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This document describes a Home Agent assisted Route Optimization functionality to IPv4 Network Mobility Protocol. The function is designed to facilitate optimal routing in cases where all nodes are connected to a single Home Agent, thus the use case is Route Optimization within single organization or similar entity. The functionality adds possibility to discover eligible peer nodes based on information received from Home Agent, Network Prefixes they represent, and how to establish direct tunnel between such nodes.
Introduction and motivations
2. Terms and definitions
3. Mobile IPv4 route optimization between mobile networks
3.1. Maintaining route optimization information
3.1.1. Advertising route-optimizable prefixes
3.1.2. Route Optimization cache
3.2. Return routability procedure
3.2.1. Router keys
3.3. Mobile-Correspondent Router operations
3.3.1. Triggering Route Optimization
3.3.2. Mobile Router routing tables
3.3.3. Inter-Mobile Router registration
3.3.4. Inter-Mobile Router tunnels
3.3.5. Constructing route-optimized packets
3.3.6. Handovers and Mobile Routers leaving network
3.4. Convergence and synchronization issues
4. Data compression schemes
4.1. Prefix compression
4.2. Realm compression
4.2.1. Encoding of compressed realms
4.2.2. Searching algorithm
4.2.3. Encoding example
5. New Mobile IPv4 messages and extensions
5.1. Mobile router Route optimization capability
5.2. Route optimization reply
5.3. Route optimization prefix advertisement
5.4. Mobile-Correspondent authentication extension
5.5. Home-Test Init message
5.6. Care-of-Test Init message
5.7. Home Test message
5.8. Care-of test message
5.9. Care-of address Extension
6. Special Considerations
6.1. NATs and stateful firewalls
6.2. Foreign Agents
6.3. Multiple Home Agents
6.4. Mutualness of Route Optimization
6.6. Load Balancing
8. Example signaling scenarios
8.1. Registration request
8.2. Route optimization with return routability
9. IANA Considerations
10. Security Considerations
10.1. Trust relationships
12.1. Normative References
12.2. Informative References
§ Authors' Addresses
Traditionally, there has been no method for route optimization in Mobile IPv4 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] apart from an early attempt [I‑D.ietf‑mobileip‑optim] (Perkins, C. and D. Johnson, “Route Optimization in Mobile IP,” September 2001.). Unlike Mobile IPv6 (Johnson, D., Perkins, C., and J. Arkko, “Mobility Support in IPv6,” June 2004.) [RFC3775], where Route Optimization has been included from the start, with Mobile IPv4 route optimization hasn't been addressed in a generalized scope.
Even though general route optimization may not be of interest in the scope of IPv4, there are still specific applications for Route Optimization in Mobile IPv4. This draft proposes method to optimize routes between networks behind mobile routers, as defined by NEMO (Leung, K., Dommety, G., Narayanan, V., and A. Petrescu, “Network Mobility (NEMO) Extensions for Mobile IPv4,” April 2008.) [RFC5177].
A particular use case concerns setting up redundant yet economical enterprise networks. Recently, a trend has emerged where customers prefer to maintain connectivity via multiple service providers. Reasons include redundancy, reliability and availability issues. These kinds of multi-homing scenarios have traditionally been solved by using such technologies as multihoming BGP. However, a more lightweight and economical solution is desirable.
From service provider perspective a common topology for enterprise customer network consists of one to several sites (typically headquarters and various branch offices). These sites are typically connected via various Layer 2 technologies (ATM or Frame relay PVCs), MPLS VPNs or Layer 3 site-to-site VPNs. With a Service Level Agreement, a customer can obtain a very reliable and well supported intranet connectivity. However, compared to the cost of "consumer-grade" broadband Internet access the SLA-guaranteed version can be considered very expensive. These consumer-grade options however, are not reliable approach for mission-critical applications.
Mobile IP, especially mobile routers, can be used to improve reliability of connectivity even when implemented over consumer-grade Internet access. The customer becomes a client for a virtual service provider, which does not take part in the actual access technology. The service provider has a backend system and an IP address pool that it distributes to customers. Access is provided by multiple, independent, possibly consumer-grade ISPs, with Mobile IP providing seamless handovers if service from a specific ISP fails. The drawback of this solution is that it creates a star topology; All Mobile IP tunnels end up at the service provider hosted home agent, causing heavy load at the backend. Route Optimization between mobile networks addresses this issue, by taking network load off the home agent and the backend.
An example network is pictured below:
+----------------------------+ | Virtual Operator Backend | +------------+ +-----+ | Home Agent | | AAA | +------------+---------+-----+ | .--. _(. `) _( ISP `)_ ( Peering `) ( ` . Point ) ) `--(_______)--' ____ / | \ / | \ .--. .--. .--. _( `. _( `. _( `. ( ISP A ) ( ISP B ) ( ISP C ) ( ` . ) ) ( ` . ) ) ( ` . ) ) `--(___.-' `--(___.-' `--(___.-' | ______/ \ / | / \ / | / \ / +----+ +----+ |MR A| |MR B| +----+ +----+ | | .--. .--. _( `. _( `. ( Site A ) ( Site B ) ( ` . ) ) ( ` . ) ) `--(___.-' `--(___.-'
| Virtual service provider architecture using NEMOv4 |
In this example case, organization network consists of two sites, that are connected via 2 ISPs for redundancy reasons. Mobile IP allows fast handovers without problems of multi-homing and BGP peering between each individual ISP and the organization. The traffic however takes a non-optimal route through the virtual operator backend.
Route optimization addresses this issue, allowing traffic between Sites A and B to flow through ISP B's network, or in case of a link failure, via the ISP peering point (such as MAE-WEST). The backend will not suffer from heavy loads.
The primary design goal is to limit the load to the backend to minimum. Additional design goals include extensibility to a more generalized scope, beyond the need of a single, coordinating Home Agent.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].
- Care-of Address (CoA)
RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] defines Care-of Address as the termination point of a tunnel toward a mobile node, for datagrams forwarded to the mobile node while it is away from home. The protocol can use two different types of care-of address: a "foreign agent care-of address" which is an address of a foreign agent with which the mobile node is registered, and a "co-located care-of address", which is an externally obtained local address which the mobile node has associated with one of its own network interfaces. However, in the case of Network Mobility, foreign agents are not used, so no foreign care-of addresses are used either.
- Correspondent Router (CR)
RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] defines a Correspondent node as a peer with which a mobile node is communicating. Correspondent Router is a peer Mobile Router which MAY also represent one or more entire networks.
- Home Address (HoA)
RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] defines Home Address as an IP address that is assigned for an extended period of time to a mobile node. It remains unchanged regardless of where the node is attached to the Internet.
- Home Agent (HA)
RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] defines Home Agent as a router on a mobile node's home network which tunnels datagrams for delivery to the mobile node when it is away from home, and maintains current location information for the mobile node. For this application, the "home network" sees limited usage.
- Host Network Prefix
Network Prefix with the mask of /32. e.g. 192.0.2.254/32, consisting of a single host.
- Mobility Binding
RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344] defines Mobility Binding as the association of Home Address with a Care-of address, along with the lifetime remaining for that association.
- Mobile Network Prefix
- RFC 5177 (Leung, K., Dommety, G., Narayanan, V., and A. Petrescu, “Network Mobility (NEMO) Extensions for Mobile IPv4,” April 2008.) [RFC5177] defines Mobile Network Prefix as the network prefix of the subnet delegated to a Mobile Router as the Mobile Network.
- Mobile Router (MR)
Mobile Router as defined by RFC 5177 (Leung, K., Dommety, G., Narayanan, V., and A. Petrescu, “Network Mobility (NEMO) Extensions for Mobile IPv4,” April 2008.) [RFC5177] and RFC 3344 (Perkins, C., “IP Mobility Support for IPv4,” August 2002.) [RFC3344]. They define a Mobile Router as a mobile node that can be a router that is responsible for the mobility of one or more entire networks moving together, perhaps on an airplane, a ship, a train, an automobile, a bicycle, or a kayak.
- Route Optimization Cache
Data structure maintained by Mobile Routers on possible destinations for Route Optimization. Contains information on peer Correspondent Routers and their associated Mobile Networks.
- Return Routability, RR
Procedure to bind a Mobile Router's Home Address to a Care-of address on a Correspondent Router with a degree of trust.
This section describes the changed functionality of Home Agent and Mobile Router compared to the base NEMOv4 operation defined in NEMO-base (Leung, K., Dommety, G., Narayanan, V., and A. Petrescu, “Network Mobility (NEMO) Extensions for Mobile IPv4,” April 2008.) [RFC5177]. The basic premise is still the same; Mobile Routers, when registering to the Home Agent, either inform the Home Agent of the mobile network prefixes they are managing (explicit mode) or get prefixes assigned by Home Agent (implicit mode). However, instead of prefix information only remaining on the Home Agent and the Mobile Router managing the prefixes, this information will now be distributed to the other Mobile Routers as well.
The Home Agent-assisted route optimization is primarily intended for helping to optimize traffic patterns between multiple sites in an single organization or administrative domain; However, extranets can also be reached with optimized routes, as long as all Mobile Routers connect to the same Home Agent. The procedure aim to maintain backwards compatibility; With legacy nodes or routers full connectivity is always preserved even though optimal routing cannot be guaranteed.
The schema requires a Mobile Router to be able to receive messages from Home Agent and other Mobile Routers unsolicited - that is, without first initiating a request. This behavior is similar to the registration revocation procedure (Glass, S. and M. Chandra, “Registration Revocation in Mobile IPv4,” August 2003.) [RFC3543]. Many of the mechanisms are same - including the fact that advertising route optimization support upon registration implies capability to receive registration requests and return routability messages from other Mobile Routers.
Compared to IPv6, where Mobile Node <-> Correspondent node bindings are maintained via Mobility Routing header and Home Address options, Mobile IPv4 always requires the use of tunnels. Therefore, inter-mobile-router tunnel establishment has to be conducted.
During registration, a joining Mobile Router MAY request information on route-optimizable network prefixes. The Mobile Router MAY also allow redistribution of information on its managed network prefixes regardless whether they are explicit or implicit (statically configured or assigned by Home Agent). These are indicated with Mobile Router route optimization capability extension, see Section 5.1 (Mobile router Route optimization capability). If the Home Agent accepts the request for Route Optimization, this is indicated with Route Optimization Reply extension (Route optimization reply) in the registration reply.
Note that the redistribution of network prefix information from the Home Agent happens only during the registration signaling. There are no "routing updates" from Home Agent except during re-registrations triggered by handovers, registration timeouts and specific solicitation. The solicitation re-registration MAY occur if a Correspondent Router receives a registration request from a unknown Mobile Router (see Section 3.3.3 (Inter-Mobile Router registration)).
As noted, NEMO-supporting Home Agent already maintains, and in some cases assigns, information on which network prefixes are reachable behind certain Mobile Routers. Only change to this functionality is that this information can now be distributed to other Mobile Routers upon request. This request is defined in Section 5.1 (Mobile router Route optimization capability).
When a Home Agent receives a registration request, standard authentication and authorization procedures are conducted.
If registration is successful and the route optimization request was present in the registration request, the reply message MUST include Route Optimization Reply extension (Route optimization reply) to indicate whether Route Optimization was accepted. Furthermore, the extension also informs Mobile Router if NAT was detected using the procedure in RFC 3519 (Levkowetz, H. and S. Vaarala, “Mobile IP Traversal of Network Address Translation (NAT) Devices,” April 2003.) [RFC3519], which is based on the discrepancy between requester's indicated Care-of address and packet's source address.
The reply message MAY also include one route optimization prefix advertisement extension which informs the Mobile Router of existing mobile network prefixes and the Mobile Routers that manage them which have given redistribution permission. The networks SHOULD be included in order of priority, with the prefixes most desired to conduct optimization listed first. The extension is constructed as shown in Section 5.3 (Route optimization prefix advertisement). The extension consists of a list where each Mobile Router, identified by Home Address, is listed with according prefix(es) and their respective realm(s).
Each network prefix can be associated to a realm, usually in the form 'organization.example.com'. Besides the routers in customer's own organization, the prefix list may also include other Mobile Routers, e.g. Default prefix (0.0.0.0/0) pointing towards Internet gateway for Internet connectivity, and possible extranets. The realm information can be used to make policy decisions on the Mobile Router, such as preferring optimization within specific realm only.
In a typical scenario where Network Prefixes are allocated to Mobile Routers connecting to a single Home Agent, the prefixes are usually either continuous or at least very close to each other. Due to these characteristics, a prefix compression mechanism is provided. Another compression scheme is in use for realm information, where realms often share same higher-level domains. These compression mechanisms are further explained in Section 4 (Data compression schemes).
Upon receiving registration reply with the route optimization prefix advertisement extension, the Mobile Router SHALL insert the Mobile Router Home Addresses included in the extension as a host-prefixes to the local Route Optimization Cache if they do not already exist. If present, any additional prefixes information SHALL also be inserted to the Route Optimization Cache.
The Mobile Router MAY discard entries from a desired starting point onwards, due to memory or other policy related constraints. The intention of listing the prefixes in order of priority is to provide implicit guidance for this decision. If the capacity of the device allows, the Mobile Router SHOULD use information on all advertised prefixes.
Mobile routers supporting route optimization will maintain a Route Optimization Cache.
The Route Optimization Cache contains mappings between Correspondent Router HoA's, network(s) associated with each HoA and return routability procedure status. The Cache is populated based on information received from Home Agent in Route optimization prefix advertisements, and in registration messages from Correspondent Routers.
The Route Optimization Cache contains the following information for all known Correspondent Routers:
Correspondent Router's Home Address.
Correspondent Router's Care-of Address. May be empty if unknown. Tunnel cannot be established until known.
Mobile Router's Care-of Address used with this Correspondent Router. Tunnel's source address.
Tunnel interface associated with this Correspondent Router. The tunnel interface itself handles all the necessary operations to keep the tunnel operational, e.g. Sending keepalive messages required by UDP encapsulation.
The Correspondent Router is behind NAT/Firewall as seen from HA. Set if 'O' bit is set in the received advertisement. Affects tunnel establishment, see Section 3.3.4 (Inter-Mobile Router tunnels). Also mandates use of UDP encapsulation.
Return routability state. States are INACTIVE, IN PROGRESS and ACTIVE. If state is INACTIVE, return routability procedure must be completed before forwarding route-optimized traffic. If state is IN PROGRESS or ACTIVE, this entry MUST NOT be removed from Route Optimization Cache as long as tunnel to the Correspondent Router is established.
Registration management key. Either established via return routability procedure or configured statically. If configured statically, RRSTATE is permanently set to ACTIVE.
- Network Prefixes
A list of destination network prefixes reachable via this Correspondent Router. Includes network and prefix length, e.g. 192.0.2.0/25. Always contains at least a single entry, the CR-HoA host network prefix in the form of 192.0.2.1/32.
A list of realms associated with each prefix. May be empty, if realm is not provided by advertisement or configuration.
HA bit is set if this entry is learned from HA. This implies that the entry can be trusted. If not set, the entry has been learned from another Mobile Router and not yet verified from HA. The entry may still be maintained while awaiting verification.
In addition, for each Correspondent Router, a list of Network Prefixes is maintained. The list contains following information for each Network Prefix, and always contains at least a single entry, the CR-HoA host prefix in the form of 192.0.2.1/32.
- Network Prefix
A destination network prefix reachable via this Correspondent Router. Includes network and prefix length, e.g. 192.0.2.0/25.
The realm associated with this prefix. May be empty, if realm is not provided by advertisement or configuration.
HA bit is set if this entry is learned from HA. This implies that the entry can be trusted. If not set, the entry has been learned from another Mobile Router and not yet verified from HA. The entry may still be maintained while awaiting verification.
Entries MAY be removed from the Route Optimization Cache if the RRSTATE is INACTIVE, or the tunnel interface status is down as desired by the Mobile Router.
The return routability procedure for Mobile IPv6 is described in [RFC3775] (Johnson, D., Perkins, C., and J. Arkko, “Mobility Support in IPv6,” June 2004.). Same principles apply to the Mobile IPv4 version: Two messages are sent to Correspondent Router's Home Address, one via Home Agent and the other directly from the Mobile Router CoA, with two responses coming through same routes. Registration management key is derived from token information carried on these messages. This registration management key (KRm) can then be used to authenticate registration requests (comparable to Binding Updates in Mobile IPv6).
The Return Routability procedure is a method provided by Mobile IP protocol to establish the KRm in a relatively lightweight fashion. If desired, the KRms can be configured to Mobile Routers statically, or using an desired external secure key provisioning mechanism. If KRm's are known to the Mobile Routers via some other mechanism, Return Routability procedure can be skipped. Such provisioning mechanisms are out of scope for this document.
Assumption on traffic patterns is that the Mobile Router that initiates the RR procedure can always send outbound messages, even when behind NAT or firewall. This basic assumption made for NAT Traversal in [RFC3519] (Levkowetz, H. and S. Vaarala, “Mobile IP Traversal of Network Address Translation (NAT) Devices,” April 2003.) is also applicable here. In case the Correspondent Router is behind such obstacles, it receives these messages via the reverse tunnel to CR's Home Address, thus any problem regarding the CR's connectivity is addressed during the registration phase.
Each Mobile Router maintains a 'correspondent router key', Kcr, which is not shared with anyone else. Kcr is used for authenticating peer Mobile Routers in the situation where mobile router is acting as a CR. This is analogous to node key, Kcn, in Mobile IPv6. Correspondent Router uses router key to verify that the keygen tokens sent by Mobile Router in registration request are its own. The router key MUST be a random number, 96 bits in length.
Each Mobile Router also maintains one or more indexed nonces. Nonces should be generated periodically with a good random number generator. The Mobile Router may use same nonces with all Mobile Routers.
Mobile Routers keep both the current nonce and small set of valid previous nonces whose lifetime have not expired yet.
Return Routability procedure may be initiated only when the Route Optimization Cache's RRSTATE field for the Correspondent Router is INACTIVE. When Return Routability procedure is initiated, the state MUST be set to IN PROGRESS.
The Return Routability procedure consists of four Mobile IP messages: Home Test Init, Care-of Test Init, Home Test and Care-of Test. They are constructed as shown in Section 5.5 (Home-Test Init message) through Section 5.8 (Care-of test message). If the Mobile Router has included the Mobile Router optimization capability extension in its Registration Request, it MUST be able to accept Return Routability messages. The messages are delivered as normal Mobile IP signaling packets. The addresses are set to Correspondent Router's HoA and Mobile Router's CoA.
The return routability procedure begins with the Mobile Router sending HoTI and CoTI messages, each containing a cookie.
Upon receiving the HoTI or CoTI message the Correspondent Router MUST have a secret Kcr. If the Kcr does not exist, it must be produced before continuing with the return routability procedure.
Correspondent Router responds to HoTI and CoTI messages by constructing HoT and CoT messages, respectively, as replies. HoT message contains current home nonce index and CoT message contains current care-of nonce index.
Upon completion of Return Routability procedure, the Routing Optimization Cache's RRSTATE field is set to ACTIVE. The Mobile Router will establish a registration management key KRm:
KRm = SHA1 (home keygen token | care-of keygen token)
Like in Mobile IPv6, the Correspondent Router does not maintain any state for the Mobile Router until after receiving a registration request.
This section deals with the operation of Mobile and Correspondent Routers performing route optimization. Note that in the context of this draft all routers work as both Mobile Router and Correspondent Router. The term "Mobile Router" applies to the router initiating the Route Optimization procedure, and "Correspondent Router" indicates the peer router.
Especially compared to Mobile IPv6 route optimization there are two issues that are different regarding IPv4. First of all, since Mobile IPv4 always uses tunnels, there must be a tunnel established between MR and CR's Care-of addresses. The Correspondent Router learns of Mobile Router's Care-of address as it is provided by the Registration Request. The Mobile Router learns Correspondent Router's Care-of address by a new extension, "Care-of Address", in registration reply. Second issue is rising from security standpoint: In a registration request, the Mobile Router claims to represent an arbitrary IPv4 network. If the CR has not yet received this information (HoA <-> Network prefix), it SHOULD perform a re-registration to Home Agent to verify the claim.
Since each Mobile Router knows the eligible route-optimizable networks, the route optimization between all Correspondent Routers can be established at any time; However a better general practice is to conduct Route Optimization on-demand only. Route optimization SHOULD only be started when receiving a packet where destination address is local (and the subnet is registered as route optimizable) and source address exists in the network prefixes of Route Optimization Cache.
Each Mobile Router maintains a routing table. In a typical situation, the Mobile Router has one or more interface(s) to the local networks, one or more interface(s) to wide-area networks (such as provided by ISPs), and a tunnel interface to the Home Agent. Additional tunnel interfaces become activated as Route Optimization is being performed.
The routing table SHOULD typically contain Network Prefixes managed by Correspondent Routers associated with established route-optimized tunnel interfaces. In addition, host-routes to Correspondent Routers' Care-of addresses SHOULD be associated with the assigned to the physical interfaces assigned with corresponding MR-CoA. A default route MAY point to the reverse tunnel to the Home Agent if not overridden by prefix information.
The route for the Home Address of Correspondent Router SHOULD also be pointing towards the optimized tunnel. However, all registration messages MUST be sent via the reverse tunnel to the Home Agent.
If two prefixes overlap each other, e.g. 192.0.2.128/25 and 192.0.2.128/29, the standard longest match rule for routing is in effect. However, overlapping private address SHOULD be considered an error situation. Any aggregation for routes in private address space SHOULD be conducted only at HA.
If route optimization between Mobile Router and Correspondent Router is desired, either Return Routability procedure must have been performed ( See Section 3.2 (Return routability procedure)), or key KRm must be pre-shared between the Mobile and Correspondent Router. If a known KRm exists, a Mobile Router MAY send a registration request to the Correspondent Router's HoA.
The registration request's source address and Care-of address field are set to the address of desired outgoing interface on the Mobile Router. The address MAY be same as the Care-of address used with Home Agent. The registration request MUST include Mobile-Correspondent Authentication extension defined in Section 5.4 (Mobile-Correspondent authentication extension) and Mobile Network Request Extension defined in [RFC5177] (Leung, K., Dommety, G., Narayanan, V., and A. Petrescu, “Network Mobility (NEMO) Extensions for Mobile IPv4,” April 2008.). The Mobile Network Request Extension MUST contain the network prefixes, as if registering in explicit mode. If timestamps are used, the Correspondent Router MUST check the identification field for validity. The registration request MUST include Home Address. The Authenticator field is hashed with the key KRm.
The encapsulation can be set as desired, except in the case where the Correspondent Router's Route Optimization Cache Entry has NAT set or the Mobile Router itself is behind NAT or firewall. If either of the conditions apply, registration request MUST specify UDP encapsulation. It is RECOMMENDED to always use UDP encapsulation to facilitate detecting of path failures via keepalive mechanism.
The Correspondent Router first checks the registration request's authentication against Kcr and nonce indexes negotiated during Return Routability procedure. This ensures that the registration request is coming from a correct Mobile Router. If the check passes, the Correspondent Router MUST check whether the Mobile Router already exists in it's Route Optimization Cache and is associated with the prefixes included in the request (Prefixes are present and Flag HA is true for each prefix).
If the check against the cache fails, the Correspondent Router SHOULD send a re-registration request to Home Agent with the 'S' (solicitation) bit set, thus obtaining the latest information on Network Prefixes managed by incoming Mobile Router. If, even after this update, the prefixes still don't match, the Correspondent Router MUST reject the registration request. This verification is done to protect against Mobile Routers claiming to represent arbitrary networks; However, since Home Agent provides trusted information, it can authorize Mobile Router's claim. If the environment itself is considered trusted, the Correspondent Router can, as a policy, accept registrations from without this check; however, this is NOT RECOMMENDED as a general practice.
If the prefixes match, the Correspondent Router MAY accept the registration. If the CR chooses to accept, the CR MUST check if a tunnel to the Mobile Router already exists. If the tunnel does NOT exist or has wrong endpoints (CoAs), the tunnel MUST be established or updated and Route Optimization Cache updated.
Upon receiving the registration reply, the Mobile Router MUST check if a tunnel to the Correspondent Router already exists. If the tunnel does NOT exist, or has wrong endpoints (CoAs), a tunnel MUST be established and Route Optimization Cache updated. This is covered in Section 3.3.4 (Inter-Mobile Router tunnels).
The Correspondent Router's routing table MUST be updated to include the Mobile Router's networks are reachable via the direct tunnel to the Mobile Router.
After the tunnel is established, the Mobile Router MAY update it's routing tables to reach all Correspondent Router's Prefixes via the tunnel, although it is RECOMMENDED to wait for the Correspondent Router to perform it's own, explicit registration. This is primarily a policy decision depending on the network environment. See section Section 6.4 (Mutualness of Route Optimization).
Inter-Mobile Router tunnel establishment follows establishing standard reverse tunnels to the Home Agent. The registration request to Correspondent Router includes information on the desired encapsulation. It is RECOMMENDED to use UDP encapsulation. In the case of GRE[RFC2784] (Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, “Generic Routing Encapsulation (GRE),” March 2000.), IP over IP[RFC2003] (Perkins, C., “IP Encapsulation within IP,” October 1996.) or minimal encapsulation[RFC2004] (Perkins, C., “Minimal Encapsulation within IP,” October 1996.) no special considerations regarding the reachability are necessary; The tunnel has no stateful information; The packets are simply encapsulated within the GRE, IP, or minimal header.
The tunnel origination point for the Correspondent Router is its Care-of Address, not the Home Address where the registration requests were sent. This is different from creation of the Reverse Tunnel to Home Agent, which reuses the channel from registration signaling.
Special considerations rise from using UDP encapsulation, especially in cases where one of the Mobile Routers is located behind NAT or firewall.A deviation from RFC 3519 (Levkowetz, H. and S. Vaarala, “Mobile IP Traversal of Network Address Translation (NAT) Devices,” April 2003.) [RFC3519] is that keepalives should be sent both from ends of the tunnel to detect path failures. Furthermore, if either end of the tunnel is located behind a NAT, the first UDP keepalive SHOULD be successfully completed, before the tunnel is considered active.
If both the Mobile Router and the Correspondent Router are behind separate NATs, route optimization cannot be performed between them. Possibilities to set up mutual tunneling when both routers are behind NAT, are outside the scope of this draft. However, some of these issues are addressed in Section 6.1 (NATs and stateful firewalls ).
Due to the fact that the route optimization procedures may occur concurrently at two Mobile Routers, each working as each other's Correspondent Router, there may be a situation where two routers are attempting to establish separate tunnels between them at the same time. If a router with a smaller Home Address (meaning a normal 32-bit integer comparison treating IPv4 addresses as 32-bit unsigned integers) receives a registration request (in CR role) while its own registration request (sent in MR role) is still pending, the reply must be deferred until the tunnel initiated by its registration request is up. This avoids the problem of two separate tunnels forming concurrently between two Mobile Routers.
The designations "MR" and "CR" only apply to the initial tunnel-establishment phase. Once a tunnel is established between two routers, either of them can opt to either tear down the tunnel or perform a handover.
All packets received by the Mobile Router are forwarded using normal routing rules according to the routing table. There are no special considerations when constructing the packets, the tunnel interface's own processes will encapsulate any packet automatically.
Handovers and connection breakdowns can be categorized as either ungraceful or graceful, also known as "break-before-make" (bbm) and "make-before-break" (mbb) situations.
As with establishment, the "Mobile Router" discussed here is the router wishing to change connectivity state, "Correspondent Router" being the peer.
When a Mobile Router wishes to leave network, it SHOULD, in addition to sending such a request to the Home Agent, also send a re-registration request to all Correspondent Routers with the lifetime set to zero. The Correspondent Router(s), upon accepting this request and sending the reply, will check if it's Route Optimization Cache contains any prefixes associated with the requesting Mobile Router. These entries should be removed and routing table updated accordingly (traffic forwarded via the Home Agent again). The tunnel MUST then be destroyed. A short grace period MAY be used to allow possible in-transit packets to be received correctly.
In the case of a handover, the Correspondent Router simply needs to update the tunnel's destination to the Mobile Router's new Care-of Address. Mobile Router SHOULD keep accepting packets from both old and new care-of Addresses for a short grace period, typically in the order of ten seconds.
If the Mobile Router was unable to send the re-registration request before handover, it MUST send it immediately after handover is completed and binding with the Home Agent is up. If care-of Address has changed, the Return Routability procedure has to be conducted first.
If a reply is not received for a registration request to a Correspondent Router, routes to the network prefixes managed by the Correspondent Router MUST be removed from the routing table, thus causing the user traffic to be forwarded via the Home Agent.
The information the Home Agent maintains on Mobile Network prefixes and the Mobile Routers' Route Optimization Caches do not need to be explicitly synchronized. This is based on the assumption is that at least some of the traffic between nodes inside mobile networks is always bidirectional. Due to this, when a node in a mobile network talks to a node in another mobile network, if the initial packet does not trigger Route Optimization, the reply packet will.
Consider a situation with three mobile networks, A, B, C handled by three Mobile Routers, MR A, MR B and MR C respectively. If they register to a Home Agent in this order, the situation goes as follows:
MR A registers; Receives no information on other networks from HA, as no other MR has registered yet.
MR B registers; Receives information on mobile network A being reachable via MR A.
MR C registers; Receives information on both of the other mobile networks.
If a node in mobile network C receives traffic from mobile network A, the route optimization is straightforward; MR C already has network A in its Route Optimization Cache. Thus, packet reception triggers Route Optimization towards MR A. When MR C registers to MR A (after Return Routability procedure is completed), MR A does not have information on mobile network C; Thus it will perform a re-registration to the Home Agent on-demand. This allows MR A to verify that MR C is indeed managing network C.
If a node in mobile network B receives to traffic from mobile network C, MR B has no information on network C. No route optimization is triggered. However, when the node in network B replies and the reply reaches MR C, route optimization happens as above. Further examples of signaling are in Section 8 (Example signaling scenarios).
Even in the very rare case of completely unidirectional traffic from an entire network, the re-registrations to the Home Agent caused by timeouts will eventually cause convergence. However, this should be treated as a special case.
Note that all Mobile Routers are connected to same Home Agent. For possibilities concerning multiple Home Agents, see Section 6.3 (Multiple Home Agents)
This section defines the two compression formats used in Route Optimization Prefix Advertisement extensions.
The prefix-compression is based on the idea that prefixes usually share common properties. The scheme is simple delta-compression. In the prefix information advertisement, Section 5.3 (Route optimization prefix advertisement), the D bit indicates whether receiving a "master" or a "delta" prefix. This, combined with the Prefix Length information, allows for compression and decompression of prefix information.
If D=0, what follows in the "Prefix" field are bits 1..n of the a new master prefix, where n is PLen. This is rounded up to nearest full octet. Thus, prefix lengths of /4 and /8 take 1 octet, /12 and /16 take 2 octets, /20 and /24 three, and larger than that full 4 octets.
If D=1, what follows in the "Prefix" field are bits m..PLen of the prefix, where m is the first changed bit of previous master prefix, with padding from master prefix filling the field to full octet. Maximum value of Plen-m is 8 (that is, delta MUST fit into one octet). If this is not possible, a new master prefix has to be declared.
Determining the order of prefix transmission should be based on saving maximum space during transmission.
Example of compression and transmitted data, where network prefixes 192.0.2.0/28, 192.0.2.64/26 and 192.0.2.128/25 are transmitted are illustrated in Figure 1 (Prefix Compression Example). Because of the padding to full octets, redundant information is also sent. The bit-patterns being transmitted are:
=+= shows the prefix mask --- shows the master prefix for delta coded prefixes 192.0.2.0/28, D=0 0 1 2 3 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|1|0|0|0|0|0|0|.|0|0|0|0|0|0|0|0|.|0|0|0|0|0|0|1|0|.|0|0|0|0|0|0|0|0| +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+-+-+-+-+ ^ ^ +---------------------------- encoded ------------------------------+ ^ ^ +-pad-+ 192.0.2.64/26, D=1 0 1 2 3 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 +-------------------------------------------------------------+-+-+-+-+ |1|1|0|0|0|0|0|0|.|0|0|0|0|0|0|0|0|.|0|0|0|0|0|0|1|0|.|0|1|0|0|0|0|0|0| +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+-+-+-+-+-+-+ ^ ^ +--- encoded ---+ ^ ^ +-- padding --+ 192.0.2.128/25, D=1 0 1 2 3 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 +-------------------------------------------------------------+-+-+-+-+ |1|1|0|0|0|0|0|0|.|0|0|0|0|0|0|0|0|.|0|0|0|0|0|0|1|0|.|1|0|0|0|0|0|0|0| +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+-+-+-+-+-+-+-+ ^ ^ +--- encoded ---+ ^ ^ +- padding -+
| Figure 1: Prefix Compression Example |
First prefix, 192.0.2.0/28, is considered a master prefix and is transmitted in full. The PLen of 28 bits determines that all four octets must be transmitted. If the prefix would have been e.g. 192.0.2.0/24, three octets would have sufficed since 24 bits fit into 3 octets.
For the following prefixes, the D=1. Thus, they are deltas of the previous prefix where D was zero.
192.0.2.64/26 includes bits 19-26 (full octet). Bits 19-25 are copied from master prefix, but bit 26 is changed to 1. The final notation in binary is "1001", or 0x09.
192.0.2.128/25 includes bits 18-25 (full octet). Bits 18-24 are copied from master prefix, but bit 25 is changed to 1. The final notation in binary is "101", or 0x05.
The final encoding thus becomes:
+----------------+--------+-+---------------------+ | Prefix | Plen |D| Transmitted Prefix | +----------------+--------+-+---------------------+ | 192.0.2.0/28 | 28 |0| 0xc0 0x00 0x02 0x00 | | 192.0.2.64/26 | 26 |1| 0x09 | | 192.0.2.128/25 | 25 |1| 0x05 | +----------------+--------+-+---------------------+
It should be noted that in this case the order of prefix transmission would not affect compression efficiency. If prefix 192.0.2.128/25 would have been considered the master prefix and the others as deltas instead, the resulting encoding still fits into one octet for the subsequent prefixes. There would be no need to declare a new master prefix.
In order to reduce the size of messages, the system introduces a realm compression scheme, which reduces the size of realms in a message. The compression scheme is a simple dynamically updated dictionary based algorithm, which is designed to compress arbitrary length text strings. In this scheme, an entire realm, a single label or a list of labels may be replaced with an index to a previous occurrence of the same string stored in the dictionary. The realm compression defined in this specification was inspired by the RFC 1035 (Mockapetris, P., “Domain names - implementation and specification,” November 1987.) [RFC1035] DNS domain name label compression. Our algorithm is, however, improved to gain more compression.
When compressing realms, the dictionary is first reset and does not contain a single string. The realms are processed one by one so the algorithm does not expect to see them all or the whole message at once. The state of the compressor is the current content of the dictionary. The realms are compressed label by label or as a list of labels. The dictionary can hold maximum 128 strings. Thus, when adding the 129th string into the dictionary, the dictionary MUST first be reset to the initial state (i.e. Emptied) and the index of the string will become 0.
The encoding of an index to the dictionary or an uncompressed run of octets representing a single label has purposely been made simple and the whole encoding works on an octet granularity. The encoding of an uncompressed label takes the form of a one octet:
0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+-+-+-+-=================-+-+-+-+ |0| LENGTH | 'length' octets long string.. | +-+-+-+-+-+-+-+-+-+-+-+-=================-+-+-+-+
This encoding allows label lengths from 1 to 127 octets. A label length of zero (0) is not allowed. The "label length" tag octet is then followed by up to 127 octets of the actual encoded label string.
The index to the dictionary (the "label index" tag octet) takes the form of a one octet:
0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |1| INDEX | +-+-+-+-+-+-+-+-+
The above encodings do not allow generating an output octet value of zero (0). The encapsulating Mobile IPv4 extension makes use of this property and uses the value of zero (0) to mark the end of compressed realm or to indicate an empty realm. It is also possible to encode the complete realm using only "label length" tags. In this case no compression takes place. This allows the sender to skip compression, for example to reduce computation requirements when generating messages. However, the receiver MUST always be prepared to receive compressed realms.
When compressing the input realm, the dictionary is searched for a matching string. If no match could be found, the last label is removed from the right-hand side of the used input realm. The search is repeated until the whole input realm has been processed. If no match was found at all, then the first label of the original input realm is encoded using the "label length" tag and the label is inserted into the dictionary. The previously described search is repeated with the remaining part of the input realm, if any. If nothing remains, the realm encoding is complete.
When a matching string is found in the dictionary the matching part of the input realm is encoded using the "label index" tag. The matching part of the input realm is removed and the search is repeated with the remaining part of the input realm, if any. If nothing remains, the octet value of zero (0) is inserted to mark the end of encoded realm.
The search algorithm also maintains the "longest non-matching string" for each input realm. Each time the search in dictionary fails and a new label gets encoded using the "label length" tag and inserted into the dictionary, the "longest non-matching string" is concatenated by this label including the separating "." (dot, i.e. Hexadecimal 0x2e). When a match is found in the dictionary the "longest non-matching string" is reset (i.e. Emptied). Once the whole input realm has been processed and encoded, all possible suffixes longer than one label are taken from the string and inserted into the dictionary.
This section shows an example how to encode a set of realms using the specified realm compression algorithm. For example, a message might need to compress the realms "foo.example.com", "bar.foo.example.com", "buz.foo.example.org", "example.com" and "bar.example.com.org". The following example shows the processing of input realms on the left side and the contents of the dictionary on the right hand side. The example uses hexadecimal representation of numbers.
COMPRESSOR: DICTIONARY: 1) Input "foo.example.com" Search("foo.example.com") Search("foo.example") Search("foo") Encode(0x03,'f','o','o') 0x00 "foo" +-> "longest non-matching string" = "foo" Search("example.com") Search("example") Encode(0x07,'e','x','a','m','p','l','e') 0x01 "example" +-> "longest non-matching string" = "foo.example" Search("com") Encode(0x03,'c','o','m') 0x02 "com" +-> "longest non-matching string" = "foo.example.com" 0x03 "foo.example.com" 0x04 "example.com" Encode(0x00) 2) Input "bar.foo.example.com" Search("bar.foo.example.com") Search("bar.foo.example") Search("bar.foo" Search("bar") Encode(0x03,'b','a','r') 0x05 "bar" +-> "longest non-matching string" = "bar" Search("foo.example.com") -> match to 0x03 Encode(0x83) +-> "longest non-matching string" = NUL Encode(0x00) 3) Input "buz.foo.example.org" Search("buz.foo.example.org") Search("buz.foo.example") Search("buz.foo") Search("buz") Encode(0x03,'b','u','z') 0x06 "buz" +-> "longest non-matching string" = "buz" Search("foo.example.org") Search("foo.example") Search("foo") -> match to 0x00 Encode(0x80) +-> "longest non-matching string" = NUL Search("example.org") Search("example") -> match to 0x01 Encode(0x81) +-> "longest non-matching string" = NUL Search("org") Encode(0x03,'o','r','g') 0x07 "org" +-> "longest non-matching string" = "org" Encode(0x00) 4) Input "example.com" Search("example.com") -> match to 0x04 Encode(0x84) Encode(0x00) 5) Input "bar.example.com.org" Search("bar.example.com.org") Search("bar.example.com") Search("bar.example") Search("bar") -> match to 0x05 Encode(0x85) Search("example.com.org") Search("example.com") -> match to 0x04 Encode(0x84) Search("org") -> match to 0x07 Encode(0x87) Encode(0x00)
As can be seen from the example, due the greedy approach of encoding matches, the search algorithm and the dictionary update function is not the most optimal one. However, we do not claim the algorithm would be the most efficient. It functions efficiently enough for most inputs. In this example, the original input realm data was 79 octets and the compressed output excluding the end mark is 35 octets.
This section describes the construction of all new information elements.
This skippable extension MAY be sent by a Mobile Router to a Home
Agent in the registration request message.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length |A|R|S|O| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Optional Mobile Router HoA ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- TBA_T1. Skippable; If Home Agent does not support route optimization advertisements, it can ignore this request and simply not include any information in the reply.
- Advertise my networks. If 'A' bit is set, the Home Agent is allowed to advertise the networks managed by this Mobile Router to other Mobile Routers. This also indicates that the Mobile Router is capable of receiving route optimization binding updates. In effect, this allows the Mobile Router to work in Correspondent Router role.
- Request mobile network information. If 'R' bit is set, the Home Agent MAY respond with information about mobile networks in the same domain.
- Soliciting prefixes managed by specific Mobile Router. The Mobile Router is specified in the Optional Mobile Router HoA field.
- Explicitly specifying the requesting Router is only able to initiate outgoing connections, not accept any incoming ones, due to NAT device, stateful firewall, or similar issue. This is reflected by the Home Agent by setting the 'O' flag for prefix information.
- Set to zero, MUST be ignored on reception.
- Optional Mobile Router HoA
Solicited Mobile Router's Home Address.
This non-skippable extension MUST be sent by a Home Agent to a Mobile Router in the registration reply message, if Mobile Router indicated support for Route Optimization in registration message and Home Agent supports Route Optimization.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Sub-Type |O|N|Reply Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- TBA_T2 (Non-skippable)
- The 'O' flag in Mobile Router Optimization capability extension was set during registration.
- Presence of NAT was detected by Home Agent. This informs the Mobile Router that it is located behind NAT. The detection procedure is specified in RFC 3519 (Levkowetz, H. and S. Vaarala, “Mobile IP Traversal of Network Address Translation (NAT) Devices,” April 2003.) [RFC3519], and is based on the discrepancy between registration packet's source address and indicated Care-of Address.
The Reply code indicates whether Route Optimization has been accepted. Values of 0..15 indicate assent and values 16..63 indicate Route Optimization is not done.
- Will do Route Optimization
- Route Optimization declined, reason unspecified.
This non-skippable extension MAY be sent by a Home Agent to a Mobile Router in the registration reply message. The extension is only included when explicitly requested by the Mobile Router in the registration request message. Implicit prioritization of prefixes is caused by the order of extensions.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Sub-type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1-n times the following information structure +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |O|D|M| Plen | Optional Mobile Router HoA, 4 octets ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ | Optional Prefix, 1,2,3 or 4 octets ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Realm (1-n characters) ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- TBA_T2 (Non-skippable)
- Delta. If D=1, the prefix is a delta from last Prefix where D=0. MUST be zero on first information structure, MAY be zero or one on subsequent information structures. If D=1, the Prefix field is one octet in length. See Section 4.1 (Prefix compression) for details.
- Outbound connections only. This bit indicates that the target Mobile Router can only initiate, not receive, connections from it's CoA for this prefix. This is set if Home Agent has determined that the Mobile Router is behind NAT, or the Mobile Router has explicitly requested setting the 'N' flag in Mobile router Route optimization capability extension (Mobile router Route optimization capability).
- Mobile Router HoA bit. If M=1, the next field is Mobile Router HoA, and Prefix is omitted. If M=0, the next field is Prefix, and Mobile Router HoA is omitted. For the first information structure, M MUST be set to 1. If M=1, the D and O bits are set to zero and ignored upon reception.
- Length of the prefix advertised. 5 bits, allows for values from 0 to 31. If M=1, MUST be set to zero and ignored upon reception.
- Mobile router HoA
Mobile Router's Home address. All prefixes in the following information structures where M=0 are maintained by this Mobile Router.
- The IPv4 prefix advertised. If D=0, the field length is Plen bits, rounded up to nearest full octet. Least-significant bits starting off Plen (and are zeros) are omitted. If D=1, field length is one octet.
- The Realm that is associated with the advertised Mobile Router HoA and prefix. If empty, MUST be set to '\0'. For realm encoding and optional compression scheme, refer to Section 4.2 (Realm compression).
Mobile-Correspondent authentication extension is included in
registration requests sent from Mobile Router to Correspondent Router.
The existence of this extension indicates that the message is not
destined to a Home Agent, but another Mobile Router. The format is
similar to the other Authentication Extensions defined in [RFC3344] (Perkins, C., “IP Mobility Support for IPv4,” August 2002.), with SPIs replaced by Nonce Indexes.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Home Nonce Index | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Care-of Nonce Index | Authenticator... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Home Nonce Index field tells the Correspondent Router which nonce value to use when producing the home keygen token. The Care-of Nonce Index field is ignored in requests to remove a binding. Otherwise, it tells the Correspondent Router which nonce value to use when producing the Care-of Keygen Token.
- TBA_T3 (non-skippable).
- Home Nonce Index
Home Nonce Index in use.
- Care-of Nonce Index
Care-of Index in use.
Authenticator field, constructed by issuing HMAC_SHA1 (KRm, Protected Data)
The protected data, just like on other cases where Authenticator is used, consists of
- the UDP payload (i.e., the Registration Request or Registration Reply data),
- all prior Extensions in their entirety, and
- the Type, Length, and Nonce Indexes of this Extension.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Sub-type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Home Init Cookie + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- TBA_T2 (Non-skippable)
- Set to zero, MUST be ignored on reception.
- Home Init Cookie
64-bit field which contains a random value, the Home Init Cookie.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Sub-type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Care-of Init Cookie + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- TBA_T2, non-skippable.
- Set to zero, MUST be ignored on reception.
- Care-of Init Cookie
64-bit field which contains a random value, the Care-of Init Cookie.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Sub-type | Nonce Index ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ | | +-+-+-+-+-+-+-+-+ Home Init Cookie + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+ Home Keygen Token + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+
- TBA_T2 (non-skippable)
- Nonce Index
This field will be echoed back by the Mobile Router to the Correspondent Router in a subsequent registration request's authentication extension.
- Home Init Cookie
64-bit field which contains a random value, the Home Init Cookie.
- Home Keygen Token
This field contains the 64 bit home keygen token used in the Return Routability procedure. Generated from cookie + nonce.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Sub-type | Nonce Index ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ | | +-+-+-+-+-+-+-+-+ Care-of Init Cookie + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | +-+-+-+-+-+-+-+-+ Care-of Keygen Token + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+
- TBA_T2 (non-skippable)
- Care-of Nonce Index
This field will be echoed back by the Mobile Router to the Correspondent Router in a subsequent registration requests' authentication extension.
- Care-of Init Cookie
64-bit field which contains a random value, the Home Init Cookie.
- Care-of Keygen Token
This field contains the 64 bit home keygen token used in the Return Routability procedure.
The Care-of Address extension is added to a registration reply sent by the Correspondent Router to inform the Mobile Router of the upcoming tunnel endpoint.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Sub-type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Care-of Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- TBA_T2 (non-skippable)
- Care-of Address
Care-of address used for tunnel with Mobile Router.
Mechanisms described in MIP NAT traversal (Levkowetz, H. and S. Vaarala, “Mobile IP Traversal of Network Address Translation (NAT) Devices,” April 2003.) [RFC3519] allow the Home Agent to work with Mobile Nodes situated behind a NAT device or a stateful firewall. Furthermore, the Home Agent may also detect whether NAT device is located between the Mobile Node and the HA. This information is passed on to the other Mobile Routers with the 'O' flag in Route optimization prefix advertisement extension (Route optimization prefix advertisement), and to the registering Mobile Router with the 'N' flag in Route Optimization Reply extension (Route optimization reply). In the case of one or both of the routers behind NAT or similarly impaired (not being able to accept incoming connections), the tunnel establishment procedure takes this into account. The existence of NAT or firewall implies that UDP encapsulation MUST be used.
In the case where Mobile Router is behind NAT (or firewall) and Correspondent Router is not, the Mobile Router will, when tunnel has been established, send keepalive messages (ICMP echo requests) through the tunnel. Until a reply has been received, the tunnel SHOULD NOT be considered active. Once reply has been received, NAT mapping is in place and traffic can be sent.
If Mobile Router and Correspondent Router are behind same NAT from HA's point of view, it is possible to establish tunnel between them. This may also be the situation in the case of nested NATs. It may be possible in specific cases that if two Mobile Routers' registration messages appear to come from same translated address, for Home Agent to strip the 'O' flag in the prefix advertisement messages. However, this does not work in case of nested NATs. Some sort of "Route optimization discovery" protocol (see Section 6.5 (Extensibility)), or more information in the Route Optimization capability advertisements is required for more generalized solution.
If both the Mobile Router and the Correspondent Router are behind two separate NATs, some sort of proxy or hole-punching technique may be needed. This is out of scope of this draft.
Since Foreign Agents have been dropped from Network Mobility for Mobile IPv4 work, they are not considered here.
Mobile Routers can negotiate and perform route optimization without the assistance of Home Agent - if they can discover each others existence and thus know where to send registration messages. This draft only addresses a logically single Home Agent that distributes network prefix information to the Mobile Routers. Problems arise from possible trust relationships; In this draft the Home Agent serves as a way to provide verification that a specific network is managed by a specific router.
If Route Optimization is desired between nodes attached to separate Home Agents, there are several possibilities. Note that standard high availability redundancy protocols, such as VRRP, can be utilized; However, in such case the Home Agent is still a single logical entity even if consisting of more than a single node.
Several possibilities exist for achieving Route Optimization between Mobile Routers attached to separate Home Agents, such as a new discovery/probing protocol, routing protocol between Home Agents or DNS SRV records, or a common AAA architecture. There already is a framework for HA to retrieve information from AAA so it can be considered as the most viable possibility. See Section 6.5 (Extensibility) for information on possibility to generalize the method.
Any discovery/probing protocols are out of scope for this draft.
The procedure as specified is asymmetric; That is, if bidirectional route optimization is desired while maintaining consistency, the route optimization (RR check and registration) has to be performed in both directions, but this is not strictly necessary. This is primarily a policy decision depending on how often the mobile prefixes are reconfigured.
Consider the case where two networks, A and B, are handled by Mobile Routers A and B respectively. If the routers are set up in such a fashion that Route Optimization is triggered when a packet is received from a Network Prefix in Route Optimization Cache, the following occurs if a node in network A starts sending ICMP echo requests (pinging) a node in network B.
MR B sees the incoming ICMP echo request packet, which is travelling inside the reverse tunnel to the Home Agent. MR B sees that the destination is in network B, and furthermore, source is in network A which exists in the cache. This triggers Route Optimization processing. Until RO is active, the ping packets (echo requests and replies) are routed via the reverse tunnel.
MR B completes RR procedure and registration with MR A, which thus becomes a Correspondent Router for MR B. A tunnel is created between the routers. MR A updates its routing tables so that network B is reachable via MR A <-> MR B tunnel.
The traffic pattern is now that packets from network B to network A are sent over the direct tunnel, but the packets from A to B are transmitted via the Home Agent and reverse tunnels. MR A now performs its own registration towards MR B. Upon completion, MR A notices that a tunnel to MR B already exists, but updates its routing table so that network B is now reachable via the MR A <-> MR B tunnel. From this point onward, traffic is bidirectional.
In this scenario, if MR A does NOT perform a separate route optimization (RR check and registration), but instead simply updates its routing table to reach network B via the tunnel, problems may arise if MR B has started to manage another network B' before the information has propagated to MR A. The end result is that MR B starts to receive packets for network B' via the Home Agent and for network B via direct tunnel. If Reverse Path checking or similar mechanism is in use on MR B, packets from network A could be black holed.
Whether to perform this mutual registration or not thus depends on the situation, and whether Mobile Routers are going to start managing additional Network Prefixes during operation.
The design considerations include several mechanisms which might not be strictly necessary if Route Optimization would only be desired between individual customer sites in a managed network. The registration procedure (with the optional Return Routability part), which allows for Correspondent Routers to learn Mobile Router's Care-of Addresses is not strictly necessary; The CoA's could have been provided by HA directly.
However, this approach allows the method to be extended to a more generic route optimization. The primary driver for having Home Agent to work as a centralized information distributer is to provide Mobile Routers with the knowledge of not only the other routers, but to provide information on which networks are managed by which routers.
The Home Agent provides the information on all feasible nodes with which it is possible to establish Route Optimization. If representing a whole Mobile Network is not necessary, in effect the typical Mobile Node <-> Correspondent Node situation, the mechanisms in this draft work just as well - only problem is discovering if the target Correspondent Node can provide Route Optimization capability. This can be performed by not including any prefixes in the information extension, just the HoA address of Mobile Router.
In addition, with Route Optimization for single node, checks on whether a Mobile Router is allowed to represent specific networks are unnecessary since there are none.
Correspondent node/router discovery protocols (whether they are based on probing or a centralized directory beyond the single Home Agent) are outside the scope of this draft.
The design simply provides possibility to create optimal paths between Mobile Routers; It doesn't dictate what should be the user traffic using these paths. One possible approach in helping facilitate load balancing and utilizing all available paths is presented in [I‑D.gundavelli‑mip4‑multiple‑tunnel‑support] (Gundavelli, S. and K. Leung, “Multiple Tunnel Support for Mobile IPv4,” February 2010.), which effectively allows for multiple Care-of addresses for a single Home Address.
Home Agent assisted Route Optimization scalability issues stem from the general Mobile IPv4 architecture which is based on tunnels. Creating, maintaining and destroying tunnel interfaces can cause load on the Mobile Routers. However, the MRs can always fall back to normal, reverse tunnelled routing if resource constraints are apparent.
If there is a large number of optimization-capable prefixes, maintaining state for all of these may be an issue also, due to limits on routing table sizes.
Registration responses from Home Agent to Mobile Router may provide information on large number of network prefixes. If thousands of networks are involved, the registration reply messages are bound to grow very large. The prefix- and realm compression mechanisms defined in Section 4 (Data compression schemes) mitigates this problem to an extent. There will, however, be some practical upper limit after which point some other delivery mechanism for the prefix information will be needed.
The following example signaling assumes that there are three Mobile Routers, MR A, B, C, each managing network prefixes A, B, and C. At the beginning, no networks are registered to the Home Agent. Any AAA processing at the Home Agent is omitted from the diagram.
+--------+ +--------+ +--------+ +--------------+ | [MR A] | | [MR B] | | [MR C] | | [Home Agent] | +--------+ +--------+ +--------+ +--------------+ | | | | x------------------------------->| Registration request, | | | | includes Mobile Router | | | | route optimization | | | | capability extension | | | | |<-------------------------------x Registration response, | | | | no known networks from HA | | | | in response | | | | | x-------------------->| Registration request, similar | | | | to the one sent by MR A | | | | | |<--------------------x Registration reply, includes | | | | network A in route optimization | | | | prefix advertisement extension | | | | | | x--------->| Registration request, similar | | | | the one sent by MR A | | | | | | |<---------x Registration reply, includes | | | | networks A and B in route | | | | optimization prefix | | | | advertisement extension. | | | | Network B is sent in | | | | compressed form. | | | |
The following example signaling has same network setup as in Section 8.1 (Registration request) - Three mobile routers, each corresponding to their respective network. Node A is in network A and Node C is in network C.
At the beginning, no mobile routers know KRm's of each other. If the KRm's would be pre-shared or provisioned with some other method, the Return Routability messages can be omitted. Signaling in Section 8.1 (Registration request) has occurred, thus MR A is not aware of the other networks, and MR C is aware of networks A and B.
======= Traffic inside Mobile IP tunnel to/from HA =-=-=-= Traffic inside Mobile IP tunnel between MRs ------- Traffic outside Mobile IP tunnel +----------+ +--------+ +------+ +--------+ +----------+ | [Node A] | | [MR A] | | [HA] | | [MR C] | | [Node C] | +----------+ +--------+ +------+ +--------+ +----------+ | | | | | |<-----------O==========O=========O-------x Mobile Router A is | | | | | unaware of network C, | | | | | thus, nothing happens | | | | | x------------O==========O=========O------>| Mobile Router C | | | | | notices packet from | | | | | Net A - begins RO | | | | | | | | | | Return Routability | | | | | (If no preshared KRms) | | | | | | |<=========O---------x | CoTI | |<=========O=========x | HoTI | | | | | | x==========O-------->| | CoT | x==========O========>| | HoT | | | | | | | | | | KRm between MR A <-> C | | | | | established | | | | | | |<=========O---------x | Registration request | | | | | | x--------->| | | Registration request | | | | | to HA due to MR A | | | | | being unaware of | | | | | network C. | | | | | Solicit bit set. | | | | | | |<---------x | | Registration reply, | | | | | contains info on Net A | | | | | | x==========O-------->| | Registration reply, | | | | | includes MR A's CoA in | | | | | Care-of-Address | | | | | extension | | | | | |<-----------O=-=-=-==-=-=-=-==-=-O-------x Packet from Node C -> A | | | | | routed to direct tunnel | | | | | at MR C, based on | | | | | MR C now knowing MR A's | | | | | CoA and tunnel being up | | | | | x------------O=-=-=-==-=-=-=-==-=-O------>| Packet from Node A -> C | | | | | routed to direct tunnel | | | | | at MR A, based on MR A | | | | | now knowing MR C's CoA | | | | | and tunnel being up
In this example signaling, MR C changes care-of address while Route Optimization between MR A is operating and data is being transferred. Both cases where the handover is graceful ("make before break") and ungraceful ("break before make") occur in similar fashion, except in the graceful version no packets get lost.
======= Traffic inside Mobile IP tunnel to/from HA =-=-=-= Traffic inside Mobile IP tunnel between MRs ------- Traffic outside Mobile IP tunnel +----------+ +--------+ +------+ +--------+ +----------+ | [Node A] | | [MR A] | | [HA] | | [MR C] | | [Node C] | +----------+ +--------+ +------+ +--------+ +----------+ | | | | | x------------O=-=-=-==-=-=-=-==-=-O------>| Nodes A and C |<-----------O=-=-=-==-=-=-=-==-=-O-------x exchanging traffic | | | | | | | xxxxxxxxxxx | Break occurs: MR C | | | | | loses connectivity to | | | | | current attachment point | | | | | x------------O=-=-=-==-=-=-=-> | | Traffic from A -> C | | | | | lost and | | | x<=-=-O-------x vice versa | | | | | | | |<--------x | MR C finds a new | | | | | point of attachment, | | | | | registers to HA, clears | | | | | routing tables | | | | | | | x-------->| | Registration reply | | | | | x------------O=-=-=-==-=-=-=-> | | Traffic from A -> C | | | | | lost |<-----------O==========O=========O-------| Traffic from C -> A | | | | | sent via HA | | | | | | |<=========O---------x | Registration request, | | | | | reusing still active KRm | | | | | | x==========O-------->| | Registration reply | | | | | x------------O=-=-=-==-=-=-=-==-=-O------>| Traffic from A -> C | | | | | forwarded again |<-----------O=-=-=-==-=-=-=-==-=-O-------x Traffic from C -> A | | | | | switches back to direct | | | | | tunnel | | | | |
IANA has assigned rules for the existing registry "Mobile IPv4 numbers - per RFC 3344". The numbering space for Extensions that may appear in Mobile IP control messages (those sent to and from UDP port number 434) should be modified.
New Mobile IP header extension and message type values are needed for the messages and extensions listed in Section 5 (New Mobile IPv4 messages and extensions). There is a skippable extension which requires it's own type number. The rest of the new extensions are non-skippable, and grouped under a single new type as subtypes, apart from authentication extension which is given it's own type number to appear similar with other authentication extensions.
|TBA_T1, 128-255||Mobile router Route optimization capability|
|TBA_T2, 0-127||Route Optimization Extension|
|TBA_T3, 0-127||Mobile-Correspondent authentication extension|
| Table 1: New Values and Names for Extensions in Mobile IP Control messages |
A new number space has been created for the Values and Names for the Sub-Type for Route Optimization Extensions. This number space is initially defined to hold the following entries, allocated by this document:
|TBA_ST1||Route optimization reply|
|TBA_ST2||Route optimization prefix advertisement|
|TBA_ST3||Home-Test Init message|
|TBA_ST4||Care-of-Test Init message|
|TBA_ST5||Home Test message|
|TBA_ST6||Care-of test message|
|TBA_ST7||Care-of address Extension|
| Table 2: New Values and Names for the Sub-type Route Optimization Extension |
Note to RFC Editor: this section may be removed on publication as an RFC.
The Return Routability check has been established in the IPv6 world.
The network of trust relationships in Home Agent assisted Route Optimization solve the issues where arbitrary Correspondent Router can trust an arbitrary Mobile Router that it is indeed the proper route to reach an arbitrary mobile network.
It is assumed that all Mobile Routers have a trust relationship with the Home Agent. Thus, they trust information provided by Home Agent.
The Home Agent provides information matching Home Addresses and network prefixes. Each Mobile Router trusts this information.
Mobile Routers may perform Return Routability procedure between each other. This creates a trusted association between Mobile Router Home Address and Care-of Address. The Mobile Router also claims to represent a specific network. This information is not trustworthy as such.
The claim can be verified by checking the Home Address <-> network prefix information received, either earlier, or due to on-demand request, from the Home Agent. If they match, the Mobile Router's claim is authentic. If the network is considered trusted, a policy decision can be made to skip this check. Exact definitions on situations where such decision can be made are out of scope of this draft. The RECOMMENDED general practice is to perform the check.
Thanks to Jyrki Soini and Kari Laihonen for initial reviews.
|[RFC2003]||Perkins, C., “IP Encapsulation within IP,” RFC 2003, October 1996 (TXT, HTML, XML).|
|[RFC2004]||Perkins, C., “Minimal Encapsulation within IP,” RFC 2004, October 1996 (TXT, HTML, XML).|
|[RFC2119]||Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML).|
|[RFC2784]||Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, “Generic Routing Encapsulation (GRE),” RFC 2784, March 2000 (TXT).|
|[RFC3344]||Perkins, C., “IP Mobility Support for IPv4,” RFC 3344, August 2002 (TXT).|
|[RFC3519]||Levkowetz, H. and S. Vaarala, “Mobile IP Traversal of Network Address Translation (NAT) Devices,” RFC 3519, April 2003 (TXT).|
|[RFC5177]||Leung, K., Dommety, G., Narayanan, V., and A. Petrescu, “Network Mobility (NEMO) Extensions for Mobile IPv4,” RFC 5177, April 2008 (TXT).|
|[I-D.gundavelli-mip4-multiple-tunnel-support]||Gundavelli, S. and K. Leung, “Multiple Tunnel Support for Mobile IPv4,” draft-gundavelli-mip4-multiple-tunnel-support-02 (work in progress), February 2010 (TXT).|
|[I-D.ietf-mobileip-optim]||Perkins, C. and D. Johnson, “Route Optimization in Mobile IP,” September 2001.|
|[RFC1035]||Mockapetris, P., “Domain names - implementation and specification,” STD 13, RFC 1035, November 1987 (TXT).|
|[RFC3543]||Glass, S. and M. Chandra, “Registration Revocation in Mobile IPv4,” RFC 3543, August 2003 (TXT).|
|[RFC3775]||Johnson, D., Perkins, C., and J. Arkko, “Mobility Support in IPv6,” RFC 3775, June 2004 (TXT).|
|Helsinki University of Technology|
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|Nokia Siemens Networks|