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Junxiao Shi, 03/12/2020 03:09 PM

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# RIB Management
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**RIB Management** is a module of [[Management|NFD Management protocol]].
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It provides:
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* commands to register and unregister routes
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* a dataset of routes
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* a dataset of routable prefixes
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RIB Management commands and datasets are available under namespace `ndn:/localhost/nfd/rib`.
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RIB Management commands are also available under namespace `ndn:/localhop/nfd/rib`.
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## RIB Entry
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A **RIB Entry** maintains a list of routes associated with a particular namespace.
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A RIB Entry contains:
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* Name prefix
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* a list of Routes
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## Route
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A **route** indicates that contents under a certain name prefix may be available via a certain nexthop.
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A route contains:
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* Name prefix
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* nexthop FaceId
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* origin
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* cost
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* route inheritance flags
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### Route origin
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**Origin** is a value in [0, 65535] range that indicates who is announcing a route.
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* **app**(=0): indicates a Route toward a local producer application
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* **static**(=255): indicates a static route
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* **nlsr**(=128): indicates a route installed by NLSR routing protocol
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* **prefixann**(=129): indicates a route installed by a prefix announcement
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* **client**(=65): indicates a Route toward an end host connected to this router, installed via [[AutoPrefixPropagation]]
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* **autoreg**(=64): indicates a Route toward an end host connected to this router, registered automatically by the `nfd-autoreg` tool
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* **autoconf**(=66): indicates a Route toward a remote router that this end host has connected to, registered automatically by the `ndn-autoconfig` tool
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### Route cost
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**Cost** indicates the preference among multiple routes with same Name prefix.
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The nexthop face on a route with lower cost is preferred.
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Unlike IP routing, the nexthop face to use is decided by forwarding strategy.
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Route cost is a suggestion to strategy; strategy MAY consider route cost when making forwarding decisions.
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### Route inheritance
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Each route can have two route inheritance flags:
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* `CHILD_INHERIT`: indicates that this route may be used even if a longer prefix is matched.
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  This flag applies on a single route.
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* `CAPTURE`: indicates that no shorter prefix can be used; overrides `CHILD_INHERIT`.
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  This flag applies on the prefix: if any route of a prefix has this flag, the prefix will have this flag.
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Example:
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Name prefix | Nexthop FaceId | CHILD\_INHERIT | CAPTURE
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------------|----------------|----------------|---------
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/           | 1              | yes            | no
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/           | 2              | no             | no
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/A          | 3              | yes            | no
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/A/B/C      | 4              | yes            | no
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/D          | 5              | yes            | yes
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/D          | 6              | yes            | no
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* Interest /A/P can go to face 1 and 3.
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    * It cannot go to face 2, because that route has CHILD\_INHERIT=no.
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* Interest /A/B/C/Q can go to face 1, 3, and 4.
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* Interest /D/R can go to face 5 and 6.
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    * It cannot go to face 1, because one of the routes on /D sets CAPTURE=yes.
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* Interest /S can go to face 1 and 2.
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### Effective routing cost
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To determine the routing cost of a nexthop face for FIB entry:
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1. Collect all routes whose name is a prefix of the FIB entry name and has the nexthop face.
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2. Select the routes with longest prefix. This could select multiple routes if they have distinct origins.
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3. Use the lowest cost among these routes.
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Example:
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Name prefix | Nexthop FaceId | Origin | Cost | CHILD\_INHERIT | CAPTURE
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------------|----------------|--------|------|----------------|---------
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/A          | 1              | static | 10   | no             | no
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/A          | 1              | nlsr   | 20   | yes            | no
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/A          | 2              | static | 30   | no             | no
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/A/B        | 1              | static | 40   | yes            | no
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/A/B        | 2              | static | 50   | yes            | no
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/A/B/C      | 3              | static | 60   | yes            | no
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/A/B/C/D    | 4              | static | 70   | yes            | yes
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The corresponding FIB should be:
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Name prefix | Nexthop records
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------------|----------------
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/A          | (face=1,cost=10) (face=2,cost=30)
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/A/B        | (face=1,cost=40) (face=2,cost=50)
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/A/B/C      | (face=1,cost=40) (face=2,cost=50) (face=3,cost=60)
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/A/B/C/D    | (face=4,cost=70)
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## Control Commands
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[[ControlCommand]] **management-module**: `rib`
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### Register a route
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**command-verb**: `register`
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This command adds a route to the RIB.  
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This command can also be accepted on `ndn:/localhop/nfd` management prefix, in addition to the default `ndn:/localhost/nfd` management prefix.
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ControlParameters fields:
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* Name (required)
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* FaceId (optional)
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* Origin (optional)
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* Cost (optional)
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* Flags (optional)
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* ExpirationPeriod (optional)
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*Name* is the name prefix of the route.
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A forwarder MAY impose a limit on the length of the name prefix. The current limit in NFD is 32 name components.
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If *Name* exceeds this limit, the command fails with code 414.
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*FaceId* is the FaceId returned by [[FaceMgmt|Face Management]].
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If *FaceId* is omitted or is set to zero, it is implied as the requesting face (self registration).
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*Origin* defaults to app(=0).
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*Cost* defaults to zero.
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*Flags* is the inclusive OR of route inheritance flags.
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`CHILD_INHERIT`=1, `CAPTURE`=2.
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It defaults to `CHILD_INHERIT`.
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*ExpirationPeriod* gives the duration (in milliseconds) for which this route is effective.
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After *ExpirationPeriod* has elapsed, or when the face fails, the route is removed.
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*ExpirationPeriod* defaults to infinity.
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If a route of same *Name*, *FaceId*, and *Origin* exists, its *Cost* and *Flags* are updated, and its lifetime is extended to now + *ExpirationPeriod*.
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If the command succeeds, \<body> in ControlResponse block contains updated ControlParameters:
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* Name: Name prefix
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* FaceId: nexthop FaceId (not zero)
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* Origin: route origin
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* Cost: route cost
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* Flags: inclusive OR of route inheritance flags
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* ExpirationPeriod: remaining lifetime (in milliseconds), or omitted if it's infinity
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Alternatively, application may use [[PrefixAnnouncement|Prefix Announcement Protocol]] to register prefixes to itself.
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### Unregister a route
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**command-verb**: `unregister`
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This command removes a route from the RIB.  
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This command can also be accepted on `ndn:/localhop/nfd` management prefix, in addition to the default `ndn:/localhost/nfd` management prefix.
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ControlParameters fields:
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* Name (required)
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* FaceId (optional)
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* Origin (optional)
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*FaceId* is the FaceId returned by [[FaceMgmt|Face Management]].
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If *FaceId* is omitted or is set to zero, it is implied as the requesting face (self unregistration).
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*Origin* defaults to app(=0).
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Self unregistration is unnecessary if the client is quitting. The forwarder SHOULD automatically remove routes belonging to a closed face.
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A client needs self unregistration when it stops serving a name prefix, but intends to continue execution.
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If the route does not exist, this command does nothing, but is still considered successful.
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If the command succeeds, \<body> in ControlResponse block contains updated ControlParameters:
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* Name: unchanged
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* FaceId: nexthop FaceId (not zero)
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* Origin: unchanged if request specifies; app(=0) if request omits
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### Semantics of successful responses
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Successful responses from these commands indicate that RIB Management has received and authorized the command, and will perform the requested updates shortly.
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RIB and FIB updates are asynchronous, and they are not necessarily completed when the response is sent.
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## RIB Dataset
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Routes are published as a [[StatusDataset|Status Dataset]] at `ndn:/localhost/nfd/rib/list`.
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Multiple routes of same Name prefix are organized into a **RIB entry**.
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Each RIB entry is represented by a **RibEntry** block:
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    RibEntry := RIB-ENTRY-TYPE TLV-LENGTH
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                  Name
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                  Route+
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    Route    := ROUTE-TYPE TLV-LENGTH
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                  FaceId
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                  Origin
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                  Cost
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                  Flags
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                  ExpirationPeriod?
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Flags is inclusive OR of route inheritance flags, encoded in the same way as `register` command.  
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ExpirationPeriod is the remaining lifetime of a route, or omitted if it's Infinity.
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## Routable Prefixes Dataset
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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`.
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Generally, a **routable prefix** is a name prefix that satisfies one of the following:
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* The prefix is advertised into a routing protocol from this router.
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* The prefix can be registered onto a connected router via [[AutoPrefixPropagation]] from this end host, and falls under a routable prefix of that router.
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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.
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However, since the network is a dynamic and distributed system, global reachability cannot be guaranteed even if a routable prefix is used.
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Each routable prefix is represented by a **Name** block in the dataset.
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## TLV-TYPE assignments
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Type                                        | Assigned value    | Assigned value (hex)
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------------------------------------------- | ----------------- | --------------------
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RibEntry                                    | 128               | 0x80
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Route                                       | 129               | 0x81