Requirements for 802.1AD Provider Bridges

June 2003

Muneyoshi SuzukiNTT

Reference Model

Provider Bridged Network

PEB PEB

PEB PEB

PCB

PCB PCB

CE

CE CE

CE

CE

User Siteof

user A

User Siteof

user B

User Siteof

user A

User Siteof

user B

User Bridged LAN

User Bridged LAN

PEB: Provider Edge BridgePCB: Provider Core BridgeCE: Customer Equipment

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 d

efine 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 port

ion of Provider Edge Bridge’s MAC address)

2. Maximum Bridge DiameterProblem: 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

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 a mechanism

for loop prevention User Bridged LAN should deploy a mechanism for loop

prevention Provider Bridged Network should deploy mechanisms

that protect the network from loops caused by users

(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

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

(3.2) Loop Prevention in User Bridged LAN

(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

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

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

Summary of Requirements

24-32 bit “ID space” for P-VIDExtend Maximum Bridge DiameterProvider-xSTP does not need to interwork with use

r-xSTPSupport of per-user-xSTP in Provider Edge Bridges Development of an OAM tool for loop detectionQ-in-Q case:

Development of unlearn signaling protocol Development of an OAM tool for path tracing