NFD

# RIB Management

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**RIB Management** is a module of [[Management|NFD Management protocol]].

It provides:

* commands to register and unregister routes

* a dataset of routes

* a dataset of routable prefixes

RIB Management commands and datasets are available under namespace `ndn:/localhost/nfd/rib`.

RIB Management commands are also available under namespace `ndn:/localhop/nfd/rib`.

## RIB Entry

A **RIB Entry** maintains a list of routes associated with a particular namespace.

A RIB Entry contains:

* Name prefix

* a list of Routes

## Route

A **route** indicates that contents under a certain name prefix may be available via a certain nexthop.

A route contains:

* Name prefix

* nexthop FaceId

* origin

* cost

* route inheritance flags

### Route origin

**Origin** is a value in [0, 65535] range that indicates who is announcing a route.

* **app**(=0): indicates a Route toward a local producer application

* **static**(=255): indicates a static route

* **nlsr**(=128): indicates a route installed by NLSR routing protocol

* **prefixann**(=129): indicates a route installed by a prefix announcement

* **client**(=65): indicates a Route toward an end host connected to this router, installed via [[AutoPrefixPropagation]]

* **autoreg**(=64): indicates a Route toward an end host connected to this router, registered automatically by the `nfd-autoreg` tool

* **autoconf**(=66): indicates a Route toward a remote router that this end host has connected to, registered automatically by the `ndn-autoconfig` tool

### Route cost

**Cost** indicates the preference among multiple routes with same Name prefix.

The nexthop face on a route with lower cost is preferred.

Unlike IP routing, the nexthop face to use is decided by forwarding strategy.

Route cost is a suggestion to strategy; strategy MAY consider route cost when making forwarding decisions.

### Route inheritance

Each route can have two route inheritance flags:

* `CHILD_INHERIT`: indicates that this route may be used even if a longer prefix is matched.

  This flag applies on a single route.

* `CAPTURE`: indicates that no shorter prefix can be used; overrides `CHILD_INHERIT`.

  This flag applies on the prefix: if any route of a prefix has this flag, the prefix will have this flag.

Example:

Name prefix | Nexthop FaceId | CHILD\_INHERIT | CAPTURE

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

/           | 1              | yes            | no

/           | 2              | no             | no

/A          | 3              | yes            | no

/A/B/C      | 4              | yes            | no

/D          | 5              | yes            | yes

/D          | 6              | yes            | no

* Interest /A/P can go to face 1 and 3.

    * It cannot go to face 2, because that route has CHILD\_INHERIT=no.

* Interest /A/B/C/Q can go to face 1, 3, and 4.

* Interest /D/R can go to face 5 and 6.

    * It cannot go to face 1, because one of the routes on /D sets CAPTURE=yes.

* Interest /S can go to face 1 and 2.

### Effective routing cost

To determine the routing cost of a nexthop face for FIB entry:

1. Collect all routes whose name is a prefix of the FIB entry name and has the nexthop face.

2. Select the routes with longest prefix. This could select multiple routes if they have distinct origins.

3. Use the lowest cost among these routes.

Example:

Name prefix | Nexthop FaceId | Origin | Cost | CHILD\_INHERIT | CAPTURE

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

/A          | 1              | static | 10   | no             | no

/A          | 1              | nlsr   | 20   | yes            | no

/A          | 2              | static | 30   | no             | no

/A/B        | 1              | static | 40   | yes            | no

/A/B        | 2              | static | 50   | yes            | no

/A/B/C      | 3              | static | 60   | yes            | no

/A/B/C/D    | 4              | static | 70   | yes            | yes

The corresponding FIB should be:

Name prefix | Nexthop records

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

/A          | (face=1,cost=10) (face=2,cost=30)

/A/B        | (face=1,cost=40) (face=2,cost=50)

/A/B/C      | (face=1,cost=40) (face=2,cost=50) (face=3,cost=60)

/A/B/C/D    | (face=4,cost=70)

## Control Commands

[[ControlCommand]] **management-module**: `rib`

### Register a route

**command-verb**: `register`

This command adds a route to the RIB.  

This command can also be accepted on `ndn:/localhop/nfd` management prefix, in addition to the default `ndn:/localhost/nfd` management prefix.

ControlParameters fields:

* Name (required)

* FaceId (optional)

* Origin (optional)

* Cost (optional)

* Flags (optional)

* ExpirationPeriod (optional)

*Name* is the name prefix of the route.

A forwarder MAY impose a limit on the length of the name prefix. The current limit in NFD is 32 name components.

If *Name* exceeds this limit, the command fails with code 414.

*FaceId* is the FaceId returned by [[FaceMgmt|Face Management]].

If *FaceId* is omitted or is set to zero, it is implied as the requesting face (self registration).

*Origin* defaults to app(=0).

*Cost* defaults to zero.

*Flags* is the inclusive OR of route inheritance flags.

`CHILD_INHERIT`=1, `CAPTURE`=2.

It defaults to `CHILD_INHERIT`.

*ExpirationPeriod* gives the duration (in milliseconds) for which this route is effective.

After *ExpirationPeriod* has elapsed, or when the face fails, the route is removed.

*ExpirationPeriod* defaults to infinity.

If a route of same *Name*, *FaceId*, and *Origin* exists, its *Cost* and *Flags* are updated, and its lifetime is extended to now + *ExpirationPeriod*.

If the command succeeds, \<body> in ControlResponse block contains updated ControlParameters:

* Name: Name prefix

* FaceId: nexthop FaceId (not zero)

* Origin: route origin

* Cost: route cost

* Flags: inclusive OR of route inheritance flags

* ExpirationPeriod: remaining lifetime (in milliseconds), or omitted if it's infinity

Alternatively, application may use [[PrefixAnnouncement|Prefix Announcement Protocol]] to register prefixes to itself.

### Unregister a route

**command-verb**: `unregister`

This command removes a route from the RIB.  

This command can also be accepted on `ndn:/localhop/nfd` management prefix, in addition to the default `ndn:/localhost/nfd` management prefix.

ControlParameters fields:

* Name (required)

* FaceId (optional)

* Origin (optional)

*FaceId* is the FaceId returned by [[FaceMgmt|Face Management]].

If *FaceId* is omitted or is set to zero, it is implied as the requesting face (self unregistration).

*Origin* defaults to app(=0).

Self unregistration is unnecessary if the client is quitting. The forwarder SHOULD automatically remove routes belonging to a closed face.

A client needs self unregistration when it stops serving a name prefix, but intends to continue execution.

If the route does not exist, this command does nothing, but is still considered successful.

If the command succeeds, \<body> in ControlResponse block contains updated ControlParameters:

* Name: unchanged

* FaceId: nexthop FaceId (not zero)

* Origin: unchanged if request specifies; app(=0) if request omits

### Semantics of successful responses

Successful responses from these commands indicate that RIB Management has received and authorized the command, and will perform the requested updates shortly.

RIB and FIB updates are asynchronous, and they are not necessarily completed when the response is sent.

## RIB Dataset

Routes are published as a [[StatusDataset|Status Dataset]] at `ndn:/localhost/nfd/rib/list`.

Multiple routes of same Name prefix are organized into a **RIB entry**.

Each RIB entry is represented by a **RibEntry** block:

    RibEntry := RIB-ENTRY-TYPE TLV-LENGTH

                  Name

                  Route+

    Route    := ROUTE-TYPE TLV-LENGTH

                  FaceId

                  Origin

                  Cost

                  Flags

                  ExpirationPeriod?

Flags is inclusive OR of route inheritance flags, encoded in the same way as `register` command.  

ExpirationPeriod is the remaining lifetime of a route, or omitted if it's Infinity.

## Routable Prefixes Dataset

RIB Management collects a list of routable prefixes and publishes them as a published as a [[StatusDataset|Status Dataset]] at `ndn:/localhost/nfd/rib/routable-prefixes` and `ndn:/localhop/nfd/rib/routable-prefixes`.

Generally, a **routable prefix** is a name prefix that satisfies one of the following:

* The prefix is advertised into a routing protocol from this router.

* The prefix can be registered onto a connected router via [[AutoPrefixPropagation]] from this end host, and falls under a routable prefix of that router.

This means, generally, a local producer can have reasonable belief that it would be able to receive Interests expressed elsewhere in the network, if it registers a prefix under a routable prefix.

However, since the network is a dynamic and distributed system, global reachability cannot be guaranteed even if a routable prefix is used.

Each routable prefix is represented by a **Name** block in the dataset.

## TLV-TYPE assignments

Type                                        | Assigned value    | Assigned value (hex)

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

RibEntry                                    | 128               | 0x80

Route                                       | 129               | 0x81