NFD

# NFD local control header

NFD local control header can be used between application and local forwarding daemon to exchange various NFD-specific local information that is not part of Interest and Data packet.

For example, the control header allows applications to request bypassing the Interest forwarding strategy by directly specify FaceId to which the Interest should be forwarded.

NFD local control header is not enabled by default and requires explicit request from the client to enable.

This request is in form of [[Signed_Interests|Signed Interest]] and have the following structure:

    /localhost/nfd/control-header/<control-module>/command-verb>/<timestamp>/<SignatureInfo>/<SignatureValue>

    \                            / \                           / \                                          /

     ------------  ------------     ------------  -------------   --------------------  --------------------

                 \/                             \/                                    \/

       NFD Control Command          "in-faceid"     "enable" or       Signed Interest related information

                                    "out-faceid"    "disable"

Control modules:

* ``in-faceid``  Enable/disable ability to receive information about incoming FaceId for each received Interest and Data packet

    After successful enable, subsequent packets will be encapsulated in within LocalControlHeader, as defined below.  And vice versa, after successful disable, subsequent packets will not be encapsulated.

    Note that the command may not be immediate.  Packets that were scheduled for transmission before the command arrival will be received without (or with) LocalControlHeader present.

* ``out-faceid`` Enable/disable ability to specify outgoing FaceId.

    After this command, NFD will accept incoming Interests encapsulated in LocalControlHeader that specifies outgoing FaceId to forward this Interest.

    Note that this will affect only Interest for namespaces that is managed by special ``ClientControl`` strategy.  If FIB entry for the Interest uses any other strategy, information specified in LocalControlHeader will be ignored.

<!--

* ``sniffer`` Enable/disable sniffing on all or specific Faces.  The format of this command is actually is a little bit different and requires one more option: ``<face-id>``:

        /localhost/nfd/control-header/sniffer/(enable|disable)/<face-id>/<timestamp>/<SignatureInfo>/<SignatureValue>

    To snif on all faces, ``<face-id>`` should be 0.

-->

## LocalControlHeader

If command to enable LocalControlHeader is authorized by NFD, all subsequent communication from NFD will include LocalControlHeader as defined below.

The authorized application will also be able to include LocalControlHeader in communication to NFD---until specifically enabled, all specified LocalControlHeaders should be ignored by NFD.

    LocalControlHeader ::= LOCAL-CONTROL-HEADER-TYPE TLV-LENGTH

                             LocalControlInfo

                             (Interest | Data)

    LocalControlInfo   ::= LOCAL-CONTROL-INFO-TYPE TLV-LENGTH

                             (IncomingFaceId |

                              NextHopFaceId+)

    IncomingFaceId     ::= INCOMING-FACE-ID-TYPE TLV-LENGTH

                              nonNegativeInteger

    NextHopFaceId      ::= NEXT-HOP-FACE-ID-TYPE TLV-LENGTH

                              nonNegativeInteger

<!--

                              SnifferInfo)

    SnifferInfo        ::= SNIFFER-INFO-TYPE TLV-LENGTH

                             ...

                             (TBD)

-->

## TLV-TYPE assignments

Type                                        | Assigned value    | Assigned value (hex)

------------------------------------------- | ----------------- | --------------------

LocalControlHeader                          | 109               | 0x6d

LocalControlInfo                            | 110               | 0x6e

IncomingFaceId                              | 111               | 0x6f

NextHopFaceId                               | 112               | 0x70

Reserved                                    | 113               | 0x71