Retrieving the Capabilities of a PCP-controlled
DeviceFrance TelecomRennes35000Francemohamed.boucadair@orange.comCisco Systems, Inc.Cessna Business Park, Varthur HobliSarjapur Marathalli Outer Ring RoadBangaloreKarnataka560103Indiatireddy@cisco.comPCP Working GroupThis document extends Port Control Protocol (PCP) with the ability to
retrieve the capabilities of PCP-controlled device: CAPABILITY
Option.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.This document extends the base PCP
with a new feature to discover the capabilities of a PCP-controlled
device. Retrieving the capabilities of a PCP-controlled device would
allow to avoid error, provide a hint why some applications fails, help
select the OpCode to issue, etc.This option can be elected to be defined as a new OpCode.The CAPABILITY option (Code: TBA, )
is used by a PCP Server to indicate to a requesting PCP Client the
capabilities it supports with regards to port forwarding operations.One single Capability option is conveyed in the same PCP response
message even if several functions are co-located in the same
PCP-controlled device (e.g., NAT44 and NAT64, NAT44 and ports set
assignment capability, etc.).This option, when received from a PCP Server, is used by a PCP Client
to constraint the content of its requests and therefore avoid
errors.A-bit when set (i.e., 1) indicates the PCP Server supports
authentication. If this bit is set to 0, is indicates plain PCP is
supported.The Capability Field is encoded in 127 bits. Each bit in the
Capability bit mask is used to represent the PCP-controlled device
capability. Several bits can be set if several functions are co-located
in the same device. The following values for the Capability field
are:Bit #: Description1: NAT442: Stateless NAT64 .4: Stateful NAT64 .8: A+P Port Range Router 9: Supports PORT_SET option . 16: IPv4 firewall.32: IPv6 Firewall .64: NPTv6 .125: DSCP re-marking function.126: FLOWDATA-aware function ().127: ILNP Translator .This section specifies the behavior of the PCP Client and the PCP
Server to handle the CAPABILITY Option.The PCP Server MAY be configured to return the CAPABILITY Option even
if it is not included in the request.Once the PCP Client is configured with its PCP Server(s), it MAY
issue an ANNOUNCE OpCode which enclose a CAPABILITY Option. Sending the
ANNOUNCE OpCode and the CAPABILITY Option allows the PCP Client to
determine whether the PCP Server is alive and also to retrieve its
capabilities. Based on the received capabilities, the PCP Client may
decide to tune its requests (e.g., ) and
decide whether all PCP Servers need to be contacted in parallel or only
a subset of them should be contacted.Upon receipt of a PCP request from a PCP Client requiring the PCP
Server to enforce an operation beyond its capabilities, the PCP Server
MAY return an error code together with the CAPABILITY option.When a new PCP Server joins the network then it MAY send an ANNOUNCE
OpCode with its capabilities (i.e., CAPABILITY Option).Below are provided examples of the CAPABILITY Option usage:In an IPv6 network with NPTv6 ,
Firewalls implementing the PCP Server are on different devices: the
PCP Client learns of the available PCP Servers by using DHCP or any other PCP Server discovery
technique defined in future specifications. PCP Client learns the
PCP Server capabilities using CAPABILITY Option. The PCP Client
sends MAP PCP request to PCP-controlled NPTv6 device with Internal
Port=0 and Protocol=0 (which means 'all ports for all protocols') to
find the external IP address. This PCP request has to be sent only
once since NPTv6 is stateless and provides a 1:1 relationship
between addresses in the "inside" and "outside" prefixes. The PCP
Client will send PCP re-request to NTPv6 only before the Assigned
Lifetime of the MAP response expires or when the host embedding the
PCP Client acquires a new IPv6 address using "inside" prefix.
However PCP Client will send MAP/PEER requests to Firewall to
create/delete dynamic outbound mapping or use PCP instead of its
default application keep-alives to maintain the Firewall state
alive.In a network with NAT64 , Firewall
implementing PCP servers are on different devices: IPv6-only PCP
Client can send PREFIX64 PCP Option only to the
PCP-controlled NAT64 device to learn the Prefix64(s) used to build
IPv4-embedded IPv6 addresses.Multiple PCP-controlled devices: See the example of a network deploying several
techniques to ensure interconnection with IPv4, provide IPv6-only
connectivity, etc. Of course, one can argue this configuration is no
realistic. In a IPv6 network with ILNP translator , Firewall implementing PCP servers are on
different devices. PCP client needs to send PCP request only to the
PCP-controlled ILNP translator to find Global Locators associated
with Internal Locators.When the PCP-controlled device is a PRR, the PCP Client should
use PORT_SET
option.Security considerations discussed in
must be considered.The following PCP Option Code is to be allocated in the
optional-to-process range (the registry is maintained in
http://www.iana.org/assignments/pcp-parameters/pcp-parameters.xml#options):CAPABILITYA sub-registry is required to track the set of capabilities of
PCP-controlled devices.