IPSECME Working Group F. Detienne Internet-Draft M. Kumar Updates: 2332 (if approved) M. Sullenberger Intended status: Standards Track Cisco Expires: June 23, 2014 December 20, 2013 Flexible Dynamic Mesh VPN draft-detienne-dmvpn-01 Abstract The purpose of a Dynamic Mesh VPN (DMVPN) is to allow IPsec/IKE Security Gateways administrators to configure the devices in a partial mesh (often a simple star topology called Hub-Spokes) and let the Security Gateways establish direct protected tunnels called Shortcut Tunnels. These Shortcut Tunnels are dynamically created when traffic flows and are protected by IPsec. To achieve this goal, this document extends NHRP ([RFC2332]) into a routing policy feed and integrates GRE tunneling with IKEv2 and IPsec to provide the necessary cryptographic security. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on June 23, 2014. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of Detienne, et al. Expires June 23, 2014 [Page 1] Internet-Draft Dynamic Mesh VPN December 2013 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Tunnel Types . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 6 4.1. Initial Connectivity . . . . . . . . . . . . . . . . . . 6 4.2. Initial Routing Table Status . . . . . . . . . . . . . . 8 4.3. Indirection Notification . . . . . . . . . . . . . . . . 9 4.4. Node Discovery via Resolution Request . . . . . . . . . . 10 4.5. Resolution Request Forwarding . . . . . . . . . . . . . . 11 4.6. Egress node NHRP cache and Tunnel Creation . . . . . . . 12 4.7. Resolution Reply format and processing . . . . . . . . . 13 4.8. From Hub and Spoke to Dynamic Mesh . . . . . . . . . . . 14 4.9. Remote Access Clients . . . . . . . . . . . . . . . . . . 15 4.10. Node mutual authentication . . . . . . . . . . . . . . . 16 5. NHRP Extension Format . . . . . . . . . . . . . . . . . . . . 17 5.1. NHRP Traffic Indication . . . . . . . . . . . . . . . . . 17 6. Security Considerations . . . . . . . . . . . . . . . . . . . 19 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 8. Compliance against ADVPN requirements . . . . . . . . . . . . 19 9. Design Considerations . . . . . . . . . . . . . . . . . . . . 26 9.1. Routing Policy and RFC4301 Security . . . . . . . . . . . 26 9.2. Using Configuration Attributes . . . . . . . . . . . . . 28 9.3. NAT Support . . . . . . . . . . . . . . . . . . . . . . . 30 10. Acknowldegements . . . . . . . . . . . . . . . . . . . . . . 30 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 11.1. Normative References . . . . . . . . . . . . . . . . . . 30 11.2. Informative References . . . . . . . . . . . . . . . . . 31 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 1. Introduction This document describes a Dynamic Mesh VPN (DMVPN), in which an initial partial mesh expands to create direct connections called Shortcut Tunnels between endpoints that need to exchange data but are not directly connected in the initial mesh. The approach used in the design of this specification gives DMVPN the following advantages: Detienne, et al. Expires June 23, 2014 [Page 2] Internet-Draft Dynamic Mesh VPN December 2013 o Can run with routing protocol or with IKEv2 policies (CP_Exchange) making the specification suitable for complex gateways and remote access clients alike. o Can handle virtually infinite number of prefixes (including mobile prefixes) thanks to routing protocol. o The tunnel approach allows load balancing over multiple Transport networks and multicast to work natively. o Routing policy can apply more complex peer selection than 5-tuple traffic selector. o The layered approach allows evolution of other specifications used over DMVPN without having to rewrite or modify DMVPN. o Non-IP protocols such as ISIS, MPLS, plain ethernet... are natively supported (e.g. for Data Center Interconnection). In a generic manner, DMVPN topologies initialize as Hub-Spoke networks where Spoke Security Gateway nodes S* connect to Hub Security Gateway nodes H* over a public transport network (such as the Internet) considered insufficiently secure so as to mandate the use of IPsec and IKE. For scalability and redundancy reasons, there may be multiple hubs; the Hubs would then be connected together through the DMVPN. The diagram Figure 1 depicts this situation. DC1 DC2 | | [H1]-----[H2] | | | | +-+ | | +-+ | | | | [S1] [S2] [S3] [S4] | | | D1 D2 D3 Figure 1: Hub and Spoke, multiple hubs, multiple spokes Initially, the Security Gateway nodes (S*) are configured to build tunnels secured with IPsec to the Security Gateway node (H*) in a hub and spoke style network (any partial mesh will do, but Hub-Spoke is common and easily understood). This initial network is then used when traffic starts flowing between the protected networks D*. DMVPN uses NHRP as a signaling mechanism over the S*-H* and H*-H* tunnels to trigger the spokes (S*) to discover each other and build dynamic, direct Shortcut Tunnels. The Shortcut Tunnels allow those spokes to communicate directly with each other without forwarding traffic through the hub, essentially creating a dynamic mesh. The spokes can be either routers or firewalls playing the role of Security Gateways or hosts such as computers, mobile phones,etc. Detienne, et al. Expires June 23, 2014 [Page 3] Internet-Draft Dynamic Mesh VPN December 2013 protecting their own traffic. Nodes S1, S2 and S3 above are routers while S4 is a host implementation. This document describes how NHRP is modified and augmented to allow the rapid creation of dynamic IPsec tunnels between two devices. Throughout this document, we will call these devices participating in the DMVPN "nodes". In the context of this document, the nodes protect a topologically dispersed Private, Overlay Network address space. The nodes allow the devices in the Overlay Network to communicate securely with each other via GRE tunnels secured by IPsec using dynamic tunnels established between the nodes over the (presumably insecure) Transport network. I.e. the protected tunnel packets are forwarded over this Transport network. The NBMA Next Hop Resolution Protocol (NHRP) as described in [RFC2332] allows an ingress node to determine the internetworking layer address and NBMA address of an egress node. The servers in such an NBMA network provide the functionality of address resolution based on a cache which contains protocol layer address to NBMA subnetwork layer address resolution information. This can be used to create a virtual network where dynamic virtual circuits can be created on an as needed basis. In this document, we will depart the underlying notion of a centralized NHS. All data traffic, NHRP frames and other control traffic needed by this DMVPN MUST be protected by IPsec. In order to efficiently support Layer 2 based protocols, all packets and frames MUST be encapsulated in GRE ([RFC2784]) first; the resulting GRE packet then MUST be protected by IPsec. IPsec transport mode MUST be supported while IPsec tunnel mode MAY be used. The usage of a GRE encapsulation protected by IPsec is described in [RFC4301]. Implementations SHOULD strongly link GRE and IPsec SA's through some form of connection latching as described in [RFC5660]. 2. Terminology The NHRP semantic is used throughout this document however some additional terminology is used to better fit to the context. o Protected Network, Private Network: a network hosted by one of the nodes. The protected network IP addresses are those that are resolved by NHRP into an NBMA address. o Overlay Network: the entire network composed with the Protected Networks and the IP addresses installed on the Tunnel interfaces instantiating the DMVPN. Detienne, et al. Expires June 23, 2014 [Page 4] Internet-Draft Dynamic Mesh VPN December 2013 o Transport Network, Public Network: the network transporting the GRE/IPsec packets. o Nodes: the devices connected by the DMVPN that implement NHRP, GRE /IPsec and IKE. o Ingress Node: The NHRP node that takes data packets from off of the DMVPN and injects them into the DMVPN on either a multi-hop tunnel path (initially) or single hop shortcut tunnel. Also the node that will send an NHRP Resolution Request and receive an NHRP Resolution Reply to build a short-cut tunnel. o Egress Node: The NHRP node that extracts data packets from the DMVPN and forwards them off of the DMVPN. Also the node that answers an NHRP Resolution Request and send an NHRP Resolution Reply. o Intermediate Node: An NHRP node that is in the middle of multi-hop tunnel path between an Ingress and Egress Node. For the particular data traffic in question the Intermediate node will receive packets from the DMVPN and resend them (hair-pin) them back onto the DMVPN. Note, a particular node in the DMVPN, may at the same time be an Ingress, Egress and Intermediate node depending on the data traffic flow being looked at. In general, DMVPN nodes make extensive use of the Local Address Groups (LAG) and Logically Independent Subnets (LIS)models as described in [RFC2332]. A compliant implementation MUST support the LAG model and SHOULD support the LIS model. 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]. 3. Tunnel Types The tunnels described in this document are of type GRE/IPsec. GRE/ IPsec allows a single pair of IPsec SA's to be negotiated between the DMVPN nodes. From an IPsec aggregation standpoint, this means less negotiation, cleaner use of expensive resources and less reprogramming of the data plane by the IKE control plane as additional networks are discovered between any two peers. In the remainder of this document, GRE and GRE/IPsec will be used interchangeably depending on the focused layer but always imply "GRE protected by IPsec" Taking advantage of the GRE encapsulation, and while NHRP could be forwarded over IP, the RFC recommended Layer 2 NHRP frames have been Detienne, et al. Expires June 23, 2014 [Page 5] Internet-Draft Dynamic Mesh VPN December 2013 retained in order to simplify the security policies (packet filters do not have to be augmented to allow NHRP through, no risk of mistakenly propagating frames where they should not, etc.). Compliant implementations MUST support L2 NHRP frames. DMVPN can be implemented in a number of ways and this document places no restriction on the actual implementation. This section covers what the authors believe are the important implementation recommendations to construct a scalable implementation. The authors recommend using a logical interface construct to represent the GRE tunnels. These interfaces are called Tunnel Interfaces or simply Interfaces from here onward. In the remainder of this document, we will assume the implementation uses point-to-point Tunnel Interfaces; routes to prefixes in the Overlay network are in the Routing Table (aka Routing Information Base). These routes forward traffic toward the tunnel interfaces. Point-to-Multipoint GRE interfaces (aka multipoint interfaces for short) can also be used. In that case there is by construction only one tunnel source NBMA address and the interface has multiple tunnel endpoints. In this case NHRP registration request and reply messages, [RFC2332], are used to pass the tunnel address to tunnel NBMA address mapping from the NHC (S*) to the NHS (H*). The NHRP registration request and reply MAY be restricted to a single direct tunnel hop between the NHC (S*) and NHS (H*). For didactic reasons, and an easier understanding of the LAG support, we will use the point-to-point construct to highlight the protocol behavior in the remainder of this document. An implementation can use different models (point-to-point, multipoint, bump in the stack,...) but MUST comply to the external (protocol level) behavior described in this document. 4. Solution Overview 4.1. Initial Connectivity We assume the following scenario where nodes (S1, S2, H1, H2) depicted in Figure 2 supporting GRE, IPsec/IKE and NHRP establish connections instantiated by GRE tunnels. Those GRE tunnels SHOULD be protected by IPsec/IKE. These tunnels will be used to secure all the data traffic as well as the NHRP control frames. In general, routing protocols (and possibly other control protocols such as NHRP or IKE) will also be protected by IPsec or IKE. Detienne, et al. Expires June 23, 2014 [Page 6] Internet-Draft Dynamic Mesh VPN December 2013 DC1 | [H1] | | ] +-+ +-+ ] GRE/IPsec tunnels over Transport network | | ] [S1] [S2] | | D1 D2 Figure 2: Hub and Spoke Initial Connectivity It is assumed that S1, H1 and S2 are connected via a shared Transport network (typically a Public, NBMA network) and there is connectivity between the nodes over that transport network. The nodes possess multiple interfaces; each of which has a dedicated IP address: o a public interface IntPub connected to the transport network; IP address: Pub{node} o one or several tunnel interface Tunnel0,1,.. (GRE/IPsec) connecting to peers; IP address: Tun{i}{node} o a private interface IntPriv facing the private network of the node; IP address: Priv{node} e.g. node S1 owns the following addresses: PubS1, TunS1 and PrivS1 The networks D1, D2, DC1 and also the tunnel address Tun{i} can and are presumed to be private in the sense that their address space is kept independent from the transport network address space. Together, they form the Overlay network. For the transport network, the address family is either IPv4 or IPv6. In the context of this document, for the overlay network, the address family is IPv4 and/or IPv6. Initially, nodes S1 and S2 create a connection to node H1. Optionally, S1 and S2 MAY register to H1 via NHRP. Typically the GRE tunnels between S* and H1 will be protected by IPsec. A compliant implementation MUST support IPsec protected GRE tunnels and SHOULD support unprotected GRE tunnels. At the end of this section, a dynamic tunnel will be set up between S1 and S2 and traffic will flow directly through S1 and S2 without going through H1. Detienne, et al. Expires June 23, 2014 [Page 7] Internet-Draft Dynamic Mesh VPN December 2013 4.2. Initial Routing Table Status In the context of this document, the authors make no assumption about how the routing tables are initially populated but one can assume that routing protocols exchange information between H1 and S1 and between H1 and S2. In this diagram, we assume each node has routes (summarized or specific) for networks D1, D2, DC1 which are IP networks. We assume the summary prefix SUM to encompass all the private networks depicted on this diagram. We assume the communication between those networks needs to be protected and therefore, the routes point to tunnels. I.e. S1 knows a route summarizing all the Overlay subnets and this route points to the GRE/IPsec tunnel leading to H1. Note, the the summary prefix is a network design choice and it can be replaced by a prefix summary manifold or individual non-summarized routes. Example 1: Node S1 has the following routing table: o TunH1 => Tunnel0 o SUM => TunH1 on Tunnel0 o 0.0.0.0/0 => IntPub o D1 => IntPriv Example 2: Node H1 has the following routing table: o TunS1 => Tunnel1 o TunS2 => Tunnel2 o D1 => TunS1 on Tunnel1 o D2 => TunS2 on Tunnel2 o 0.0.0.0/0 => IntPub o DC1 => IntPriv The exact format of the routing table is implementation dependent but the node discovery principle MUST be enforced and the implementation MUST be compatible with an implementation using the routing tables outlined above. This document does not specify how the routes are installed but it can be assumed that the routes (1) and (2) in the tables above are exchanged between S* and H* nodes after the S*-H* connections have been duly authenticated. In a DMVPN solution, it is typical that the routes are exchanged by a route exchange protocol (e.g. BGP or IKE as shown in Section 9.2) or are installed statically (usually a mix of both). It is important that routing updates be filtered in order to prevent a node from advertising improper routes to another node. This filtering is out of the scope of this document as most routing protocol implementations are already capable of such filtering. In Detienne, et al. Expires June 23, 2014 [Page 8] Internet-Draft Dynamic Mesh VPN December 2013 order to meet these criteria, an implementation SHOULD offer identity-based policies to filter those routes on a per peer basis. When a device Ds on network D1 needs to connect to a device Dd on network D2 o a data packet ip(Ds, Dd) is sent and reaches S1 on IntPriv o the data packet is routed by S1 via Tunnel0 toward H1; S1 encapsulates, protects and forwards this packet out IntPub via the transport network to H1 o H1 receives the protected packet on IntPub; H1 decrypts and decapsulates this packet; the resulting data packet looks to the IP stack on H1 as if it arrived on interface Tunnel1 o the data packet is routed by H1 via Tunnel2 toward S2; H1 encapsulates, protects and forwards this out IntPub via the transport network to S2 o S2 receives the protected packet on IntPub; S2 decrypts and decapsulates this packet; the resulting data packet looks to the IP stack as if it arrived on interface Tunnel0 o S2 routes the data packet out of its IntPriv interface to the destination Dd 4.3. Indirection Notification Considering the packet flow seen in {previous section}. When H1 (Intermediate Node) receives a packet from the ingress node S1 and forwards it to the Next Node S2, it technically re-injects the packet back into the DMVPN. At this point H1 SHOULD an Indirection Notification message to S1. The Indirection Notification is a dedicated NHRP message indicating the ingress node that it sent an IP packet that had to be forwarded via the intermediate node to another node. The Indirection Notification MUST contain the first 64 bytes of the clear text IP packet that was forwarded to the next node. The exact format of this message is detailed in the section [PACKET_FORMAT]. The Indirection Notification MUST be sent back to the ingress node through the same GRE/IPsec tunnel upon which the hair-pinned IP packet was received and MUST be rate limited. This message is a hint that a direct tunnel SHOULD be built between the end-nodes, bypassing intermediate nodes. This tunnel is called a "Shortcut Tunnel". Compliant implementations MUST be able to send and accept the Indirection Notification, however implementations MUST continue to Detienne, et al. Expires June 23, 2014 [Page 9] Internet-Draft Dynamic Mesh VPN December 2013 accept traffic over the spoke-hub-spoke path during spoke-spoke path establishment (Shortcut Tunnel). When a node receives such a notification, it MUST perform the following: o parse and accept the message o extract the source address of the original protected IP packet from the 64 bytes available o perform a route lookup on this source address * If the routing to this source address is also via the DMVPN network upon which it received the Indirect Notification then this node is an intermediate node on the tunnel path from the ingress node (injection point) to the egress node (extraction point). In this case this intermediate node MUST silently drop the Indirect Notification that it received. Note that if the node is an intermediate node, it is likely that it has generated and sent an Indirect Notification about this same protected IP packet to its tunnel neighbor on the tunnel path back towards the ingress node (injection point). This is correct behavior. o if the previous step did succeed, extract the destination IP address (Dd) of the original protected IP packet from the 64 bytes available. The ingress node MAY also extract additional information from those 64 bytes such as the protocol type, port numbers etc. In steady state, Indirection Notifications MUST be accepted and processed as above from any trusted peer with which the node has a direct connection. 4.4. Node Discovery via Resolution Request After processing the information in the Indirection Notify, the ingress node local policy SHOULD determine whether a shortcut tunnel needs to be established. Assuming the local policy requests a shortcut tunnel, the ingress node MUST emit a Resolution Request for the destination IP address Dd. More specifically, the NHRP Resolution Request emitted by S1 to resolve Dd will contain the following fields: o Fixed Header * ar$op.version = 1 * ar$op.type = 1 Detienne, et al. Expires June 23, 2014 [Page 10] Internet-Draft Dynamic Mesh VPN December 2013 o Common Header (Mandatory Header) * Source NBMA Address = PubS1 * Source Protocol Address = TunS1 * Destination Protocol Address = Dd The resolution request is routed by S1 to H1 over the GRE/IPsec tunnel. If an intermediate node has a valid (authoritative) NHRP mapping in its cache, it MAY respond. An intermediate node SHOULD NOT answer Resolution Requests in any other case. Note that a Resolution Request can be voluntarily emitted by Security Gateway and is not strictly limited to a response to the Indirection Notify message. Such cases and policies are out of the scope of the document. The sending of Resolution Requests by a ingress node MUST be rate limited. 4.5. Resolution Request Forwarding The Resolution Request can be sent by S1 to an explicit or implicit next-hop-server. In the explicit scenario, the NHS is defined in the node configuration. In the implicit case, the node can infer the NHS to use. Similarly, an intermediate node that cannot answer a Resolution Request SHOULD forward the Resolution Request to an implicit or explicit NHS in the same manner unless local policy forbids resolution forwarding between Spokes. There can be an undetermined number of intermediate node. A DMVPN compliant implementation MUST be able to infer the NHS from its routing table in the following way: o the address Dd to be resolved is looked up in the routing table (other parameters can be considered by the ingress node but these will not be available to intermediate nodes) o the best route for Dd is selected (longest prefix match) * if several routes match (same prefix length) only the routes pointing to a DMVPN Tunnel interface are kept. This SHOULD NOT occur in practice. o if the best route found points to a DMVPN Tunnel interface, the next-hop address MUST be used as NHS o if the best route found does not point to a DMVPN Tunnel interface the forwarding of the packet stops and the matching prefix P and prefix len (Plen) is kept temporarily. Very often, P/Plen == D2/ D2len (this is the case in the diagram used in this document) but this may not always be true depending on the structure of the Detienne, et al. Expires June 23, 2014 [Page 11] Internet-Draft Dynamic Mesh VPN December 2013 networks protected by S2. The associated prefix length (Plen) is also preserved. If the Resolution Request forwarding stops at the ingress node (at emission), the Resolution Request process MUST be stopped with an error for address Dd. If the lookup succeeds, the next-hop's NBMA address is used as destination address of the GRE encapsulation. Before forwarding, each intermediate node MUST add a Forward Transit Extension record to the NHRP Resolution Request. Any intermediate nodes SHOULD NOT cache any information while forwarding Resolution Requests. In the case an intermediate node implementation caches information, it MUST NOT assume that other intermediate nodes will also cache that information. Thanks to the forwarding model described in this document and due to the absence of intermediate caching, Server Cache Synchronization is not needed and even recommended against. Therefore, a DMVPN compliant implementation MUST NOT rely on such a synchronization which would have adverse effects on the scalability of the entire system. If the TTL of the request drops to zero or the current node finds itself on a Forward Transit Extension record then the NHRP Resolution Request MUST be dropped and an NHRP error message sent to the source. When the Resolution Request eventually reaches a node where the route(s) to the destination would take it out through a non-DMVPN interface, the Resolution Request process MUST be stopped and this node becomes the egress node. The egress node is typically (by virtue of network design) the topologically closest node to the resolved address Dd. The egress node must then prepare itself for replying with a Resolution Reply. 4.6. Egress node NHRP cache and Tunnel Creation When a node declares itself an egress node while attempting to forward a Resolution Request, it MUST evaluate the need for establishing a shortcut tunnel according to a user policy. Note that an implementation is not mandated to support a user policy but then the implicit policy MUST request the shortcut establishment. If policies are supported, one of the possible policies MUST be shortcut establishment. If a shortcut is required, the egress node MUST perform the following operations: Detienne, et al. Expires June 23, 2014 [Page 12] Internet-Draft Dynamic Mesh VPN December 2013 o the source NBMA address (PubS1) is extracted from the NHRP Resolution Request o if a GRE/IPsec tunnel already exists between PubS2 and PubS1, this tunnel is selected (assuming interface TunnelX) o otherwise, a new GRE shortcut tunnel is created between PubS2 and PubS1 (assuming interface TunnelX); the GRE tunnel SHOULD be protected by IPsec and the SA's immediately negotiated by IKE o an NHRP cache entry is created for TunS1 => PubS1. The entry SHOULD NOT remain in the cache for more than the specified Hold Time (from the NHRP Resolution Request). This NHRP cache entry may be 'refreshed' for another hold time period prior to expiry by receipt of another matching NHRP Resolution Request or by sending an NHRP Resolution Request and receiving an NHRP Resolution Reply. o a route is inserted into the RIB: TunS1/32 => PubS1 on TunnelX (assuming IPv4) Regardless how the shortcut tunnel is created a node SHOULD NOT try to establish more than one tunnel with a remote node. If there are other tunnels not managed by DMVPN, the tunnel selectors (source, destination, tunnel key) MUST NOT interfere with the DMVPN shortcut tunnels. If a tunnel has to be created and SA's established, a node SHOULD wait for the tunnel to be in place before proceeding with further operations. Regardless of how those operations are timed in the implementation, a node SHOULD avoid dropping data packets during the cache and SA installation. The order of operations SHOULD ensure continuous forwarding. 4.7. Resolution Reply format and processing After the operations described in the previous section are completed, a Resolution Reply MUST be emitted by the egress node. Instead of strictly answering with just the host address being looked up, the Reply will contain the entire prefix (P/Plen) that was found during the stopped Resolution Request forwarding phase. The Resolution Reply main fields MUST be populated as follows: o Fixed Header * ar$op.version = 1 * ar$op.type = 2 o Common Header (Mandatory Header) * Source NBMA Address = PubS1 * Source Protocol Address = TunS1 * Destination Protocol Address = Dd Detienne, et al. Expires June 23, 2014 [Page 13] Internet-Draft Dynamic Mesh VPN December 2013 o CIE-1 * Prefix-len = Plen * Client NBMA Address = PubS2 * Client Protocol Address = TunS2 The Destination Protocol address remains the address being resolved (Dd) while the CIE actually contains the remainder of the response (Plen via NBMA PubS2, Protocol TunS2). The Resolution Reply MUST be forwarded to the ingress node S1 either through the shortcut tunnel or via the Hub. If the address family of the resolved address Dd is IPv6, the Resolution Reply SHOULD be augmented with a second CIE containing the egress node's link local address. If a node decides to block the resolution process, it MAY simply drop the Resolution Request or avoid sending a Resolution Reply. A node MAY also send a NACK Resolution Reply. When the Resolution Reply is received by the ingress node, a new tunnel TunnelY MUST be created pointing to PubS2 if one does not already exist (which depends on whether the Resolution Reply was routed via the Hub(s) or directly on the shortcut tunnel). The ingress node MUST process the reply in the following way: o Validate that this Resolution Reply corresponds to a Request emitted by S1. If not, issue an error and stop processing the Reply. o An NHRP Cache entry is created for TunS2 => PubS2 o Two routes are added to the routing table: * TunS2 => TunnelY * P/Plen => TunS2 on TunnelY Though implementations may be entirely different, a compliant implementation MUST exhibit a functional behavior strictly equivalent to the one described above. I.e. IP packets MUST eventually be forwarded according to the above implementation. DMVPN compliant implementations MUST support providing and receiving aggregated address resolution information. 4.8. From Hub and Spoke to Dynamic Mesh At the end of the resolution process, the overlay topology will be as follows: Detienne, et al. Expires June 23, 2014 [Page 14] Internet-Draft Dynamic Mesh VPN December 2013 DC1 | [H1] | | ] +-+ +-+ ] GRE/IPsec tunnels over Transport network | | ] [S1]===[S2] | | D1 D2 Shortcut tunnel established Where the tunnel depicted with = is a GRE/IPsec shortcut tunnel created by NHRP. The Routing Table on S1 will now look as follows: o TunH1 => Tunnel0 o SUM => TunH1 on Tunnel0 o 0.0.0.0/0 => IntPub o D1 => IntPriv o TunS2 => TunnelY o P/Plen => TunS2 on TunnelY It is easy to see that traffic from D1 to D2 will follow the shortcut path under the assumption that P == D2 or D2 is a subnet included in P. The tunnels between S* and H* are actually tunnels created automatically to bootstrap the DMVPN. In practice the initial topology will be a static star (aka Hub and Spoke) topology between S* and H* that will evolve into a dynamic mesh between the nodes S*. From the spokes (S*) standpoint, the bootstrap tunnels can be established with a node H1 statically defined or discovered by DNS. The problem of finding the initial hubs in a DMVPN is not different than finding regular hubs in a traditional Hub and Spoke network. For scalability reasons, it is expected that the NHRP Indirection/ Resolution is the only way by which routes are exchanged between S* nodes. While this does not fall in the context of this document, it is worth mentioning that actual implementations SHOULD NOT establish a routing protocol adjacency directly over the shortcut tunnels. 4.9. Remote Access Clients The specification in this document allows a node to not protect any private network. I.e. in a degenerate case, it MUST be possible for a node S1 to not have a D1 network attached to it. Instead, S1 only owns a PubS1? and TunS1? address. This would typically the case of a Detienne, et al. Expires June 23, 2014 [Page 15] Internet-Draft Dynamic Mesh VPN December 2013 remote access client (PC, mobile device,...) that only has a tunnel address and an NBMA address. DC1 | [H1] | | ] +-+ +-+ ] GRE/IPsec tunnels over Transport network | | ] [S1]===[S2] | D2 Remote Access Client On the diagram above, S1 is actually a simple PC or mobile node that is not protecting any other network other than its own tunnel address. These nodes may fully participate in a DMVPN network, including building spoke-spoke tunnels as long as they support GRE, NHRP, IPsec /IKE, and have a way to separate tunneled traffic (virtual interfaces) and be able to update a local routing table to associate networks with different next-hops out either their IntTun (data traffic going over the tunnel) or (IntPub) (tunnel packets themselves and/or non-tunneled data traffic). They may not need to run a routing protocol since they can rely on the Configuration Payload Exchange described in Section 9.2. 4.10. Node mutual authentication Nodes authenticate each other using the IKE protocol, while they attempt to establish a tunnel. Because the system is by nature extremely distributed, it is recommended to use X.509 certificates for authentication. Internet Public Key Infrastructure is described in [RFC5280] The structured names and various fields in the certificate can be useful for filtering undesired connectivity in large administrative domains or when two domains are being partially merged. It is indeed easy for a system administrator to define filters to prevent connectivity between nodes that are not supposed to communicate directly (e.g. filtering based on the O or OU fields). Though nodes may be blocked from building a direct tunnel by the above means they may or may not be allowed to communicate via a spoke-hub-spoke path. Allowing or blocking communication via the spoke-hub-spoke path is outside the scope of this document. Detienne, et al. Expires June 23, 2014 [Page 16] Internet-Draft Dynamic Mesh VPN December 2013 5. NHRP Extension Format As described in [RFC2332], an NHRP packet consists of a fixed part, a mandatory part and an extensions part. The Fixed Part is common to all NHRP packet types. The Mandatory Part MUST be present, but varies depending on packet type. The Extensions Part also varies depending on packet type, and need not be present. This section describes the packet format of the new messages introduced as well as extensions to the existing packet types. 5.1. NHRP Traffic Indication The fixed part of an NHRP Traffic Indication packet picks itself directly from the standard NHRP fixed part and all fields pick up the same meaning as in [RFC2332] unless otherwise explicitly stated. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ar$afn | ar$pro.type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ar$pro.snap | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ar$pro.snap | ar$hopcnt | ar$pktsz | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ar$chksum | ar$extoff | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ar$op.version | ar$op.type | ar$shtl | ar$sstl | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: Traffic Indication Fixed Header o ar$op.type With ar$op.version = 1, this is an NHRP packet. Further, [RFC2332] uses the numbers 1-7 for standard NHRP messages. When ar$op.type = 8, this indicates a traffic indication packet. The mandatory part of the NHRP Traffic Indication packet is slightly different from the NHRP Resolution/Registration/Purge Request/Reply packets and bears a much closer resemblance with the mandatory part of NHRP Error Indication packet. The mandatory part of an NHRP Traffic Indication has the following format Detienne, et al. Expires June 23, 2014 [Page 17] Internet-Draft Dynamic Mesh VPN December 2013 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Src Proto Len | Dst Proto Len | unused | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Traffic Code | unused | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source NBMA Address (variable length) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source NBMA Subaddress (variable length) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Protocol Address (variable length) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination Protocol Address (variable length) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Contents of Data Packet in traffic (variable length) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: Traffic Indication Mandatory Part o Src Proto Len: This field holds the length in octets of the Source Protocol Address. o Dst Proto Len: This field holds the length in octets of the Destination Protocol Address. o Traffic Code: A code indicating the type of traffic indication message, chosen from the following list * 0: NHRP Traffic Redirect/Indirection message.This indirection is an indication,to the receiver, of the possible existence of a 'better' path in the NBMA network. o Source NBMA Address: The Source NBMA address field is the address of the station which generated the traffic indication. o Source NBMA SubAddress: The Source NBMA subaddress field is the address of the station generated the traffic indication. If the field's length as specified in ar$sstl is 0 then no storage is allocated for this address at all. o Source Protocol Address: This is the protocol address of the station which issued the Traffic Indication packet. o Destination Protocol Address: This is the destination IP address from the packet which triggered the sending of this Traffic Indication message. Note that unlike NHRP Resolution/Registration/Purge messages, Traffic Indication message doesn't have a request/reply pair nor does it contain any CIE though it may contain extension records. Detienne, et al. Expires June 23, 2014 [Page 18] Internet-Draft Dynamic Mesh VPN December 2013 6. Security Considerations The use of NHRP and its protocol extensions described in this document do not open a direct security hole. The peers are duly authenticated with each other by IKE and the traffic is protected by IPsec. The only risk may come from inside the network itself; this is not different from static meshes. Implementers must be diligent in offering all the control and data plane filtering options that an administrator would need to secure the communication inside the overlay network. 7. IANA Considerations The following values are used experimentally: o The ar$op.type value of 8 representing Traffic Indication o Traffic Code value of 0 indicating a Traffic Indirection message. Full standardization would require official IANA numbers to be assigned. 8. Compliance against ADVPN requirements This section compares the adequacy of DMVPN to the requirement list stated in [RFC7018]. 8.1. Requirement 1: minimize configuration change There are three requirements from requirement 1 from [RFC7018] which reads: "For any network topology (star, full mesh, and dynamic full mesh), when a new gateway or endpoint is added, removed, or changed, configuration changes are minimized as follows. Adding or removing a spoke in the topology MUST NOT require configuration changes to hubs other than where the spoke was connected and SHOULD NOT require configuration changes to the hub to which the spoke was connected. The changes also MUST NOT require configuration changes in other spokes. Specifically, when evaluating potential proposals, we will compare them by looking at how many endpoints or gateways must be reconfigured when a new gateway or endpoint is added, removed, or changed and how substantial this reconfiguration is, in addition to the amount of static configuration required." Detienne, et al. Expires June 23, 2014 [Page 19] Internet-Draft Dynamic Mesh VPN December 2013 The three requirements are (1a) all hub change, (1b) connected hub change, and (1c) other spokes. (1a), (1b), and (1c) are met by the ability for tunnels transport addresses to be dynamically discovered by NHRP and the tunnels dynamically created and configured by IKE when the authentication succeeds. 8.2. Requirement 2: IPsec without config change, even with peer address change There is one requirement from Requirement 2 of [RFC7018] which reads: "ADVPN Peers MUST allow IPsec tunnels to be set up with other members of the ADVPN without any configuration changes, even when peer addresses get updated every time the device comes up. This implies that Security Policy Database (SPD) entries or other configuration based on a peer IP address will need to be automatically updated, avoided, or handled in some manner to avoid a need to manually update policy whenever an address changes." Each proposal meets this requirement as described below: This requirement is met, and uses the Summary route from Hub (Section 4.2), then method of Indirection (Section 4.3) then a Resolution Request (Section 4.4) and finally a Resolution reply (Section 4.7) to identify the overlay address to transport address mapping in a dynamic manner. 8.3. Requirement 3: Tunnel, Routing, and no Additional Configuration There are two requirements from requirement 3 of [RFC7018] which reads: "In many cases, additional tunneling protocols (e.g., GRE) or routing protocols (e.g., OSPF) are run over the IPsec tunnels. Gateways MUST allow for the operation of tunneling and routing protocols operating over spoke-to-spoke IPsec tunnels with minimal or no configuration impact. The ADVPN solution SHOULD NOT increase the amount of information required to configure protocols running over IPsec tunnels." The two requirements are: (3a) minimal or no configuration impact incurred by the tunneling protocols between spokes, (3b) minimal configuration impact incurred by routing protocols operating over the spoke-to-spoke tunnels. Detienne, et al. Expires June 23, 2014 [Page 20] Internet-Draft Dynamic Mesh VPN December 2013 Requirement (3a) is met as dynamic tunnels are dynamically created at the same time as the IKE SA is authenticated. Requirement (3b) is met as routing protocols do not operate over spoke-to-spoke tunnels; only NHRP is responsible for exchanging prefixes between spokes and NHRP is entirely dynamic. 8.4. Requirement 4: Spoke-to-Spoke Optimization There are two requirements from requirement 4 of [RFC7018] which reads: "In the full-mesh and dynamic full-mesh topologies, spokes MUST allow for direct communication with other spoke gateways and endpoints. In the star topology mode, direct communication between spokes MUST be disallowed." The two requirements are: (4a) in full-mesh and dynamic full-mesh topologies, allow direct spoke-to-spoke communication and (4b) in star topology, disallow direct spoke-to-spoke communication. Requirement (4a) is met by the Resolution Request/Reply mechanism described from Section 4.4 to Section 4.7. Requirement (4b) is met by disabling the NHRP protocol handler from a tunnel pointing to a remote peer. As NHRP is disabled, NHRP messages to and from that peer will be dropped and the peer will be unable to forge a new dynamic endpoint with any other spoke. It is sufficient to disable NHRP to that spoke at the hub level to impede the Resolution mechanism causing the spoke-spoke optimization. Requirement (4b) can be applied globally (for all spokes) or individually (for selected spokes) the activation or deactivation of NHRP on a given peer to peer tunnel can be driven by static configuration or on a per-identity basis. Additionally, peers can filter NHRP Resolution Requests or Replies if partial meshing is allowed to specific prefixes only. Additional identity and certificate filters can be imposed to further restrict which devices can connect to others. For instance, Certificates Subject Names fields such as Organization or Organization Unit are frequently used to that effect. 8.5. Requirement 5: Credentials and Compromise There are three requirements from requirement 5 of [RFC7018] which reads: "ADVPN Peers MUST NOT have a way to get the long-term authentication credentials for any other ADVPN Peers. The Detienne, et al. Expires June 23, 2014 [Page 21] Internet-Draft Dynamic Mesh VPN December 2013 compromise of an endpoint MUST NOT affect the security of communications between other ADVPN Peers. The compromise of a gateway SHOULD NOT affect the security of the communications between ADVPN Peers not associated with that gateway." The three requirements are: (5a) no way to get the long-term authentication credentials from any other ADVPN peers, (5b) compromise of an endpoint does not affect security of communications with other peers, and (5c) compromise of a gateway does not affect the security of communications between ADVPN peers not associated with that gateway. Requirement (5a) and is met by Section 4.10 which recommends PKI. Requirement (5b) is met with mutual authentication. If an endpoint is compromised, its corresponding certificate will be revoked and it will be impossible for this endpoint to create any new connection to any new peer. Requirement (5c), is met by the same mechanism as (5b). 8.6. Requirement 6: Handoff and Roaming There are two requirements from requirement 6 of [RFC7018] which reads: "Gateways SHOULD allow for seamless handoff of sessions in cases where endpoints are roaming, even if they cross policy boundaries. This would mean the data traffic is minimally affected even as the handoff happens. External factors like firewalls and NAT boxes that will be part of the overall solution when ADVPN is deployed will not be considered part of this solution. Such endpoint roaming may affect not only the endpoint-to- endpoint SA but also the relationship between the endpoints and gateways (such as when an endpoint roams to a new network that is handled by a different gateway)." The two requirements are (6a) gateways allow for seamless handoff of sessions when clients roaming (6b) even if they cross policy boundaries. Requirement (6a) is met by the fact that tunnels can be established dynamically but will not be available for traffic until the IPsec SA is fully available. This is ensured by the fact that NHRP does not install prefixes into the routing policy until the SA's are fully negotiated, as described in Section 4.6 Detienne, et al. Expires June 23, 2014 [Page 22] Internet-Draft Dynamic Mesh VPN December 2013 Requirement (6b) is met because DMVPN is agnostic to policy boundaries or domains. 8.7. Requirement 7: Easy handoff and Migration The are two requirements from requirement 7 of [RFC7018] which reads: "Gateways SHOULD allow for easy handoff of a session to another gateway, to optimize latency, bandwidth, load balancing, availability, or other factors, based on policy. This ability to migrate traffic from one gateway to another applies regardless of whether the gateways in question are hubs or spokes. It even applies in the case where a gateway (hub or spoke) moves in the network, as may happen with a vehicle-based network." The two requiremets are: (7a) Easy handoff os a session to another gateway to optimize requirements based on policy, and (7b) ability to migrate from one gateway to another. Requirement (7a) can be achieved by using IKEv2 Redirect ([RFC5685]) to redirect a peer entirely to another gateway. Specific Indirection Notification can be used to redirect specific networks or peers. Requirement (7b) is met because IKEv2 Redirect, Resolution Request and Indirection Notification can be sent on a voluntary basis by any device (hub or spoke) which means than a source node or an egress node can be of any type (hub or spoke). In practice, this is an unusual mode of operation (seldom desirable) but it is legitimate. 8.8. Requirement 8: NAT There are three requirements from requirement 8 of [RFC7018] which reads: "Gateways and endpoints MUST have the capability to participate in an ADVPN even when they are located behind NAT boxes. However, in some cases they may be deployed in such a way that they will not be fully reachable behind a NAT box. It is especially difficult to handle cases where the hub is behind a NAT box. When the two endpoints are both behind separate NATs, communication between these spokes SHOULD be supported using workarounds such as port forwarding by the NAT or detecting when two spokes are behind uncooperative NATs, and using a hub in that case." The three requirements are: (8a) Gateways and endpoints MUST have the capability to participate in an ADVPN even when they are located behind NAT boxes. (8b) When the two endpoints are both behind Detienne, et al. Expires June 23, 2014 [Page 23] Internet-Draft Dynamic Mesh VPN December 2013 separate NAT boxes. (8c) Shortcuts should continue to work seamlessly when NAT prevents direct spoke-spoke connectivity. All requirements (8a,8b) are met by the use of NAT Traversal to detect NAT devices within the network. If a hub is deployed behind a NAT address, the spokes need to point their tunnel destination towards the public address of the Hub,as described in Section 9.3 Requirement (8c) is met since NHRP does not install prefixes into the routing policy until the SA's are fully negotiated, as described in Section 4.6. 8.9. Requirement 9: Changes reported There is one requirement from requirement 9 of [RFC7018] which reads: "Changes such as establishing a new IPsec SA SHOULD be reportable and manageable. However, creating a MIB or other management technique is not within scope for this effort." Requirement (9) is met by taking advantage of the various MIB's defined in existing documents such as [RFC2677], [RFC4292], etc. There is no standard IPsec MIB but various vendors have developed a proprietary MIB (typically based on draft-ietf-ipsec-flowmon-mib and draft-ietf-ipsec-mib) that implementations of this specification can use. Traps can be triggered as tunnel interfaces come up and down dynamically as defined in [RFC2863] section 3.1.9. Additional logging message can be triggered at various levels of the implementation. 8.10. Requirement 10: Federation between organisations There is one requirement from requirement 10 of [RFC7018] which reads: "To support allied and federated environments, endpoints and gateways from different organizations SHOULD be able to connect to each other." Requirement (10) is met is met by the use of PKI ([RFC5280]), described in Section 4.6. NHRP can resolve networks across multiple domains as long as those domains are somehow initially connected to the topology. Detienne, et al. Expires June 23, 2014 [Page 24] Internet-Draft Dynamic Mesh VPN December 2013 8.11. Requirement 11: Configuration of star, full-mesh, or partial full-mesh topologies There is one requirement from requirement 11 of [RFC7018] which reads: "The administrator of the ADVPN SHOULD allow for the configuration of a star, full-mesh, or partial full-mesh topology, based on which tunnels are allowed to be set up." Requirement (11) is met by the same principle as Requirement (4b). 8.12. Requirement 12: Scale for Multicast There is one requirement from requirement 12 of [RFC7018] which reads: "The ADVPN solution SHOULD be able to scale for multicast traffic." Requirement (12) is met by the use of a full tunneling interface as described in Section 1. All multicast control protocols such as PIM ([RFC4601]) or IGMP ([RFC4604]) or even MLD ([RFC3810]) will work seamlessly on the overlay medium (GRE/IPsec tunnels). 8.13. Requirement 13: Monitoring and Reporting There is one requirement from requirement 13 of [RFC7018] which reads: "The ADVPN solution SHOULD allow for easy monitoring, logging, and reporting of the dynamic changes to help with troubleshooting such environments." Requirement (13) is met by the use of multiple existing technologies (IPsec, IKE, NHRP, GRE, interfaces) which all generate their own monitoring, logging, and reporting. 8.14. Requirement 14: L3 VPNs There is one requirement from requirement 14 of [RFC7018] which reads: "There is also the case where L3VPNs operate over IPsec tunnels, for example, Provider-Edge-based VPNs. An ADVPN MUST support L3VPNs as applications protected by the IPsec tunnels." Detienne, et al. Expires June 23, 2014 [Page 25] Internet-Draft Dynamic Mesh VPN December 2013 Requirement (14) is met by the use of GRE to encapsulate all traffic which allows for L2 headers to be transported over DMVPN providing L3VPN functionality. L3VPN labels can be exchanged by running a routing protocol over the tunnels. In accordance to Requirements (1) and (2) about minimal configuration, the tunnel interfaces only need to activate MPLS as a supported encapsulation format. This activation can be performed globally for all tunnels or can be performed for individual tunnels based on the peer identity. 8.15. Requirement 15: QoS There is one requirement from requirement 15 of [RFC7018] which reads: "The ADVPN solution SHOULD allow the enforcement of per-peer QoS in both the star and full-mesh topologies." Requirement (15) is met by applying a QoS policy on the point-to- point (GRE/IPsec) tunnels, allowing the policy to only parse traffic that is destined to a specific remote peer. 8.16. Requirement 16: Hub Redundancy There is one requirement from requirement 16 of [RFC7018] which reads: "The ADVPN solution SHOULD take care of not letting the hub be a single point of failure." Requirement (16) is met by the ability to use multiple Hubs and an overlay routing protocol as described in Sections 1 and 4.2. This method allows a routing based resiliency. Additionally, a spoke can define multiple addresses or a DNS names to be used as a backup hub. 9. Design Considerations This section contains a number of points that do not augment the specification explained so far but instead clarify its use. 9.1. Routing Policy and RFC4301 Security The notion of routing policy is extensively used throughout this document. This routing policy is a mechanism used to lookup which peer or node the packet should be sent to. The exact representation of a Routing Policy is left to the implementer. It may represent but is not limited to a unique routing table, a manifold of routing Detienne, et al. Expires June 23, 2014 [Page 26] Internet-Draft Dynamic Mesh VPN December 2013 table, a policy route or any other mechanism that can take a forwarding decision. A key conceptual difference between a Routing Policy and a plain SADB or a routing table is that packets can be routed to a peer based on complex rules that may be more complex than just the usual destination prefix of a RIB or the 3- or 5-tuple (source/destination IP, source/destination port, protocol) of the SADB. Most systems can take forwarding decisions that are more elaborate than that. This includes policy-based-routing, application based forwarding, multi-topology routing, etc. that are used to evaluate packets before they optionally undergo the basic routing table or SADB. A notable example of a Routing Policy is a manifold of Routing Tables in the context of VPN Instances (see [RFC4026]); these dedicated tables are called VRF's. In this example, a dedicated VRF that we will call VRF Red is associated to the overlay network and exclusively routes protected packets. In effect, the private interfaces and the tunnel interfaces are considered Red Interfaces and exclusively make use of VRF Red as a routing table. Packets entering the system on a Red interface undergo a VRF Red lookup and can only leave the device on a Red interface (which tunnels are part of). Another routing table called VRF Black is associated to the transport network (or NBMA network) and exclusively routes traffic to and from Unprotected Network. This means the physical interfaces facing the transport network are Black interfaces and traffic entering that interface is driven by the Black VRF routing table. GRE/IPsec packets entering the Unprotected interface are such packets. As noted earlier in this document, GRE tunnels request to be IPsec protected through a crypto socket as explained in [RFC5660]. A corresponding SPD and SADB will be created by that socket. Plain GRE packets will be discarded as they were not duly protected and no SPD covers that traffic flow ([RFC4301], section 5). IPsec packets will be accepted by the IPsec stack, their SPI looked up, get validated (hash, anti-replay) and decrypted. The clear text packet undergoes the SADB check and MUST be a GRE packet. If it is not a GRE packet of adequate source/destination, the packet is discarded. In the light of [RFC5660], the packets will be given to their application without further intermediate lookup; in this case, the application is the corresponding GRE Tunnel Interface. Detienne, et al. Expires June 23, 2014 [Page 27] Internet-Draft Dynamic Mesh VPN December 2013 The protected/overlay packet is now in the clear, ready to be processed by the GRE Input Features. In particular, security features can be applied on the clear text, overlay packet (access- filter, Unicast Reverse Path Forwarding, Layer 7 inspection via Firewall or Intrusion Prevention system,...). Those policies can be applied on the fly at IKE negotiation time when the remote peer identity is known. The clear text packet, should it survive the security policies, will be forwarded to another Red Interface according to the VRF Red table. In the egress direction, clear text packets enter a VRF Red Interface, get forwarded to a Tunnel interface according to VRF Red. The packet undergoes output features on the output interface (this may include filters, firewalling etc.) and is encapsulated into GRE. The GRE encapsulation function passes the packet to IPsec for protection through the crypto socket. The packet is now an ESP or AH packet and can be routed out the public interface according to the VRF Black table. For compliance with [RFC4301], explicit leaks may be configured between VRF's to allow specific traffic to bypass IPsec encryption or other security policies if necessary but by default, the Red and Black VRF's are absolutely compartmented. Various operating systems such as Linux do support VRFs but also have other methods of implementing a routing policy (e.g. iproute2) that they can use to their advantage to achieve beyond-routing or beyond- SADB policy enforcement. 9.2. Using Configuration Attributes As outlined earlier in this document, this specification lets any administratively authorized control protocol set up the routing policy of the base topology. This section explains how IKEv2 can perform that task. IKEv2 natively features Configuration Attributes exchanged in Configuration Payloads ([RFC5996], section 3.15). These payloads can be used to exchange prefix between peers. The exchange looks like Detienne, et al. Expires June 23, 2014 [Page 28] Internet-Draft Dynamic Mesh VPN December 2013 Spoke1 Hub HDR, SK {IDi, [CERT,] [CERTREQ,] [IDr,] AUTH, CP(CFG_REQUEST), SAi2, TSi, TSr} --> <-- HDR, SK {IDr, [CERT,] AUTH, CP(CFG_REPLY), SAr2, TSi, TSr} HDR, SK {CP(CFG_SET)} --> <-- HDR, SK {CP(CFG_ACK)} Config Exchange In accordance to the previous notation, the config payloads and attributes in order to set up the routing table depicted in Section 4.2 looks as follows: CP(CFG_REQUEST)= INTERNAL_ADDRESS() CP(CFG_REPLY)= INTERNAL_ADDRESS(TunS1) INTERNAL_NETMASK(255.255.255.255) INTERNAL_SUBNET(SUM/SUM_MASK) ... (other INTERNAL_SUBNETs if necessary) CP(CFG_SET)= INTERNAL_SUBNET(D1/D1_MASK) ... (other INTERNAL_SUBNETs if necessary) CP(CFG_ACK) Config Exchange The information exchange can be achieved by both sides requesting and responding solely using CFG_REQUEST and CFG_ACK but it has been expanded to showcase the conformance to the IKEv2 protocols. Due to limited packet size and issues caused by fragmentation, the number of prefixes exchanged by CP exchange is expected to be limited in practice. This mechanism is not meant to transfer a large number of prefixes. Should the prefix count be high, the authors strongly recommend the use of a routing protocol instead. A peer receiving INTERNAL_SUBNET attributes from another peer MUST be free to ignore or otherwise interpret that INTERNAL_SUBNET in Detienne, et al. Expires June 23, 2014 [Page 29] Internet-Draft Dynamic Mesh VPN December 2013 accordance to a security policy. This is necessary in accordance to [RFC4301] PAD and a recommended practice.Interpretation of that INTERNAL_SUBNET includes plain rejection (ignore), modification of the received subnet, logging a warning message and/or termination of the connection. 9.3. NAT Support IKEv2 supports NAT Traversal natively. Since GRE provides the tunneling capability, GRE itself can be protected by IPsec Transport Mode. See [RFC5996], sections 2.23 for NAT support and 2.23.1 in particular for NAT Traversal in Transport Mode for the protocol details. If a hub is deployed behind a NAT address, the spokes need to point their tunnel destination towards the public address of the Hub, assuming the hub is reachable via a well known NAT translation (static mapping or dynamic public address published via DNS for instance). 10. Acknowldegements The authors would like to thank Graham Bartlett, Brian Weis, Mark Comeadow and Mark Jackson from Cisco for their help in publishing and reviewing this document. We would also like to acknowledge the historical DMVPN team, in particular Jan Vilhuber and Pratima Sethi. 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2332] Luciani, J., Katz, D., Piscitello, D., Cole, B., and N. Doraswamy, "NBMA Next Hop Resolution Protocol (NHRP)", RFC 2332, April 1998. [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000. [RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery Version 2 (MLDv2) for IPv6", RFC 3810, June 2004. [RFC4026] Andersson, L. and T. Madsen, "Provider Provisioned Virtual Private Network (VPN) Terminology", RFC 4026, March 2005. Detienne, et al. Expires June 23, 2014 [Page 30] Internet-Draft Dynamic Mesh VPN December 2013 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. [RFC5660] Williams, N., "IPsec Channels: Connection Latching", RFC 5660, October 2009. [RFC5685] Devarapalli, V. and K. Weniger, "Redirect Mechanism for the Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 5685, November 2009. [RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, "Internet Key Exchange Protocol Version 2 (IKEv2)", RFC 5996, September 2010. [RFC7018] Manral, V. and S. Hanna, "Auto-Discovery VPN Problem Statement and Requirements", RFC 7018, September 2013. 11.2. Informative References [RFC2677] Greene, M., Cucchiara, J., and J. Luciani, "Definitions of Managed Objects for the NBMA Next Hop Resolution Protocol (NHRP)", RFC 2677, August 1999. [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", RFC 2863, June 2000. [RFC4292] Haberman, B., "IP Forwarding Table MIB", RFC 4292, April 2006. [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", RFC 4601, August 2006. [RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet Group Management Protocol Version 3 (IGMPv3) and Multicast Listener Discovery Protocol Version 2 (MLDv2) for Source- Specific Multicast", RFC 4604, August 2006. [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, May 2008. Detienne, et al. Expires June 23, 2014 [Page 31] Internet-Draft Dynamic Mesh VPN December 2013 Authors' Addresses Frederic Detienne Cisco De Kleetlaan 7 Diegem 1831 Belgium Email: fd@cisco.com Manish Kumar Cisco Mail Stop BGL14/G/ SEZ Unit, Cessna Business Park Varthur Hobli, Sarjapur Marathalli Outer Ring Road Bangalore, Karnataka 560 103 India Email: manishkr@cisco.com Mike Sullenberger Cisco Mail Stop SJCK/3/1 225 W. Tasman Drive San Jose, California 95134 United States Email: mls@cisco.com Detienne, et al. Expires June 23, 2014 [Page 32]