802.1aq Shortest Path Bridging Design and Evolution: The Architects Perspective
Nigel Bragg has spent twenty years in the telecommunications industry, thirteen of them with Nortel-where he was elected a Nortel Fellow in before joining Ciena where he works on packet transport and Carrier Ethernet technologies.
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Viscous Flow in Pipes 9. Flow Over Immersed Bodies Physical Properties of Fluids Appendix C: Properties of the U. Standard Atmosphere Appendix D: Reynolds Transport Theorem Appendix E: The second is separated out, and uses a narrative form to describe the design process and decisions that led to SPB, in order to provide further context in understanding the first part. The book is rounded out with applications and potential futures for the technology to suggest where it could go. This title facilitates both the understanding and adoption of Harry Potter Years by J.
802.1aq Shortest Path Bridging Design and Evolution: The Architect's Perspective
Rowling , Hardcover Harry Potter and the Sorcerer's Stone 1 by J. Harry Potter Boxset Books by J. The only real limiting factors are the FIB table sizes and computational power of the individual devices both of which are growing yearly in leaps and bounds. The IS-IS extensions that carry the information required by An implementation of The hellos would normally run untagged.
The links are assigned The calculations will always use the maximum of the two unidirectional link metrics to enforce symmetric route weights. A box mac would normally serve this purpose. The Area-Id is not directly used by This can often be the low 20 bits of the SYSID if unique or can be dynamically negotiated or manually configured.
As previously discussed the link weights are forced to be symmetric for the purpose of computation by taking the min of two dissimilar values. There will be one unique symmetric shortest path per ECMT behavior.
Description
The tie breaking used to enforce this uniqueness and ECMT is described below. The transit multicast computation which only applies when transit replication is desired and not applicable to services that have chosen head end replication can be implemented in many ways, care must be taken to keep this efficient, but in general a series of shortest path computations must be done. The above pseudo code computes many more SPF's than strictly necessary in most cases and better algorithms are known to decide if a node is on a shortest path between two other nodes. A reference to a paper presented at the IEEE which gives a much faster algorithm that drastically reduces the number of outer iterations required is given below.
For ISIDs that have chosen head end replication the computation is trivial and involves simply finding the other attachment points that receive that ISID and creating a serial unicast table to replicate to them one by one. This means that not only must a given node compute the same path forward and reverse but all the other nodes downstream and upstream on that path must also produce the same result.
This downstream congruence is a consequence of the hop by hop forwarding nature of Ethernet since only the destination address and VID are used to decide the next hop. It is important to keep this in mind when trying to design other ECMT algorithms for This is done by simply taking the MIN of the two values at both ends prior to doing any computations. This alone does not guarantee symmetry however. This is a useful logical way to understand how to deterministically break ties but is not how one would implement such a tie-breaker in practice.
This ensures that every node will make the same decision.
For example, in Figure 7 above, there are four equal-cost paths between node 7 and node 5 as shown by the colors blue, green, pink and brown. The first is that it can be done progressively by simply looking for the lowest SYSID along a path and secondly because an efficient implementation that operates stepwise is possible by simply back-tracking two competing paths and looking for the minimum of the two paths minimum SYSIDs.
It should be clear [ citation needed ] that different permutations will result in the purple and green paths being lowest in turn. The 17 individual bit masks used by the ECT algorithm are made up of the same byte value repeated eight times to fill each bit mask.
These 17 byte values are as follows:. In addition the ECMT tie-breaking algorithms also permit some degree of human override or tweaking. By adjusting the BridgePriority up or down a path's PATHID can be raised or lowered relative to others and a substantial degree of tunability is afforded. The above description gives an easy to understand way to view the tie breaking; an actual implementation simply backtracks from the fork point to the join point in two competing equal-cost paths usually during the Dijkstra shortest path computation and picks the path traversing the lowest after masking BridgePriority SysId.
The first public interoperability tests of IEEE Further events were held in Ottawa in January with 5 vendors and 6 implementations, [26] at 's Interop event at Las Vegas where an SPBM network was used as a backbone. Extreme Networks, by virtue of their acquisition of the Avaya Networking business and assets, is currently the leading exponent of SPB-based deployments; their enhanced and extended implementation of SPB - including integrated Layer 3 IP Routing and IP Multicast functionality - is marketed under the banner of the "Fabric Connect" technology.
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From Wikipedia, the free encyclopedia. This article may be too technical for most readers to understand. Please help improve it to make it understandable to non-experts , without removing the technical details. January Learn how and when to remove this template message. Figure 6 - Animated ECT example in a 66 node Figure 7 - Animated ECT example 36 node Retrieved 11 September Retrieved 25 December Retrieved 19 June Archived from the original PDF on 15 May Retrieved 11 May Retrieved 12 May Retrieved 2 April Retrieved 20 December Archived from the original PDF on 13 May Retrieved 10 December Retrieved 1 May Archived from the original on 7 April Retrieved 11 August Retrieved 18 April Retrieved 20 July Retrieved 1 February Handbook of Data Intensive Computing.
Retrieved 29 May Retrieved 30 May Retrieved 7 January Archived from the original on 16 December Retrieved 13 April Retrieved 17 April Retrieved 26 March The interoperable alternate to spanning tree".
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