Requirements for 802 1AD Provider Bridges

Requirements for 802.1AD Provider Bridges: 

Requirements for 802.1AD Provider Bridges June 2003 Muneyoshi Suzuki NTT

Reference Model: 

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

P-VID Space : 

P-VID Space Problem: 12bit VID space defined 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

Maximum Bridge Diameter: 

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

Loop Prevention: 

Loop Prevention Problem: A loop fatally affects a Bridged LAN Requirements: Provider Bridged Network should deploy a mechanism for loop prevention User Bridged LAN should deploy a mechanism for loop prevention Provider Bridged Network should deploy a mechanism that protects the network from loops caused by users

Loop Prevention in Provider Bridged Network: 

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 closed to the provider and need not to interwork with user-xSTP

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 xSTP for the user 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 customer-xSTP for loop prevention Provider Bridged Network may support per-user-xSTP, otherwise, it must forward user-xSTP BPDUs transparently Loop Prevention in User Bridged LAN

Provider Bridged Network Protection from Loops Caused by Users: 

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 may support per-user-xSTP to protect the network Otherwise, development of an OAM tool that detects loop through User and Provider Bridge Networks is indispensable

Unlearning User Addresses: 

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 limited 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

Path Tracing : 

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 frequently 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

Summary of Requirements: 

Summary of Requirements 24-32 bit ID space for P-VID Extend Maximum Bridge Diameter Provider-xSTP is usually closed to the Provider If Provider Bridged Network supports per-user-xSTP It can protect the Network from loops (but not perfect) It can detect topology change of User Bridged LANs If Provider Bridged Network forwards User-xSTP BPDUs transparently Development of an OAM tool for loop detection is needed A snooping mechanism for User-xSTP BPDUs is needed If Q-in-Q is used for encapsulation Development of CCN BPDU is needed Development of an OAM tool for path tracing is needed