| Mobile Ad hoc Networks Working Group | C. Perkins |
| Internet-Draft | Futurewei |
| Intended status: Standards Track | S. Ratliff |
| Expires: September 25, 2015 | Idirect |
| J. Dowdell | |
| Airbus Defence and Space | |
| L. Steenbrink | |
| HAW Hamburg, Dept. Informatik | |
| V. Mercieca | |
| Airbus Defence and Space | |
| March 24, 2015 |
Dynamic MANET On-demand (AODVv2) Routing
draft-ietf-manet-aodvv2-08
The revised Ad Hoc On-demand Distance Vector (AODVv2) routing protocol is intended for use by mobile routers in wireless, multihop networks. AODVv2 determines unicast routes among AODVv2 routers within the network in an on-demand fashion, offering rapid convergence in dynamic topologies.
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This Internet-Draft will expire on September 25, 2015.
Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved.
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The revised Ad Hoc On-demand Distance Vector (AODVv2) routing protocol [formerly named DYMO] enables on-demand, multihop unicast routing among AODVv2 routers in mobile ad hoc networks [MANETs][RFC2501]. The basic operations of the AODVv2 protocol are route discovery and route maintenance. Route discovery is performed when an AODVv2 router must transmit a packet towards a destination for which it does not have a route. Route maintenance is performed to avoid prematurely expunging routes from the route table, and to avoid dropping packets when a route breaks.
During route discovery, the originating AODVv2 router (RREQ_Gen) disseminates a Route Request message (RREQ) to find a route toward some target destination. Using a hop-by-hop regeneration algorithm, each AODVv2 router receiving the RREQ message records a route toward the originator. When the target's AODVv2 router (RREP_Gen) receives the RREQ, it records a route toward RREQ_Gen and generates a Route Reply (RREP) unicast toward RREQ_Gen. Each AODVv2 router that receives the RREP stores a route toward the target, and again unicasts the RREP toward the originator. When RREQ_Gen receives the RREP, routes have then been established between RREQ_Gen (the originating AODVv2 router) and RREP_Gen (the target's AODVv2 router) in both directions.
Route maintenance consists of two operations: continuously extending the lifetime of active routes, and using Route Error (RERR) message to invalidate routes that cannot be used to forward packets. In order to maintain routes, AODVv2 routers extend route lifetimes upon successfully forwarding a packet. When a data packet is received to be forwarded and no valid route exists, then the upstream routers and AODVv2 router of the source of the packet is notified of the error by way of an RERR message. Route discovery would re-establish the route. RERR messages are also used to notify upstream routers when routes break (say, due to loss of a link to a neighbor).
AODVv2 uses sequence numbers to assure loop freedom [Perkins99], similarly to AODV. Sequence numbers enable AODVv2 routers to determine the temporal order of AODVv2 route discovery messages, thereby avoiding use of stale routing information.
See Section 10 for the mapping of AODVv2 data elements to RFC 5444 Address Block, Address TLV, and Message TLV formats. Security for authentication of AODVv2 routers, and/or encryption of traffic is dealt with by the underlying transport mechanism (e.g., by using the techniques for Authentication, Integrity, and Confidentiality documented in [RFC5444]).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. In addition, this document uses terminology from [RFC5444], and defines the following terms:
This document uses the Data Elements and conventions found in Table 1 and Table 2.
| Data Elements | Meaning |
|---|---|
| msg_hop_limit | Number of hops allowable for the message |
| msg_hop_count | Number of hops traversed so far by the message |
| AckReq | Acknowledgement Requested for RREP |
| PktSource | Source address of a data packet |
| AddressList | A list of IP addresses |
| OrigAddr | IP address of the Originating Node |
| TargAddr | IP address of the Target Node |
| UnreachableAddress | An unreachable IP address |
| PrefixLengthList | Routing prefixes associated with addresses in AddressList |
| SeqNum | Sequence Number, used in RERR messages |
| SeqNumList | A list of SeqNums |
| OrigSeqNum | Originating Node Sequence Number |
| TargSeqNum | Target Node Sequence Number |
| MetricType | The metric type for values in MetricList |
| MetricList | Metric values for routes to addresses in AddressList |
| OrigAddrMetric | Metric value for route to OrigAddr |
| TargAddrMetric | Metric value for route to TargAddr |
| ValidityTime | Included in ValidityTimeList |
| ValidityTimeList | ValidityTime values for routes to Addresses in AddressList |
| Notation | Meaning |
|---|---|
| Route[Address] | A route table entry towards Address |
| Route[Address].{field} | A field in such a route table entry |
| -- | -- |
| RREQ_Gen | AODVv2 router originating an RREQ |
| RREP_Gen | AODVv2 router responding to an RREQ |
| RERR_Gen | AODVv2 router originating an RERR |
| RteMsg | Either RREQ or RREP |
| RteMsg.{field} | Field in RREQ or RREP |
| AdvRte | A route advertised in an incoming RteMsg |
| HandlingRtr | Handling Router |
The AODVv2 routing protocol is a reactive routing protocol designed for stub (i.e., non-transit) or disconnected (i.e., from the Internet) mobile ad hoc networks (MANETs). AODVv2 handles a wide variety of mobility patterns by determining routes on-demand. AODVv2 also handles a wide variety of traffic patterns. In networks with a large number of routers, AODVv2 is best suited for relatively sparse traffic scenarios where any particular router forwards packets to only a small percentage of the AODVv2 routers in the network, due to the on-demand nature of route discovery and route maintenance. AODVv2 supports routers with multiple interfaces, as long as each interface has its own (unicast routeable) IP address; the set of all network interfaces supporting AODVv2 is administratively configured in a list (namely, AODVv2_INTERFACES).
Ad Hoc networks have been deployed in many circumstances, including for emergency and disaster relief. In those circumstances, it is sometimes the case that the simple ability to communicate is much more important than being assured of secure operations. AODVv2 is very well suited for such reactive scenarios. For other ad hoc networking applications, in which insecure operation could negate the value of establishing communication paths, it is important for neighboring AODVv2 nodes to establish security associations with one another.
Although AODVv2 is closely related to AODV [RFC3561], and shares some features of DSR [RFC4728], AODVv2 is not interoperable with either of those other two protocols.
AODVv2 is applicable to memory constrained devices, since only a little routing state is maintained in each AODVv2 router. Routes that are not needed for forwarding data do not have to be maintained, in contrast to proactive routing protocols that require routing information to all routers within the MANET be maintained.
In addition to routing for its own local applications, each AODVv2 router can also route on behalf of other non-routing nodes (in this document, "Router Clients") that are directly reachable via its network interfaces. Each AODVv2 router, if serving router clients other than itself, SHOULD be configured with information about the IP addresses of its clients, using any suitable method. In the initial state, no AODVv2 router is required to have information about the relationship between any other AODVv2 router and its Router Clients (see Section 6.3).
The coordination among multiple AODVv2 routers to distribute routing information correctly for a shared address (i.e. an address that is advertised and can be reached via multiple AODVv2 routers) is not described in this document. The AODVv2 router operation of shifting responsibility for a routing client from one AODVv2 router to another is described in Appendix I. Address assignment procedures are entirely out of scope for AODVv2. A Router Client SHOULD NOT be served by more than one AODVv2 router at any one time.
AODVv2 routers perform route discovery to find a route toward a particular destination. AODVv2 routers MUST must be configured to respond to RREQs for themselves and their clients. When AODVv2 is the only protocol interacting with the forwarding table, AODVv2 MAY be configured to perform route discovery for all unknown unicast destinations. Such routers will reply for each address request.
By default, AODVv2 only supports bidirectional links. In the case of possible unidirectional links, blacklists (see Section 6.2) SHOULD be used, or other means (e.g. adjacency establishment with only neighboring routers that have bidirectional communication as indicated by NHDP HELLO messages [RFC6130]) of assuring and monitoring bi-directionality are recommended. Otherwise, persistent packet loss or persistent protocol failures could occur. If received over a link that is unidirectional, metric information from incoming AODVv2 messages MUST NOT be used for route table updates.
The routing algorithm in AODVv2 may be operated at layers other than the network layer, using layer-appropriate addresses. The routing algorithm makes use of some persistent state; if there is no persistent storage available for this state, recovery can impose a performance penalty (e.g., in case of AODVv2 router reboots).
In its default mode of operation, AODVv2 sends messages using the parameters for port number and IP protocol specified in [RFC5498]. Unless otherwise specified, the address for AODVv2 multicast messages (for example, RREQ or RERR) is the link-local multicast address LL-MANET-Routers [RFC5498]. All AODVv2 routers MUST subscribe to LL-MANET-Routers [RFC5498] to receive AODVv2 messages. Implementations are free to choose their own heuristics for reducing multicast overhead. Some methods for doing so are described in [RFC6621]. AODVv2 does not specify which method should be used to restrict the set of AODVv2 routers that have the responsibility to regenerate multicast packets. Note that multicast packets MAY be sent via unicast. For example, this may occur for certain link-types (non-broadcast media), for manually configured router adjacencies, or in order to improve robustness.
When multiple interfaces are available, a node transmitting a multicast packet to LL-MANET-Routers MUST send the packet on all interfaces that have been configured for AODVv2 operation. Similarly, AODVv2 routers MUST subscribe to LL-MANET-Routers on all their AODVv2 interfaces.
IP packets containing AODVv2 protocol messages SHOULD be given priority queuing and channel access.
The route table entry is a conceptual data structure. Implementations MAY use any internal representation so long as it provides access to the information specified below.
A route table entry has the following fields:
A route table entry (i.e., a route) is in one of the following states:
MAX_SEQNUM_LIFETIME is the time after a reboot during which an AODVv2 router MUST NOT respond to any routing messages that require information about its Sequence Number. Thus, if all other AODVv2 routers expunge routes to the rebooted router after that time interval, the rebooted AODVv2 router's sequence number will not be considered stale by any other AODVv2 router in the MANET.
The invalidation of a Timed route is controlled by the ExpirationTime time of the route table entry (instead of MAX_IDLETIME). Until that time, a Timed route can be used for forwarding packets. A route is indicated to be a Timed route by the setting of the Timed flag in the route table entry. Afterwards, the route MAY be expunged; otherwise the route must be must be marked as Invalid.
Neighboring routers MAY form an adjacency based on AODVv2 messages, other protocols (e.g. NDP [RFC4861] or NHDP [RFC6130]), or manual configuration. Loss of a routing adjacency may also be indicated similarly. AODVv2 routers SHOULD monitor connectivity to adjacent routers along active routes. In the absence of other information about bidirectional connectivity, the default approach for AODVv2 routers to monitor connectivity to neighboring AODVv2 routers is to include the AckReq data element in RREP messages, and send RREP_Ack messages to fulfill the requests (see Sections 9.2 and 9.4). However, when routers perform other operations such as those from the list below, these can also be used as indications of connectivity.
For example, receipt of a Neighborhood Discovery message would signal a connection to the sender. In this case, the AODVv2 router doesn't need to request an acknowledgement in the RREP. Similarly, if AODVv2 received notification of a timeout, this may possibly be due to a disconnection, and the AODVv2 router SHOULD attempt to verify connectivity by including AckReq data element when sending a RREP to that neighbor.
When a link to a neighbor is determined to be unidirectional, either by failure to respond with a RREP_Ack as requested, or by some other means, the neighbor MUST be placed in a blacklist. However, the blacklisted neighbor SHOULD NOT be permanently blacklisted; after a certain time (MAX_BLACKLIST_TIME), it SHOULD once again be considered as a viable neighbor for route discovery operations.
For this purpose, a list of blacklisted routers along with their time of removal SHOULD be maintained:
RREQs received from a blacklisted router, or any router over a link that is known to be incoming-only, MUST be disregarded. If other indications are received that a blacklisted router has restored bidirectional connectivity, for instance receiving NHDP HELLO messages, then the router SHOULD be immediately removed from the blacklist.
An AODVv2 router may offer routing services to other nodes that are not AODVv2 routers; such nodes are called Router Clients in this document.
For this purpose, CLIENT_ADDRESSES must be configured on each AODVv2 router with the following information:
The list of Routing Clients for an AODVv2 router is never empty, since an AODVv2 router is always its own client as well. If the Client Prefix Length is not the full length of the Client IP address, then the prefix defines a Client Network. If an AODVv2 router is configured to serve a Client Network, then the AODVv2 router MUST serve every node that has an address within the range defined by the routing prefix of the Client Network.
Sequence Numbers allow AODVv2 routers to evaluate the freshness of routing information. Each AODVv2 router in the network MUST maintain its own sequence number (SeqNum). Each RREQ and RREP generated by an AODVv2 router includes its SeqNum. Each AODVv2 router MUST ensure that its SeqNum is monotonically increasing. The router can ensure this by incrementing SeqNum whenever it generates RREQ or RREP .
A router receiving a RREQ or RREP message uses the Sequence Number in the message to determine the freshness of a route update: if a new Sequence Number in the message is lower than the one stored in the route table, the stored information for that route is considered stale.
As a consequence, loop freedom is assured.
If the router has multiple network interfaces, it can use the same SeqNum for the IP addresses of all of them, or it can assign different SeqNums for use with different IP addresses. However, the router MUST NOT use multiple SeqNums for any particular IP address. A Router Client has the same SeqNum as the IP address of the network interface that the AODVv2 router uses to forward packets to that Router Client. Similarly, a route to a subnet has the same SeqNum as the IP address of the network interface that the AODVv2 router uses to forward packets to that subnet. The Sequence Number fulfills the same role as the "Destination Sequence Number" of DSDV [Perkins94], and as the AODV Sequence Number in RFC 3561[RFC3561].
An AODVv2 router increments its SeqNum as follows. Most of the time, SeqNum is incremented by simply adding one (1). But when the SeqNum has the value of the largest possible number representable as a 16-bit unsigned integer (i.e., 65,535), it MUST be incremented by setting to one (1). In other words, the sequence number after 65,535 is 1.
An AODVv2 router SHOULD maintain its SeqNum in persistent storage. If an AODVv2 router's SeqNum is lost, it MUST take the following actions to avoid the danger of routing loops. First, the AODVv2 router MUST set Route.State := Invalid for each entry. Furthermore the AODVv2 router MUST wait for at least MAX_SEQNUM_LIFETIME before transmitting or regenerating any AODVv2 RREQ or RREP messages. If an AODVv2 protocol message is received during this waiting period, the AODVv2 router SHOULD perform normal route table entry updates, but not forward the message to other nodes. If, during this waiting period, a data packet is received to be forwarded to another destination that is not among the router's Clients, then the AODVv2 router MUST transmit a RERR message indicating that no route is available. However, packets destined to a Client are forwarded as usual. At the end of the waiting period the AODVv2 router sets its SeqNum to one (1) and begins performing AODVv2 protocol operations again.
Two multicast RteMsgs (i.e., RREQ or RREP) are considered to be "comparable" if they have the same Message Type, OrigAddr, TargAddr, and MetricType. When RteMsgs are flooded in a MANET, an AODVv2 router may well receive such comparable RteMsgs from its neighbors. A router, after receiving a RteMsg, MUST check against previous RteMsgs to assure that its response message would contain information that is not redundant. Otherwise, multicast RteMsgs are likely to be regenerated repeatedly with almost no additional benefit, but generating a great deal of unnecessary signaling traffic and interference. See Section 8.6 regarding suppression of redundant RteMsgs.
To avoid transmission of redundant RteMsgs, while still enabling the proper handling of earlier RteMsgs that may have somehow been delayed in the network, each AODVv2 router keeps a list of certain information about recently received RteMsgs. This list is called the AODVv2 Multicast RteMsg Table -- or, more briefly, the RteMsg Table.
Each entry in the RteMsg Table has the following fields:
The RteMsg Table is maintained so that no two entries in the RteMsg Table are comparable -- that is, all RteMsgs represented in the RteMsg Table either have different Message Types, different OrigAddr, different TargAddr, or different metric types. If two RteMsgs have the same Message Type, MetricType, OrigAddr, and TargAddr, the information from the one with the older Sequence Number is not needed in the table; in case they have the same Sequence Number, the one with the greater Metric value is not needed; in case they have the same Metric as well, it does not matter which table entry is maintained. Whenever a RteMsg Table entry is updated, its Timestamp field MUST also set to be the Current_Time.
Metrics measure a cost or quality associated to a route or a link. They can account for various characteristics such as latency, delay, financial, energy, etc. A metric value is included in each routing table entry. Determining whether to use incoming information about a route requires comparing metric values. Whenever an AODV router receives metric information in an incoming message, the received value of the metric is as measured by the neighbor router, and does not reflect the cost of traversing the link to that neighbor.
Each metric has a MetricType, which is allocated by IANA as specified in [RFC6551]. Apart from its default metric type as detailed in Section 7.3, AODVv2 enables the use of monotonically increasing metrics, whose data type depends on the metric used. Using non-default metrics in a RteMsg requires the inclusion of the MetricType data element. Routes are looked up according to metric type, and intermediate routers handling a RteMsg assign the same metric type to all metric information in the RteMsg.
For each type of metric, a maximum value is defined, denoted MAX_METRIC[i] where 'i' is the MetricType. AODVv2 cannot store routes in its route table that cost more than MAX_METRIC[i].
In order to simplify the description of storing accumulated route costs in the route table, a Cost() function is defined. This function returns the Cost of traversing a Route ('Cost(R)') or a Link ('Cost(L)'). Cost(L) for DEFAULT_METRIC_TYPE is specified in Section 7.3. The Cost() function for other metrics is beyond the scope of this document.
Since determining loop freedom is known to depend on comparing the Cost(R1) of advertised route update information to the Cost(R2) of an existing stored route using the same metric type, AODVv2 invokes a function called "LoopFree(R1, R2)". LoopFree(R1, R2) returns TRUE when R1 is guaranteed to not rely on the route R2, i.e. R2 is not a subroute of the route R1. An AODVv2 router invokes LoopFree() to compare an advertised route to a stored route. The advertised route is referred to as AdvRte and is used as parameter R1. The stored route is referred to as Route and is used as parameter R2.
The default MetricType (DEFAULT_METRIC_TYPE) is HopCount (but see Section 7.4). HopCount is the only metric described in detail in this document. For the HopCount metric, Cost(L) is always 1, and Cost(R) is the hop count between the router and the destination.
MAX_METRIC[DEFAULT_METRIC_TYPE] is defined to be MAX_HOPCOUNT. MAX_HOPCOUNT MUST be larger than the AODVv2 network diameter. Otherwise, AODVv2 protocol messages may not reach their intended destinations.
Using MetricType DEFAULT_METRIC_TYPE, LoopFree (AdvRte, Route) is TRUE when Cost(AdvRte) ≤ Cost(Route). The specification of Cost(R) and LoopFree(AdvRte, Route) for metric types other than DEFAULT_METRIC_TYPE is beyond the scope of this document.
Some applications may require metric information other than HopCount, which has traditionally been the default metric associated with routes in MANET. It is well known that reliance on HopCount can cause selection of the worst possible route in some situations. For this reason, AODVv2 enables route selection based on metric information other than HopCount -- in other words, based on "alternate metrics".
The range and data type of each such alternate metric may be different. For instance, the data type might be integers, or floating point numbers, or restricted subsets thereof. It is out of the scope of this document to specify for alternate metrics the Cost(L) and Cost(R) functions, or their return type. Where necessary these should take into account any differences in the link cost in each direction.
In this section, operations are specified for updating the route table using information within AODVv2 RteMsgs (either RREQ or RREP), and due to timeouts. AdvRte is the route advertised by the RteMsg. RteMsgs include IP addresses as well as possibly the SeqNum and the prefix lengths associated with those IP addresses. The AdvRte also includes the metric measured from the neighbor transmitting the RteMsg to the IP address originating the route update. All SeqNum comparisons use signed 16-bit arithmetic.
After determining that the incoming information is correctly formatted and contains values in the correct ranges, the AODVv2 router will use the information to update local routing information if possible. This section explains how to determine whether the incoming information should be used to update the route table, and how to perform the update.
The incoming RteMsg may be a RREQ or a RREP. If it is a RREQ, it contains information about a route to OrigAddr. Prefix length information in a RREQ, if present, describes the subnet on which OrigAddr resides. If it is a RREP, it contains information about a route to TargAddr. AdvRte is used to denote the route information contained in the RteMsg. AdvRte has the following properties: Section 8.2. Otherwise determine whether or not to use AdvRte for updating the route entry (Route) matching the AdvRte's Address and MetricType as follows: Appendix A.1.1.
In the description below, Route denotes the stored routing table entry and HandlingRtr is the router receiving the RteMsg. HandlingRtr MUST process the incoming information as follows. If the routing table does not contain an entry matching AdvRte's Address and MetricType, create a new route table entry according to the procedure in
To briefly summarize, AdvRte must satisfy the following conditions compared to the existing route table entry before it can be used:
Also see the pseudocode in
If the route has been updated based on information in a received RREQ, the AODVv2 router MAY force regeneration of the RREQ, to ensure the most recent information is propagated to other routers, but it MAY suppress this to avoid extra control traffic.
To apply the route update, a route table entry for AdvRte.Address is either found to already exist in the route table, or else a new route table entry for AdvRte.Address is created and inserted into the route table. If the route table entry had to be created, or if the state is Invalid, the state is set to be Idle. The fields of route table entry are assigned as follows:
With these assignments to the route table entry, a route has been made available, and the route can be used to send any buffered data packets (and subsequently to forward any incoming data packets) for Route.Address. An updated route entry also fulfills any outstanding route discovery (RREQ) attempts for Route.Address. Any retry timers for the RREQ SHOULD be cancelled.
AODVv2 routers attempt to maintain active routes. Before using a route to forward a packet, an AODVv2 router MUST check the status of the route as specified in Section 8.4. If the route has been marked as Invalid, it cannot be used for forwarding. Otherwise, set Route.LastUsed := Current_Time, Route.State := Active, and forward the packet to the route's next hop.
When a routing problem is encountered, an AODVv2 router (denoted RERR_Gen) sends the RERR to quickly notify upstream routers. Two kinds of routing problems can trigger generation of a RERR message. The first happens when the router receives a packet but does not have a valid route for the destination of the packet. The second case happens immediately upon detection of a broken link (see Section 6.2) for an valid route.
Optionally, if a precursor list is maintained for the route, see Section 12.2 for precursor lifetime operations.
During normal operation, AODVv2 does not require any explicit timeouts to manage the lifetime of a route. At any time, any route table entry can be examined and then either expunged or marked as Invalid according to the following rules.
The following rules are used to manage the state of route table entries: Section 12.2) then the precursor lists must also be expunged at the same time that the route itself is expunged.
Memory constrained devices MAY choose to expunge routes from the AODVv2 route table at other times, but MUST adhere to the following rules:
If precursor lists are maintained for the route (as described in
AODVv2 message types RREQ and RREP are together known as Routing Messages (RteMsgs) and are used to discover a route between an Originating and Target Address, denoted by OrigAddr and TargAddr. The constructed route is bidirectional, enabling packets to flow between OrigAddr and TargAddr. RREQ and RREP have similar information and function, but have some differences in their rules for handling. When a node receives a RREQ or a RREP, the node then creates or updates a route to the OrigAddr or the TargAddr respectively (see Section 8.1). The main difference between the two messages is that, by default, RREQ messages are multicast to solicit a RREP, whereas RREP is unicast as a response to RREQ.
When an AODVv2 router needs to forward a data packet from a node (with IP address OrigAddr) in its set of router clients, and it does not have a forwarding route toward the packet's IP destination address (TargAddr), the AODVv2 router (RREQ_Gen) generates a RREQ (as described in Section 9.1.1) to discover a route toward TargAddr. Subsequently RREQ_Gen awaits reception of an RREP message (see Section 9.2.1) or other route table update (see Section 8.2) to establish a route toward TargAddr. The RREQ message contains routing information to enable RREQ recipients to route packets one hop towards the OrigAddr, and the RREP message contains routing information to enable RREP recipients to route packets one hop towards the TargAddr.
After issuing a RREQ, as described above RREQ_Gen awaits a RREP providing a bidirectional route toward the Target Address. If the RREP is not received within RREQ_WAIT_TIME, RREQ_Gen MAY retry the Route Discovery by generating another RREQ. Route Discovery SHOULD be considered to have failed after DISCOVERY_ATTEMPTS_MAX and the corresponding wait time for a RREP response to the final RREQ. After the attempted Route Discovery has failed, RREQ_Gen MUST wait at least RREQ_HOLDDOWN_TIME before attempting another Route Discovery to the same destination.
To reduce congestion in a network, repeated attempts at route discovery for a particular Target Address SHOULD utilize a binary exponential backoff, as described in [RFC3561], where the initial wait time is RREQ_WAIT_TIME and the wait time is doubled for each retry based.
Data packets awaiting a route SHOULD be buffered by RREQ_Gen. This buffer SHOULD have a fixed limited size (BUFFER_SIZE_PACKETS or BUFFER_SIZE_BYTES). Determining which packets to discard first is a matter of policy at each AODVv2 router; in the absence of policy constraints, by default older data packets SHOULD be discarded first. Buffering of data packets can have both positive and negative effects (albeit usually positive). Nodes without sufficient memory available for buffering SHOULD be configured to disable buffering by configuring BUFFER_SIZE_PACKETS = 0 and BUFFER_SIZE_BYTES = 0. This will affect the latency required for launching TCP applications to new destinations.
If a route discovery attempt has failed (i.e., DISCOVERY_ATTEMPTS_MAX attempts have been made without receiving a RREP) to find a route toward the Target Address, any data packets buffered for the corresponding Target Address MUST BE dropped and a Destination Unreachable ICMP message (Type 3) SHOULD be delivered to the source of the data packet. The code for the ICMP message is 1 (Host unreachable error). If RREQ_Gen is not the source (OrigNode), then the ICMP is sent to OrigAddr.
When RREQ messages are flooded in a MANET, an AODVv2 router may receive similar RREQ messages from more than one of its neighbours. To avoid processing and transmission associated with redundant RteMsgs, while still enabling proper handling of earlier RteMsgs that may have somehow been delayed in the network, it is necessary for each AODVv2 router store information about RteMsgs which it has recently received (see the RteMsg table defined in Section 6.5).
When a RREQ is received, it is checked against the RteMsg Table to see if it contains redundant information. If so it does not need to be processed.
For RREQ messages, the process for comparison is as follows:
The process of comparison for optional multicast RREP messages is analogous, substituting RREP for RREQ, and TargAddr for OrigAddr. Entries in the RteMsg Table MUST be deleted after MAX_SEQNUM_LIFETIME, but should be maintained for at least RteMsg_ENTRY_TIME in order to account for long-lived RREQs traversing the network.
This section specifies the data elements and values required in AODVv2 protocol messages, namely RREQ, RREP, RERR, and RREP_Ack.
To avoid congestion, each AODVv2 router's rate of packet/message generation SHOULD be limited. The rate and algorithm for limiting messages (CONTROL_TRAFFIC_LIMIT) is left to the implementor and should be administratively configurable. AODVv2 messages SHOULD be discarded in the following order of preference: RREQ, RREP, RERR, and finally RREP_Ack.
See Section 10 for the mapping of AODVv2 data elements to RFC 5444 Message TLVs, Address Blocks, and Address TLVs.
RREQ messages are used in Route Discovery operations to request a route to a specified Target address. RREQ messages have the following general structure:
+-----------------------------------------------------------------+
| msg_hop_limit, msg_hop_count |
+-----------------------------------------------------------------+
| AddressList := {OrigAddr, TargAddr} |
+-----------------------------------------------------------------+
| PrefixLengthList := {PrefixLength for OrigAddr, null}(optional) |
+-----------------------------------------------------------------+
| OrigSeqNum, (optional) TargSeqNum |
+-----------------------------------------------------------------+
| MetricType (optional) |
+-----------------------------------------------------------------+
| MetricList := {Metric for OrigAddr, null} |
+-----------------------------------------------------------------+
| ValidityTimeList := {ValidityTime for OrigAddr, null}(optional) |
+-----------------------------------------------------------------+
Figure 1: RREQ message structure
RREQ messages carry information about OrigAddr and TargAddr, as identified in the context of the RREQ_Gen. The OrigSeqNum MUST appear. Both MAY appear in the same RREQ when SeqNum is available for both OrigAddr and TargAddr.
The OrigSeqNum data element in a RteMsg MUST apply only to OrigAddr. The other address in the AddressList is TargAddr.
If the TargSeqNum data element appears, then it MUST apply only to TargAddr. The other address in the AddressList is OrigAddr.
Upon receiving an IP packet from one of its Router Clients, it often happens that an AODVv2 router has no valid route to the destination. In this case the AODVv2 router is responsible for generating a RREQ and associated data elements on behalf of its client OrigNode. The router is referred to as RREQ_Gen. Before creating a RREQ, RREQ_Gen should check if an RREQ has recently been sent for this destination and a response is awaited, or if the limit of AODVv2 RREQ retries has been reached.
In constructing the RREQ, RREQ_Gen uses AddressList, OrigSeqNum, MetricList, and optionally PrefixLengthList, TargSeqNum, MetricType, and ValidityTime.
RREQ_Gen follows the steps in this section. OrigAddr MUST be a unicast address. The order of data elements is illustrated schematically in Figure 1. RREQ_Gen SHOULD include TargSeqNum, if a previous value of the TargAddr's SeqNum is known (e.g. from an invalid route table entry using longest-prefix matching). If TargSeqNum is not included, AODVv2 routers handling the RREQ assume that RREQ_Gen does not have that information.
Upon receiving an RREQ, an AODVv2 router performs the following steps.
Unless the router is prepared to advertise the new route, it halts processing. By sending a RREQ, a router advertises that it will forward packets to the OrigAddr contained in the RREQ according to the information enclosed. The router MAY choose not to regenerate the RREQ, though this could decrease connectivity in the network or result in non-optimal paths.
The circumstances under which a router MAY choose not to regenerate a RREQ are not specified in this document. Some examples may include the router being heavily loaded and not advertising routing for more traffic, or being low on energy and having to reduce energy expended for sending AODVv2 messages or packet forwarding.
The procedure for RREQ regeneration is as follows:
If the received RREQ was unicast, the regenerated RREQ can be unicast to the next hop address of the route towards TargAddr, if known. Otherwise, the RREQ SHOULD be multicast to the LL-MANET-Routers IP and MAC address [RFC5498], [RFC4291].
RREP messages are used to offer a route to a target address, and are sent in response to a RREQ message. RREP messages have the following general structure:
+-----------------------------------------------------------------+
| msg_hop_limit, msg_hop_count |
+-----------------------------------------------------------------+
| AckReq (optional) |
+-----------------------------------------------------------------+
| AddressList := {OrigAddr,TargAddr} |
+-----------------------------------------------------------------+
| PrefixLengthList := {null, PrefixLength for TargAddr(optional)} |
+-----------------------------------------------------------------+
| TargSeqNum |
+-----------------------------------------------------------------+
| MetricList := {null, metric for TargAddr} |
+-----------------------------------------------------------------+
| MetricType (optional) |
+-----------------------------------------------------------------+
| ValidityTimeList := {null, ValidityTime for TargAddr}(optional) |
+-----------------------------------------------------------------+
Figure 2: RREP message structure
RREP messages carry information about OrigAddr and TargAddr, as known in the context of the RREP_Gen. The TargSeqNum MUST appear. It MUST apply only to TargAddr. The other address in the AddressList is OrigAddr.
This section specifies the generation of an RREP by an AODVv2 router (RREP_Gen) that provides connectivity for TargAddr, thus enabling the establishment of a route between OrigAddr and TargAddr. In constructing the RREP, AODVv2 uses AddressList, TargSeqNumber List, MetricList, and optionally AckReq, PrefixLengthList and/or ValidityTimeList. These elements are then used to create a RFC5444 message; see Section 10 for details.
The AckReq data element indicates that an acknowledgement to the RREP has been requested. If no corresponding RREP_Ack is received within the RREP_Ack_SENT_TIMEOUT, the next hop is added to the blacklist as discussed in Section 6.2.
The procedure for RREP generation is as follows:
By default, the RREP is sent by unicast to the IP address of the next hop of the RREP_Gen's route to OrigAddr.
Upon receiving an RREP, an AODVv2 router performs the following steps.
Similar to rules for RREQ regeneration, unless the router is prepared to advertise the route to TargAddr, it halts processing. By forwarding a RREP, a router advertises that it will forward packets to the TargAddr contained in the RREP according to the information enclosed. The router MAY choose not to regenerate the RREP, for the same reasons as mentioned under RREQ regeneration Section 9.1.3, though this could decrease connectivity in the network or result in non-optimal paths.
If no valid route exists to OrigAddr, a RERR SHOULD be transmitted to TargAddr as specified in Section 9.3.1 and the RREP should not be regenerated.
The procedure for RREP regeneration is as follows:
The RREP SHOULD be unicast to the next hop on the route to OrigAddr.
+-----------------------------------------------------------------+
| msg_hop_limit |
+-----------------------------------------------------------------+
| PktSource (optional) |
+-----------------------------------------------------------------+
| RERR AddressList |
+-----------------------------------------------------------------+
| PrefixLengthList for UnreachableAddresses (optional) |
+-----------------------------------------------------------------+
| SeqNumList (one entry per address) |
+-----------------------------------------------------------------+
| MetricType (optional) |
+-----------------------------------------------------------------+
Figure 3: RERR message structure
An RERR message is generated by a AODVv2 router (i.e., RERR_Gen) in order to notify upstream routers that packets cannot be delivered to one or more destinations. An RERR message has the following general structure:
There are two types of events which trigger generation of a RERR message. The first is the arrival of a packet for which there is no route to the destination address. This can be a packet forwarded by the routing process, or a RREP when there is no route to OrigAddr. In this case, exactly one UnreachableAddress will be included in RERR's AddressList (either the Destination Address of the IP header from a data packet, or the OrigAddr found in the AddressList of an RREP message). RERR_Gen MUST discard the packet or message that triggered generation of the RERR.
The second type of event happens when a link breaks. All routes (whether valid or not) that use the broken link MUST be marked as Invalid. If the broken link was not used by any Active route, no RERR message is generated. Every Invalid route reported in the RERR MUST have the same MetricType. If the broken link affects routes to destinations that have different MetricTypes, multiple RERR messages must be generated.
If an AODVv2 router receives an ICMP packet to or from the address of one of its client nodes, it simply forwards the ICMP packet, and does not generate any RERR message.
In constructing the RERR, AODVv2 uses MetricType, AddressList, SeqNumList, and in some cases PktSource and PrefixLengthList. These elements are then used to create a RFC5444 message; see Section 10 for details.
The procedure for RERR generation is as follows:
If the RERR is sent in response to an Undeliverable Packet:
If the RERR is sent in response to a broken link:
Upon receiving an RERR, the following steps are performed.
If there are no UnreachableAddresses which need to be advertised in a regenerated RERR, take no further action.
Otherwise regenerate the RERR as specified in Section 9.3.3.
The procedure for RERR regeneration is as follows:
If the original RERR contained the PktSource data element, and a route exists to the source address, the regenerated RERR MUST be sent unicast to the next hop of the route towards PktSource.
Otherwise, if precursor lists are maintained, the regenerated RERR SHOULD be sent to the active precursors of the Invalid routes as specified in Section 12.2.
Otherwise the regenerated RERR MUST be sent to the multicast IP and MAC address for LL-MANET-Routers.
RREP_Ack is modeled on the RREP_Ack message type from AODV [RFC3561]. RREP_Ack messages have the following general structure:
+-----------------------------------------------------------------+ | msg_hop_limit := 1 | +-----------------------------------------------------------------+
Figure 4: RREP_Ack message structure
This section specifies the generation of an RREP_Ack by an AODVv2 router. The procedure is as follows:
The RREP_Ack is sent by unicast to the IP address of router that inserted a AckReq data element into a RREP message.
Upon receiving an RREP_Ack, an AODVv2 router performs the following steps.
AODVv2 specifies that all control plane messages between Routers SHOULD use the Generalised Mobile Ad-hoc Network Packet and Message Format [RFC5444], which provides a multiplexed transport for multiple protocols. AODVv2 therefore specifies Route Messages comprising data elements that map to message elements in RFC5444 but, in line with the concept of use, does not specify which order the messages should be arranged in an RFC5444 packet. An implementation of an RFC5444 multiplexer may choose to optimise the content of certain message elements to reduce control plane overhead. For handling of messages that contain unknown TLV types, the multiplexer SHOULD ignore the information for processing, but preserve it unmodified for forwarding.
Here is a brief summary of the RFC 5444 format.
The following table shows how AODVv2 data elements are represented in RFC 5444 messages.
| Data Element | RFC 5444 Message Representation |
|---|---|
| msg_hop_limit | RFC 5444 Message Header <msg-hop-limit> |
| msg_hop_count | RFC 5444 Message Header <msg-hop-count> |
| AckReq | Acknowledgement Request Message TLV |
| PktSource | The Packet Source Message TLV |
| RteMsg AddressList | RFC 5444 Address Block |
| - OrigAddr | |
| - TargAddr | |
| - PrefixLengthList | |
| RERR AddressList | RFC 5444 Address Block |
| - UnreachableAddress | |
| - PrefixLengthList | |
| SeqNumList | Sequence Number Address Block TLV |
| - SeqNum | |
| OrigSeqNum | Originating Node Sequence Number Address Block TLV |
| TargSeqNum | Target Node Sequence Number Address Block TLV |
| MetricType | Extension byte of Metric Address Block TLV |
| MetricList | Metric Address Block TLV |
| - OrigAddrMetric | - corresponds to OrigAddr |
| - TargAddrMetric | - corresponds to TargAddr |
| ValidityTimeList | VALIDITY_TIME Address Block TLV |
| - ValidityTime |
AODVv2 neither requires any inclusion nor uses any information from the packet header. The length of an address (32 bits for IPv4 and 128 bits for IPv6) inside an AODVv2 message is indicated by the msg-addr-length (MAL) in the msg-header. Although the addresses in an Address Block may appear in any order, each TLV value in a TLV Block is associated with exactly one Address in the Address Block. So, for instance, the ordering of the OrigAddrMetric and TargAddrMetric values in the MetricList is determined by the order of OrigAddr and TargAddr in the preceding RteMsg Address List. See Section 14.2 for more information about AODVv2 Message TLVs. See Section 14.3 for more information about AODVv2 Address Block TLVs.
Simple Internet attachment means attachment of a stub (i.e., non-transit) network of AODVv2 routers to the Internet via a single Internet AODVv2 router (called IAR).
As in any Internet-attached network, AODVv2 routers, and their clients, wishing to be reachable from hosts on the Internet MUST have IP addresses within the IAR's routable and topologically correct prefix (e.g. 191.0.2.0/24).
/-------------------------\
/ +----------------+ \
/ | AODVv2 Router | \
| | 191.0.2.2/32 | |
| +----------------+ | Routable
| +-----+--------+ Prefix
| | Internet | /191.0.2/24
| | AODVv2 Router| /
| | 191.0.2.1 |/ /---------------\
| | serving net +------+ Internet \
| | 191.0.2/24 | \ /
| +-----+--------+ \---------------/
| +----------------+ |
| | AODVv2 Router | |
| | 191.0.2.3/32 | |
\ +----------------+ /
\ /
\-------------------------/
Figure 5: Simple Internet Attachment Example
When an AODVv2 router within the AODVv2 MANET wants to discover a route toward a node on the Internet, it uses the normal AODVv2 route discovery for that IP Destination Address. The IAR MUST respond to RREQ on behalf of all Internet destinations.
When a packet from a node on the Internet destined for a node in the AODVv2 MANET reaches the IAR, if the IAR does not have a route toward that destination it will perform normal AODVv2 route discovery for that destination.
Some optional features of AODVv2, associated with AODV, are not required by minimal implementations. These features are expected to apply in networks with greater mobility, or larger node populations, or requiring reduced latency for application launches. The optional features are as follows:
For multicast RREQ, msg_hop_limit MAY be set in accordance with an expanding ring search as described in [RFC3561] to limit the RREQ propagation to a subset of the local network and possibly reduce route discovery overhead.
This section specifies an interoperable enhancement to AODVv2 (and possibly other reactive routing protocols) enabling more economical RERR notifications to traffic sources upon determination that a route needed to forward such traffic to its destination has become Invalid.
In many circumstances, there can be several sources of traffic for a certain destination. Each such source of traffic is known as a "precursor" for the destination, as well as all upstream routers between the forwarding AODVv2 router and the traffic source. There is no need to keep track of upstream routers any farther away than the next hop. For each destination, an AODVv2 router MAY choose to keep track of the upstream neighbors that have provided traffic for that destination.
Moreover, any particular link to an adjacent AODVv2 router may be a path component of multiple routes towards various destinations. The precursors for all destinations using the next hop across any link are collectively known as the precursors for that next hop.
When an AODVv2 router marks a route as Invalid, the precursors of the Invalid route should be notified (using RERR) about the change in status of their route to the destination of that Invalid route.
During normal operation, each AODVv2 router wishing to maintain precursor lists as described above, maintains a precursor table and updates the table whenever the node forwards traffic to one of the destinations in its route table. For each precursor in the precursor list, a record must be maintained to indicate whether the precursor has been used for recent traffic (in other words, whether the precursor is an Active precursor). So, when traffic arrives from a precursor, the Current_Time is used to mark the time of last use for the precursor list element associated with that precursor.
When an AODVv2 router detects that a link is broken, then for each Active precursor using that next hop, the node MAY notify the precursor using either unicast or multicast RERR:
Each neighbor receiving the RERR MAY then execute the same procedure until all upstream routers have received the RERR notification.
The RREQ Target Router (RREP_Gen) MAY, as an alternative to unicasting a RREP, be configured to use multicast to distribute routing information about the route toward TargAddr. RREP_Gen does this as described in Section 9.2.1, but multicasting the RREP to LL-MANET-Routers [RFC5498]. Routers receiving the multicast RREP must perform RteMsg suppression (see Section 8.6).
Broadcast RREP response to incoming RREQ was originally specified to handle unidirectional links, but it is expensive. Due to the significant overhead, AODVv2 routers MUST NOT use multicast RREP unless configured to do so by setting the administrative parameter USE_MULTICAST_RREP. This technique can be used to find the best return path rather than follow the same path as the RREQ took.
This specification has been published as a separate Internet Draft [I-D.perkins-irrep].
The aggregation of multiple messages into a packet is specified in RFC 5444 [RFC5444].
Implementations MAY choose to briefly delay transmission of messages for the purpose of aggregation (into a single packet) or to improve performance by using jitter [RFC5148].
AODVv2 uses various configurable parameters of various types:
The tables in the following sections show the parameters along their definitions and default values (if any).
Note: several fields have limited size (bits or bytes). These sizes and their encoding may place specific limitations on the values that can be set. For example, <msg-hop-count> is a 8-bit field and therefore MAX_HOPCOUNT cannot be larger than 255.
AODVv2 requires certain timing information to be associated with route table entries. The default values are as follows:
| Name | Default Value |
|---|---|
| ACTIVE_INTERVAL | 5 second |
| MAX_IDLETIME | 200 seconds |
| MAX_BLACKLIST_TIME | 200 seconds |
| MAX_SEQNUM_LIFETIME | 300 seconds |
| RteMsg_ENTRY_TIME | 12 seconds |
| RREQ_WAIT_TIME | 2 seconds |
| RREP_Ack_SENT_TIMEOUT | 1 second |
| RREQ_HOLDDOWN_TIME | 10 seconds |
The above timing parameter values have worked well for small and medium well-connected networks with moderate topology changes. The timing parameters SHOULD be administratively configurable for the network where AODVv2 is used. Ideally, for networks with frequent topology changes the AODVv2 parameters should be adjusted using either experimentally determined values or dynamic adaptation. For example, in networks with infrequent topology changes MAX_IDLETIME may be set to a much larger value.
AODVv2 protocol constants typically do not require changes. The following table lists these constants, along with their values and a reference to the specification describing their use.
| Name | Default Value | Description |
|---|---|---|
| DISCOVERY_ATTEMPTS_MAX | 3 | Section 8.5 |
| MAX_HOPCOUNT | 20 hops | Section 7 |
| MAX_METRIC[i] | Specified only for HopCount | Section 7 |
| MAXTIME | [TBD] | Maximum expressible clock time Section 8.4 |
These values MUST have the same values for all AODVv2 routers in the ad hoc network. If the configured values are different, the following consequences may be observed:
The following administrative controls may be used to change the operation of the network, by enabling optional behaviors. These options are not required for correct routing behavior, although they may potentially reduce AODVv2 protocol messaging in certain situations. The default behavior is typically to NOT enable the options. Inconsistent settings at different nodes in the network will not result in protocol errors. In the case of inconsistent settings for DEFAULT_METRIC_TYPE, inconsistent setting might result in messages specifying metric types unknown to some nodes and consequent poor performance.
| Name | Description |
|---|---|
| DEFAULT_METRIC_TYPE | 3 (i.e, Hop Count (see [RFC6551])) |
| ENABLE_IDLE_IN_RERR | Section 9.3.1 |
| ENABLE_IRREP | Section 9.1.1 |
| USE_MULTICAST_RREP | Section 12.3 |
The following table lists contains AODVv2 parameters which should be administratively configured for each node.
| Name | Default Value | Cross Reference |
|---|---|---|
| AODVv2_INTERFACES | Section 4 | |
| BUFFER_SIZE_PACKETS | 2 | Section 8.5 |
| BUFFER_SIZE_BYTES | MAX_PACKET_SIZE [TBD] | Section 8.5 |
| CLIENT_ADDRESSES | AODVv2_INTERFACES | Section 6.3 |
| CONTROL_TRAFFIC_LIMIT | TBD [50 packets/sec?] | Section 9 |
This section specifies several RFC 5444 message types, message tlv-types, and address tlv-types. Also, a new registry of 16-bit alternate metric types is specified.
| Name of AODVv2 Message | Type |
|---|---|
| Route Request (RREQ) | 10 (TBD) |
| Route Reply (RREP) | 11 (TBD) |
| Route Error (RERR) | 12 (TBD) |
| Route Reply Acknowledgement (RREP_Ack) | 13 (TBD) |
| Name of Message TLV | Type | Length (octets) | Cross Reference |
|---|---|---|---|
| AckReq (Acknowledgment Request) | 10 (TBD) | 0 | Section 6.2 |
| PktSource (Packet Source) | 11 (TBD) | 4 or 16 | Section 9.3.1 |
| Name of Address Block TLV | Type | Length | Value |
|---|---|---|---|
| Metric | 10 (TBD) | depends on MetricType | Section 9.1 |
| Sequence Number (SeqNum) | 11 (TBD) | 2 octets | Section 9.1 |
| Originating Node Sequence Number (OrigSeqNum) | 12 (TBD) | 2 octets | Section 9.1 |
| Target Node Sequence Number (TargSeqNum) | 13 (TBD) | 2 octets | Section 9.1 |
| VALIDITY_TIME | 1 | 1 octet | [RFC5497] |
Metric types are identified according to the assignments as specified in [RFC6551]. The metric type of the Hop Count metric is assigned to be 3, in order to maintain compatibility with that existing table of values from RFC 6551.
| Name of MetricType | Type | Metric Size |
|---|---|---|
| Unallocated | 0 -- 2 | TBD |
| Hop Count | 3 - TBD | 1 octet |
| Unallocated | 4 -- 254 | TBD |
| Reserved | 255 | Undefined |
The objective of the AODVv2 protocol is for each router to communicate reachability information about addresses for which it is responsible. Positive routing information (i.e. a route exists) is distributed via RREQ and RREP messages. Negative routing information (i.e. a route does not exist) is distributed via RERRs. AODVv2 routers store the information contained in these messages in order to properly forward data packets, and they generally provide this information to other AODVv2 routers.
This section describes various security considerations and potential avenues to secure AODVv2 routing. Security for authentication of AODVv2 routers, and/or encryption of traffic is dealt with by the underlying transport mechanism (e.g., by using the techniques for Authentication, Integrity, and Confidentiality documented in [RFC5444]). The most important security mechanism for AODVv2 routing is integrity/authentication.
In situations where routing information are suspect, integrity and authentication techniques SHOULD be applied to AODVv2 messages. In these situations, routing information that is distributed over multiple hops SHOULD also verify the integrity of information based on originator of the routing information.
In situations where confidentiality of AODVv2 messages is important, cryptographic techniques can be applied.
In certain situations, for example sending a RREP or RERR, an AODVv2 router could include proof that it has previously received valid routing information to reach the destination, at one point of time in the past. In situations where routers are suspected of transmitting maliciously erroneous information, the original routing information along with its security credentials SHOULD be included.
Note that if multicast is used, any confidentiality and integrity algorithms used MUST permit multiple receivers to handle the message [RFC7182].
Routing protocols, however, are prime targets for impersonation attacks. In networks where the node membership is not known, it is difficult to determine the occurrence of impersonation attacks, and security prevention techniques are difficult at best. However, when the network membership is known and there is a danger of such attacks, AODVv2 messages must be protected by the use of authentication techniques, such as those involving generation of unforgeable and cryptographically strong message digests or digital signatures.
Most AODVv2 messages are transmitted to the multicast address LL-MANET-Routers [RFC5498]. It is therefore required for security that AODVv2 neighbors exchange security information that can be used to insert an ICV [RFC7182] into the AODVv2 message block [RFC5444]. This enables hop-by-hop security. For destination-only RREP discovery procedures, AODVv2 routers that share a security association SHOULD use the appropriate mechanisms as specified in [RFC7182]. The establishment of these security associations is out of scope for this document.
AODVv2 is a descendant of the design of previous MANET on-demand protocols, especially AODV [RFC3561] and DSR [RFC4728]. Changes to previous MANET on-demand protocols stem from research and implementation experiences. Thanks to Elizabeth Belding and Ian Chakeres for their long time authorship of AODV. Additional thanks to Derek Atkins, Emmanuel Baccelli, Abdussalam Baryun, Ramon Caceres, Thomas Clausen, Christopher Dearlove, Ulrich Herberg, Henner Jakob, Luke Klein-Berndt, Lars Kristensen, Tronje Krop, Koojana Kuladinithi, Kedar Namjoshi, Alexandru Petrescu, Henning Rogge, Fransisco Ros, Pedro Ruiz, Christoph Sommer, Lotte Steenbrink, Romain Thouvenin, Richard Trefler, Jiazi Yi, Seung Yi, and Cong Yuan, for their reviews AODVv2 and DYMO, as well as numerous specification suggestions.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC4291] | Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. |
| [RFC5082] | Gill, V., Heasley, J., Meyer, D., Savola, P. and C. Pignataro, "The Generalized TTL Security Mechanism (GTSM)", RFC 5082, October 2007. |
| [RFC5444] | Clausen, T., Dearlove, C., Dean, J. and C. Adjih, "Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format", RFC 5444, February 2009. |
| [RFC5497] | Clausen, T. and C. Dearlove, "Representing Multi-Value Time in Mobile Ad Hoc Networks (MANETs)", RFC 5497, March 2009. |
| [RFC5498] | Chakeres, I., "IANA Allocations for Mobile Ad Hoc Network (MANET) Protocols", RFC 5498, March 2009. |
| [RFC6551] | Vasseur, JP., Kim, M., Pister, K., Dejean, N. and D. Barthel, "Routing Metrics Used for Path Calculation in Low-Power and Lossy Networks", RFC 6551, March 2012. |
The following subsections show example algorithms for protocol operations required by AODVv2, including RREQ, RREP, RERR, and RREP_Ack.
Processing for RREQ, RREP, and RERR messages follows the following general outline:
Once the route table has been updated, the information contained there is known to be the most recent available information for any fields in the outgoing message. For this reason, the algorithms are written as if outgoing message field values are assigned from the route table information, even though it is often equally appropriate to use fields from the incoming message.
AODVv2_algorithms:
The following lists indicate the meaning of the field names used in subsequent sections to describe message processing for the above algorithms.
RteMsg parameters, where rteMsg can be inRREQ, outRREQ, inRREP or outRREP:
AdvRte has the following properties as described in Section 8.1:
A route table entry has properties as described in Section 6.1:
/* Compare incoming route information to stored route, maybe use
linkMetric: either Cost(inRREQ.netif) or (inRREP.netif) */
Process_Routing_Info (advRte)
{
rte := Fetch_Route_Table_Entry (advRte);
if (!rte exists)
{
rte := Create_Route_Table_Entry(advRte);
return rte;
}
/* rule from 8.1 */
if (
(AdvRte.SeqNum > Route.SeqNum) /* stored route is stale */
OR
((AdvRte.SeqNum == Route.SeqNum) /* same SeqNum */
AND
[( (Route.State == Invalid)
AND
(LoopFree(advRte, rte))) /* advRte can repair stored */
OR
(AdvRte.Cost < Route.Metric)])) /* advRte is better */
{
Update_Route_Table_Entry (rte, advRte);
}
return rte;
}
/* lookup a route table entry matching an advertised route */
Fetch_Route_Table_Entry (advRte)
{
foreach (rteTableEntry in rteTable)
{
if (rteTableEntry.Address == advRte.Address AND
rteTableEntry.MetricType == advRte.MetricType)
return rteTableEntry;
}
return null;
}
/* lookup a route table entry matching address and metric type */
Fetch_Route_Table_Entry (destination, metricType)
{
foreach (rteTableEntry in rteTable)
{
if (rteTableEntry.Address == destination AND
rteTableEntry.MetricType == metricType)
return rteTableEntry;
}
return null;
}
/* update a route table entry using AdvRte in received RteMsg */
Update_Route_Table_Entry (rte, advRte);
{
rte.SeqNum := advRte.SeqNum;
rte.NextHop := advRte.NextHopIp;
rte.NextHopInterface := advRte.NextHopIntf;
rte.LastUsed := Current_Time;
rte.LastSeqNum := Current_Time;
if (validityTime)
{
rte.ExpirationTime := Current_Time + advRte.validityTime;
rte.Timed := true;
}
else
{
rte.Timed := false;
rte.ExpirationTime := MAXTIME;
}
rte.Metric := advRte.Cost;
if (rte.State == Invalid)
rte.State := Idle;
}
/* Create a route table entry from address and prefix length */
Create_Route_Table_Entry (address, prefixLength,
seqNum, metricType)
{
rte := allocate_memory();
rte.Address := address;
rte.PrefixLength := prefixLength;
rte.SeqNum := seqNum;
rte.MetricType := metricType;
}
/* Create a route table entry from the advertised route */
Create_Route_Table_Entry(advRte)
{
rte := allocate_memory();
rte.Address := advRte.Address;
if (advRte.PrefixLength)
rte.PrefixLength := advRte.PrefixLength;
else
rte.PrefixLength := maxPrefixLenForAddressFamily;
rte.SeqNum := advRte.SeqNum;
rte.NextHop := advRte.NextHopIp;
rte.NextHopInterface := advRte.NextHopIntf;
rte.LastUsed := Current_Time
rte.LastSeqnum := Current_Time
if (validityTime)
{
rte.ExpirationTime := Current_Time + advRte.ValidityTime;
rte.Timed := true;
}
else
{
rte.Timed := false;
rte.ExpirationTime := MAXTIME;
}
rte.MetricType := advRte.MetricType;
rte.Metric := advRte.Metric;
rte.State := Idle;
}
/* return TRUE if the route advRte is LoopFree compared to rte */
LoopFree(advRte, rte)
{
if (advRte.Cost ≤ rte.Cost)
return true;
else
return false;
}
/* Find an entry in the RteMsg table matching the given
message's msg-type, OrigAddr, TargAddr, MetricType */
Fetch_Rte_Msg_Table_Entry (rteMsg)
{
foreach (entry in RteMsgTable)
{
if (entry.msg-type == rteMsg.msg-type AND
entry.OrigAddr == rteMsg.OrigAddr AND
entry.TargAddr == rteMsg.TargAddr AND
entry.MetricType == rteMsg.MetricType)
{
return entry;
}
}
return NULL;
}
/* update the multicast route message suppression table based
on the received RteMsg, return true if it was created or
the SeqNum was updated (i.e. it needs to be regenerated) */
Update_Rte_Msg_Table(rteMsg)
{
/* search for a comparable entry */
entry := Fetch_Rte_Msg_Table_Entry(rteMsg)
/* if there is none, create one (see 6.5 and 8.6) */
if (entry does not exist)
{
entry.MessageType := rteMsg.msg_type
entry.OrigAddr := rteMsg.OrigAddr
entry.TargAddr := rteMsg.TargAddr
entry.OrigSeqNum := rteMsg.origSeqNum (if present)
entry.TargSeqNum := rteMsg.targSeqNum (if present)
entry.MetricType := rteMsg.MetricType
entry.Metric := rteMsg.origAddrMetric(for RREQ)
or rteMsg.targAddrMetric(for RREP)
entry.Timestamp := Current_Time
return true;
}
/* if current entry is stale */
if ( (rteMsg.msg-type == RREQ AND
entry.OrigSeqNum < rteMsg.OrigSeqNum)
OR
(rteMsg.msg-type == RREP AND
entry.TargSeqNum < rteMsg.TargSeqNum))
{
entry.OrigSeqNum := rteMsg.OrigSeqNum (if present)
entry.TargSeqNum := rteMsg.TargSeqNum (if present)
entry.Timestamp := Current_Time
return true;
}
/* if received rteMsg is stale */
if ( (rteMsg.msg-type == RREQ AND
entry.OrigSeqNum > rteMsg.OrigSeqNum)
OR
(rteMsg.msg-type == RREP AND
entry.TargSeqNum > rteMsg.TargSeqNum))
{
entry.Timestamp := Current_Time
return false;
}
/* if same SeqNum but rteMsg has lower metric */
if (entry.Metric > rteMsg.Metric)
entry.Metric := rteMsg.Metric
entry.Timestamp := Current_Time
return false;
}
/* This pseudocode shows possible RFC 5444 actions, and
would not be performed by the AODVv2 implementation.
It is shown only to provide more understanding about
the AODVv2 message that will be constructed by RFC 5444 */
Build_RFC_5444_message_header (msgType, Flags,
AddrFamily, Size, hopLimit, hopCount, tlvLength)
{
/* Build RFC 5444 message header fields */
msg-type := msgType
MF (Message Flags) := Flags
MAL (Message Address Length) := 3 for IPv4, 15 for IPv6
msg-size := Size (octets - counting MsgHdr, AddrBlk, AddrTLVs)
msg-hop-limit := hopLimit
if (hopCount != 0) /* hopCount == 0 means do not include */
msg-hop-count := hopCount
msg.tlvs-length := tlvLength
}
Generate_RREQ
{
/* Increment sequence number */
mySeqNum := (1 + mySeqNum) /* from nonvolatile storage */
/* Marshall parameters */
outRREQ.hopLimit := MAX_HOPCOUNT /* RFC 5444 */
outRREQ.hopCount := (if included) 0
outRREQ.metricType := if not DEFAULT_METRIC_TYPE,
metric type needed by application
outRREQ.origAddr := IP address of Router Client which generated
the packet to be forwarded
outRREQ.targAddr := destination IP address in
the packet to be forwarded
outRREQ.origPrefixLen := if included, the prefix length
associated with the Router Client
outRREQ.origSeqNum := mySeqNum
outRREQ.targSeqNum := if known from route table,
target sequence number
outRREQ.origAddrMetric := 0 (default) or
MIN_METRIC(outRREQ.metricType)
outRREQ.validityTime := if included, the validity time
for route to OrigAddr
/* Build Address Blk */
AddrBlk := outRREQ.origAddr and outRREQ.targAddr addresses
/* using prefix length information from
outRREQ.origPrefixLen if necessary */
/* Include each available Sequence Number in appropriate
Address Block TLV */
/* OrigSeqNum Address Block TLV */
origSeqNumAddrBlkTlv.value := outRREQ.origSeqNum
/* TargSeqNum Address Block TLV */
if (outRREQ.targSeqNum is known)
{
targSeqNumAddrBlkTlv.value := outRREQ.targSeqNum
}
/* Build Metric Address Block TLV */
metricAddrBlkTlv.value := outRREQ.origAddrMetric
if (outRREQ.metricType != DEFAULT_METRIC_TYPE)
{ /* include Metric AddrBlkTlv Extension byte */
metricAddrBlkTlv.typeExtension := outRREQ.MetricType
}
if (outRREQ.validityTime is required)
{
/* Build VALIDITY_TIME Address Block TLV */
VALIDITY_TIMEAddrBlkTlv.value := outRREQ.validityTime
}
/* multicast RFC 5444 message to LL-MANET-Routers */
}
Receive_RREQ (inRREQ)
{
if (inRREQ.nbrIP present in blacklist) {
if (blacklist_expiration_time < current_time)
return; /* don't process or regenerate RREQ... */
else
remove nbrIP from blacklist;
}
if (inRREQ does not contain msg_hop_limit, OrigAddr,
TargAddr, OrigSeqNum, OrigAddrMetric)
return;
if (inRREQ.origAddr and inRREQ.targAddr are not valid
routable and unicast addresses)
return;
if (inRREQ.metricType is present but an unknown value)
return;
if (inRREQ.origAddrMetric >
MAX_METRIC[inRREQ.metricType] - Cost(Link)
return;
/* Extract inRREQ values */
advRte.Address = inRREQ.origAddr
advRte.PrefixLength = inRREQ.origPrefixLen (if present),
or the maximum address length for the
address family of advRte.Address
advRte.SeqNum = inRREQ.origSeqNum
advRte.MetricType = inRREQ.metricType
advRte.Metric = inRREQ.origAddrMetric
advRte.Cost = inRREQ.origAddrMetric + Cost(L)
according to the indicated MetricType, where
L is the link from the advertising router
advRte.ValidityTime = inRREQ.validityTime (if present)
advRte.NextHopIP = inRREQ.nbrIP
advRte.NextHopIntf = interface the RteMsg was received on
advRte.HopCount = inRREQ.hopCount
advRte.HopLimit = inRREQ.hopLimit
rte = Process_Routing_Info (advRte)
/* update the RteMsgTableand determine if the RREQ needs
to be regenerated */
regenerate = Update_Rte_Msg_Table(inRREQ)
if (inRREQ.targAddr is in Router Client list)
Generate_RREP(inRREQ, rte)
else if (regenerate)
Regenerate_RREQ(inRREQ, rte)
}
Regenerate_RREQ (inRREQ, rte) /* called from receive_RREQ(),
rte is the route to OrigAddr */
{
outRREQ.hopLimit := inRREQ.hopLimit - 1
if (outRREQ.hopLimit == 0)
return; /* don't regenerate */
if (inRREQ.hopCount exists)
{
if (inRREQ.hopCount >= MAX_HOPCOUNT)
return; /* don't regenerate */
outRREQ.hopCount := inRREQ.hopCount + 1
}
/* Marshall parameters */
outRREQ.metricType := rte.MetricType
outRREQ.origAddr := rte.Address
outRREQ.targAddr := inRREQ.targAddr
outRREQ.origPrefixLen := rte.PrefixLength
(if not equal to address length)
outRREQ.origSeqNum := rte.SeqNum
outRREQ.targSeqNum := inRREQ.targSeqNum /* if present */
outRREQ.origAddrMetric := rte.Metric
outRREQ.validityTime := rte.ValidityTime or length of time
HandlingRtr wishes to advertise route to OrigAddr
/* Build Address Block */
AddrBlk := outRREQ.origAddr and outRREQ.targAddr addresses
using prefix length information from outRREQ.origPrefixLen
if necessary
/* Include available Sequence Numbers in Address Block TLV */
/* OrigSeqNum Address Block TLV */
origSeqNumAddrBlkTlv.value := outRREQ.origSeqNum
/* TargSeqNum Address Block TLV */
if (outRREQ.targSeqNum is known) {
targSeqNumAddrBlkTlv.value := outRREQ.targSeqNum
}
/* Build Metric Address Block TLV */
metricAddrBlkTlv.value = outRREQ.origAddrMetric
if (outRREQ.metricType != DEFAULT_METRIC_TYPE)
{ /* include Metric AddrBlkTlv extension byte */
metricAddrBlkTlv.typeExtension := outRREQ.MetricType
}
if (outRREQ.validityTime is required)
{
/* Build VALIDITY_TIME Address Block TLV */
VALIDITY_TIMEAddrBlkTlv.value = outRREQ.validityTime
}
Build_RFC_5444_message_header (RREQ, 4, IPv4 or IPv6, NN,
outRREQ.hopLimit, outRREQ.hopCount, tlvLength)
/* multicast RFC 5444 message to LL-MANET-Routers, or if
inRREQ was unicast the message can be unicast to the next
hop on the route to TargAddr, if known */
}
Generate_RREP(inRREQ, rte)
{
/* Increment Sequence Number */
mySeqNum := (1 + mySeqNum) /* from nonvolatile storage */
/* Marshall parameters */
outRREP.hopLimit := inRREQ.hopCount
outRREP.hopCount := 0
/* Include the AckReq when:
- previous RREP does not seem to enable any data flow, OR
- when RREQ is received from same OrigAddr after RREP was
unicast to rte.nextHop
*/
outRREP.ackReq := if included, TRUE otherwise FALSE
if (rte.metricType != DEFAULT_METRIC_TYPE)
outRREP.metricType := rte.metricType
outRREP.origAddr := rte.Address
outRREP.targAddr := inRREQ.targAddr
outRREP.targPrefixLen := rte.PrefixLength
(if not equal to address length)
outRREP.targSeqNum := mySeqNum
outRREP.targAddrMetric := 0 (default) or
MIN_METRIC(rte.metricType)
outRREP.validityTime := (if included) the validity time
for route to TargAddr
if (outRREP.ackReq == TRUE)
{
/* include AckReq Message TLV */
}
/* Build Address Block */
AddrBlk := outRREP.origAddr and outRREP.targAddr addresses
using prefix length information from outRREP.targPrefixLen
if necessary
/* TargSeqNum Address Block TLV */
targSeqNumAddrBlkTlv.value := outRREP.targSeqNum
/* Build Metric Address Block TLV containing TargAddr metric */
metricAddrBlkTlv.value := outRREP.targAddrMetric
if (outRREP.metricType != DEFAULT_METRIC_TYPE)
{ /* include Metric AddrBlkTlv extension byte */
metricAddrBlkTlv.typeExtension := outRREP.MetricType
}
if (outRREP.validityTime is required)
{
/* Build VALIDITY_TIME Address Block TLV */
VALIDITY_TIMEAddrBlkTlv.value = outRREP.validityTime
}
Build_RFC_5444_message_header (RREP, 4, IPv4 or IPv6, NN,
outRREP.hopLimit, outRREQ.hopCount, tlvLength)
/* unicast RFC 5444 message to rte[OrigAddr].NextHop */
}
Receive_RREP (inRREP)
{
if (inRREP.nbrIP present in blacklist) {
if (blacklist_expiration_time < current_time)
return; /* don't process or regenerate RREQ... */
else
remove nbrIP from blacklist;
}
if (inRREP does not contain msg_hop_limit, OrigAddr,
TargAddr, TargSeqNum, TargAddrMetric)
return;
if (inRREP.origAddr and inRREQ.targAddr are not
valid routable and unicast addresses)
return;
if (inRREP.metricType is present but an unknown value)
return;
if (inRREP.targAddrMetric >
MAX_METRIC[MetricType] - Cost(Link)
return;
/* Extract inRREP values */
advRte.Address := inRREP.targAddr
advRte.PrefixLength := inRREP.targPrefixLen f present), or the
maximum address length for address family of advRte.Address
advRte.SeqNum := inRREP.targSeqNum
advRte.MetricType := inRREP.metricType
advRte.Metric := inRREP.targAddrMetric
advRte.Cost := inRREP.targAddrMetric + Cost(L) according to
inRREP's MetricType. L is the link from the advertising router
advRte.ValidityTime := inRREP.validityTime (if present)
advRte.NextHopIP := inRREP.nbrIP
advRte.NextHopIntf := interface the RteMsg was received on
advRte.HopCount := inRREP.hopCount
advRte.HopLimit := inRREP.hopLimit (if included)
rte := Process_Routing_Info (advRte)
if (inRREP includes AckReq data element)
Generate_RREP_Ack(inRREP)
/* update the RteMsgTable and determine if the RREP needs
to be regenerated */
regenerate := Update_Rte_Msg_Table(inRREP)
if (inRREP.targAddr is in the Router Client list)
send_buffered_packets(rte) /* start to use the route */
else if (regenerate)
Regenerate_RREP(inRREP, rte)
}
Regenerate_RREP(inRREP, rte)
{
if (rte does not exist)
{
Generate_RERR(inRREP)
return;
}
outRREP.hopLimit := inRREP.hopLimit - 1
if (outRREP.hopLimit == 0) /* don't regenerate */
return;
if (inRREP.hopCount exists)
{
if (inRREP.hopCount >= MAX_HOPCOUNT)
return; /* don't regenerate */
outRREP.hopCount := inRREP.hopCount + 1
}
/* Marshall parameters */
/* Include the AckReq when:
- previous unicast RREP seems not to enable data flow, OR
- when RREQ is received from same OrigAddr after RREP
was unicast to rte.nextHop
*/
outRREP.ackReq := true or false whether to include
/* if included, set timeout RREP_Ack_SENT_TIMEOUT */
if (rte.metricType != DEFAULT_METRIC_TYPE)
outRREP.metricType := rte.metricType
outRREP.origAddr := inRREP.origAddr
outRREP.targAddr := rte.Address
outRREP.targPrefixLen := rte.PrefixLength
(if not equal to address length)
outRREP.targSeqNum := rte.SeqNum
outRREP.targAddrMetric := rte.Metric
outRREP.validityTime := (if included) the validity time
for route to TargAddr
outRREP.nextHop := rte.nextHop
if (outRREP.ackReq == TRUE)
{
/* include AckReq Message TLV */
/* set timeout RREP_Ack_SENT_TIMEOUT */
}
/* Build Address Block */
AddrBlk := {outRREP.origAddr and outRREP.targAddr}
using prefix length information from
outRREP.targPrefixLen if necessary
/* TargSeqNum Address Block TLV */
targSeqNumAddrBlkTlv.value := outRREP.targSeqNum
/* Build Metric Address Block TLV containing TargAddrMetric*/
metricAddrBlkTlv.value := outRREP.targAddrMetric
if (outRREP.metricType != DEFAULT_METRIC_TYPE)
{ /* include Metric AddrBlkTlv extension byte */
metricAddrBlkTlv.typeExtension := outRREP.MetricType
}
if (outRREP.validityTime is required)
{
/* Build VALIDITY_TIME Address Block TLV */
VALIDITY_TIMEAddrBlkTlv.value := outRREP.validityTime
}
Build_RFC_5444_message_header (RREP, 4, IPv4 or IPv6, NN,
outRREP.hopLimit, 0, tlvLength)
/* unicast RFC 5444 message to rte[OrigAddr].NextHop */
}
RERR message parameters, where RERR can be inRERR or outRERR:
Generate_RERR(errorType, triggerPkt, brokenLinkNbrIp)
/* errorType is either undeliverablePacket or brokenLink */
{
switch (errorType)
{
case (brokenLink):
/* a RERR will be required for each MetricType */
foreach metric type in use
{
doGenerate := FALSE
num-broken-addr := 0
precursors[] := new empty precursor list
outRERR.hopLimit := MAX_HOPCOUNT
outRERR.metricType := the metric type for this loop
/* find routes which are now Invalid */
foreach (rte in route table)
{
if (brokenLinkNbrIp == rte.nextHop AND
rte.MetricType == outRERR.metricType AND
(rte.State == Active OR
(rte.State == Idle AND ENABLE_IDLE_IN_RERR)))
{
if (rte.State == Active)
{
doGenerate := TRUE
}
rte.State := Invalid
precursors += rte.Precursors (if any)
outRERR.unreachableAddressList[num-broken-addr] :=
rte.Address
outRERR.prefixLengthList[num-broken-addr] :=
rte.PrefixLength
outRERR.seqNumList[num-broken-addr] := rte.SeqNum
num-broken-addr := num-broken-addr + 1
}
}
if (doGenerate == TRUE)
{ /* build and send RFC5444 message as below, then
repeat loop for other MetricTypes */ }
}
case (undeliverablePacket):
num-broken-addr := 1
outRERR.hopLimit := MAX_HOPCOUNT
outRERR.pktSource := triggerPkt.srcIP or
triggerPkt.targAddr if packet was a RREP
/* optional to include outRERR.metricType */
outRERR.unreachableAddressList[0] := triggerPkt.destIP or
triggerPkt.origAddr if packet was a RREP
}
if (triggerPkt exists)
{ /* Build PktSource Message TLV */
pktSourceMessageTlv.value := outRERR.pktSource
}
/* The remaining steps add address, prefix length
and sequence number information for each
UnreachableAddress, while conforming to the allowed MTU.
If the MTU is reached, a new message MUST be created. */
/* Build Address Block */
AddrBlk := outRERR.unreachableAddressList[]
using prefix length information from
outRERR.prefixLengthList[] if necessary
/* Add SeqNum Address Block TLV including index values */
seqNumAddrBlkTLV := outRERR.seqNumList[]
if (outRERR.metricType != DEFAULT_METRIC_TYPE)
{ /* include Metric AddrBlkTlv extension byte */
metricAddrBlkTlv.typeExtension := outRERR.MetricType
}
Build_RFC_5444_message_header (RERR, 4, IPv4 or IPv6, NN,
outRERR.hopLimit, 0, tlvLength)
if (undeliverablePacket)
/* unicast outRERR to rte[outRERR.pktSource].NextHop */
else if (brokenLink)
/* unicast to precursors, or multicast to LL-MANET-Routers */
}
There are two parts to this function, based on whether it was triggered by an undeliverable packet or a broken link to neighboring AODVv2 router.
Receive_RERR (inRERR)
{
if (inRERR does not contain msg_hop_limit and at least
one UnreachableAddress)
return;
if (inRERR.metricType is present but an unknown value)
return;
/* Extract inRERR values, copy relevant UnreachableAddresses,
their prefix lengths, and sequence numbers to outRERR */
num-broken-addr := 0;
precursors[] := new empty list of type precursors/;
foreach (unreachableAddress in inRERR.unreachableAddressList)
{
if (unreachableAddress is not valid routable
and unicast address)
continue;
/* find a matching route table entry, assume
DEFAULT_METRIC_TYPE if no MetricType included */
rte := Fetch_Route_Table_Entry (unreachableAddress,
inRERR.metricType)
if (rte does not exist)
continue;
if (rte.State == Invalid)/* ignore already invalid routes */
continue;
if (rte.NextHop != inRERR.nbrIP OR
rte.NextHopInterface != inRERR.intf)
continue;
if (unreachableAddress SeqNum (if known) < rte.SeqNum)
continue;
/* keep a note of all precursors of newly Invalid routes */
precursors += rte.Precursors (if any)
/* assume prefix length is address length if not included*/
if (rte.PrefixLength != unreachableAddress prefixLength)
{
/* create new route with unreachableAddress information */
invalidRte := Create_Route_Table_Entry(unreachableAddress,
unreachableAddress prefixLength,
unreachableAddress seqNum, inRERR.metricType)
invalidRte.State := Invalid
if (rte.PrefixLength > unreachableAddress prefixLength)
expunge_route(rte);
rte := invalidRte;
}
else if (rte.PrefixLength == unreachableAddress prefixLength)
rte.State := Invalid;
outRERR.unreachableAddressList[num-broken-addr] :=rte.Address
outRERR.prefixLengthList[num-broken-addr] := rte.PrefixLength
outRERR.seqNumList[num-broken-addr] := rte.SeqNum
num-broken-addr := num-broken-addr + 1
}
if (num-broken-addr)
Regenerate_RERR(outRERR, inRERR, precursors)
}
Regenerate_RERR (outRERR, inRERR, precursors)
{
/* Marshal parameters */
outRERR.hopLimit := inRERR.hopLimit - 1
if (outRERR.hopLimit == 0) /* don't regenerate */
return;
outRERR.pktSource := inRERR.pktSource (if included)
outRERR.metricType := inRERR.MetricType (if included)
or DEFAULT_METRIC_TYPE
/* UnreachableAddressList[], SeqNumList[], and
PrefixLengthList[] are already up-to-date */
if (outRERR.pktSource exists)
{
/* Build PktSource Message TLV */
pktSourceMessageTlv.value := outRERR.pktSource
}
if (outRERR.metricType != DEFAULT_METRIC_TYPE)
{
/* Build MetricType Message TLV */
metricMsgTlv.value := outRERR.metricType
}
/* Build Address Block */
AddrBlk := outRERR.unreachableAddressList[] using prefix length
information from outRERR.prefixLengthList[] if necessary
/* Add SeqNum AddressBlock TLV including index values */
seqNumAddrTLV := outRERR.seqNumList[]
Build_RFC_5444_message_header (RERR, 4, IPv4 or IPv6, NN,
outRERR.hopLimit, 0, tlvLength)
if (outRERR.pktSource exists) {
/* unicast RFC 5444 message to outRERR.pktSource */
} else if (number of precursors == 1) {
/* unicast RFC 5444 message to precursors[0] */
} else if (number of precursors > 1) {
/* unicast RFC 5444 message to all precursors, or multicast
RFC 5444 message to RERR_PRECURSORS if preferable */
} else {
/* multicast RFC 5444 message to LL-MANET-Routers */
}
}
/* To be sent when RREP includes the AckReq data element */
Generate_RREP_Ack(inRREP)
{
Build_RFC_5444_message_header (RREP_Ack, 4, IPv4 or IPv6, NN,
1, 0, 0)
/* unicast RFC 5444 message to inRREP.nbrIP */
}
Receive_RREP_Ack(inRREP_Ack)
{
/* cancel timeout event for the node sending RREP_Ack */
}
Timeout_RREP_Ack(outRREP)
{
/* insert unresponsive node into blacklist */
}
This section lists the changes since AODVv2 revision ...-06.txt
This section lists the changes between AODVv2 revisions ...-05.txt and ...-06.txt.
This section lists the changes between AODVv2 revisions ...-04.txt and ...-05.txt.
This section lists the changes between AODVv2 revisions ...-03.txt and ...-04.txt.
This section lists the changes between AODVv2 revisions ...-02.txt and ...-03.txt.
AODVv2 needs the following:
A reactive protocol reacts when a route is needed. One might say that a route is requested when an application tries to send a packet. The fundamental concept of reactive routing is to avoid creating routes that are not needed, and the way that has been used to know whether a route is needed is when an application tries to send a packet.
If an application tries to send a packet, and the route is not available, the packet has to wait until the route is available.
This non-normative information is provided simply to document the results of previous efforts to enable multi-homing. The intention is to simplify the task of future specification if multihoming becomes needed for reactive protocol operation.
Multi-homing is not supported by the AODVv2 specification. There has been previous work indicating that it can be supported by expanding the sequence number to include the AODVv2 router's IP address as a parsable field of the SeqNum. Otherwise, comparing sequence numbers would not work to evaluate freshness. Even when the IP address is included, there isn't a good way to compare sequence numbers from different IP addresses, but at least a handling node can determine whether the two given sequence numbers are comparable. If the route table can store multiple routes for the same destination, then multi-homing can work with sequence numbers augmented by IP addresses.
This non-normative information is provided simply to document the results of previous efforts to enable multi-homing. The intention is to simplify the task of future specification if multihoming becomes needed for reactive protocol operation.
Only one AODVv2 router within a MANET SHOULD be responsible for a particular address at any time. If two AODVv2 routers dynamically shift the advertisement of a network prefix, correct AODVv2 routing behavior must be observed. The AODVv2 router adding the new network prefix must wait for any existing routing information about this network prefix to be purged from the network. Therefore, it must wait at least ROUTER_SEQNUM_AGE_MAX_TIMEOUT after the previous AODVv2 router for this address stopped advertising routing information on its behalf.