5. Tenant System Types This section describes a number of special Tenant System types and how they fit into an NVO3 system. 5.1. Overlay-Aware Network Service Appliances Some Network Service Appliances [NVE-NVA] (virtual or physical) provide tenant-aware services. That is, the specific service they provide depends on the identity of the tenant making use of the service. For example, firewalls are now becoming available that support multitenancy where a single firewall provides virtual firewall service on a per-tenant basis, using per-tenant configuration rules and maintaining per-tenant state. Such appliances will be aware of the VN an activity corresponds to while processing requests. Unlike server virtualization, which shields VMs from needing to know about multitenancy, a Network Service Appliance may explicitly support multitenancy. In such cases, the Network Service Appliance itself will be aware of network virtualization and either embed an NVE directly or implement a split-NVE as described in Section 4.2. Unlike server virtualization, however, the Network Service Appliance may not be running a hypervisor, and the VM orchestration system may not interact with the Network Service Appliance. The NVE on such appliances will need to support a control plane to obtain the necessary information needed to fully participate in an NV Domain.
5.2. Bare Metal Servers Many data centers will continue to have at least some servers operating as non-virtualized (or "bare metal") machines running a traditional operating system and workload. In such systems, there will be no NVE functionality on the server, and the server will have no knowledge of NVO3 (including whether overlays are even in use). In such environments, the NVE functionality can reside on the first- hop physical switch. In such a case, the network administrator would (manually) configure the switch to enable the appropriate NVO3 functionality on the switch port connecting the server and associate that port with a specific virtual network. Such configuration would typically be static, since the server is not virtualized and, once configured, is unlikely to change frequently. Consequently, this scenario does not require any protocol or standards work. 5.3. Gateways Gateways on VNs relay traffic onto and off of a virtual network. Tenant Systems use gateways to reach destinations outside of the local VN. Gateways receive encapsulated traffic from one VN, remove the encapsulation header, and send the native packet out onto the data-center network for delivery. Outside traffic enters a VN in a reverse manner. Gateways can be either virtual (i.e., implemented as a VM) or physical (i.e., a standalone physical device). For performance reasons, standalone hardware gateways may be desirable in some cases. Such gateways could consist of a simple switch forwarding traffic from a VN onto the local data-center network or could embed router functionality. On such gateways, network interfaces connecting to virtual networks will (at least conceptually) embed NVE (or split- NVE) functionality within them. As in the case with Network Service Appliances, gateways may not support a hypervisor and will need an appropriate control-plane protocol to obtain the information needed to provide NVO3 service. Gateways handle several different use cases. For example, one use case consists of systems supporting overlays together with systems that do not (e.g., bare metal servers). Gateways could be used to connect legacy systems supporting, e.g., L2 VLANs, to specific virtual networks, effectively making them part of the same virtual network. Gateways could also forward traffic between a virtual network and other hosts on the data-center network or relay traffic between different VNs. Finally, gateways can provide external connectivity such as Internet or VPN access.
5.3.1. Gateway Taxonomy As can be seen from the discussion above, there are several types of gateways that can exist in an NVO3 environment. This section breaks them down into the various types that could be supported. Note that each of the types below could be either implemented in a centralized manner or distributed to coexist with the NVEs. 22.214.171.124. L2 Gateways (Bridging) L2 Gateways act as Layer 2 bridges to forward Ethernet frames based on the MAC addresses present in them. L2 VN to Legacy L2: This type of gateway bridges traffic between L2 VNs and other legacy L2 networks such as VLANs or L2 VPNs. L2 VN to L2 VN: The main motivation for this type of gateway is to create separate groups of Tenant Systems using L2 VNs such that the gateway can enforce network policies between each L2 VN. 126.96.36.199. L3 Gateways (Only IP Packets) L3 Gateways forward IP packets based on the IP addresses present in the packets. L3 VN to Legacy L2: This type of gateway forwards packets between L3 VNs and legacy L2 networks such as VLANs or L2 VPNs. The original sender's destination MAC address in any frames that the gateway forwards from a legacy L2 network would be the MAC address of the gateway. L3 VN to Legacy L3: This type of gateway forwards packets between L3 VNs and legacy L3 networks. These legacy L3 networks could be local to the data center, be in the WAN, or be an L3 VPN. L3 VN to L2 VN: This type of gateway forwards packets between L3 VNs and L2 VNs. The original sender's destination MAC address in any frames that the gateway forwards from a L2 VN would be the MAC address of the gateway. L2 VN to L2 VN: This type of gateway acts similar to a traditional router that forwards between L2 interfaces. The original sender's destination MAC address in any frames that the gateway forwards from any of the L2 VNs would be the MAC address of the gateway. L3 VN to L3 VN: The main motivation for this type of gateway is to create separate groups of Tenant Systems using L3 VNs such that the gateway can enforce network policies between each L3 VN.
5.4. Distributed Inter-VN Gateways The relaying of traffic from one VN to another deserves special consideration. Whether traffic is permitted to flow from one VN to another is a matter of policy and would not (by default) be allowed unless explicitly enabled. In addition, NVAs are the logical place to maintain policy information about allowed inter-VN communication. Policy enforcement for inter-VN communication can be handled in (at least) two different ways. Explicit gateways could be the central point for such enforcement, with all inter-VN traffic forwarded to such gateways for processing. Alternatively, the NVA can provide such information directly to NVEs by either providing a mapping for a target Tenant System (TS) on another VN or indicating that such communication is disallowed by policy. When inter-VN gateways are centralized, traffic between TSs on different VNs can take suboptimal paths, i.e., triangular routing results in paths that always traverse the gateway. In the worst case, traffic between two TSs connected to the same NVE can be hair- pinned through an external gateway. As an optimization, individual NVEs can be part of a distributed gateway that performs such relaying, reducing or completely eliminating triangular routing. In a distributed gateway, each ingress NVE can perform such relaying activity directly so long as it has access to the policy information needed to determine whether cross-VN communication is allowed. Having individual NVEs be part of a distributed gateway allows them to tunnel traffic directly to the destination NVE without the need to take suboptimal paths. The NVO3 architecture supports distributed gateways for the case of inter-VN communication. Such support requires that NVO3 control protocols include mechanisms for the maintenance and distribution of policy information about what type of cross-VN communication is allowed so that NVEs acting as distributed gateways can tunnel traffic from one VN to another as appropriate. Distributed gateways could also be used to distribute other traditional router services to individual NVEs. The NVO3 architecture does not preclude such implementations but does not define or require them as they are outside the scope of the NVO3 architecture.
5.5. ARP and Neighbor Discovery Strictly speaking, for an L2 service, special processing of the Address Resolution Protocol (ARP) [RFC826] and IPv6 Neighbor Discovery (ND) [RFC4861] is not required. ARP requests are broadcast, and an NVO3 can deliver ARP requests to all members of a given L2 virtual network just as it does for any packet sent to an L2 broadcast address. Similarly, ND requests are sent via IP multicast, which NVO3 can support by delivering via L2 multicast. However, as a performance optimization, an NVE can intercept ARP (or ND) requests from its attached TSs and respond to them directly using information in its mapping tables. Since an NVE will have mechanisms for determining the NVE address associated with a given TS, the NVE can leverage the same mechanisms to suppress sending ARP and ND requests for a given TS to other members of the VN. The NVO3 architecture supports such a capability. 6. NVE-NVE Interaction Individual NVEs will interact with each other for the purposes of tunneling and delivering traffic to remote TSs. At a minimum, a control protocol may be needed for tunnel setup and maintenance. For example, tunneled traffic may need to be encrypted or integrity protected, in which case it will be necessary to set up appropriate security associations between NVE peers. It may also be desirable to perform tunnel maintenance (e.g., continuity checks) on a tunnel in order to detect when a remote NVE becomes unreachable. Such generic tunnel setup and maintenance functions are not generally NVO3-specific. Hence, the NVO3 architecture expects to leverage existing tunnel maintenance protocols rather than defining new ones. Some NVE-NVE interactions may be specific to NVO3 (in particular, be related to information kept in mapping tables) and agnostic to the specific tunnel type being used. For example, when tunneling traffic for TS-X to a remote NVE, it is possible that TS-X is not presently associated with the remote NVE. Normally, this should not happen, but there could be race conditions where the information an NVE has learned from the NVA is out of date relative to actual conditions. In such cases, the remote NVE could return an error or warning indication, allowing the sending NVE to attempt a recovery or otherwise attempt to mitigate the situation. The NVE-NVE interaction could signal a range of indications, for example: o "No such TS here", upon a receipt of a tunneled packet for an unknown TS
o "TS-X not here, try the following NVE instead" (i.e., a redirect) o "Delivered to correct NVE but could not deliver packet to TS-X" When an NVE receives information from a remote NVE that conflicts with the information it has in its own mapping tables, it should consult with the NVA to resolve those conflicts. In particular, it should confirm that the information it has is up to date, and it might indicate the error to the NVA so as to nudge the NVA into following up (as appropriate). While it might make sense for an NVE to update its mapping table temporarily in response to an error from a remote NVE, any changes must be handled carefully as doing so can raise security considerations if the received information cannot be authenticated. That said, a sending NVE might still take steps to mitigate a problem, such as applying rate limiting to data traffic towards a particular NVE or TS. 7. Network Virtualization Authority (NVA) Before sending traffic to and receiving traffic from a virtual network, an NVE must obtain the information needed to build its internal forwarding tables and state as listed in Section 4.3. An NVE can obtain such information from a Network Virtualization Authority (NVA). The NVA is the entity that is expected to provide address mapping and other information to NVEs. NVEs can interact with an NVA to obtain any required information they need in order to properly forward traffic on behalf of tenants. The term "NVA" refers to the overall system, without regard to its scope or how it is implemented. 7.1. How an NVA Obtains Information There are two primary ways in which an NVA can obtain the address dissemination information it manages: from the VM orchestration system and/or directly from the NVEs themselves. On virtualized systems, the NVA may be able to obtain the address- mapping information associated with VMs from the VM orchestration system itself. If the VM orchestration system contains a master database for all the virtualization information, having the NVA obtain information directly from the orchestration system would be a natural approach. Indeed, the NVA could effectively be co-located with the VM orchestration system itself. In such systems, the VM orchestration system communicates with the NVE indirectly through the hypervisor.
However, as described in Section 4, not all NVEs are associated with hypervisors. In such cases, NVAs cannot leverage VM orchestration protocols to interact with an NVE and will instead need to peer directly with them. By peering directly with an NVE, NVAs can obtain information about the TSs connected to that NVE and can distribute information to the NVE about the VNs those TSs are associated with. For example, whenever a Tenant System attaches to an NVE, that NVE would notify the NVA that the TS is now associated with that NVE. Likewise, when a TS detaches from an NVE, that NVE would inform the NVA. By communicating directly with NVEs, both the NVA and the NVE are able to maintain up-to-date information about all active tenants and the NVEs to which they are attached. 7.2. Internal NVA Architecture For reliability and fault tolerance reasons, an NVA would be implemented in a distributed or replicated manner without single points of failure. How the NVA is implemented, however, is not important to an NVE so long as the NVA provides a consistent and well-defined interface to the NVE. For example, an NVA could be implemented via database techniques whereby a server stores address- mapping information in a traditional (possibly replicated) database. Alternatively, an NVA could be implemented in a distributed fashion using an existing (or modified) routing protocol to maintain and distribute mappings. So long as there is a clear interface between the NVE and NVA, how an NVA is architected and implemented is not important to an NVE. A number of architectural approaches could be used to implement NVAs themselves. NVAs manage address bindings and distribute them to where they need to go. One approach would be to use the Border Gateway Protocol (BGP) [RFC4364] (possibly with extensions) and route reflectors. Another approach could use a transaction-based database model with replicated servers. Because the implementation details are local to an NVA, there is no need to pick exactly one solution technology, so long as the external interfaces to the NVEs (and remote NVAs) are sufficiently well defined to achieve interoperability. 7.3. NVA External Interface Conceptually, from the perspective of an NVE, an NVA is a single entity. An NVE interacts with the NVA, and it is the NVA's responsibility to ensure that interactions between the NVE and NVA result in consistent behavior across the NVA and all other NVEs using the same NVA. Because an NVA is built from multiple internal components, an NVA will have to ensure that information flows to all internal NVA components appropriately.
One architectural question is how the NVA presents itself to the NVE. For example, an NVA could be required to provide access via a single IP address. If NVEs only have one IP address to interact with, it would be the responsibility of the NVA to handle NVA component failures, e.g., by using a "floating IP address" that migrates among NVA components to ensure that the NVA can always be reached via the one address. Having all NVA accesses through a single IP address, however, adds constraints to implementing robust failover, load balancing, etc. In the NVO3 architecture, an NVA is accessed through one or more IP addresses (or an IP address/port combination). If multiple IP addresses are used, each IP address provides equivalent functionality, meaning that an NVE can use any of the provided addresses to interact with the NVA. Should one address stop working, an NVE is expected to failover to another. While the different addresses result in equivalent functionality, one address may respond more quickly than another, e.g., due to network conditions, load on the server, etc. To provide some control over load balancing, NVA addresses may have an associated priority. Addresses are used in order of priority, with no explicit preference among NVA addresses having the same priority. To provide basic load balancing among NVAs of equal priorities, NVEs could use some randomization input to select among equal-priority NVAs. Such a priority scheme facilitates failover and load balancing, for example, by allowing a network operator to specify a set of primary and backup NVAs. It may be desirable to have individual NVA addresses responsible for a subset of information about an NV Domain. In such a case, NVEs would use different NVA addresses for obtaining or updating information about particular VNs or TS bindings. Key questions with such an approach are how information would be partitioned and how an NVE could determine which address to use to get the information it needs. Another possibility is to treat the information on which NVA addresses to use as cached (soft-state) information at the NVEs, so that any NVA address can be used to obtain any information, but NVEs are informed of preferences for which addresses to use for particular information on VNs or TS bindings. That preference information would be cached for future use to improve behavior, e.g., if all requests for a specific subset of VNs are forwarded to a specific NVA component, the NVE can optimize future requests within that subset by sending them directly to that NVA component via its address.
8. NVE-NVA Protocol As outlined in Section 4.3, an NVE needs certain information in order to perform its functions. To obtain such information from an NVA, an NVE-NVA protocol is needed. The NVE-NVA protocol provides two functions. First, it allows an NVE to obtain information about the location and status of other TSs with which it needs to communicate. Second, the NVE-NVA protocol provides a way for NVEs to provide updates to the NVA about the TSs attached to that NVE (e.g., when a TS attaches or detaches from the NVE) or about communication errors encountered when sending traffic to remote NVEs. For example, an NVE could indicate that a destination it is trying to reach at a destination NVE is unreachable for some reason. While having a direct NVE-NVA protocol might seem straightforward, the existence of existing VM orchestration systems complicates the choices an NVE has for interacting with the NVA. 8.1. NVE-NVA Interaction Models An NVE interacts with an NVA in at least two (quite different) ways: o NVEs embedded within the same server as the hypervisor can obtain necessary information entirely through the hypervisor-facing side of the NVE. Such an approach is a natural extension to existing VM orchestration systems supporting server virtualization because an existing protocol between the hypervisor and VM orchestration system already exists and can be leveraged to obtain any needed information. Specifically, VM orchestration systems used to create, terminate, and migrate VMs already use well-defined (though typically proprietary) protocols to handle the interactions between the hypervisor and VM orchestration system. For such systems, it is a natural extension to leverage the existing orchestration protocol as a sort of proxy protocol for handling the interactions between an NVE and the NVA. Indeed, existing implementations can already do this. o Alternatively, an NVE can obtain needed information by interacting directly with an NVA via a protocol operating over the data-center underlay network. Such an approach is needed to support NVEs that are not associated with systems performing server virtualization (e.g., as in the case of a standalone gateway) or where the NVE needs to communicate directly with the NVA for other reasons. The NVO3 architecture will focus on support for the second model above. Existing virtualization environments are already using the first model, but they are not sufficient to cover the case of
standalone gateways -- such gateways may not support virtualization and do not interface with existing VM orchestration systems. 8.2. Direct NVE-NVA Protocol An NVE can interact directly with an NVA via an NVE-NVA protocol. Such a protocol can be either independent of the NVA internal protocol or an extension of it. Using a purpose-specific protocol would provide architectural separation and independence between the NVE and NVA. The NVE and NVA interact in a well-defined way, and changes in the NVA (or NVE) do not need to impact each other. Using a dedicated protocol also ensures that both NVE and NVA implementations can evolve independently and without dependencies on each other. Such independence is important because the upgrade path for NVEs and NVAs is quite different. Upgrading all the NVEs at a site will likely be more difficult in practice than upgrading NVAs because of their large number -- one on each end device. In practice, it would be prudent to assume that once an NVE has been implemented and deployed, it may be challenging to get subsequent NVE extensions and changes implemented and deployed, whereas an NVA (and its associated internal protocols) is more likely to evolve over time as experience is gained from usage and upgrades will involve fewer nodes. Requirements for a direct NVE-NVA protocol can be found in [NVE-NVA]. 8.3. Propagating Information Between NVEs and NVAs Information flows between NVEs and NVAs in both directions. The NVA maintains information about all VNs in the NV Domain so that NVEs do not need to do so themselves. NVEs obtain information from the NVA about where a given remote TS destination resides. NVAs, in turn, obtain information from NVEs about the individual TSs attached to those NVEs. While the NVA could push information relevant to every virtual network to every NVE, such an approach scales poorly and is unnecessary. In practice, a given NVE will only need and want to know about VNs to which it is attached. Thus, an NVE should be able to subscribe to updates only for the virtual networks it is interested in receiving updates for. The NVO3 architecture supports a model where an NVE is not required to have full mapping tables for all virtual networks in an NV Domain. Before sending unicast traffic to a remote TS (or TSs for broadcast or multicast traffic), an NVE must know where the remote TS(s) currently reside. When a TS attaches to a virtual network, the NVE obtains information about that VN from the NVA. The NVA can provide
that information to the NVE at the time the TS attaches to the VN, either because the NVE requests the information when the attach operation occurs or because the VM orchestration system has initiated the attach operation and provides associated mapping information to the NVE at the same time. There are scenarios where an NVE may wish to query the NVA about individual mappings within a VN. For example, when sending traffic to a remote TS on a remote NVE, that TS may become unavailable (e.g., because it has migrated elsewhere or has been shut down, in which case the remote NVE may return an error indication). In such situations, the NVE may need to query the NVA to obtain updated mapping information for a specific TS or to verify that the information is still correct despite the error condition. Note that such a query could also be used by the NVA as an indication that there may be an inconsistency in the network and that it should take steps to verify that the information it has about the current state and location of a specific TS is still correct. For very large virtual networks, the amount of state an NVE needs to maintain for a given virtual network could be significant. Moreover, an NVE may only be communicating with a small subset of the TSs on such a virtual network. In such cases, the NVE may find it desirable to maintain state only for those destinations it is actively communicating with. In such scenarios, an NVE may not want to maintain full mapping information about all destinations on a VN. However, if it needs to communicate with a destination for which it does not have mapping information, it will need to be able to query the NVA on demand for the missing information on a per-destination basis. The NVO3 architecture will need to support a range of operations between the NVE and NVA. Requirements for those operations can be found in [NVE-NVA]. 9. Federated NVAs An NVA provides service to the set of NVEs in its NV Domain. Each NVA manages network virtualization information for the virtual networks within its NV Domain. An NV Domain is administered by a single entity. In some cases, it will be necessary to expand the scope of a specific VN or even an entire NV Domain beyond a single NVA. For example, an administrator managing multiple data centers may wish to operate all of its data centers as a single NV Region. Such cases are handled by having different NVAs peer with each other to exchange mapping information about specific VNs. NVAs operate in a federated manner
with a set of NVAs operating as a loosely coupled federation of individual NVAs. If a virtual network spans multiple NVAs (e.g., located at different data centers), and an NVE needs to deliver tenant traffic to an NVE that is part of a different NV Domain, it still interacts only with its NVA, even when obtaining mappings for NVEs associated with a different NV Domain. Figure 3 shows a scenario where two separate NV Domains (A and B) share information about a VN. VM1 and VM2 both connect to the same VN, even though the two VMs are in separate NV Domains. There are two cases to consider. In the first case, NV Domain B does not allow NVE-A to tunnel traffic directly to NVE-B. There could be a number of reasons for this. For example, NV Domains A and B may not share a common address space (i.e., traversal through a NAT device is required), or for policy reasons, a domain might require that all traffic between separate NV Domains be funneled through a particular device (e.g., a firewall). In such cases, NVA-2 will advertise to NVA-1 that VM1 on the VN is available and direct that traffic between the two nodes be forwarded via IP-G (an IP Gateway). IP-G would then decapsulate received traffic from one NV Domain, translate it appropriately for the other domain, and re-encapsulate the packet for delivery. xxxxxx xxxx +-----+ +-----+ xxxxxx xxxxxx xxxxxx xxxxx | VM2 | | VM1 | xx xx xxx xx |-----| |-----| xx x xx x |NVE-B| |NVE-A| x x +----+ x x +-----+ +--+--+ x NV Domain A x |IP-G|--x x | +-------x xx--+ | x xx | x x +----+ x NV Domain B x | +---x xx xx x---+ | xxxx xx +->xx xx | xxxxxxxx | xx xx +---+-+ | xx xx |NVA-1| +--+--+ xx xxx +-----+ |NVA-2| xxxx xxxx +-----+ xxxxx Figure 3: VM1 and VM2 in Different NV Domains NVAs at one site share information and interact with NVAs at other sites, but only in a controlled manner. It is expected that policy and access control will be applied at the boundaries between different sites (and NVAs) so as to minimize dependencies on external NVAs that could negatively impact the operation within a site. It is an architectural principle that operations involving NVAs at one site not be immediately impacted by failures or errors at another site.
(Of course, communication between NVEs in different NV Domains may be impacted by such failures or errors.) It is a strong requirement that an NVA continue to operate properly for local NVEs even if external communication is interrupted (e.g., should communication between a local and remote NVA fail). At a high level, a federation of interconnected NVAs has some analogies to BGP and Autonomous Systems. Like an Autonomous System, NVAs at one site are managed by a single administrative entity and do not interact with external NVAs except as allowed by policy. Likewise, the interface between NVAs at different sites is well defined so that the internal details of operations at one site are largely hidden to other sites. Finally, an NVA only peers with other NVAs that it has a trusted relationship with, i.e., where a VN is intended to span multiple NVAs. Reasons for using a federated model include: o Provide isolation among NVAs operating at different sites at different geographic locations. o Control the quantity and rate of information updates that flow (and must be processed) between different NVAs in different data centers. o Control the set of external NVAs (and external sites) a site peers with. A site will only peer with other sites that are cooperating in providing an overlay service. o Allow policy to be applied between sites. A site will want to carefully control what information it exports (and to whom) as well as what information it is willing to import (and from whom). o Allow different protocols and architectures to be used for intra- NVA vs. inter-NVA communication. For example, within a single data center, a replicated transaction server using database techniques might be an attractive implementation option for an NVA, and protocols optimized for intra-NVA communication would likely be different from protocols involving inter-NVA communication between different sites. o Allow for optimized protocols rather than using a one-size-fits- all approach. Within a data center, networks tend to have lower latency, higher speed, and higher redundancy when compared with WAN links interconnecting data centers. The design constraints and trade-offs for a protocol operating within a data-center network are different from those operating over WAN links. While a single protocol could be used for both cases, there could be
advantages to using different and more specialized protocols for the intra- and inter-NVA case. 9.1. Inter-NVA Peering To support peering between different NVAs, an inter-NVA protocol is needed. The inter-NVA protocol defines what information is exchanged between NVAs. It is assumed that the protocol will be used to share addressing information between data centers and must scale well over WAN links. 10. Control Protocol Work Areas The NVO3 architecture consists of two major distinct entities: NVEs and NVAs. In order to provide isolation and independence between these two entities, the NVO3 architecture calls for well-defined protocols for interfacing between them. For an individual NVA, the architecture calls for a logically centralized entity that could be implemented in a distributed or replicated fashion. While the IETF may choose to define one or more specific architectural approaches to building individual NVAs, there is little need to pick exactly one approach to the exclusion of others. An NVA for a single domain will likely be deployed as a single vendor product; thus, there is little benefit in standardizing the internal structure of an NVA. Individual NVAs peer with each other in a federated manner. The NVO3 architecture calls for a well-defined interface between NVAs. Finally, a hypervisor-NVE protocol is needed to cover the split-NVE scenario described in Section 4.2. 11. NVO3 Data-Plane Encapsulation When tunneling tenant traffic, NVEs add an encapsulation header to the original tenant packet. The exact encapsulation to use for NVO3 does not seem to be critical. The main requirement is that the encapsulation support a Context ID of sufficient size. A number of encapsulations already exist that provide a VN Context of sufficient size for NVO3. For example, Virtual eXtensible Local Area Network (VXLAN) [RFC7348] has a 24-bit VXLAN Network Identifier (VNI). Network Virtualization using Generic Routing Encapsulation (NVGRE) [RFC7637] has a 24-bit Tenant Network ID (TNI). MPLS-over-GRE provides a 20-bit label field. While there is widespread recognition that a 12-bit VN Context would be too small (only 4096 distinct values), it is generally agreed that 20 bits (1 million distinct values) and 24 bits (16.8 million distinct values) are sufficient for a wide variety of deployment scenarios.
12. Operations, Administration, and Maintenance (OAM) The simplicity of operating and debugging overlay networks will be critical for successful deployment. Overlay networks are based on tunnels between NVEs, so the Operations, Administration, and Maintenance (OAM) [RFC6291] framework for overlay networks can draw from prior IETF OAM work for tunnel- based networks, specifically L2VPN OAM [RFC6136]. RFC 6136 focuses on Fault Management and Performance Management as fundamental to L2VPN service delivery, leaving the Configuration Management, Accounting Management, and Security Management components of the Open Systems Interconnection (OSI) Fault, Configuration, Accounting, Performance, and Security (FCAPS) taxonomy [M.3400] for further study. This section does likewise for NVO3 OAM, but those three areas continue to be important parts of complete OAM functionality for NVO3. The relationship between the overlay and underlay networks is a consideration for fault and performance management -- a fault in the underlay may manifest as fault and/or performance issues in the overlay. Diagnosing and fixing such issues are complicated by NVO3 abstracting the underlay network away from the overlay network (e.g., intermediate nodes on the underlay network path between NVEs are hidden from overlay VNs). NVO3-specific OAM techniques, protocol constructs, and tools are needed to provide visibility beyond this abstraction to diagnose and correct problems that appear in the overlay. Two examples are underlay-aware traceroute [TRACEROUTE-VXLAN] and ping protocol constructs for overlay networks [VXLAN-FAILURE] [NVO3-OVERLAY]. NVO3-specific tools and techniques are best viewed as complements to (i.e., not as replacements for) single-network tools that apply to the overlay and/or underlay networks. Coordination among the individual network tools (for the overlay and underlay networks) and NVO3-aware, dual-network tools is required to achieve effective monitoring and fault diagnosis. For example, the defect detection intervals and performance measurement intervals ought to be coordinated among all tools involved in order to provide consistency and comparability of results. For further discussion of NVO3 OAM requirements, see [NVO3-OAM].
13. Summary This document presents the overall architecture for NVO3. The architecture calls for three main areas of protocol work: 1. A hypervisor-NVE protocol to support split-NVEs as discussed in Section 4.2 2. An NVE-NVA protocol for disseminating VN information (e.g., inner to outer address mappings) 3. An NVA-NVA protocol for exchange of information about specific virtual networks between federated NVAs It should be noted that existing protocols or extensions of existing protocols are applicable. 14. Security Considerations The data plane and control plane described in this architecture will need to address potential security threats. For the data plane, tunneled application traffic may need protection against being misdelivered, being modified, or having its content exposed to an inappropriate third party. In all cases, encryption between authenticated tunnel endpoints (e.g., via use of IPsec [RFC4301]) and enforcing policies that control which endpoints and VNs are permitted to exchange traffic can be used to mitigate risks. For the control plane, a combination of authentication and encryption can be used between NVAs, between the NVA and NVE, as well as between different components of the split-NVE approach. All entities will need to properly authenticate with each other and enable encryption for their interactions as appropriate to protect sensitive information. Leakage of sensitive information about users or other entities associated with VMs whose traffic is virtualized can also be covered by using encryption for the control-plane protocols and enforcing policies that control which NVO3 components are permitted to exchange control-plane traffic. Control-plane elements such as NVEs and NVAs need to collect performance and other data in order to carry out their functions. This data can sometimes be unexpectedly sensitive, for example, allowing non-obvious inferences of activity within a VM. This provides a reason to minimize the data collected in some environments in order to limit potential exposure of sensitive information. As
noted briefly in RFC 6973 [RFC6973] and RFC 7258 [RFC7258], there is an inevitable tension between being privacy sensitive and taking into account network operations in NVO3 protocol development. See the NVO3 framework security considerations in RFC 7365 [RFC7365] for further discussion. 15. Informative References [FRAMEWORK-MCAST] Ghanwani, A., Dunbar, L., McBride, M., Bannai, V., and R. Krishnan, "A Framework for Multicast in Network Virtualization Overlays", Work in Progress, draft-ietf-nvo3-mcast-framework-05, May 2016. [IEEE.802.1Q] IEEE, "IEEE Standard for Local and metropolitan area networks--Bridges and Bridged Networks", IEEE 802.1Q-2014, DOI 10.1109/ieeestd.2014.6991462, <http://ieeexplore.ieee.org/servlet/ opac?punumber=6991460>. [M.3400] ITU-T, "TMN management functions", ITU-T Recommendation M.3400, February 2000, <https://www.itu.int/rec/T-REC-M.3400-200002-I/>. [NVE-NVA] Kreeger, L., Dutt, D., Narten, T., and D. Black, "Network Virtualization NVE to NVA Control Protocol Requirements", Work in Progress, draft-ietf-nvo3-nve-nva-cp-req-05, March 2016. [NVO3-OAM] Chen, H., Ed., Ashwood-Smith, P., Xia, L., Iyengar, R., Tsou, T., Sajassi, A., Boucadair, M., Jacquenet, C., Daikoku, M., Ghanwani, A., and R. Krishnan, "NVO3 Operations, Administration, and Maintenance Requirements", Work in Progress, draft-ashwood-nvo3-oam-requirements-04, October 2015. [NVO3-OVERLAY] Kumar, N., Pignataro, C., Rao, D., and S. Aldrin, "Detecting NVO3 Overlay Data Plane failures", Work in Progress, draft-kumar-nvo3-overlay-ping-01, January 2014. [RFC826] Plummer, D., "Ethernet Address Resolution Protocol: Or Converting Network Protocol Addresses to 48.bit Ethernet Address for Transmission on Ethernet Hardware", STD 37, RFC 826, DOI 10.17487/RFC0826, November 1982, <http://www.rfc-editor.org/info/rfc826>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December 2005, <http://www.rfc-editor.org/info/rfc4301>. [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 2006, <http://www.rfc-editor.org/info/rfc4364>. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007, <http://www.rfc-editor.org/info/rfc4861>. [RFC6136] Sajassi, A., Ed. and D. Mohan, Ed., "Layer 2 Virtual Private Network (L2VPN) Operations, Administration, and Maintenance (OAM) Requirements and Framework", RFC 6136, DOI 10.17487/RFC6136, March 2011, <http://www.rfc-editor.org/info/rfc6136>. [RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu, D., and S. Mansfield, "Guidelines for the Use of the "OAM" Acronym in the IETF", BCP 161, RFC 6291, DOI 10.17487/RFC6291, June 2011, <http://www.rfc-editor.org/info/rfc6291>. [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., Morris, J., Hansen, M., and R. Smith, "Privacy Considerations for Internet Protocols", RFC 6973, DOI 10.17487/RFC6973, July 2013, <http://www.rfc-editor.org/info/rfc6973>. [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 2014, <http://www.rfc-editor.org/info/rfc7258>. [RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger, L., Sridhar, T., Bursell, M., and C. Wright, "Virtual eXtensible Local Area Network (VXLAN): A Framework for Overlaying Virtualized Layer 2 Networks over Layer 3 Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014, <http://www.rfc-editor.org/info/rfc7348>. [RFC7364] Narten, T., Ed., Gray, E., Ed., Black, D., Fang, L., Kreeger, L., and M. Napierala, "Problem Statement: Overlays for Network Virtualization", RFC 7364, DOI 10.17487/RFC7364, October 2014, <http://www.rfc-editor.org/info/rfc7364>.
[RFC7365] Lasserre, M., Balus, F., Morin, T., Bitar, N., and Y. Rekhter, "Framework for Data Center (DC) Network Virtualization", RFC 7365, DOI 10.17487/RFC7365, October 2014, <http://www.rfc-editor.org/info/rfc7365>. [RFC7637] Garg, P., Ed. and Y. Wang, Ed., "NVGRE: Network Virtualization Using Generic Routing Encapsulation", RFC 7637, DOI 10.17487/RFC7637, September 2015, <http://www.rfc-editor.org/info/rfc7637>. [TRACEROUTE-VXLAN] Nordmark, E., Appanna, C., Lo, A., Boutros, S., and A. Dubey, "Layer-Transcending Traceroute for Overlay Networks like VXLAN", Work in Progress, draft-nordmark-nvo3- transcending-traceroute-03, July 2016. [USECASES] Yong, L., Dunbar, L., Toy, M., Isaac, A., and V. Manral, "Use Cases for Data Center Network Virtualization Overlay Networks", Work in Progress, draft-ietf-nvo3-use-case-15, December 2016. [VXLAN-FAILURE] Jain, P., Singh, K., Balus, F., Henderickx, W., and V. Bannai, "Detecting VXLAN Segment Failure", Work in Progress, draft-jain-nvo3-vxlan-ping-00, June 2013. Acknowledgements Helpful comments and improvements to this document have come from Alia Atlas, Abdussalam Baryun, Spencer Dawkins, Linda Dunbar, Stephen Farrell, Anton Ivanov, Lizhong Jin, Suresh Krishnan, Mirja Kuehlwind, Greg Mirsky, Carlos Pignataro, Dennis (Xiaohong) Qin, Erik Smith, Takeshi Takahashi, Ziye Yang, and Lucy Yong.