1 Tech Topic: Link State Paul Bowden Program Manager Exchange Server Product Unit

2 What do we have today?  GWART  Consolidated map of the Organization  Costs associated with connectors  Updated on a schedule  What’s missing from the GWART?  Downstream link intelligence  Intelligent routing  Loop free routing  Dynamic updates

3 Link State  Background  Algorithm developed by “Dijkstra” in 1959  Used in OSPF at the network layer  In use on the Internet today  Exchange 2000’s implementation  In memory database held on all 2000 servers  Immediate propagation of new link data  Master for each Routing Group

4 RG Master  The RID for the Routing Group  Only one master per Routing Group  Can be manually set through Sys. Man.  Responsibilities  Incrementing the major routing version  Propagating new data to member servers

5 RG Members  Responsibilities for bridgeheads  Telling the master about link failures  Acting upon new information from other Routing Groups  Telling other members about new external information when the master is down

6 Protocol Communication  Inside the Routing Group  All servers listen on port 3044 (691 for RC1+)  Plain text information update  Between Routing Groups  RGC = X-LINK2STATE SMTP command verb  X.400 = Dummy message with link state payload  New link information is published immediately to the entire Organization  For scheduled connections, the broadcast is dropped  Link state messages do not appear in queues

7 Looking at Link State  NETMON  Good for understanding at a low-level  Plain text  Tools -> Monitors  View basic status information  Web Management  Like Tools -> Monitors (PT-SHOWCASE)  WinRoute  Admin tool for troubleshooting (PT-SHOWCASE)

8 What causes a state change?  Member OR Master initiated  Link UP or link DOWN  Master initiated  Changing the cost on a connector  Changing Address Spaces  Adding/removing connectors  Master gets a notification from the AD when changes are made in Routing Group configuration  System Manager only updates AD

9 In-memory database  Not persisted to disk  Reboot and learn  Contains RG GUIDs, Connector GUIDs, Costs Address Spaces, Bridgehead GUIDs, and link state (UP/DOWN)  Connector definition and configuration is held in the Active Directory (Configuration NC)  Size of database  32 bytes for every server, connector and Routing Group in the Organization  Example:  250 Routing Groups = 8Kb  150 Exchange Servers = 4.8Kb  800 Connectors = 25.6Kb 38.4Kb total

10 Simple Scenario RGC Member RG Master Routing Group Connector RG1 RG2 RG1 = 5 RG2 = A RG1 = 5 RG2 = A Cost: 10 Link State Update: RG2 to RG3 Link DOWN RG1 = 5 RG2 = B RG1 = 5 RG2 = A RG1 = 5 RG2 = A RG1 = 5 RG2 = A RG1 = 5 RG2 = A Link State Update: RG2 to RG3 Link DOWN RG1 = 5 RG2 = B RG1 = 5 RG2 = B RG1 = 5 RG2 = B Link State Update: RG2 to RG3 Link DOWN RG1 = 5 RG2 = B Link State Update: RG2 to RG3 Link DOWN RG1 = 5 RG2 = B Link State Update: RG2 to RG3 Link DOWN RG3 X

11 What does it look like?  Port 3044/691 Netmon trace  Bytes remaining  GUID of connector affected  GUID of bridgehead that noticed change  Status of connection B D { } F 43 4F 4E 4E VS_CONN.7fe12ef ee8f1654dbc d7f7d1.c380ab f7b7bff438efb F 57 4E cf8b9.DOWN

12 What does it look like?  Link State query (check knowledge) Port C7 33 D C7 33 3B V...3;e..E F D 0D 9D 3A D B2 86 A B7 F8 F !.....C$.....cP DB E9 AE D 4C 49 4E 4B B.....X-LINK2STA C E 4B 3D 7B 30 TE.LAST.CHUNK={ D 20 4D 55 4C c8}.MULTI.( B D 1.2).({ } F DIGEST_QUERY.3a f a82a4ba ec7fca5efe25ce.f A fe1b2771c B b9d2877e43ca12c C B D { }.DIG D F EST_QUERY.3af E a82a4ba5ec7f F ca5efe25ce.f7fe b2771c065317b9d e43ca12c..) D 0A..

13 Master Down Scenario #1 RGC Member RG Master Routing Group Connector RG1 RG2 RG1 = 5 RG2 = A RG1 = 5 RG2 = A Cost: 10 Link State Update: RG2 to RG3 Link DOWN RG1 = 5 RG2 = A RG1 = 5 RG2 = A RG1 = 5 RG2 = A RG1 = 5 RG2 = A X RG3 X

14 Master Down – Local change  RG Master is the only one that can increment the version number of the local Routing Group  Re-broadcast of this new information is not possible  Changed member drops the broadcast

15 Master Down Scenario #2 RGC Member RG Master Routing Group Connector RG1 RG2 RG1 = 5 RG2 = A RG1 = 5 RG2 = A Cost: 10 Link State Update: RG2 to RG3 Link DOWN RG1 = 5 RG2 = B RG1 = 5 RG2 = A RG1 = 5 RG2 = A RG1 = 5 RG2 = A RG1 = 5 RG2 = A Link State Update: RG2 to RG3 Link DOWN RG1 = 5 RG2 = B RG1 = 5 RG2 = B RG1 = 5 RG2 = B Link State Update: RG2 to RG3 Link DOWN RG1 = 5 RG2 = B Link State Update: RG2 to RG3 Link DOWN Link State Update: RG2 to RG3 Link DOWN X RG3 X

16 Master Down – Remote change  Members can act upon information received from other Routing Groups  Members can update each other with new remote information as they perform a link state swap for every SMTP session

17 Complex Routing Walkthrough RG1 RG2 RG5 RG3 RG4 Member RG Master X Link Down Routing Group Connector Link Down X Infinite Cost? Wait in queue Glitch Retry Open Poll Link Down Glitch Retry New messages wait here

18 Multiple Bridgehead Scenario RGC RG1 RG2 X BH1 BH2 RG2 to RG1 BH1: CONN_AVAIL BH2: CONN_AVAIL State: STATE UP GetNextHop = BH1 RG2 to RG1 BH1: CONN_NOT_AVAIL BH2: CONN_AVAIL State: STATE UP X GetNextHop = BH2 RG2 to RG1 BH1: CONN_NOT_AVAIL BH2: CONN_NOT_AVAIL State: STATE UP RG2 to RG1 BH1: CONN_NOT_AVAIL BH2: CONN_NOT_AVAIL State: STATE DOWN State Down

19Caveats  New information is broadcast everywhere and immediately  EDK-based connectors are always UP

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