Network Working Group Eric Gray, Editor Internet Draft Ericsson Expires: August, 2006 February 23, 2006 The Architecture of an RBridge Solution to TRILL draft-gray-trill-rbridge-arch-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on August 23, 2006. Abstract RBridges are link layer (L2) devices that use routing protocols as a control plane. They combine the link layer ability to allow hosts to reattach without renumbering with network layer routing benefits. RBridges use existing link state routing to provide higher RBridge to RBridge cross-section bandwidth, fast Gray Expires August, 2006 [Page 1] Internet-Draft RBridge Architecture February 2006 convergence on reconfiguration, and more robust under link interruption than an equivalent set of conventional bridges using existing spanning tree forwarding. They are intended to apply to similar L2 network sizes as conventional bridges and are intended to be backward compatible with those bridges as both ingress/egress and transit. They also attempt to retain as much 'plug and play' as is already available in existing bridges. This document proposes an RBridge system as a solution to the TRILL problem. It also defines the RBridge architecture, defines its terminology, and describes basic components and desired behavior. One or more separate documents specify the protocols and mechanisms that satisfy the architecture presented herein. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [1]. Table of Contents 1. Introduction................................................3 2. Background..................................................4 2.1. Existing Terminology...................................4 2.2. RBridge Terminology....................................8 3. Components.................................................10 3.1. RBridge Device........................................10 3.2. CFT...................................................11 3.3. CFT-IRT...............................................11 3.4. CTT...................................................13 4. Functional Description.....................................13 4.1. RBridge Campus Auto-configuration.....................13 4.2. RBridge Peer Discovery................................15 4.3. Tunneling.............................................16 4.4. RBridge General Operation.............................17 4.5. Ingress/Egress Operations.............................19 4.6. Transit Forwarding Operations.........................20 4.6.1. Unicast..........................................21 4.6.2. Broadcast, Multicast and Flooding................22 4.6.2.1. Broadcast...................................22 4.6.2.2. Multicast...................................23 4.6.2.3. Flooding....................................24 4.7. Routing Protocol Operation............................26 4.7.1. Determining CFT..................................26 Gray Expires August, 2006 [Page 2] Internet-Draft RBridge Architecture February 2006 4.7.2. Determing CFT-IRT................................26 4.7.3. Determining CTT..................................26 4.8. Other Bridging and Ethernet Protocol Operations.......26 4.8.1. Outgoing BPDU Interactions.......................27 4.8.2. Incoming BPDU Interactions.......................27 4.8.2.1. Transparent-STP.............................28 4.8.2.2. Participate-STP.............................29 4.8.2.3. Block-STP...................................30 5. How RBridges Address TRILL.................................30 6. Conclusions................................................30 7. Security Considerations....................................31 8. IANA Considerations........................................31 9. Acknowledgments............................................32 9.1. Normative References..................................32 9.2. Informative References................................32 Author's Addresses............................................32 Intellectual Property Statement...............................33 Disclaimer of Validity........................................33 Copyright Statement...........................................34 Acknowledgment................................................34 1. Introduction This document describes an architecture that addresses the TRILL problem and applicability statement [3]. This architecture is composed of a set of devices called RBridges that cooperate together within an Ethernet network to provide a layer two delivery service that makes efficient use of available links using a link state routing protocol. The service provided is analogous to creation of a single, virtual device composed of an overlay of tunnels, constructed between RBridge devices, using link state routing. RBridges thus support increased RBridge to Rbridge bandwidth and fault tolerance, when compared to conventional Ethernet bridges (which forward frames via a spanning tree), while still being compatible with bridges and hubs. The remainder of this document outlines the TRILL architecture of an RBridge-based solution and describes RBridge components, interactions and functions. Note that this document is not intended to represent the only solution to the TRILL problem statement, nor does it specify the protocols that instantiate this architecture - or that only one such set of protocols is prescribed. The former may be contained in other architecture documents and the latter would be contained in separate specification documents (e.g. - [4]). Gray Expires August, 2006 [Page 3] Internet-Draft RBridge Architecture February 2006 2. Background This architecture is based on the RBridge system described in an Infocom paper [2]. That paper describes the RBridge system as a specific instance; this document abstracts architectural features only. The remainder of this section describes the terminology of this document, which may differ from that of the original paper. 2.1. Existing Terminology The following terminology is defined in other documents. A brief definition is included in this section for convenience and - in some cases - to remove any ambiguity in how the term may be used in this document, as well as derivative documents intended to specify components, protocol, behavior and encapsulation relative to the architecture specified in this document. o 802: IEEE Specification for Ethernet, i.e., including hubs and switches. o 802.1D: IEEE Specification for bridged Ethernet, including the BPDUs used in spanning tree protocol (STP) [6]. o ARP: Address Resolution Protocol - the protocol used to resolve L2 (MAC) addresses, using a given L3 (IP) address. o Bridge: an Ethernet (L2, 802.1D) device with multiple ports that receives incoming frames on a port and transmits them on some or all of the other ports; bridges support both bridge learning and STP. o Bridge Learning: process by which a switch or bridge determines on which single outgoing port to transmit (forward or copy) an incoming frame. This process depends on consistent forwarding as "learning" uses the source MAC address of frames received on each interface. Layer 2 (L2) forwarding devices "learn" the location of L2 destinations by peeking at layer 2 source addresses during frame forwarding, and store the association of source address and receiving interface. L2 forwarding devices use this information to create "filtering database" entries and - gradually - eliminate the need for flooding. o Bridge Protocol Data Unit (BPDU): the frame type associated with bridge control functions (for example: STP/RSTP). Gray Expires August, 2006 [Page 4] Internet-Draft RBridge Architecture February 2006 o Bridge Spanning Tree (BST): an Ethernet (L2, 802.1D) forwarding protocol based on the topology of a spanning tree. o Broadcast Domain: the set of (layer 2) devices that MUST be reached (or reachable) by any (layer 2) broadcast traffic injected into the domain. o Broadcast Traffic: traffic intended for receipt by all devices in a broadcast domain. o Ethernet: See "802" above. o Filtering Database - database containing association information of (source layer 2 address, arrival interface). The interface that is associated with a specific layer 2 source address, is the same interface which is used to forward frames having that address as a destination. When a layer 2 forwarding device has no entry for the destination layer 2 address of any frame it receives, the frame is "flooded". o Flooded Traffic - traffic forwarded on all interfaces, except those on which it was received, within the same broadcast domain. Flooding is the mechanism by which traffic is delivered to a destination that is currently "unknown" (i.e. - either not yet "learned", or aged out of the "filtering database"). o Flooding - the process of forwarding traffic to ensure that frames reach all possible destinations when the destination location is not known. In "flooding", a layer 2 forwarding device forwards a frame for any destination not "known" (i.e. - not in the filtering database) on every active interface except that one on which it was received. See also VLAN flooding. o Frame: in this document, frame refers to an Ethernet (L2) unit of transmission, including header, data, and trailer (or payload and envelope). o Hub: an Ethernet (L2, 802) device with multiple ports which transparently transmits frames arriving on any port to all other ports. This is a functional definition, as there are devices that combine this function with certain bridge-like functions that may - under certain conditions - be referred to as "hubs". Gray Expires August, 2006 [Page 5] Internet-Draft RBridge Architecture February 2006 o IGP: Interior Gateway Protocol - any of the potential routing protocols candidates considered as potentially useful RBridge routing protocols. o IS-IS: Intermediate System to Intermediate System routing protocol. o LAN: Local Area Network. A LAN is an L2 forwarding domain. This term is synonymous with Ethernet Subnet in the context of this document. o LPT: Learned Port Table. See Filtering Database. o MAC: Media Access Control - mechanisms and addressing for L2 frame forwarding. o Multicast Forwarding: forwarding methods that apply to frames with broadcast or multicast destination MAC addresses. o ND: Neighbor Discovery - peer RBridge discovery, potentially based on routing peer (neighbor) discovery. o Node: a device with an L2 (MAC) address that sources and/or sinks L2 frames. o OSPF: Open Shortest Path First routing protocol. o Packet: in this document, packet refers to L3 (or above) data transmission units (e.g. - an IP Packet (RFC791 [5]), including header and data. o Router: a device that performs IP (L3) forwarding (the "routing function"); RBridges typically do not span routers. o Routing Function: in this document, the "routing function" consists of forwarding IP packets between L2 broadcast domains, based on L3 addressing and forwarding information. In the process of performing the "routing function", devices (typically routers) usually forward packets from one L2 broadcast domain to another (one, or more in the IP multicast case) - distinct - L2 broadcast domain(s). RBridges cannot span the routing function. o Segment: an Ethernet link, either a single physical link or emulation thereof (e.g., via hubs) or a logical link or emulation thereof (e.g., via bridges). Gray Expires August, 2006 [Page 6] Internet-Draft RBridge Architecture February 2006 o Spanning Tree Protocol (STP): an Ethernet (802.1D) protocol for establishing and maintaining a single spanning tree among all the bridges on a local Ethernet segment. Also, Rapid Spanning Tree Protocol (RSTP). In this document, STP and RSTP are considered to be the same. o Spanning Tree Table (STT): a table containing port activation status information as determined during STP. o SPF: Shortest Path First - the algorithm name associated with routing based on use of the Dijkstra algorithm (Edsger Wybe Dijkstra) to determine a shortest path graph traversal. o Subnet, Ethernet: a single segment, or a set of segments interconnected by an RBridge campus; in the latter case, the subnet may or may not be equivalent to a single segment. Also may be referred to as a broadcast domain or LAN. By definition, all nodes within an Ethernet Subnet (broadcast domain or LAN) must have L2 connectivity with all other nodes in the same Ethernet Subnet. o Switch: an Ethernet (L2, 802) device with multiple point-to- point ports which transmits (forwards or copies) frames that arrive on one port to one or more other ports. Switches may include bridge learning. Switches may also exclude STP/RSTP. o TRILL: Transparent Interconnect over Lots of Links - the working group and working name for the problem domain to be addressed in this document. o Unicast Forwarding: forwarding methods that apply to frames with unicast destination MAC addresses. o Unknown Destination - a destination for which a receiving device has no filtering database entry. Destination (layer 2) addresses are typically "learned" by (layer 2) forwarding devices via a process commonly referred to as "bridge learning". o VLAN: Virtual Local Area Network. VLANs in general fall into two categories: link (or port) specific VLANs and tagged VLANs. In the former case, all frames forwarded and all directly connected nodes are assumed to be part of a single VLAN. In the latter case, VLAN tagged frames are used to distinguish which VLAN each frame is intended for. Gray Expires August, 2006 [Page 7] Internet-Draft RBridge Architecture February 2006 o VLAN Flooding: flooding as described previously, except that frames are only forwarded on those interfaces configured for participation in the applicable VLAN. 2.2. RBridge Terminology The following terms are defined in this document and intended for use in derivative documents intended to specify components, protocol, behavior and encapsulation relative to the architecture specified in this document. o Campus (RBridge Campus): a set of cooperating RBridges, and the forwarding tunnels that connect them. Unless otherwise stated, the term "campus" is used in this document to mean "RBridge campus". o Campus Forwarding Table (CFT): the per-hop forwarding table populated by the RBridge IGP based on lookups of the campus Transit Header (CTH) encapuslated within the outermost received L2 header, rather than that encapsulating L2 header. The outermost L2 encapsulation in this case includes the source MAC address of the immediate upstream RBridge transmitting the frame and destination MAC address of the receiving RBridge for use in the unicast forwarding case. o CFT-IRT: a forwarding table used for propagation of broadcast, multicast or flooded frames along the Ingress RBridge Tree (IRT). o Campus Transit Header (CTH): a 'shim' header that encapsulates the ingress L2 frame and persists throughout the transit of a campus, which is further encapsulated within a hop-by-hop L2 header (and trailer). The hop-by-hop L2 encapsulation in this case includes the source MAC address of the immediate upstream RBridge transmitting the frame and destination MAC address of the receiving RBridge - at least in the unicast forwarding case. o Campus Transit Table (CTT): a table that maps ingress frame L2 destinations to egress RBridge addresses, used to determine encapsulation of ingress frames for transit of the campus. o Cooperating RBridges - those RBridges within a single Ethernet Subnet (broadcast domain or LAN) not having been configured to ignore each other. By default, all RBridges within a single Ethernet subnet will cooperate with each Gray Expires August, 2006 [Page 8] Internet-Draft RBridge Architecture February 2006 other. It is possible for implementations to allow for configuration that will restrict "cooperation" between an RBridge and an apparent neighboring RBridge. One reason why this might occur is if the trust model that applies in a particular deployment imposes a need for configuration of security information. By default no such configuration is required however - should it be used in any specific scenario - it is possible (either deliberately or inadvertently) to configure neighboring RBridges so that they do not "cooperate". In the remainder of this document, all RBridges are assumed to be in a cooperating (default) configuration. o Designated RBridge (DR): the RBridge associated with ingress and egress traffic to a particular Ethernet link having shared access among multiple RBridges; that RBridge is such a link's "Designated RBridge". The Designated RBridge is determined by an election process among those RBridges having shared access via a single Segment. o Edge RBridge (edge of an RBridge campus): describes RBridges that serve to ingress frames into the RBridge campus and egress frames from the RBridge Campus. L2 frames transiting an RBridge campus enter, and leave, the campus via one or more edge RBridges. o Egress RBridge: for any specific frame, the RBridge through which that frame leaves the RBridge campus. For frames transiting an RBridge Campus, the egress RBridge is an edge RBridge where RBridge encapsulation is removed from the transit frames prior to exiting the Campus. o Forwarding Tunnels: in this document, Campus Forwarding Tunnels (or Forwarding Tunnels) is used to refer to the paths for forwarding transit frames, encapsulated at an RBridge ingress and decapsulated at an RBridge egress. o Ingress RBridge: for any specific frame, the RBridge through which that frame enters the RBridge campus. For frames transiting an RBridge Campus, the ingress RBridge is the edge RBridge where RBridge encapsulation is added to the transit traffic entering the Campus. Gray Expires August, 2006 [Page 9] Internet-Draft RBridge Architecture February 2006 o Ingress RBridge Tree: a tree computed for each edge RBridge - and potentially for each VLAN in which that RBridge participates - for delivery of broadcast, multicast and flooded frames from that RBridge to all relevant egress RBridges. This is the point-to-multipoint delivery tree used by an ingress RBridge to deliver multicast, broadcast or flooded traffic. The tree consists of a set of one or more next-hops to be used when the ingress RBridge receives a multicast or broadcast frame (frame with a multicast or broadcast destination address), or frame with unknown destination addresses. If forwarding frames hop-by-hop, next hop RBridges will, in turn, have a similar set of one or more next-hops to be used for forwarding these frames - when received from an upstream, or ingress, RBridge. This progression continues until frames arrive at egress RBridges. o Rbridge: a logical device as specified in this document, which incorporate both routing and bridging features, thus allowing for the achievment of TRILL Architecture goals. A single RBridge device which can aggregate with other RBridge devices to create an RBridge Campus. o RBridge Campus: See "Campus". 3. Components An RBridge campus is composed of RBridge devices and the forwarding tunnels that connect them; all other Ethernet link subnet devices, such as bridges, hubs, and nodes, operate conventionally in the presence of an RBridge. 3.1. RBridge Device An RBridge is a bridge-like device that forwards frames on an Ethernet link segment. It has one or more Ethernet ports which may be wired or wireless; the particular physical layer is not relevant. An RBridge is defined more by its behavior than its structure, although it contains two tables which distinguish it from conventional bridges. Conventional bridges contain a learned port table (LPT), or filtering database, and a spanning tree table (STT). The LPT allows a bridge to avoid flooding all received frames, as is typical for a hub or repeater. The bridge learns which nodes are accessible from a particular port by assuming bi-directional consistency: the source addresses of incoming frames indicate that the incoming port is to be used as output for frames Gray Expires August, 2006 [Page 10] Internet-Draft RBridge Architecture February 2006 destined to that address. Incoming frames are checked against the LPT and forwarded to the particular port if a match occurs, otherwise they are flooded out all ports except the incoming port. The STT indicates the ports used in the spanning tree. Details of STP operation are out of scope for this document, however the result of STP is to disable ports which would otherwise result in more than one path traversing a portion of the spanning tree. RBridges, by comparison, have a Campus Forwarding Table (CFT) and a Campus Transit Table (CTT), described in the following sections. 3.2. CFT The CFT is a forwarding table for unicast traffic within the RBridge campus, allowing tunneled traffic to transit the campus from ingress to egress. The size of a fully-populated CFT is maximally bounded by the product of the number of egress RBridges and corresponding VLANs - assuming that hop-by-hop frame forwarding is not used. If hop-by-hop frame forwarding is used, the size of a fully populated CFT at each RBridge is maximally bounded by the product of the number of directly connected RBridge peers (where "directly connected" in this context refers to RBridges connected to each other without transiting one or more additional RBridges) and VLANs. RBridges may have separate CFTs for each VLAN, if this is supported by manual configuration. The CFT is continually maintained by RBridge routing protocol (see Section 4.7). 3.3. CFT-IRT The CFT-IRT consists of a special-case set of forwarding entries used for support of Ingress RBridge Trees (IRT). The CFT-IRT may be part of the CFT, or instantiated as a separate table. In discussing entries to be included in the CFT-IRT, the following entities are temporarily defined, or further qualified: o Ingress RBridge - the RBridge that is the head end of an IRT. All RBridges within an RBridge campus are potential ingress RBridges. Gray Expires August, 2006 [Page 11] Internet-Draft RBridge Architecture February 2006 o Egress RBridge - an RBridge that is the tail end of a path corresponding to a specific CFT-IRT entry. All RBridges within an RBridge campus are potential egress RBridges. Not all RBridges within an RBridge campus will be on the shortest path between any ingress RBridge and any other egress RBridge. o Local RBridge - the RBridge that forms and maintains the CFT- IRT entry (or entries) under discussion. The local RBridge may be an Ingress RBridge, or an egress RBridge with respect to any set of entries in the CFT-IRT. o RBridge Campus Egress Interface - an interface on any RBridge where a transit RBridge encapsulated frame would be decapsulated prior to forwarding. With respect to such an interface, the local RBridge is the egress RBridge. Each local RBridge will maintain a set of entries for at least the following - corresponding to a subset of all possible forwarding paths: o Zero or more entries grouped for each ingress RBridge - keyed by the ingress RBridge identifier - used to determine downstream forwarding of broadcast, multicast, and flooded frames originally RBridge encapsulated by that ingress within the RBridge campus. o Corresponding to each of these entry groups, one entry for each of zero or more egress RBridge - where the local RBridge is on the shortest path toward that egress RBridge. o Corresponding to each of these entry groups, one entry for each of zero or more RBridge campus egress interfaces. Each entry would contain an indication of which single interface a broadcast, multicast or flooded frame would be forwarded for each (ingress RBridge, egress RBridge) pair - as well as any required encapsulation information, etc. required for forwarding on that interface, toward the corresponding specific egress RBridge. A local RBridge could maintain a full set of entries from every RBridge to every other RBridge, however - depending on topology - only a subset of these entries would ever be used. In addition, a topology change that changed selection of shortest paths would also very likely change other elements of the Gray Expires August, 2006 [Page 12] Internet-Draft RBridge Architecture February 2006 entries, negating possible benefits from having pre-computed CFT-IRT entries. CFT-IRT entries should also include VLAN identification information relative to each set of ingress RBridge, to allow scoping of broadcast, multicast and flooding forwarding by configured VLANs. How the CFT-IRT is maintained will be defined in appropriate protocol specifications used to instantiate this architecture. The protocol specification needs to include mechanisms and procedures required to establish and maintain the CFT-IRT in consideration of potential SPF recomputations resulting from network topology changes. 3.4. CTT The CTT determines how arriving traffic will be encapsulated, for forwarding to the egress RBridge, via the RBridge Campus. The CTT can be considered a version of the LPT that operates across the RBridge campus as a whole. It becomes configured in much the same way as the LPT: by snooping incoming traffic, and assuming bi-directional consistency (see Section 4.7.2). The information is learned at the egress RBridge and propagated to all other RBridges in the campus via the RBridge routing protocol (also Section 4.7.2). The CTT may be populated on- demand or a-priori, and may be as large as the number of nodes on the Ethernet subnet, across all VLANs. RBridges may have separate CTTs for each VLAN, if separate VLANs are supported by manual configuration. 4. Functional Description The design of an RBridge is largely defined by its behavior; the physical components are minimal, as outlined in Section 3. 4.1. RBridge Campus Auto-configuration Cooperating RBridges self-organize to compose a single RBridge campus system. Consider first a set of bridges on a single Ethernet link subnet (Figure 1). Here bridges are shown as 'b', hubs as 'h', and nodes as 'N'; bridges and hubs are numbered. Note that the figure does not distinguish between types of nodes, i.e., hosts and routers; both are just nodes at the link layer, and are otherwise indistinguishable. The bridges organize into a single spanning tree, as shown by double lines ('=', '||', and '//') in the figure. Gray Expires August, 2006 [Page 13] Internet-Draft RBridge Architecture February 2006 N N---b3---N | || | || N---h1--b4===b5==h2==b6 | // | || | // N || | // || N---b7====b8-----b9-----N | |\ | | \ N N N Figure 1 Conventionally bridged Ethernet link subnet It is useful to note that hubs are relatively transparent to bridges, both for traffic from nodes to bridges (h1) and for traffic between bridges (h2). Also note that the same hub can support traffic between bridges and from a host to a bridge (h2), but that the spanning tree is exclusively between bridges. Bridges are thus compatible with hubs, both as transits and ingress/egress. An RBridge campus operates similarly, and can be viewed as a variant of the way bridges self-organize. Figure 2 shows the same topology where some of the RBridges are replaced by RBridges. In this figure, stars ('*') represent the paths the RBridge is capable of utilizing, due to the use of link state routing. Rbridges can tunnel directly to each other (r4-r5), or through hubs (h2) or bridges (b8). N N---b3---N | || | || N---h1--r4***r5**h2**r6 * * | * * * N * * * * N---r7****b8*****r9-----N | |\ | | \ N N N Figure 2 RBridged Ethernet link subnet Every node in an RBridge is considered to have a primary point of attachment to the RBridge campus, as defined by the designated RBridge. Each Ethernet link segment attached to an Gray Expires August, 2006 [Page 14] Internet-Draft RBridge Architecture February 2006 RBridge campus has a single designated RBridge; that RBridge is where all traffic that transits the RBridge enters and exits. In Figure 2, it is easy to see that the nodes off of h1 must attach at r4; the nodes off of b3, however, attach at either r5 or r6, depending on which is the designated RBridge. Without loss of generality, an RBridge topology can be reorganized (ignoring link length) such that all nodes, hubs, and bridges are arranged around the periphery, and all RBridges are considered directly connected by their tunnels (Figure 3). Note that this view ignores the ways in which hubs and bridges may serve both on the ingress/egress and for transit, hence this view is not useful for traffic analysis. Using this view, it is easy to distinguish between RBridge to RBridge traffic and other traffic on shared devices, such as h2 and b8, because RBridge to RBridge traffic content is hidden from non RBridge devices by the RBridge encapsulation. N N---b3---N | || | || | h2 | /| \ | / N \ | / \ N---h1--r4***r5******r6 * * * * * * * * * N---r7***********r9-----N \ /|\ \ / | \ \ / N N \ / \ / b8 | N Figure 3 Reorganized RBridge Ethernet link subnet 4.2. RBridge Peer Discovery Proper operation of the TRILL solution using RBridges depends on the existence of a mechanism for discovering peer RBridges and the RBridge topology. An accurate determination of RBridge topology is required in order to determine how traffic frames Gray Expires August, 2006 [Page 15] Internet-Draft RBridge Architecture February 2006 will flow in the topology and thus avoid the establishment of persistent loops in frame forwarding. The discovery mechanisms must use protocol messages which will be propagated throughout the LAN, or broadcast domain, in order to ensure that all RBridges in the same broadcast domain are discovered and to allow for accurate determination of RBridge topology. These protocol messages should be distinguished in a manner that is consistent with the chosen RBridge routing protocol, or any other discovery mechanism used. An RBridge intercepts protocol messages that it recognizes as being of this type, performs any processing required and forwards these messages as required by the discovery protocol. For example, a receiving RBridge may first determine if it has seen this message before and insert itself in a list of RBridges traversed by this message prior to forwarding the message on at least all interfaces other than the one on which it was received. Note that forwarding the modified message on all interfaces in the example above is safe, if somewhat wasteful. RBridges must forward all other protocol messages in a manner consistent with L2 addressing and forwarding - as would be done by a typical 802.1D bridge. This includes any frames of the same type that are - for one reason or another - not recognized by the receiving RBridge. Note that forwarding unrecognized messages - even when of the same type - has the effect of providing some degree of robustness in the solution against configuration errors and against future variations of the discovery protocol. Handling of 802.1D BPDUs is as determined in section 4.8.2. 4.3. Tunneling Rbridges pass encapsulated frame traffic to each other effectively using tunnels. These tunnels use an Ethernet link layer header, together with a shim header; it is the combination of these headers that distinguishes RBridge to RBridge traffic from other traffic. The link header includes source and destination addresses, which typically identify the ingress and egress RBridges. For incoming multicast and broadcast traffic, one of these addresses may represent the multicast group or broadcast address. Additionally, these addresses may be VLAN- Gray Expires August, 2006 [Page 16] Internet-Draft RBridge Architecture February 2006 specific, i.e., such that each ingress and egress address have per-VLAN addresses. If using hop-by-hop frame forwarding, the destination MAC address is determined as the next-hop RBridge. Typically, the enclosed shim header will not change. An exception would be if the egress RBridge has changed for a frame while in transit within the campus. The additional shim header is required to support loop prevention for traffic within the RBridge campus; traffic loops in forwarding between RBridges and non-RBridge nodes, as well as across non-RBridge devices between RBridges, is prevented by loop prevention mechanisms that are beyond the scope of this document (but typically include STP or RSTP) on the applicable LAN segments. In addition, the shim header and encapsulation: o must clearly identify the traffic as RBridge traffic - the outer Ethernet header may, for instance, use a protocol number unique to RBridges; o should also identify a specific (egress) RBridge - the shim header may, for example, include an identifier unique to the egress RBridge; o should include the RBridge transit route, a hopcount, or a timestamp to prevent indefinite looping of a frame. 4.4. RBridge General Operation Operations that apply to all RBridges include peer and topology discovery (which may include negotiation of RBridge identifiers), designated RBridge election, link-state routing, SPF computation and advertising reach-ability for specific L2 (MAC Ethernet destination) addresses within a broadcast domain. In addition, all RBridges will compute Ingress RBridge Trees for delivery of (potentially VLAN-scoped) broadcast, multicast and flooded frames to each peer RBridge. Setting up these trees early is important as there is otherwise no means for frame delivery across the RBridge campus during the learning phase. Because it is very likely to be impossible (at an early stage) for RBridges to determine which RBridges are edge RBridges, it is preferable that each RBridge compute these trees for all Gray Expires August, 2006 [Page 17] Internet-Draft RBridge Architecture February 2006 RBridges as early as possible - even if some entries will not be used. The initial phase is the peer and topology discovery phase. This should continue for a sufficient amount of time to reduce the amount of re-negotiation (designated RBridge and - possibly - identifiers) and re-computation that will be triggered by discovery of new peers. The time values selected for delaying the next phase should take into account the time required for local STP and availability of segment connectivity between RBridge peers. The next phase is negotiation of designated RBridges for all shared access segments. This phase cannot complete before completion of peer and topology discovery. In parallel, RBridge routing protocol should begin the process of building the LSDB - assuming this was not done during the peer and topology discovery phase. It is at about this time that RBridges should start the process of establishing one or more ingress RBridge trees. If the discovery process has resulted in determination that a designated RBridge election will be required for all segments that any specific RBridge is connected to, that RBridge may delay setup of its Ingress RBridge Tree(s) pending the results of those elections. This is not required and will result in saving time only if that specific RBridge loses all elections (or all elections associated with a given VLAN). Once RBridges have established Ingress RBridge Trees, the learning and forwarding phase may begin. In this phase, RBridges initially forward frames by flooding them via Ingress RBridge Tree(s). Also during this phase, RBridges begin "learning" MAC address locations from local segments and propagating L2 reach- ability information via the RBridge routing protocol to all other RBridges. Gradually, the CFT will be built up for all RBridges, and fewer frames will require flooding via the Ingress RBridge Tree(s). The learning phase typically does not complete. Consequently, the learning phase is also the operational phase. During the combined learning and operational phase, all RBridges maintain both an Ingress RBridge Tree and a CFT. RBridges not elected as designated RBridge may be required to become one in the event that the DR goes off-line. Gray Expires August, 2006 [Page 18] Internet-Draft RBridge Architecture February 2006 4.5. Ingress/Egress Operations Operation specific to edge RBridges involves RBridge learning, advertisement, encapsulation (at ingress RBridges) and decapsulation (at egress RBridges). As described elsewhere, RBridge learning is similar to typical bridge learning - i.e. - all RBridges listen promiscuously to L2 Frames on a local LAN segment and acquire location information associated with source MAC addresses in L2 frames they observe. In instances where more than one RBridge is connected to the same local LAN segment, only the designated RBridge performs RBridge learning for interface(s) connected to that segment. Except in the case where a designated RBridge exists, all RBridges participate in this learning activity as it is primarily by way of this activity that an RBridge can determine it is an edge RBridge. In addition, each RBridge (except where a designated RBridge exists) is expected to forward frames it receives in a manner essentially the same as it would if it were an 802.1D bridge. As each RBridge learns segment-local MAC source addresses, it creates an entry in its reachability table that associates that MAC source address with the interface on which it was learned. Periodically, as determined by the RBridge routing protocol, each RBridge advertises this learned information to its RBridge peers. These advertisements propagate to all edge RBridges (as potentially scoped by associated VLAN information for each advertisement). Each edge RBridge incorporates this information in the form of a CFT entry. Other RBridges may create such entries as well, either in anticipation of subsequent discovery that they are an edge RBridge, or in support of hop-by-hop frame forwarding. RBridges also discover that they are an edge RBridge as a result of receiving un-encapsulated frames that require forwarding. Assuming that an RBridge is the designated - or only - RBridge for a segment, and that it has not previously learned that the MAC destination for a frame is local (this will be the case - for instance - for the very first frame it observes), then the RBridge would be required to forward (or flood) the frame via the RBridge campus. Gray Expires August, 2006 [Page 19] Internet-Draft RBridge Architecture February 2006 The RBridge in this case would flood the frame unless it has already created a CFT entry for the frame's MAC destination address. If it has a corresponding CFT, then it would use that. This RBridge would be an ingress RBridge with respect to the frame being forwarded. The encapsulation used by this ingress RBridge would be determined by the CFT - if one exists - or the CFT-equivalent entry for the Ingress RBridge Tree. The encapsulation - as discussed elsewhere - should include (in the shim header) information to identify the egress RBridge (for example, the RBridge identifier negotiated previously during the peer and topology discovery phase). When the encapsulated frame arrives at egress RBridge(s), it is decapsulated and forwarded via the egress interface(s) onto the local segment. Note that an egress RBridge will be either the designated - or only - RBridge on the local segment accessed via its egress interface(s). If the received frame does not correspond to a learned MAC destination address at an egress interface, it will forward the frame on all interfaces for which it is either the designated - or only - RBridge. If the received frame does correspond to a learned MAC destination address at an egress interface, the RBridge will forward the frame via that interface only. 4.6. Transit Forwarding Operations There are two possible models for transit forwarding within an RBridge campus: edge-to-edge and hop-by-hop. The difference between the two is in how the encapsulation is determined when the flow of RBridge encapsulated frames from an ingress RBridge to an egress RBridges includes one or more transit RBridges. Exactly one of these models will be selected - in any instantiation of this architecture- for each of the following forwarding modes: o Unicast frame forwarding o Forwarding of non-unicast frames o Broadcast frame forwarding o Multicast frame forwarding o Frame flooding Gray Expires August, 2006 [Page 20] Internet-Draft RBridge Architecture February 2006 4.6.1. Unicast Edge to edge: In edge to edge unicast forwarding, both the MAC destination in the outer Ethernet encapsulation and the shim header are specific to the egress RBridge associated with the unicast MAC destination address of the inner Ethernet header. Hop by hop: In hop by hop unicast forwarding, the shim header is specific to the egress RBridge and the MAC destination in the outer Ethernet encapsulation is specific to the next hop RBridge. Prior to preparing the frame for forwarding to the next hop RBridge, the MAC source address is examined and - if the MAC source address is an address of the local RBridge, the frame is discarded. As the frame is prepared for transmission at each RBridge, the next hop MAC destination information is determined at that RBridge based on the corresponding CFT for the destination MAC address of the inner Ethernet header (exactly as if this RBridge were the ingress RBridge for this frame). In addition, prior to re-writing the outer MAC destination address, the next hop MAC destination address is compared to the MAC source address of the outer Ethernet header and the frame is discarded if the two are equivalent. Comparison between the approaches in the Unicast case: The edge to edge approach is simplest from a unicast forwarding perspective, however it is not generally consistent with the routing paradigm. Using this approach frames will not loop within the campus because the outer Ethernet encapsulation will ensure that the frame is forwarded consistently toward the determined egress RBridge until it arrives there. There could be potential efficiency issues - and potentially looping traffic - if a MAC destination node moves from one egress to another. The hop by hop approach uses more complex frame handling, but is also more consistent with the routing paradigm. Also, it is inconsistent with bridge forwarding in that it changes the MAC destination address in the outer encapsulation at each hop, and inconsistent with router forwarding in that it does not change the MAC source address at each hop. Gray Expires August, 2006 [Page 21] Internet-Draft RBridge Architecture February 2006 Better efficiencies may be achieved as a result of the fact that the path followed by a frame may change while the frame is still in transit within the RBridge campus. However this may also result in transient looping of unicast frames within the campus as well. 4.6.2. Broadcast, Multicast and Flooding Ingress RBridge Trees are used for forwarding of broadcast, multicast and unknown destination frames across the RBridge campus. In a simple implementation, it is possible to use the CFT-IRT entries for all frames of these types. However, this approach results in potentially extreme inefficiencies in the multicast and unknown destination flooding cases. As a consequence, instantiations of this architecture should allow for local optimizations on a hop by hop basis. Examples of such optimizations are included in the sections below. 4.6.2.1. Broadcast The path followed in transit forwarding of broadcast frames will have been established through actions initiated by each RBridge (as any RBridge is eligible to subsequently become an ingress RBridge) in the process of computing CFT-IRT entries. Each RBridge assumes that it may be a transit as well as an ingress and egress RBridge and will establish forwarding information relative to itself and each of its peer RBridges, and stored in the CFT-IRT. CFT-IRT entries are computed at each RBridge for paths going toward all other RBridges - at least in cases where the RBridge performing CFT-IRT computations is on the shortest path. Forwarding information is in two forms: transit encapsulation information for interfaces over which the RBridge will forward a broadcast frame to one or more peer RBridges and a decapsulation indication for each interface over which the RBridge may egress frames from the campus. In each case, the CFT-IRT includes some identification of the interface on which a frame is forwarded toward any specific egress RBridge for frames received from any specific ingress RBridge. Gray Expires August, 2006 [Page 22] Internet-Draft RBridge Architecture February 2006 Note that an interface over which an RBridge may egress frames is any interface for which the RBridge is the designated, or only, RBridge. RBridges must not wait to determine that one (or more) non-RBridge Ethernet nodes is present in an interface before deciding to forward decapsulated broadcast frames on that interface. Forwarding information is selected for each broadcast frame received by any RBridge (based on identifying the ingress RBridge for the frame) for all corresponding CFT-IRT entries. Each RBridge is thus required to replicate one RBridge encapsulated broadcast frame for each interface that is determined from CFT-IRT entries corresponding to the frames ingress RBridge. This includes decapsulated broadcast frames for each interface for which it is the designated (or only) RBridge. Note that frame replication and forwarding should be scoped by VLAN if VLAN support is provided. Also note that a designated RBridge (DR) may be required to transmit a decapsulated frame on the interface on which it received the RBridge encapsulated frame. This hop by hop approach for broadcast forwarding might be considered to add complexity because replication occurs at all RBridges along the ingress RBridge tree, potentially for both RBridge encapsulated and decapsulated broadcast frames. However, the replication process is similar to replication of broadcast traffic in 802.1D bridges with the exception that additional replication may be required at each interface for egress from the RBridge campus. Note that the additional replication associated with campus egress may be made to exactly conform to 802.1D bridge broadcast replication in implementations that model a campus egress as a separate logical interface. Using this approach results in one and only one copy of the broadcast frame being delivered to each egress RBridge. 4.6.2.2. Multicast Multicast forwarding is reducible to broadcast forwarding in the simplest (default) case. However implementations may choose - using mechanisms that are out of scope for this document - to optimize multicast forwarding. In order for this to work effectively, however, hop by hop frame header evaluation is required. Gray Expires August, 2006 [Page 23] Internet-Draft RBridge Architecture February 2006 Without optimization, multicast frames are injected by the ingress RBridge onto an IRT by - for instance - encapsulating the frame with a MAC destination multicast address, and forwarding it according to its local CFT-IRT. Without optimization, each RBridge along the path toward all egress RBridges will similarly forward the frame according to their local CFT-IRT. Using this approach results in one and only one copy of the multicast frame being delivered to appropriate egress RBridges. In any optimization approach, RBridge encapsulated multicast frames will use either a broadcast or a group MAC destination address. In either case, the recognizably distinct destination addressing allows a frame forwarding decision to be made at each RBridge hop. RBridges may thus be able to take advantage of local knowledge of multicast distribution requirements to eliminate the forwarding requirement on interfaces for which there is no recipient interested in receiving frames associated with any specific group address. Note that, because the multicast optimization would - in principle - further scope and reduce broadcast traffic, two things may be said: o It is not necessary that all implementations in a deployment support the optimization in order for any local multicast optimization (consistent with the above description) to work (hence such an optimization is optional); o Introduction of a multicast optimization will not result in potential forwarding loops where broadcast forwarding would not do so. In the simplest case, the ingress RBridge for a given multicast frame will re-use the MAC destination group address of a received multicast frame. However this may not be required as it is possible that the mechanisms specified to support multicast will require examination of the decapsulated MAC destination group address at each RBridge that implements the optimization. 4.6.2.3. Flooding Flooding is similarly reducible to broadcast forwarding in the simplest (default) case - with the exception that a frame being flooded across the RBridge campus is typically a unicast frame for which no CFT exists at the ingress RBridge. This is not a Gray Expires August, 2006 [Page 24] Internet-Draft RBridge Architecture February 2006 minor distinction, however, because it impacts the way that addressing may be used to accomplish flooding within the RBridge campus. An ingress RBridge that does not have a CFT entry for a received frame MAC destination address, will inject the frame onto the ingress RBridge Tree by - for instance - encapsulating the frame with a MAC destination broadcast address, and forwarding it according to its local CFT-IRT. Without optimization, each RBridge along the path toward all egress RBridges will similarly forward the frame according to their local CFT-IRT. Using this approach results in one and only one copy of the flooded frame being delivered to all egress RBridges. However implementations may choose to optimize flooding. A Flooding optimization will only work at any specific RBridge if that RBridge re-evaluates the original (decapsulated) unicast frame. Any flooding optimization would operate similarly to the multicast optimization described above, except that - instead of requiring local information about multicast distribution - each RBridge implementing the optimization will need only to lookup the MAC destination address of the original (decapsulated) frame in its local CFT. If an entry is found, the frame could then be forwarded only if the specific RBridge is on the shortest path between the originating ingress RBridge and the appropriate egress RBridge. This could be implemented - for example - as a specialized CFT-IRT entry. Note that, because the flooding optimization would - in principle - further scope and reduce flooded traffic, two things may be said: o It is not necessary that all implementations in a deployment support the optimization in order for any local flooding optimization (consistent with the above description) to work (hence such an optimization is optional); o Introduction of the flooding optimization will not result in potential forwarding loops where flooded forwarding would not do so. Because a forwarding decision can be made at each hop, it is possible to terminate flooding early if a CFT for the original MAC destination was in the process of being propagated when Gray Expires August, 2006 [Page 25] Internet-Draft RBridge Architecture February 2006 flooding for the frame was started. It is therefore possible to reduce the amount of flooding to some degree in this case. 4.7. Routing Protocol Operation The details of routing protocol operation can be determined once a specific routing protocol has been selected. 4.7.1. Determining CFT Specifics of mechanisms for initially determining, and subsequently maintaining, CFT entries are dependent on the routing protocol used. CFT contents and use should be consistent with section 3.2, and 4.6.1 above. 4.7.2. Determing CFT-IRT Specifics of mechanisms for initially determining, and subsequently maintaining, CFT-IRT entries are dependent on routing protocol use. CFT-IRT contents and use should be consistent with section 3.3, and 4.6.2 above. 4.7.3. Determining CTT CTT contents should be exceptional, and require configuration. Typically, encapsulation would be explicitly defined in protocol instantiations of this architecture but may be modified by - for example - VLAN configuration, or Ethernet media changes. 4.8. Other Bridging and Ethernet Protocol Operations In defining this architecture, several interaction models have been considered for protocol interaction between RBridges and other L2 forwarding devices - in particular, 802.1D bridges. Whatever model we adopt for these interactions must allow for the possibility of other types of L2 forwarding devices. Hence, a minimal participation model is most likely to be successful over the long term, assuming that RBridges are used in a L2 topology that would be functional if RBridges were replaced by other types of L2 forwarding devices. Toward this end, RBridges - and the RBridge campus as a whole - may participate in Ethernet link protocols, notably the spanning Gray Expires August, 2006 [Page 26] Internet-Draft RBridge Architecture February 2006 tree protocol (STP) on the ingress/egress links using exactly one of the following interaction models: o Transparent Participation (Transparent-STP) o Active Participation (Participate-STP) o Blocking Participation (Block-STP) Only one of these variants would be supported by an instance of this architecture. All RBridges within a single campus must use the same model for interacting with non-RBridge protocols. Furthermore, it is the explicit intent that only one of these models is ultimately supported - at least as a default mode of compliant implementations. 4.8.1. Outgoing BPDU Interactions All three approaches describe reactions of an RBridge campus to incoming BPDUs, but do not preclude preemptive emission, by RBridges, of BPDUs to the segments external to the RBridge campus. Such BPDUs might indicate that the a Designated RBridge is to become the root of its corresponding segment's spanning tree, which may be necessary for proper - or efficient - overall operation. This architecture adopts the following model for this type of interaction: the logical RBridge component does not itself initiate STP BPDUs, however an implementation may use one (or more) co-located 802.1D bridge instance(s) to do this. In this way, discussion of how - or when - to originate STP BPDUs is out of scope for this document. 4.8.2. Incoming BPDU Interactions RBridges, and an RBridge campus, may interact with received BPDUs using exactly one of the following interaction models: o Transparent Participation (Transparent-STP) o Active Participation (Participate-STP) o Blocking Participation (Block-STP) The first of these, Transparent-STP, causes the entire RBridge campus to appear as an 802 transparent device (e.g. - a Hub). Loops are prevented, among non-RBridge nodes, by mechanisms beyond the scope of this document, however this would typically be via the operation of STP between 802.1D bridges connected to the RBridge campus. Gray Expires August, 2006 [Page 27] Internet-Draft RBridge Architecture February 2006 The second, causes the RBridge campus to emulate the behavior of 802.1D bridges and corresponding direct replacement devices. In this case, the effect is to have the RBridge campus - as a whole - behave as a single 802.1D bridge. Loops are prevented, among non-RBridge nodes, by the operation of 802.1D STP. In the third variant, Block-STP, the campus appears transparent to non-RBridge devices - precisely as if all Ethernet nodes connected to any segment via one or more RBridges, were directly attached to that segment. Loops are prevented by the combined operation of link-state routing protocol between RBridges and mechanisms beyond the scope of this document (typically via STP operation between 802.1D bridges). 4.8.2.1.Transparent-STP An RBridge campus could broadcast spanning tree messages (BPDUs) arriving at designated RBridges within the RBridge campus, emitting one copy on each egress link. Such an RBridge campus is said to support "Transparent-STP", and that Campus would effectively emulate a hub network connected to each link at the designated RBridge. Because hubs are compatible with bridges running STP, a transparent-STP campus may be similarly compatible. Transparent-STP would reduce the complexity of the spanning tree in an Ethernet link subnet because RBridges would not participate in the spanning tree protocol. It still would require BPDUs to be broadcast throughout the RBridge campus, which can cause spanning tree protocol to be delayed until the RBridge Campus is configured. The cost of these broadcasts can be reduced by use of an efficient RBridge routing protocol (e.g., supporting broadcast), but the cost is higher than in unicast (e.g., Participate-STP) and blocking (e.g., Block-STP) schemes. This approach may be further complicated by the possibility that links/segments connecting RBridges may include 802.1D bridges in a configuration requiring STP operation. In this case, either the BDPUs issued outside of the campus are propagated into the campus - and vice-versa - or BPDUs issued outside of the campus are tunneled from the receiving edge RBridge to all other RBridges for propagation into additional 802.1D segments. This approach has been considered and is not recommended because of the fact that it complicates STP interactions on the whole, and can potentially result in significant inefficiencies in Gray Expires August, 2006 [Page 28] Internet-Draft RBridge Architecture February 2006 forwarding across the RBridge campus as a result of STP port blocking activity. 4.8.2.2. Participate-STP An RBridge campus may interpret BPDUs received at its edge RBridges and emit new BPDUs at other RBridges to reflect connectivity within the RBridge campus. In this case, the "spanning tree" within the RBridge campus consists of tunnels connecting edge RBridges. In order to keep the interactions with 802.1D bridges manageable, it is necessary for the entire campus to appear as a single multi-port bridge to all 802.1D bridges in the broadcast domain. An RBridge campus is expected to have the equivalent of one or more spanning trees within the RBridge campus (e.g. - to use for broadcast traffic) but these trees are computed by RBridge routing protocol rather than STP. These trees are referred to as Ingress RBridge Trees. Participate-STP would cause the spanning tree(s) within the RBridge campus to be spliced to the spanning trees on segments external to the RBridge campus, in the form of a single 802.1D bridge. A participate-STP Campus would emulate a single bridge device, just as transparent-STP would emulate a single hub device or network. Participate-STP is similarly compatible with existing bridges and hubs, although the resulting Ethernet subnet spanning tree may be different. As with transparent-STP, the benefit to spanning tree scalability lies in the (presumably) more efficient and stable computation of the RBridge campus forwarding paths using the RBridge routing protocol. Here too, spanning tree protocol is affected by waiting for path computation within the RBridge campus. In this case, there are concerns about the 'chicken and egg' problem; spanning tree protocol needs to complete before links between RBridges can transit traffic, notably traffic between RBridges used to exchange the RBridge routing protocol. This case must be addressed in the protocol if this variant is selected. This approach has also been considered and is not recommended because it complicates STP interactions on the whole, is expected to have a significant impact on time required to establish an extended spanning tree, and can potentially result Gray Expires August, 2006 [Page 29] Internet-Draft RBridge Architecture February 2006 in some inefficiencies in forwarding across the RBridge campus as a result of STP port blocking activity. 4.8.2.3. Block-STP An bridge campus may completely block STP BPDUs that are received at any RBridge. Using this approach is a departure from the existing models for interactions in an 802.1D Ethernet broadcast domain. However, this approach has some significant advantages in terms of reducing the impact of extended spanning trees on over-all STP resolution time. The reason for this is that - by blocking STP BPDUs - RBridges (and the RBridge campus) effectively partition the domain spanning tree into a number of smaller spanning trees connected by a RBridge campus. The Connections via the RBridge campus are free of persistent loops as a result of RBridge peer and topology discovery mechanisms working in conjucntion with an RBridge (link-state) routing protocol. This peer discovery mechanism ensures that RBridges become aware of all of the paths connecting them to other RBridges, and the RBridge routing protocol ensures that non-looping paths are established for frame forwarding across RBridge-to-RBridge connection. The net effect is to ensure that persistent loops in frame forwarding do not occur - either between RBridges, or between RBridges and other Ethernet nodes. 5. How RBridges Address TRILL This section is for further study, after determining the set of TRILL requirements that this architecture document is expected to address. 6. Conclusions This document discusses options considered and factors affecting any protocol specific choices that may be made in instantiating the TRILL architecture using RBridges. Specific architectural and protocol instantiations should take these into consideration. In particular, protocol, encapsulation and procedure specifications should allow for potential optimizations described in the architectural document to the maximum extent possible. Gray Expires August, 2006 [Page 30] Internet-Draft RBridge Architecture February 2006 Also, this document addresses considerations relative to interaction with existing technology and "future-proofing" solutions. For both simplicity in description, and robust long term implementation of the technology, this document recommends the use of clear distinction - at all possible points - of definitions, protocols, procedures, etc. from related (but not identical) specifications and interactions. In particular, this document recommends the use of a "colocation model" in addressing issues with combining RBridge, Router and 802.1D bridge behavior. 7. Security Considerations As one stated requirement of this architecture is the need to be able to provide an L2 delivery mechanism that is potentially configuration free, the default operation mode for instances of this architecture should assume a trust model that does not require configuration of security information. This is - in fact - an identical trust model to that used by Ethernet devices in general. In consequence, the default mode does not require - but also does not preclude - the use of established security mechanisms associated with the existing protocols that may be extended or enhanced to satisfy this document's architectural definitions. In general, this architecture suggest the use of a link-state routing protocol - modified as required to support L2 reach- ability and link state between RBridges. Any mechanisms defined to support secure protocol exchanges between link-state routing peers may be extended to support this architecture as well. This architecture also suggests use of additional encapsulation mechanisms and - to the extent that any proposed mechanism may include (or be extended to include) secure transmission - it may be desirable to provide such (optional) extensions. To the extent possible, any extensions of protocol or encapsulation should allow for at least one mode of operation that doesn't require configuration - if necessary, for limited use in a physically secure deployment. 8.IANA Considerations This document has no direct IANA considerations. It does suggest, that protocols that instantiate the architecture use a Gray Expires August, 2006 [Page 31] Internet-Draft RBridge Architecture February 2006 shim header as a wrapper on the payload for RBridge to RBridge traffic, And this shim header may be identified by a new protocol type in the tunneled Ethernet link header. This protocol type, identified in an 802 header, would be allocated by the IEEE in cooperation with IANA. 9.Acknowledgments The initial work for this document was largely done by Joe Touch, based on work he and Radia Perlman completed earlier. Subsequent changes are not to be blamed on them. 9.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 9.2. Informative References [2] Perlman, R., "RBridges: Transparent Routing", Proc. Infocom 2005, March 2004. [3] Touch, J., (ed.) "Transparent Interconnection of Lots of Links (TRILL): Problem and Applicability Statement", work in progress, draft-touch-trill-prob-00.txt, Nov. 17, 2005. [4] Perlman, R., "RBridges: Base Protocol Specification", work in progress, draft-perlman-rbridge-06.txt, January, 2006. [5] Postel, J., "INTERNET PROTOCOL", RFC 791, September, 1981. [6] 802.1D-2004 IEEE Standard for Local and Metropolitan Area Networks: Media Access Control (MAC) Bridges Author's Addresses Editor: Eric Gray Ericsson 900 Chelmsford Street Lowell, MA, 01851 Phone: +1 (978) 275-7470 EMail: Eric.Gray@Ericsson.com Gray Expires August, 2006 [Page 32] Internet-Draft RBridge Architecture February 2006 Contributors: Joe Touch USC/ISI 4676 Admiralty Way Marina del Rey, CA 90292-6695, U.S.A. Phone: +1 (310) 448-9151 EMail: touch@isi.edu URL: http://www.isi.edu/touch Radia Perlman Sun Microsystems EMail: Radia.Perlman@sun.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND Gray Expires August, 2006 [Page 33] Internet-Draft RBridge Architecture February 2006 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Gray Expires August, 2006 [Page 34]