requests and forwards them upstream to the
ISP's PCP server, with whose address it has been provisioned through
regular PCP client provisioning means.
This particular use case assumes that provisioning the server's
address on the CPE is feasible while doing it on the clients in the
LAN is not, which is what makes the PCP proxy valuable.
Note that [I-D.ietf-pcp-anycast] documents an alternate solution to
the PCP proxy. Nevertheless, as discussed in
[I-D.boucadair-pcp-deployment-cases], the anycast solution may be
problematic when multiple PCP servers are to be contacted.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119].
Where this document uses the terms "upstream" and "downstream", the
term "upstream" refers to the direction outbound packets travel
towards the public Internet, and the term "downstream" refers to the
direction inbound packets travel from the public Internet towards
client systems. Typically when a home user views a web site, their
computer sends an outbound TCP SYN packet upstream towards the public
Internet, and an inbound downstream TCP SYN ACK reply comes back from
the public Internet.
3. Operation of the PCP Proxy
Upon receipt of a PCP mapping-creation request from a downstream PCP
client, a PCP proxy first examines its local mapping table to see if
it already has a valid active mapping matching the Internal Address
and Internal Port (and in the case of PEER requests, remote peer)
given in the request.
If the PCP proxy does not already have a valid active mapping for
this mapping-creation request, then it allocates an available port on
its external interface. We assume for the sake of this description
that the address of its external interface is itself a private
address, subject to translation by an upstream NAT. The PCP proxy
then constructs an appropriate corresponding PCP request of its own
(described below), and sends it to its upstream NAT, and the newly-
created local mapping is considered temporary until a confirming
reply is received from the upstream PCP server.
Perreault, et al. Expires January 15, 2016 [Page 5]
Internet-Draft PCP Proxy July 2015
If the PCP proxy does already have a valid active mapping for this
mapping-creation request, and the lifetime remaining on the local
mapping is at least 3/4 of the lifetime requested by the PCP client,
then the PCP proxy SHOULD send an immediate reply giving the
outermost External Address and Port (previously learned using PCP
recursively, as described below), and the actual lifetime remaining
for this mapping. If the lifetime remaining on the local mapping is
less than 3/4 of the lifetime requested by the PCP client, then the
PCP proxy MUST generate an upstream request as described below.
For mapping-deletion requests (Lifetime = 0), the local mapping, if
any, is deleted, and then (regardless of whether a local mapping
existed) a corresponding upstream request is generated.
The PCP proxy knows the destination IP address for its upstream PCP
request using the same means that are available for provisioning a
PCP client. In particular, the PCP proxy MUST follow the procedure
defined in Section 8.1 of [RFC6887] to discover its PCP server. This
does not preclude other means from being used in addition.
In the upstream PCP request:
o The PCP Client's IP Address and Internal Port are the PCP proxy's
own external address and port just allocated for this mapping.
o The Suggested External Address and Port in the upstream PCP
request SHOULD be copied from the original PCP request.
o The Requested Lifetime is as requested by the client if it falls
within the acceptable range for this PCP server; otherwise it
SHOULD be capped to appropriate minimum and maximum values
configured for this PCP server.
o The Mapping Nonce is copied from the original PCP request.
o For PEER requests, the Remote Peer IP Address and Port are copied
from the original PCP request.
Upon receipt of a PCP reply giving the outermost (i.e., publicly
routable) External Address, Port and Lifetime, the PCP proxy records
this information in its own mapping table and relays the information
to the requesting downstream PCP client in a PCP reply. The PCP
proxy therefore records, among other things, the following
information in its mapping table:
o Client's Internal Address and Port.
o External Address and Port allocated by this PCP proxy.
Perreault, et al. Expires January 15, 2016 [Page 6]
Internet-Draft PCP Proxy July 2015
o Outermost External Address and Port allocated by the upstream PCP
server.
o Mapping lifetime (also dictated by the upstream PCP server).
o Mapping nonce.
In the downstream PCP reply:
o The Lifetime is as granted by the upstream PCP server, or less, if
the granted lifetime exceeds the maximum lifetime this PCP server
is configured to grant. If the downstream Lifetime is more than
the Lifetime granted by the upstream PCP server (which is NOT
RECOMMENDED) then this PCP proxy MUST take responsibility for
renewing the upstream mapping itself.
o The Epoch Time is this PCP proxy's Epoch Time, not the Epoch Time
of the upstream PCP server. Each PCP server has its own
independent Epoch Time. However, if the Epoch Time received from
the upstream PCP server indicates a loss of state in that PCP
server, the PCP proxy can either recreate the lost mappings
itself, or it can reset its own Epoch Time to cause its downstream
clients to perform such state repairs themselves. A PCP proxy
MUST NOT simply copy the upstream PCP server's Epoch Time into its
downstream PCP replies, since if it suffers its own state loss it
needs the ability to communicate that state loss to clients. Thus
each PCP server has its own independent Epoch Time. However, as a
convenience, a downstream PCP proxy may simply choose to reset its
own Epoch Time whenever it detects that its upstream PCP server
has lost state. Thus, in this case, the PCP proxy's Epoch Time
always resets whenever its upstream PCP server loses state; it may
also reset at other times too.
o The Mapping Nonce is copied from the reply received from the
upstream PCP server.
o The Assigned External Port and Assigned External IP Address are
copied from the reply received from the upstream PCP server (i.e.,
they are the outermost External IP Address and Port, not the
locally-assigned external address and port.)
o For PEER requests, the Remote Peer IP Address and Port are copied
from the reply received from the upstream PCP server.
Perreault, et al. Expires January 15, 2016 [Page 7]
Internet-Draft PCP Proxy July 2015
3.1. Optimized Hairpin Routing
A PCP proxy SHOULD implement Optimized Hairpin Routing. What this
means is the following:
o If a PCP proxy observes an outgoing packet arriving on its
internal interface that is addressed to an External Address and
Port appearing in the NAT gateway's own mapping table, then the
NAT gateway SHOULD (after creating a new outbound mapping if one
does not already exist) rewrite the packet appropriately and
deliver it to the internal client currently allocated that
External Address and Port.
o If a PCP proxy observes an outgoing packet arriving on its
internal interface which is addressed to an Outermost External
Address and Port appearing in the NAT gateway's own mapping table,
then the NAT gateway SHOULD do likewise: create a new outbound
mapping if one does not already exist, and then rewrite the packet
appropriately and deliver it to the internal client currently
allocated that Outermost External Address and Port. This is not
necessary for successful communication, but for efficiency.
Without this Optimized Hairpin Routing, the packet will be
delivered all the way to the outermost NAT gateway, which will
then perform standard hairpin translation and send it back. Using
knowledge of the Outermost External Address and Port, this
rewriting can be anticipated and performed locally, which will
typically offer higher throughput and lower latency than sending
it all the way to the outermost NAT gateway and back.
Note that traffic counters maintained by an upstream PCP server will
differ from the ones of a PCP Proxy implementing the optimized
hairpin routing.
3.2. Termination of Recursion
Any recursive algorithm needs a mechanism to terminate the recursion
at the appropriate point. This termination of recursion can be
achieved in a variety of ways. The following (non exhaustive)
examples are provided for illustration purposes:
o An ISP's PCP-controlled gateway (that may embed a NAT, firewall or
any function that can be controlled with PCP) could be configured
to know that it is the outermost PCP-controlled gateway, and
consequently does not need to relay PCP requests upstream.
o A PCP-controlled gateway could determine automatically that if its
external address is not one of the known private addresses
[RFC1918][RFC6598], then its external address is a public routable
Perreault, et al. Expires January 15, 2016 [Page 8]
Internet-Draft PCP Proxy July 2015
IP address, and consequently it does not need to relay PCP
requests upstream.
o Recursion may be terminated if there is no explicit list of PCP
servers configured to the PCP Proxy (e.g., [RFC7291]) or if its
default router is not responsive to PCP requests.
o Recursion may also be terminated if the upstream PCP-controlled
device does not embed a PCP Proxy.
3.3. Source Address for PCP Requests Sent Upstream
As with a regular PCP server, the PCP-controlled device can be a NAT,
a firewall, or even some sort of hybrid. In particular, a PCP proxy
that simply relays all requests upstream can be thought of as the
degenerate case of a PCP server controlling a wide-open firewall
back-to-back with a regular PCP client.
One important property of the PCP-controlled device will affect the
PCP proxy's behaviour: when the proxy's server part instructs the
device to create a mapping, that mapping's external address may or
may not be one that belongs to the proxy node.
o When the mapping's external address belongs to the proxy node, as
would presumably be the case for a NAT, then the proxy's client
side sends out an upstream PCP request using the mapping's
external IP address as source.
o When the mapping's external address does not belong to the proxy
node, as would presumably be the case for a firewall, then the
proxy's client side needs to install upstream mappings on behalf
of its downstream clients. To do this, it MUST insert a
THIRD_PARTY Option in its upstream PCP request carrying the
mapping's external address.
Note that hybrid PCP-controlled devices may create NAT-like mappings
in some circumstances and firewall-like mappings in others. A proxy
controlling such a device would adjust its behavior dynamically
depending on the kind of mapping created.
3.4. Unknown OpCodes and Options
3.4.1. No NAT is Co-located with the PCP Proxy
When no NAT is co-located with the PCP Proxy, the port numbers
included in received PCP messages (from the PCP server or PCP
client(s)) are not altered by the PCP Proxy. The PCP Proxy relays to
Perreault, et al. Expires January 15, 2016 [Page 9]
Internet-Draft PCP Proxy July 2015
the PCP server unknown Options and OpCodes because there is no
reachability failure risk.
3.4.2. PCP Proxy Co-located with a NAT Function
By default, the proxy MUST relay unknown OpCodes and mandatory-to-
process unknown Options. Rejecting unknown Options and OpCodes has
the drawback of preventing a PCP client to make use of new
capabilities offered by the PCP server but not supported by the PCP
Proxy even if no IP address and/or port is included in the Option/
OpCode.
Because PCP messages with an unknown OpCode or mandatory-to-process
unknown Options can carry a hidden internal address or internal port
that will not be translated, a PCP Proxy MUST be configurable to
disable relaying unknown OpCodes and mandatory-to-process unknown
Options. If the PCP Proxy is configured to disable relaying unknown
OpCodes and mandatory-to-process unknown Options, the PCP Proxy MUST
behave as follows:
o a PCP Proxy co-located with a NAT MUST reject by an UNSUPP_OPCODE
error response a received request with an unknown OpCode.
o a PCP Proxy co-located with a NAT MUST reject by an UNSUPP_OPTION
error response a received request with a mandatory-to-process
unknown Option.
3.5. Mapping Repair
ANNOUNCE requests received from PCP clients are handled locally; as
such these requests MUST NOT be relayed to the provisioned PCP
server.
Upon receipt of an unsolicited ANNOUNCE response from a PCP server,
the PCP Proxy proceeds to renew the mappings and checks whether there
are changes compared to a local cache if it is maintained by the PCP
Proxy. If no change is detected, no unsolicited ANNOUNCE is
generated towards PCP clients. If a change is detected, the PCP
Proxy MUST generate unsolicited ANNOUNCE message(s) to appropriate
PCP clients. If the PCP Proxy does not maintain a local cache for
the mappings, unsolicited multicast ANNOUNCE messages are sent to PCP
clients.
Upon change of its external IP address, the PCP Proxy SHOULD renew
the mappings it maintained. If the PCP server assigns a different
external port, the PCP Proxy SHOULD follow the mapping repair
procedure defined in [RFC6887]. This can be achieved only if a full
state table is maintained by the PCP Proxy.
Perreault, et al. Expires January 15, 2016 [Page 10]
Internet-Draft PCP Proxy July 2015
3.6. Multiple PCP Servers
A PCP Proxy MAY handle multiple PCP servers at the same time. Each
PCP server is associated with its own epoch value. PCP clients are
not aware of the presence of multiple PCP servers.
According to [RFC7488], if several PCP Names are configured to the
PCP Proxy, it will contact in parallel all these PCP servers.
In some contexts (e.g., PCP-controlled CGNs), the PCP Proxy MAY load
balance the PCP clients among available PCP servers. The PCP Proxy
MUST ensure requests of a given PCP client are relayed to the same
PCP server.
The PCP Proxy MAY rely on some fields (e.g., Zone ID
[I-D.penno-pcp-zones]) in the PCP request to redirect the request to
a given PCP server.
4. IANA Considerations
This document makes no request of IANA.
5. Security Considerations
The PCP Proxy MUST follow the security considerations elaborated in
[RFC6887] for both the client and server side.
Section 3.3 specifies the cases where a THIRD_PARTY option is
inserted by the PCP Proxy. In those cases, means to prevent a
malicious user from creating mappings on behalf of a third party must
be enabled as discussed in Section 13.1 of [RFC6887]. In particular,
THIRD_PARTY options MUST NOT be enabled unless the network on which
the PCP messages are to be sent is fully trusted. For example if
access control lists (ACLs) are installed on the PCP Proxy, PCP
server, and the network between them, so those ACLs allow only
communications from a trusted PCP Proxy to the PCP server.
A received request carrying an unknown OpCode or Option SHOULD be
dropped (or in the case of an unknown Option which is not mandatory-
to-process the Option SHOULD be removed) if it is not compatible with
security controls provisioned to the PCP Proxy.
The device embedding the PCP Proxy MAY block PCP requests directly
sent to the PCP server. This can be enforced using access control
lists.
Perreault, et al. Expires January 15, 2016 [Page 11]
Internet-Draft PCP Proxy July 2015
6. Acknowledgements
Many thanks to C. Zhou, T. Reddy, and D. Thaler for their review
and comments.
Special thanks to F. Dupont who contributed to this document.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
2013.
7.2. Informative References
[I-D.boucadair-pcp-deployment-cases]
Boucadair, M., "Port Control Protocol (PCP) Deployment
Models", draft-boucadair-pcp-deployment-cases-03 (work in
progress), July 2014.
[I-D.ietf-pcp-anycast]
Kiesel, S., Penno, R., and S. Cheshire, "Port Control
Protocol (PCP) Anycast Addresses", draft-ietf-pcp-
anycast-06 (work in progress), May 2015.
[I-D.penno-pcp-zones]
Penno, R., "PCP Support for Multi-Zone Environments",
draft-penno-pcp-zones-01 (work in progress), October 2011.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets", BCP
5, RFC 1918, February 1996.
[RFC6598] Weil, J., Kuarsingh, V., Donley, C., Liljenstolpe, C., and
M. Azinger, "IANA-Reserved IPv4 Prefix for Shared Address
Space", BCP 153, RFC 6598, April 2012.
[RFC7291] Boucadair, M., Penno, R., and D. Wing, "DHCP Options for
the Port Control Protocol (PCP)", RFC 7291, July 2014.
[RFC7488] Boucadair, M., Penno, R., Wing, D., Patil, P., and T.
Reddy, "Port Control Protocol (PCP) Server Selection", RFC
7488, March 2015.
Perreault, et al. Expires January 15, 2016 [Page 12]
Internet-Draft PCP Proxy July 2015
Authors' Addresses
Simon Perreault
Jive Communications
Quebec, QC
Canada
Email: sperreault@jive.com
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
Stuart Cheshire
Apple Inc.
1 Infinite Loop
Cupertino, California 95014
USA
Phone: +1 408 974 3207
Email: cheshire@apple.com
Perreault, et al. Expires January 15, 2016 [Page 13]
