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 the application. A Data packet that satisfies the following requirements is a prefix announcement object:

* Name starts with the announced prefix, followed by `prefix-announcement` constant component, followed by a version component and a segment component as defined in NDN Naming Convention.

* ContentType is "prefix announcement".

* Content contains zero or more TLV elements.

A prefix announcement object, by default, is valid indefinitely. Its **validity period** can be constrained with ValidityPeriod or FreshnessPeriod element.

* 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.

* FreshnessPeriod gives the duration in which the prefix announcement remains valid. The duration begins when a node or program receives the prefix announcement.

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

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

## 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 announce object.

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

Response is same as `rib/register` command.

### 'unannounce'

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