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More on SPB-V

More on SPB-V. Shortest Path Bridging V-mode Norman Finn Ver. 01. Overview. Spanning Tree. A(0) . A advertises “ I am the root.”. A. B. C. A(0) . D. E. F. Spanning Tree. A(0) . A(1) . A advertises “I am the root.” B and D advertise “I am one hop from the root.”. A.

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More on SPB-V

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  1. More on SPB-V Shortest Path Bridging V-mode Norman Finn Ver. 01

  2. Overview

  3. Spanning Tree A(0) • A advertises “I am the root.” A B C A(0) D E F

  4. Spanning Tree A(0) A(1) • A advertises “I am the root.” • B and D advertise “I am one hop from the root.” A B C A(1) A(0) D E F A(1)

  5. Spanning Tree A(0) A(1) • A advertises “I am the root.” • B and D advertise “I am one hop from the root.” • E advertises “I am two hops from the root.” A B C A(1) A(0) D E F A(1) A(2)

  6. Spanning Tree A(0) A(1) • A advertises “I am the root.” • B and D advertise “I am one hop from the root.” • E advertises “I am two hops from the root.” • F knows nothing of the path to A; only the distance. Each bridge modifies the data along the way. That is “global information distributed locally.” A B C A(1) A(0) D E F A(1) A(2)

  7. IS-IS A:B,D  • A advertises, “I am A. I connect to B and D.” A B C A:B,D  D E F

  8. IS-IS B:ACE B:ACE • A advertises, “I am A. I connect to B and D.” • B advertises, “I am B. I connect to A, C and E.” A B C B:ACE D E F

  9. IS-IS B:ACE, A:BD B:ACE, A:BD • Furthermore, as soon as B hears A’s advertisement, it relays A’s information to its neighbors. • That is, B says, “I am B. I connect to A, C, and E. A says that it connects to B and D.” A B C B:ACE A:BD D E F

  10. IS-IS • Eventually, every switch in the network has the state of every other switch, and relays all bridges’ data to its neighbors verbatim. That is “local information distributed globally.” • (Of course, there are tricks so that a huge volume of information is not constantly retransmitted.) A:BD B:ACE C:B D:AE E:BDF F:E A B C D E F

  11. Shortest Path Bridging – V-mode • 802.1aq SPB-V control plane is IS-IS • Standard IS-IS, SPB-V code points granted from IETF. Can mix bridging and routing TLVs in one packet. • Data frames use Q-tag; no extra header, no MAC-in-MAC. • Q-tag encodes both source bridge ID (multicast tree ID) and VLAN (community of interest) in the VLAN ID. • Data plane is almost identical to classical bridge data plane. • Uses control-plane interlocks to prevent loops, not TTL to mitigate them (but avoids MSTP brain-death issue). • Data plane learns source MAC addresses (and flushes learned addresses when necessary), but this need not prevent distributing MAC addresses in IS-IS (“host routing”).

  12. Frame formats for bridging schemes MSTP Dest. Src. Qtag* Data CRC • Q-tag in MSTP codes 4094 VLANs • Q-tag in SPB-V codes (VLAN) • (Bridge ID) < 4095, e.g. 4 VLANs and 1023 bridges, or 15 VLANs and 256 bridges. SPB-V Dest. Src. Qtag* Data CRC SPB-M(MAC-in-MAC) last B first B Btag Itag Dest. Src. Ctag Data CRC TRILL next B prev B Qtag TRILL Dest. Src. Ctag Data CRC

  13. SPB-V vs. Multiple Spanning Tree Prot. • Every frame, unicast or multicast, takes the least-cost path. • SPB-V is compatible with MSTP in that: • SPB-V can control some VLANs, while MSTP runs simultaneously, controlling other VLANs (and other protocols control other VLANs). • SPB-V interfaces seamlessly with MSTP at cloud boundaries. • Only VLAN translation (no encapsulation) at MSTP/SPB-V boundaries. • SPB-V, based on IS-IS, has much faster worst-case convergence time. • Loop-prevention interlocks are faster than MSTP interlocks in the worst case, because they are link-state based. • SPB-V can replace protocols (e.g. VLAN pruning) that run after MSTP convergence with link state advertisements requiring only recomputation after a topology change. • SPB-V limits the number of VLANs available.

  14. SPB-V vs. SPB-M with MAC-in-MAC • SPB-V uses only the usual VLAN tag. 802.1aq SPB-M + MAC-in-MAC encapsulates the customer frame. • SPB-V core bridges use customer addresses == the only addresses in the frame, so SPB-M is better for large networks. • SPB-V limits the number of VLANs available. • Given an MSTP data plane, support for an SPB-V data plane is a small change, compared to MAC-in-MAC.

  15. SPB-V vs. SPB-M without MAC-in-MAC • SPB-V uses only the usual VLAN tag. 802.1aq SPB-M adds an I-tag (VLAN-tag is optional). • SPB-V limits the number of VLANs available. SPB-M supports 16M VLANs, somewhat more than the typical home requires. • SPB-Vsupports the existing multicast MAC addresses used by all of the protocols developed over the past 30 years. • SPB-M without MAC-in-MAC supports only engineered multicast MAC addresses, does not support existing multicast MAC addresses, and thus requires changes to most existing end stations’ software.

  16. MSTP/SPB-V data plane difference

  17. SPB-V unicastignores bridge ID q sends a frame to x • E floods qx frame because address x is unknown. • C learns address qwithout Bridge ID E, because it will transmit to q using its own Bridge ID C. • D learns both addresses without Bridge ID. source p C A Each bridge ( )is a spanning treeroot. Tree B isblocked at D source q B E B VID = E + VLAN B B VID = C + VLAN E C D sink y sink x A

  18. SPB-V multicastuses bridge ID p and q are both sourcesfor multicast group G • To reach C, D must pass frames from E. • To avoid duplication, D must not pass frames from A. • (C is reached fromAviaB.) source p C A D source q E B VID = A + VLAN x and y are bothsinks formulticast group G B VID = E + VLAN E C D sink y sink x A

  19. MAC address lookups: MSTP unicast frame multicast frame • Multicast lookup is same as unicast lookup. VLAN ID unicast source unicast dest. VLAN ID unicast source multicast dest. map map map map FDB ID unicast source FDB ID unicast dest. FDB ID unicast source FDB ID multicast dest. Sourcelookup Destinationlookup Sourcelookup Destinationlookup

  20. MAC address lookups: SPB-V unicast frame multicast frame • Multicast lookup is different than unicast lookup. VLAN ID unicast source unicast dest. VLAN ID unicast source multicast dest. no map map map map FDB ID unicast source FDB ID unicast dest. FDB ID unicast source VLAN ID multicast dest. Sourcelookup Destinationlookup Sourcelookup Destinationlookup

  21. The Filtering Database: MSTP One entry per VLANfor unicasts One entry per VLANfor multicasts

  22. The Filtering Database: SPB-V One entry per VLANfor unicasts One entry per VLANper Bridge formulticasts

  23. Additional multicast FDB entries • The additional entries are the inevitable price for optimal forwarding. • One can trade off table size vs. pruning accuracy. • For Reserved Streams, one need only install multicast entries for specific source Bridges, not for all bridges.

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