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Text of the page (random words):
customers a further consequence of spbm s transparency in both data plane and control plane is that it delivers the mef 6 1 service set it also provides the carrier with the toolkit to support geo redundant broadband backhaul in these applications many dslams or other access equipment must be backhauled to multiple broadband remote access server bras sites with application determined binding of sessions to a bras however dslams must not be allowed to communicate with each other because carriers then lose the ability to control peer to peer connectivity mef e tree does just this and further provides an efficient multicast fabric for the distribution of iptv spbm offers both an ideal multicast replication model where packets are replicated only at fork points in the shortest path tree that connects members and also the less state intensive head end replication model where in essence serial unicast packets are sent to all other members along the same shortest path first tree these two models are selected by specifying properties of the service at the edge which affect the transit node decisions on multicast state installation this allows for a trade off to be made between optimum transit replication points with their larger state costs vs reduced core state but much more traffic of the head end replication model these selections can be different for different members of the same individual service id i sid allowing different trade offs to be made for different members figure 5 below is a quick way to understand what spbm is doing on the scale of the entire network figure 5 shows how a 7 member e lan is created from the edge membership information and the deterministic distributed calculation of per source per service trees with transit replication head end replication is not shown as it is trivial and simply uses the existing unicast forwarding information base fib to forward copies serially to the known other receivers operations and management edit 802 1aq builds on all existing ethernet operations administration and management oa m since 802 1aq ensures that its unicast and multicast packets for a given virtual lan vlan follow the same forward and reverse path and use completely standard 802 encapsulations all the methods of ieee 802 1ag and y 1731 27 operate unchanged on an 802 1aq network high level edit see also data center bridging other groups 802 1aq is the ieee sanctioned link state ethernet control plane for all ieee vlans covered in ieee 802 1q 28 the shortest path bridging virtual local area network identifier vlan id or shortest path bridging vid spbv provides a capability that is backward compatible with spanning tree technologies the spbm provides additional values that use provider backbone bridge pbb capabilities spb the generic term for both combines an ethernet data path either ieee 802 1q in the case of spbv or pbbs per ieee 802 1ah in the case of spbm with an is is link state control protocol running between shortest path bridges network to network interface nni links the link state protocol is used to discover and advertise the network topology and compute spts from all bridges in the spt region in spbm the backbone mac b mac addresses of the participating nodes and also the service membership information for interfaces to non participating devices user network interface uni ports is distributed topology data is then input to a calculation engine which computes symmetric shortest path trees based on minimum cost from each participating node to all other participating nodes in spbv these trees provide a shortest path tree where individual mac address can be learned and group address membership can be distributed in spbm the shortest path trees are then used to populate forwarding tables for each participating node s individual b mac addresses and for group addresses group multicast trees are subtrees of the default shortest path tree formed by source group pairing depending on the topology several different equal cost multi path trees are possible and spb supports multiple algorithms per is is instance in spb as with other link state based protocols the computations are done in a distributed fashion each node computes the ethernet compliant forwarding behavior independently based on a normally synchronized common view of the network and uni ports ethernet filtering database or forwarding tables are populated locally to independently and deterministically implement its portion of the network forwarding behavior the two different flavors of data path give rise to two slightly different versions of this protocol one spbm is intended where complete isolation of many separate instances of client lans and their associated device mac addresses is desired and it therefore uses a full encapsulation mac in mac a k a ieee 802 1ah the other spbv is intended where such isolation of client device mac addresses is not necessary and it reuses only the existing vlan tag on participating nni links chronologically spbv came first with the project originally being conceived to address scalability and convergence of mstp at the time the specification for pbb was progressing it became apparent that leveraging both the pbb data plane and a link state control plane would significantly extend ethernet s capabilities and applications provider link state bridging plsb was a straw man proposal brought to the ieee 802 1aq shortest path bridging working group to provide a concrete example of such a system as ieee 802 1aq standardization progressed some of the detailed mechanisms proposed by plsb were replaced by functional equivalents but all of the key concepts embodied in plsb were carried forward into the standard shortest path bridging vid edit this section does not cite any sources please help improve this section by adding citations to reliable sources unsourced material may be challenged and removed may 2023 learn how and when to remove this message a primary feature of shortest path bridging is the ability to use link state is is to learn network topology in spbv the mechanism used to identify the tree is to use a different shortest path vlan id spvid for each source bridge the is is topology is used both to allocate unique spvids and to enable shortest path forwarding for individual and group addresses originally targeted for small low configuration networks spb grew into a larger project encompassing the latest provider control plane for spbv and harmonizing the concepts of ethernet s data plane spb defines a shortest path region which is the boundary of the shortest path topology and the rest of the vlan topology which may be any number of legacy bridges spb operates by learning the spb capable bridges and growing the region to include the spb capable bridges that have the same base vid and mstid configuration digest allocation of vids for spb purposes spbv builds shortest path trees that support loop prevention and optionally support loop mitigation on the spvid spbv still allows learning of ethernet mac addresses but it can distribute multicast addresses that can be used to prune the shortest path trees according to the multicast membership either through multiple mac registration protocol mmrp or directly using is is distribution of multicast membership spbv builds shortest path trees but also interworks with legacy bridges running rapid spanning tree protocol and multiple spanning tree protocol mstp spbv uses techniques from mstp regions to interwork with non spt regions behaving logically as a large distributed bridge as viewed from outside the region spbv supports shortest path trees but spbv also builds a spanning tree which is computed from the link state database and uses the base vid this means that spbv can use this traditional spanning tree for computation of the common and internal spanning tree cist the cist is the default tree used to interwork with other legacy bridges it also serves as a fallback spanning tree if there are configuration problems with spbv spbv has been designed to manage a moderate number of bridges spbv differs from spbm in that mac addresses are learned on all bridges that lie on the shortest path and shared vlan learning is used since destination macs may be associated with multiple spvids spbv learns all macs it forwards even outside the spbv region shortest path bridging mac edit this section does not cite any sources please help improve this section by adding citations to reliable sources unsourced material may be challenged and removed may 2023 learn how and when to remove this message shortest path bridging mac spbm reuses the pbb data plane which does not require that the backbone core bridges bcb learn encapsulated client addresses at the edge of the network the c mac client addresses are learned spbm is very similar to provider link state bridging plsb using the same data and control planes but the format and contents of the control messages in plsb are not compatible individual mac frames of unicast traffic from an ethernet attached device that are received at the spbm edge are encapsulated in a pbb ieee 802 1ah header and then traverse the ieee 802 1aq network unchanged until they are stripped of the encapsulation as they egress back to the non participating attached network at the far side of the participating network ethernet destination addresses from uni port attached devices perform learning over the logical lan and are forwarded to the appropriate participating b mac address to reach the far end ethernet destination in this manner ethernet mac addresses are never looked up in the core of an ieee 802 1aq network when comparing spbm to pbb the behavior is almost identical to a pbb ieee 802 1ah network pbb does not specify how b mac addresses are learned and pbb may use a spanning tree to control the b vlan in spbm the main difference is that b mac addresses are distributed or computed in the control plane eliminating the b mac learning in pbb also spbm ensures that the route followed is the shortest path tree the forward and reverse paths used for unicast and multicast traffic in an ieee 802 1aq network are symmetric this symmetry permits ieee 802 1ag continuity fault management cfm to operate unchanged for spbv and spbm and has desirable properties with respect to time distribution protocols such as precision time protocol group address and unknown destination individual frames are optimally transmitted to only members of the same ethernet service ieee 802 1aq supports the creation of thousands of logical ethernet services in the form of e line e lan or e tree constructs which are formed between non participating logical ports of the ieee 802 1aq network these group address packets are encapsulated with a pbb header which indicates the source participating address in the sa while the da indicates the locally significant group address this frame should be forwarded on and the source bridge where the frame originated the ieee 802 1aq multicast forwarding tables are created based on computations such that every bridge that is on the shortest path between a pair of bridges that are members of the same service group will create proper forwarding database fdb state to forward or replicate frames it receives to those members of that service group since the group address computation produces shortest path trees there is only ever one copy of a multicast packet on any given link since only bridges on the shortest path between participating logical ports create fdb state the multicast makes efficient use of network resources the actual group address forwarding operation operates more or less identically to classical ethernet the backbone destination address b da backbone vlan identifier b vid combination is looked up to find the egress set of next hops the only difference compared with classical ethernet is that reverse learning is disabled for participating bridge backbone media access control b mac addresses and is replaced with an ingress check and discard when the frame arrives on an incoming interface from an unexpected source learning is however implemented at the edges of the spbm multicast tree to learn the b mac to mac address relationship for correct individual frame encapsulation in the reverse direction as packets arrive over the interface properly implemented an ieee 802 1aq network can support up to 1000 participating bridges and provide tens of thousands of layer 2 e lan services to ethernet devices this can be done by simply configuring the ports facing the ethernet devices to indicate they are members of a given service as new members come and go the is is protocol will advertise the i sid membership changes and the computations will grow or shrink the trees in the participating node network as necessary to maintain the efficient multicast property for that service ieee 802 1aq has the property that only the point of attachment of a service needs configuration when a new attachment point comes or goes the trees produced by the computations will automatically be extended or pruned as necessary to maintain connectivity in some existing implementations this property is used to automatically as opposed to through configuration add or remove attachment points for dual homed technologies such as rings to maintain optimum packet flow between a nonparticipating ring protocol and the ieee 802 1aq network by activating a secondary attachment point and deactivating a primary attachment point failure recovery edit this section does not cite any sources please help improve this section by adding citations to reliable sources unsourced material may be challenged and removed may 2023 learn how and when to remove this message failure recovery is driven by is is with the link failure being advertised and new computations being performed resulting in new fdb tables since no ethernet addresses are advertised or known by is is there is no re learning required by the spbm core and its learned encapsulations are unaffected by a transit node or link failure link failure detection may be improved using ieee 802 1ag continuity check protocol ccp which tests link status and reports a failure to the is is protocol this allows much faster failure detection than is possible using the is is hello message loss mechanisms both spbv and spbm inherit the rapid convergence of a link state control plane a special attribute of spbm is its ability to rebuild multicast trees in a similar time to unicast convergence because it substitutes computation for signaling when an spbm bridge has performed the computations on a topology database it knows whether it is on the shortest path between a root and one or more leaves of the spt and can install state accordingly convergence is not gated by incremental discovery of a bridge s place on a multicast tree by the use of separate signaling transactions however spbm on a node does not operate completely independently of its peers and enforces agreemen...