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Requirements for 802.1AD Provider Bridges

Requirements for 802.1AD Provider Bridges. June 2003 Muneyoshi Suzuki NTT. Reference Model. User Bridged LAN. Provider Bridged Network. User Site of user A. User Site of user A. CE. PEB. PEB. CE. PCB. PCB. PCB. CE. User Site of user B. User Site of user B. CE. PEB.

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Requirements for 802.1AD Provider Bridges

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  1. Requirements for 802.1AD Provider Bridges June 2003 Muneyoshi Suzuki NTT

  2. Reference Model User Bridged LAN Provider Bridged Network User Site of user A User Site of user A CE PEB PEB CE PCB PCB PCB CE User Site of user B User Site of user B CE PEB PEB CE User Bridged LAN PEB: Provider Edge Bridge PCB: Provider Core Bridge CE: Customer Equipment

  3. 1. P-VID Space • Problem: 12bit VID space defined in 802.1Q-1998 is too small for public service • Requirements: • If a P-VID identifies an User Bridged LAN, 24 bit (16M users) ID space is needed • If a P-VID identifies an user site, 32 bit (4G sites) ID space is needed • Note: Providers need “ID space,” so solution does not need to define a single 24-32 bit “P-VID format” • Hierarchical ID space (e.g., a P-VID consists of 2 VIDs) • MAC-in-MAC (e.g., a P-VID consists of single VID and a portion of Provider Edge Bridge’s MAC address)

  4. 2. Maximum Bridge Diameter • Problem: Recommended value of the Maximum Bridge Diameter is 7 (802.1D-1998, 802.1w-2001), but it is too small for public service • The standards don’t address technical background of the value (What happens if it exceeds 7? xSTP does not converge in periodic time?) • Requirements: • The value should be extended tens for Provider Bridged Network and 10 for User Bridged LAN • Diameter of a Provider Bridged Network should not affect diameter of User Bridged LANs

  5. 3. Loop Prevention • Problem: A loop fatally affects a Bridged LAN • If an user sends broadcast or unknown destination frames to the provider, then the frames are sent to the user sites but back to the provider through a looped path, ....... • Requirements: • Provider Bridged Network should deploy amechanism for loop prevention • User Bridged LAN should deploy amechanism for loop prevention • Provider Bridged Network should deploy mechanisms that protect the network from loops caused by users

  6. (3.1) Loop Prevention in Provider Bridged Network • It is provider’s responsibility to ensure loop-free tree topology for the Provider Bridged Network • Thus, the topology is decided by the provider’s policy and control • Therefore, it is quite unrealistic scenario to change the topology based on user-xSTP • Requirements: • Provider Bridged Network should deploy provider-xSTP for loop prevention • However, it is usually limited to the provider and does not need to interwork with user-xSTP

  7. (3.2) Loop Prevention in User Bridged LAN • It is user’s responsibility to ensure loop-free tree topology for the User Bridged LAN • This is because, an user can cause a loop whether the provider supports per-user-xSTP or not • However, if xSTP is used in an User Bridged LAN and if the provider forwards it transparently, loops can be prevented • This is because, the provider ensures loop-free topology and a single xSTP instance on a loop can detect and cut it • Requirements: • User Bridged LAN should deploy user-xSTP for loop prevention • Provider Bridged Network may support per-user-xSTP, otherwise, it must forward user-xSTP BPDUs transparently

  8. (3.3) Provider Bridged Network Protection from Loops Caused by Users • If Provider Bridged Network supports per-user-xSTP, it can be protected from loops caused by users • Only Provider Edge Bridges need to support it, because a single xSTP instance on a loop can detect and cut it • However, this is not perfect solution, but it does not mean Providers don’t need protection • Requirements: • Provider Edge Bridges optionally support per-user-xSTP to protect the network • Development of an OAM tool that detects loop through User and Provider Bridge Networks is indispensable

  9. 4. Unlearning User Addresses • Problem: If topology of an User Bridged LAN is changed by the user-xSTP, the Provider Bridges must clear related entries in the FDB • However, this is needed only if the User Site is multihomed to the Provider Network • Requirements: • Provider Edge Bridges should support per-user-xSTP or a snooping mechanism for it. • Q-in-Q: If topology change is detected, clear related entries in the FDB, then notify that the fact to the other Provider Bridges using Customer Change Notification BPDU to be developed • MAC-in-MAC: If topology change is detected, clear related entries in the FDB

  10. 5. Path Tracing • When a provider tests a path that forwards frames for an user, the provider verifies consistency of FDBs in the Provider Bridges • Problem: Verification is not easy in Q-in-Q case, because, the Provider Bridged Network uses user MAC addresses which subject to change and are purged from FDBs in 5 minutes • Requirement: An OAM tool for path tracing is indispensable in Q-in-Q case • Note: In MAC-in-MAC case, path tracing is easy, because the Network uses Provider Edge Bridge addresses

  11. Summary of Requirements • 24-32 bit “ID space” for P-VID • Extend Maximum Bridge Diameter • Provider-xSTP does not need to interwork with user-xSTP • Support of per-user-xSTP in Provider Edge Bridges • Development of an OAM tool for loop detection • Q-in-Q case: • Development of unlearn signaling protocol • Development of an OAM tool for path tracing

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