PCP Working Group M. Boucadair
Internet-Draft France Telecom
Intended status: Standards Track R. Dupont
Expires: September 30, 2012 Internet Systems Consortium
R. Penno
Juniper Networks
D. Wing
Cisco
March 29, 2012
Port Control Protocol (PCP) Proxy Function
draft-ietf-pcp-proxy-00
Abstract
This document specifies the behavior of a PCP Proxy element, for
instance embedded in Customer Premise routers.
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 September 30, 2012.
Copyright Notice
Copyright (c) 2012 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
(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
Boucadair, et al. Expires September 30, 2012 [Page 1]
Internet-Draft PCP Proxy March 2012
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. PCP Server Discovery and Provisioning . . . . . . . . . . . . 3
3. PCP Proxy as a PCP Server . . . . . . . . . . . . . . . . . . 4
4. Control of the Firewall . . . . . . . . . . . . . . . . . . . 4
5. Embedded NAT in the CP Router . . . . . . . . . . . . . . . . 4
6. Simple PCP Proxy . . . . . . . . . . . . . . . . . . . . . . . 6
7. Advanced Functions . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Multiple PCP Servers . . . . . . . . . . . . . . . . . . . 7
7.2. Epoch Handling . . . . . . . . . . . . . . . . . . . . . . 8
7.3. Request/Response Caching . . . . . . . . . . . . . . . . . 8
7.4. Retransmission Handling . . . . . . . . . . . . . . . . . 9
7.5. Full State . . . . . . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
Boucadair, et al. Expires September 30, 2012 [Page 2]
Internet-Draft PCP Proxy March 2012
1. Introduction
PCP [I-D.ietf-pcp-base] discusses the implementation of NAT control
features that rely upon Carrier Grade NAT (CGN) devices such as DS-
Lite AFTR [RFC6333].
The Customer Premise router, the B4 element in DS-Lite, is in charge
to enforce some security controls on PCP requests so implements a PCP
Proxy function: it acts as a PCP server receiving PCP requests on
internal interfaces, and as a PCP client forwarding accepted PCP
requests on an external interface to a CGN PCP server. The CGN PCP
server in turn send replies (PCP responses) to the PCP Proxy external
interface which are finally forwarded to PCP clients.
The PCP Proxy can be simple, i.e., implement as transparent/minimal
processing as possible, or it can be smart, i.e., handle multiple CGN
PCP servers, cache requests/responses, etc. A smart Proxy can be
associated with UPnP IGD [I-D.ietf-pcp-upnp-igd-interworking] or/and
NAT-PMP [I-D.bpw-pcp-nat-pmp-interworking] Interworking Function
(IWF).
+------------+ |
| PCP Client |-----+ |
+--(Host 1)--+ | +-----------+ | +----------+
+---| | | | |
| PCP Proxy |-------|PCP Server|
+---| | | | |
+------------+ | +-----------+ | +----------+
| PCP Client |-----+ |
+--(Host 2)--+ possible boundary
<- Home side | ISP side ->
Figure 1: Reference Architecture
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].
2. PCP Server Discovery and Provisioning
The PCP Proxy MUST implement one of the discovery methods listed in
[I-D.ietf-pcp-base] (e.g., DHCP [I-D.ietf-pcp-dhcp]).
The address of the PCP Proxy is provisioned to local PCP Clients as
their default PCP Server: If the PCP DHCP option is supported by an
Boucadair, et al. Expires September 30, 2012 [Page 3]
Internet-Draft PCP Proxy March 2012
internal PCP Client, it will retrieve the PCP Server IP address to
use from its local DHCP server (usually embedded on the CP router);
otherwise internal PCP Clients will assume their default router being
the PCP Server.
3. PCP Proxy as a PCP Server
The PCP Proxy acts as a PCP server for internal hosts and accepts PCP
requests on the interface(s) facing them, e.g., it creates servicing
socket(s) and bound them to each address of this (these) interface(s)
on UDP port 44323.
When the topology makes a routing loop possible, the PCP Proxy MAY
check it is not the source of a PCP message it's received.
4. Control of the Firewall
A security policy to accept PCP messages from the provisioned PCP
Server is to be enabled on the CP router. This policy can be for
instance triggered by DHCP configuration or by outbound PCP requests
issued from the PCP Proxy to the provisioned PCP Server.
In order to accept inbound and outbound traffic associated with PCP
mappings instantiated in the upstream PCP Server, appropriate
security policies are to be configured on the firewall.
For instance if the firewall rules have a lifetime, PCP response can
be snooped in order to instantiate the corresponding firewall rules
with the same lifetime. If they have no lifetime, an explicit
dynamic mapping table can be kept in the PCP Proxy state in order to
instantiate and remove corresponding firewall rules. This is in fact
an easy subcase of Section 5.
REMOTE_PEER_FILTER Options can be installed into the local firewall,
forwarded to the PCP Server so installed into the remote NAT/firewall
or both.
[Ed. Note: should we say the firewall function is already handled
by the PCP controlled device so it is useless at the local level?]
5. Embedded NAT in the CP Router
When no NAT is embedded in the CP router, the port number included in
received PCP messages (from the PCP Server or PCP Client(s)) are not
altered by the PCP Proxy.
Boucadair, et al. Expires September 30, 2012 [Page 4]
Internet-Draft PCP Proxy March 2012
[Ed. Note: NAT444 seems to be the only exception?]
When the PCP Proxy is co-located with a NAT function in the CP
router, it MUST update the content of received requested messages
with the mapped port number and the address belonging to the external
interface of the CP router (i.e., after the NAT operation) and not as
initially positioned by the PCP Client. For the reverse path, PCP
response messages MUST be updated by the PCP Proxy to replace the
target port number to what has been initially positioned by the PCP
Client. For this purpose the PCP Proxy has an access to the local
NAT state. Note PCP messages with an unknown OpCode or Option can
carry a hidden target address or internal port which will not be
translated:
o a PCP Proxy co-located with a NAT SHOULD reject by an
UNSUPP_OPCODE error response a received request with an unknown
OpCode;
o a PCP Proxy co-located with a NAT SHOULD reject by an
UNSUPP_OPTION error response a received request with a mandatory-
to-process unknown Option;
o a PCP Proxy co-located with a NAT SHOULD remove any optional-to-
process unknown Options from received requests before forwarding
them.
When a PCP request is received and accepted by the PCP Proxy the
corresponding mapping (explicit dynamic mapping for a MAP request,
implicit dynamic mapping for a PEER request) is looked for in the
local NAT state and temporary created if it does not exist.
Temporary means it is deleted if no SUCCESS response is received,
either explicitly or because of its short lifetime at creation.
If the local NAT associates explicit dynamic mappings to a lifetime,
the requested lifetime in MAP requests SHOULD be adjusted to be in
the accepted range of the local NAT, and the assigned lifetime copied
from MAP responses to the corresponding mapping in the local NAT.
The same processing applies to implicit dynamic mappings and PEER
requests/responses (but the valid requested lifetime range begins by
zero in this case).
Otherwise explicit dynamic mappings have an undefined lifetime in the
local NAT and the PCP Proxy SHOULD maintain an explicit dynamic
mapping table and SHOULD delete corresponding explicit dynamic
mappings in the local NAT when they expire or are deleted by the MAP
request with a zero requested lifetime.
Boucadair, et al. Expires September 30, 2012 [Page 5]
Internet-Draft PCP Proxy March 2012
6. Simple PCP Proxy
A simple PCP Proxy performs minimal modifications to PCP requests and
responses, in particular it does not change the Epoch value in
responses. So it does not handle more than one PCP server.
The detailed behavior at the reception of a PCP request on an
internal interface is as follows:
o check if the source IP address and the PCP target address are the
same.
o apply security controls, including with the result of the previous
item.
o if the request is rejected, build a synthetic error response and
send it back to the PCP client.
o if the request is accepted, adjust it (e.g., adding a THIRD_PARTY
Option, updating the internal address and port to their translated
values as specified in Section 5 and forward it on a fresh UDP
socket connected to the PCP server.
o Wait for the response during a reasonable delay.
o when the response is received from the PCP server, adjust it back
(e.g., removing the THIRD_PARTY Option added previously, updating
the internal address and port to their initial values as specified
in Section 5), forward it to the source PCP client and close the
socket to the PCP server.
[Ed. Note: is there extra validation useful? The response
comes from the PCP server and the PCP client will validated it
anyway.]
o on a hard error on the UDP socket, build a synthetic ICMP error
and send it to the source PCP client.
The reasonable delay minimum value is 20 seconds, request
retransmission is handled by PCP clients.
For each pending request, the proxy MUST maintain in a data record:
o the request payload
o the interface where the request was received
Boucadair, et al. Expires September 30, 2012 [Page 6]
Internet-Draft PCP Proxy March 2012
o the source IP address of the request
o the source UDP port of the request
o the UDP socket connected to the PCP server
o an expire timeout
Receiving interfaces can be implemented by a set of servicing
sockets, each socket bound to an address of an internal interface.
Interface, source address and port are used to send back packets to
the source PCP client. The request payload is used to generate
synthetic ICMP. Responses are received on the UDP socket.
There is no (not yet) standardized way to build a synthetic error
response, in particular no way to determine which Epoch value to put
into it. This is why it is better to build a synthetic ICMP error
than a synthetic error response with NETWORK_FAILURE on a socket hard
error.
Too large requests SHOULD be forwarded to the PCP server in order to
relay back the error response, i.e., the PCP Proxy is not in charge
to enforce the message size limit and in general the PCP Proxy SHOULD
NOT generate error response for a reason other than security
controls. No behavior is specified in the case the PCP Proxy
processing (e.g., adding a THIRD_PARTY Option) makes a valid request
too large when it is sent to the PCP Server.
7. Advanced Functions
When a simple PCP Proxy uses as global variables only the CGN PCP
server IP address, a set of servicing sockets and a list of pending
request handlers, a smart PCP Proxy implements more services.
Even if most services rely on the Epoch handling one Section 7.2,
services are described below in a natural order.
7.1. Multiple PCP Servers
A smart PCP Proxy MAY offer to handle multiple PCP servers at the
same time, each PCP server is associated to each own handled Epoch
value according to Section 7.2.
The only constraint is to maintain a reasonable coherency as PCP
clients cannot be assumed to be prepared to this, i.e., this has to
be transparent for / hidden to them.
Boucadair, et al. Expires September 30, 2012 [Page 7]
Internet-Draft PCP Proxy March 2012
[Ed. Note: we propose to require a partition of clients, clients
on the same host or sharing a target address SHOULD be in the same
subset, i.e., the same PCP server and the same Epoch.]
[Ed. Note: the Proxy can get per PCP server capabilities, for
instance from the error responses.]
7.2. Epoch Handling
With Epoch handling the Epoch value is related to internal timers and
not blindly copied from PCP responses. There should be no advantages
to have more than one managed Epoch per PCP server.
The Epoch MUST be reset when explicit dynamic mappings are lost,
i.e.:
o at startup if the PCP proxy can't recover the state.
[Ed. Note: as it is very optional to manage state in the Proxy
it should be the default.]
o when the WAN address is changed or any similar events which show
any previous state is no longer valid.
o when the Epoch value in a PCP response is too small (cf. Epoch
value validation rules in [I-D.ietf-pcp-base]).
o when the External Address has changed
The last two rules are per PCP server, a PCP Proxy MAY check these
conditions in all received responses for a PCP server, including when
the PCP Proxy is a part of an IWF
[I-D.ietf-pcp-upnp-igd-interworking]
[I-D.bpw-pcp-nat-pmp-interworking].
7.3. Request/Response Caching
A PCP Proxy providing request/response caching checks each time it
receives a PCP request if it has already seen the same request
recently and got the corresponding PCP response. In this case, it
sends back directly the cached response with the proper Epoch value
and not forward the request to the PCP server.
[Ed. Note: this is an easy optimization, the only difficult point
can be solved by the Epoch handling.]
Boucadair, et al. Expires September 30, 2012 [Page 8]
Internet-Draft PCP Proxy March 2012
7.4. Retransmission Handling
An extension of the previous service is to manage the retransmission
of pending requests to the server internally, i.e., no longer driven
by the PCP client. A cache entry SHOULD be expired after a delay
short enough to keep it easy to distinguish it from a replay.
[Ed. Note: this allows smart retransmission scheduling as the
Proxy "sees" all PCP exchanges with the PCP server.]
7.5. Full State
A smart PCP Proxy can keep the full state: an image of all active
explicit dynamic mappings is kept in memory. This service is not
interesting by itself but it can be necessary to support embedded
firewall or NAT Section 5 and if the PCP Proxy is integrated in an
IWF (e.g., to support UPnP IGD [I-D.ietf-pcp-upnp-igd-interworking]).
In conclusion this service MAY be supported. Note when it is
supported the state SHOULD be recovered in case of failures according
to [I-D.boucadair-pcp-failure].
8. IANA Considerations
This document makes no request of IANA.
9. Security Considerations
The security controls are applied on PCP requests and are about:
o authorized target addresses, in particular in case of a third
party.
o authorized internal and external ports (note the external port is
in general assigned by the CGN PCP server).
The default policy for requests for a third party when such a policy
exists is be to not allow them. The exact rule is: PCP requests
including a THIRD_PARTY option enclosing an IP address distinct than
the source IP address of the request MUST be rejected (by a
NOT_AUTHORIZED error response).
When a PCP Proxy is at the boundary of two trust domains (named
"internal" and "external" sides), it MUST provide at least these two
security controls:
Boucadair, et al. Expires September 30, 2012 [Page 9]
Internet-Draft PCP Proxy March 2012
o split horizon anti-spoofing: requests from the external side and
responses from the internal side MUST be dropped.
o a policy about requests on the behalf of a third party MUST be
enforced.
A PCP Proxy MAY implement only the simple rule about third party: all
received requests including a THIRD_PARTY option are rejected.
[Ed. Note: this is stricter than the default but keeps the
minimal implementation as simple as possible.]
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 be removed) if it is not a priori compatible
with security controls or correct processing. This includes at least
all cases where received requests are scanned for elements like the
protocol, an address or a port.
[Ed. Note: magically a minimal implementation in favorable
environments (no embedded NAT!) MAY accept unknown Opcodes and
Options. There is no need for a similar rule for responses as the
proxy can do nothing with a "bad" response anyway...]
10. References
10.1. 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-24 (work in progress), March 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-02
(work in progress), January 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
10.2. Informative References
[I-D.boucadair-pcp-failure]
Boucadair, M., Dupont, F., and R. Penno, "Port Control
Protocol (PCP) Failure Scenarios",
draft-boucadair-pcp-failure-02 (work in progress),
Boucadair, et al. Expires September 30, 2012 [Page 10]
Internet-Draft PCP Proxy March 2012
September 2011.
[I-D.bpw-pcp-nat-pmp-interworking]
Boucadair, M., Penno, R., Wing, D., and F. Dupont, "Port
Control Protocol (PCP) NAT-PMP Interworking Function",
draft-bpw-pcp-nat-pmp-interworking-00 (work in progress),
March 2011.
[I-D.ietf-pcp-upnp-igd-interworking]
Boucadair, M., Dupont, F., Penno, R., and D. Wing,
"Universal Plug and Play (UPnP) Internet Gateway Device
(IGD)-Port Control Protocol (PCP) Interworking Function",
draft-ietf-pcp-upnp-igd-interworking-01 (work in
progress), March 2012.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
Authors' Addresses
Mohamed Boucadair
France Telecom
Rennes 35000
France
Email: mohamed.boucadair@orange.com
Francis Dupont
Internet Systems Consortium
Email: fdupont@isc.org
Reinaldo Penno
Juniper Networks
1194 N Mathilda Avenue
Sunnyvale, California 94089
USA
Email: rpenno@juniper.net
Boucadair, et al. Expires September 30, 2012 [Page 11]
Internet-Draft PCP Proxy March 2012
Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, California 95134
USA
Email: dwing@cisco.com
Boucadair, et al. Expires September 30, 2012 [Page 12]
