1. Jan 08, 2008CS573: Network Protocols and Standards1 GARP Network Protocols and Standards Winter 2007-2008

2. Jan 08, 2008CS573: Network Protocols and Standards2 GARP Architecture LAN segment

3. Jan 08, 2008CS573: Network Protocols and Standards3 GARP Participant Components A GARP Participant consists of: A GARP application component A GID component GID: GARP Information Declaration Remember: There is one GARP Participant For each port For each application GMRP (Multicast) and GVRP (VLANs) are examples

4. Jan 08, 2008CS573: Network Protocols and Standards4 The Application Component Defines a set of one or more Attribute Types Defines for each Attribute Type Their set of values Their semantics Their structure and encoding Their values in the GARP PDU For each application, a unique Group MAC Address is specified Used as destination MAC address for all GARP protocol exchanges pertaining to that application

5. Jan 08, 2008CS573: Network Protocols and Standards5 The GID Component Declares attribute information among participants on the same segment Contains two state machines for each attribute Registrar state machine Applicant state machine

6. Jan 08, 2008CS573: Network Protocols and Standards6 GARP Participant There is an instance of the Applicant and the Registrar per Attribute GARP Participant

7. Jan 08, 2008CS573: Network Protocols and Standards7 GARP Participant There is an instance of the Applicant and the Registrar per Attribute

8. Jan 08, 2008CS573: Network Protocols and Standards8 Participant: Protocol Elements Registrar Records attribute registration declared by other participants on the same segment Required in bridges (Used in forwarding decisions!) May be implemented in stations for source pruning Applicant Ensures that this participant’s declarations are registered by other participants

9. Jan 08, 2008CS573: Network Protocols and Standards9 Registrar State Machine IN Someone registered this attribute value on this segment MT (Empty) All declarations for this attribute value on this segment have been withdrawn LV (Leaving) Timing out the registration; if no re-declaration is received before the Leave Timer expires, transition will be made to the MT state

10. Jan 08, 2008CS573: Network Protocols and Standards10 Registrar State Machine

11. Jan 08, 2008CS573: Network Protocols and Standards11 Applicant State Machine Three levels of complexity defined: For participants that do not include a registrar (stations) Simple applicant Applicant only For participants that implement a registrar (bridges and some stations) Full applicant

12. Jan 08, 2008CS573: Network Protocols and Standards12 Simple Applicant Simplest type of applicant – no registrar Three states V (very anxious) Applicant has no reason to believe that the other registrars have registered this value (No JoinIN message has been received and no Join message has been sent) A (anxious) If no message has been lost, other registrars will have registered this attribute value A second Join still needs to be sent or seen Q (Quiet) No need to send more messages

13. Jan 08, 2008CS573: Network Protocols and Standards13 Simple Applicant State Machine Messages are labeled by the registrar state of the sender The JoinIN sent when a Join timer expires is shown as sJoinIN Other transitions happen in response to received messages (prefixed with r) Note that even though the Participant doesn’t have a Registrar, it sends JoinIN and LeaveEmpty by default

14. Jan 08, 2008CS573: Network Protocols and Standards14 Applicant Only In order to save on Join and Leave messages when there are several Members on the same segment, stations may track the GARP message activity on the segment for a given Attribute, even when they are not currently interested in registering the Attribute For this purpose, a distinction is made within an applicant between being a Member or an Observer An Observer is a Participant that tracks the Attribute state, but does not wish to make a declaration A Member is also a Participant that is interested in maintaining a declaration for a given attribute value

15. Jan 08, 2008CS573: Network Protocols and Standards15 Applicant Only: Member Types Two types of Members Passive member (P): attempts to maintain the registration of an attribute value, but hasn’t itself sent a Join message to declare it Active member (A): attempts to maintain the registration of an attribute value and has sent a Join message to declare it Note that the observer is always “passive” Tracks the attribute state, but … Does not maintain declaration Observer is NOT a member

16. Jan 08, 2008CS573: Network Protocols and Standards16 Applicant Only An observer can become a member without sending a Join message if it is in the Quiet state A Passive member can quit without sending a Leave message State Machine Acronyms (States) VO: very anxious, observer AO: anxious, observer QO: quiet, observer VP: very anxious, passive VA: very anxious, active LA: Leaving, active (a substate where leave message is generated)

17. Jan 08, 2008CS573: Network Protocols and Standards17 Applicant Only State Machine

18. Jan 08, 2008CS573: Network Protocols and Standards18 Applicant Only When a Participant becomes interested in a given Attribute The Applicant transitions first from Observer to Passive Member If the Observer was in the Quiet state, the Applicant becomes Passive and Quiet Otherwise, it schedules a Join for the earliest transmission occasion A Passive Member that sends a Join becomes an Active Member

19. Jan 08, 2008CS573: Network Protocols and Standards19 Full Applicant Full applicant state machine Used in bridges Also used in stations that include a registrar for source pruning Differences with Applicant only A sent Join message is labeled with the current state of the registrar When registrar is in IN state, send JoinIN When registrar is not in IN state, send JoinEmpty NOTE: A JoinEmpty causes the Applicants on a segment to go to Very Anxious state. The goal is to force other members to update the sender’s state by not considering this Join message valid for that purpose

20. Jan 08, 2008CS573: Network Protocols and Standards20 Full Applicant An observer has an additional state LO state: Leaving Observer Similar to LA (Leaving Active) Enters after hearing a LeaveEmpty message (unless it hears a Join) Like JoinEmpty, LeaveEmpty forces the Applicants to go to very anxious state Purpose: To protect against problems incurred when other Participants fail to see a Leave

21. Jan 08, 2008CS573: Network Protocols and Standards21 Full Applicant What if Join Messages are not labeled with the registrar state? Consider the scenario … Two bridges A and B on the same segment Both interested in an attribute AT Both have registrars in the MT state What happens when A sends 2 Joins? Registrar states: MT for A and IN for B This is because A’s Join has no indication about it’s knowledge of B’s wish to register the attribute AT Therefore, by labeling Join with registrar state, A will force B to send Joins for AT

22. Jan 08, 2008CS573: Network Protocols and Standards22 GIP GARP Information Propagation Propagates attribute registration information between participants for the same application on all ports which are in the forwarding state in a bridge A registration is propagated on a port if any other port in the bridge has seen a registration for the concerned attribute A de-registration is propagated on a port if all other ports are de-registered for the concerned attribute