GARP

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GARP

• Network Protocols and Standards
• Winter 2008-2009

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GARP Architecture
LAN segment
LAN segment
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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

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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

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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

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GARP Participant
GARP Participant
There is an instance of the Applicant and the
Registrar per Attribute
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GARP Participant
GARP Participant
There is an instance of the Applicant and the
Registrar per Attribute
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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 participants declarations are
  registered by other participants

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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  segment have been withdrawn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

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Registrar State Machine
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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

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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

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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 doesnt
  have a Registrar, it sends JoinIN and LeaveEmpty
  by default

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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

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Applicant Only Member Types

• Two types of Members
• Passive member (P) attempts to maintain the
  registration of an attribute value, but hasnt
  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

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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)

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Applicant Only State Machine
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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

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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 senders
  state by not considering this Join message valid
  for that purpose

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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

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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 As Join has no indication about
  its knowledge of Bs wish to register the
  attribute AT
• Therefore, by labeling Join with registrar state,
  A will force B to send Joins for AT

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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