NFD

# Prefix Announcement Protocol

The **prefix announcement protocol** allows registering prefixes using a *prefix announcement object*. It is an alternative to NFD [[RibMgmt|RIB Management protocol]]'s `rib/register` verb.

## Prefix Announcement object

The **prefix announcement object** is a Data packet that represents an application's intent of registering a prefix toward itself. A Data packet that satisfies the following requirements is a prefix announcement object:

* Name starts with the announced prefix, followed by a fixed `32=PA` keyword name component, followed by a version component and a segment component as defined by the [NDN Naming Conventions](https://named-data.net/publications/techreports/ndn-tr-22-ndn-memo-naming-conventions/). In this specification revision, segment number is always zero.

* ContentType is 5 (prefix announcement).

* Content contains a sequence of TLV elements, including at least an ExpirationPeriod element. Ordering of these TLV elements is insignificant. Unrecognized non-critical TLV elements are permitted and will be ignored.

**Validity period** of a prefix announcement object is given in ExpirationPeriod and ValidityPeriod elements in its Content.

* ExpirationPeriod gives the duration for which the prefix announcement remains valid. The duration begins when a node or program receives the prefix announcement. This element is required.

* ValidityPeriod gives the absolute time range in which the prefix announcement remains valid. It is ignored if the receiving node does not have a UnixTime clock. This element is optional.

* When both ExpirationPeriod and ValidityPeriod are present, the most restricted constraint applies.

Trust model of prefix announcement is to be defined by the application.

### Example

```

Data

  Name /net/example/32=PA/%FD%01/%00%00

  MetaInfo

    ContentType 5 (prefix announcement)

  Content

    ExpirationPeriod 3600000

    ValidityPeriod

      NotBefore 20181030T000000

      NotAfter  20181124T235959

  SignatureInfo

  SignatureValue 

```

This prefix announcement object announces the prefix `/net/example`.

It is valid for one hour since receipt, within the date range 30OCT2018 and 24NOV2018.

## Command Verbs

### 'announce'

This command announces a prefix using a prefix announcement object.

NFD-RIB accepts this command as a [[ndn-cxx:CommandInterest|Command Interest]] with the following syntax:

```

/localhost/nfd/rib/announce/<params-sha256>/<command-interest-components>

/localhop/nfd/rib/announce/<params-sha256>/<command-interest-components>

```

The Interest's Parameters element carries the prefix announcement object.

NFD-RIB converts this command into an equivalent `rib/register` command. Route *origin* is set to "prefix announcement" (number 129).

Response is the same as `rib/register` command.

### 'unannounce'

There is no 'unannounce' command. Instead, use `rib/unregister` command.