draft-ietf-pim-sm-v2-new-05.txt

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terms of this state.  Most implementations will use this state to build
a multicast forwarding table, which would then be updated when the
relevant state in the TIB changes.

Although we specify precisely the state to be kept, this does not mean
that an implementation of PIM-SM needs to hold the state in this form.



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This is actually an abstract state definition, which is needed in order
to specify the router's behavior.  A PIM-SM implementation is free to
hold whatever internal state it requires, and will still be conformant
with this specification so long as it results in the same externally
visible protocol behavior as an abstract router that holds the following
state.

We divide TIB state into four sections:

(*,*,RP) state
     State that maintains per-RP trees, for all groups served by a given
     RP.

(*,G) state
     State that maintains the RP tree for G.

(S,G) state
     State that maintains a source-specific tree for source S and group
     G.

(S,G,rpt) state
     State that maintains source-specific information about source S on
     the RP tree for G.  For example, if a source is being received on
     the source-specific tree, it will normally have been pruned off the
     RP tree.  This prune state is (S,G,rpt) state.

The state that should be kept is described below.  Of course,
implementations will only maintain state when it is relevant to
forwarding operations - for example, the "NoInfo" state might be assumed
from the lack of other state information, rather than being held
explicitly.

4.1.1.  General Purpose State

A router holds the following non-group-specific state:

     For each interface:

          o Override Interval

          o Propagation Delay

          o Suppression state: One of {"Enable", "Disable"}

          Neighbor State:

            For each neighbor:




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                 o Information from neighbor's Hello

                 o Neighbor's Gen ID.

                 o Neighbor liveness timer (NLT)

          Designated Router (DR) State:

            o Designated Router's IP Address

            o DR's DR Priority

The Override Interval, the Propagation Delay and the Interface
suppression state are described in section 4.3.3. Designated Router
state is described in section 4.3.

4.1.2.  (*,*,RP) State

For every RP a router keeps the following state:

     (*,*,RP) state:
          For each interface:

               PIM (*,*,RP) Join/Prune State:

                    o State: One of {"NoInfo" (NI), "Join" (J),
                      "PrunePending" (PP)}

                    o Prune Pending Timer (PPT)

                    o Join/Prune Expiry Timer (ET)

          Not interface specific:

               o Upstream Join/Prune Timer (JT)

               o Last RPF Neighbor towards RP that was used

PIM (*,*,RP) Join/Prune state is the result of receiving PIM (*,*,RP)
Join/Prune messages on this interface, and is specified in section
4.5.1.

The upstream (*,*,RP) Join/Prune timer is used to send out periodic
Join(*,*,RP) messages, and to override Prune(*,*,RP) messages from peers
on an upstream LAN interface.

The last RPF neighbor towards the RP is stored because if the MRIB
changes then the RPF neighbor towards the RP may change.  If it does so,



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then we need to trigger a new Join(*,*,RP) to the new upstream neighbor
and a Prune(*,*,RP) to the old upstream neighbor.  Similarly, if a
router detects through a changed GenID in a Hello message that the
upstream neighbor towards the RP has rebooted, then it should re-
instantiate state by sending a Join(*,*,RP).  These mechanisms are
specified in Section 4.5.5.

4.1.3.  (*,G) State

For every group G a router keeps the following state:

     (*,G) state:
          For each interface:

               Local Membership:
                    State: One of {"NoInfo", "Include"}

               PIM (*,G) Join/Prune State:

                    o State: One of {"NoInfo" (NI), "Join" (J),
                      "PrunePending" (PP)}

                    o Prune Pending Timer (PPT)

                    o Join/Prune Expiry Timer (ET)

               (*,G) Assert Winner State

                    o State: One of {"NoInfo" (NI), "I lost Assert" (L),
                      "I won Assert" (W)}

                    o Assert Timer (AT)

                    o Assert winner's IP Address

                    o Assert winner's Assert Metric

          Not interface specific:

               o Upstream Join/Prune Timer (JT)

               o Last RP Used

               o Last RPF Neighbor towards RP that was used

Local membership is the result of the local membership mechanism (such
as IGMP or MLD) running on that interface.  It need not be kept if this
router is not the DR on that interface unless this router won a (*,G)



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assert on this interface for this group, although implementations may
optionally keep this state in case they become the DR or assert winner.
We recommend storing this information if possible, as it reduces latency
converging to stable operating conditions after a failure causing a
change of DR.  This information is used by the pim_include(*,G) macro
described in section 4.1.6.

PIM (*,G) Join/Prune state is the result of receiving PIM (*,G)
Join/Prune messages on this interface, and is specified in section
4.5.2. The state is used by the macros that calculate the outgoing
interface list in section 4.1.6, and in the JoinDesired(*,G) macro
(defined in section 4.5.6) that is used in deciding whether a Join(*,G)
should be sent upstream.

(*,G) Assert Winner state is the result of sending or receiving (*,G)
Assert messages on this interface.  It is specified in section 4.6.2.

The upstream (*,G) Join/Prune timer is used to send out periodic
Join(*,G) messages, and to override Prune(*,G) messages from peers on an
upstream LAN interface.

The last RP used must be stored because if the RP Set changes (section
4.8) then state must be torn down and rebuilt for groups whose RP
changes.

The last RPF neighbor towards the RP is stored because if the MRIB
changes then the RPF neighbor towards the RP may change.  If it does so,
then we need to trigger a new Join(*,G) to the new upstream neighbor and
a Prune(*,G) to the old upstream neighbor.  Similarly, if a router
detects through a changed GenID in a Hello message that the upstream
neighbor towards the RP has rebooted, then it should re-instantiate
state by sending a Join(*,G).  These mechanisms are specified in Section
4.5.6.

4.1.4.  (S,G) State

For every source/group pair (S,G) a router keeps the following state:

     (S,G) state:

          For each interface:

               Local Membership:
                    State: One of {"NoInfo", "Include"}

               PIM (S,G) Join/Prune State:





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                    o State: One of {"NoInfo" (NI), "Join" (J),
                      "PrunePending" (PP)}

                    o Prune Pending Timer (PPT)

                    o Join/Prune Expiry Timer (ET)

               (S,G) Assert Winner State

                    o State: One of {"NoInfo" (NI), "I lost Assert" (L),
                      "I won Assert" (W)}

                    o Assert Timer (AT)

                    o Assert winner's IP Address

                    o Assert winner's Assert Metric

          Not interface specific:

               o Upstream (S,G) Join/Prune Timer (JT)

               o Last RPF Neighbor towards S that was used

               o SPT bit (indicates (S,G) state is active)

               o (S,G) KeepAlive Timer (KAT)

Local membership is the result of the local source-specific membership
mechanism (such as IGMP version 3) running on that interface and
specifying that this particular source should be included.  As stored
here, this state is the resulting state after any IGMPv3 inconsistencies
have been resolved.  It need not be kept if this router is not the DR on
that interface unless this router won a (S,G) assert on this interface
for this group.  However, we recommend storing this information if
possible, as it reduces latency converging to stable operating
conditions after a failure causing a change of DR.  This information is
used by the pim_include(S,G) macro described in section 4.1.6.

PIM (S,G) Join/Prune state is the result of receiving PIM (S,G)
Join/Prune messages on this interface, and is specified in section
4.5.2. The state is used by the macros that calculate the outgoing
interface list in section 4.1.6, and in the JoinDesired(S,G) macro
(defined in section 4.5.7) that is used in deciding whether a Join(S,G)
should be sent upstream.

(S,G) Assert Winner state is the result of sending or receiving (S,G)
Assert messages on this interface.  It is specified in section 4.6.1.



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The upstream (S,G) Join/Prune timer is used to send out periodic
Join(S,G) messages, and to override Prune(S,G) messages from peers on an
upstream LAN interface.

The last RPF neighbor towards S is stored because if the MRIB changes
then the RPF neighbor towards S may change.  If it does so, then we need
to trigger a new Join(S,G) to the new upstream neighbor and a Prune(S,G)
to the old upstream neighbor.  Similarly, if the router detects through
a changed GenID in a Hello message that the upstream neighbor towards S
has rebooted, then it should re-instantiate state by sending a
Join(S,G).  These mechanisms are specified in Section 4.5.7.

The SPTbit is used to indicate whether forwarding is taking place on the
(S,G) Shortest Path Tree (SPT) or on the (*,G) tree.  A router can have
(S,G) state and still be forwarding on (*,G) state during the interval
when the source-specific tree is being constructed.  When SPTbit is
FALSE, only (*,G) forwarding state is used to forward packets from S to
G.  When SPTbit is TRUE, both (*,G) and (S,G) forwarding state are used.

The (S,G) Keepalive Timer is updated by data being forwarded using this
(S,G) forwarding state.  It is used to keep (S,G) state alive in the
absence of explicit (S,G) Joins.  Amongst other things, this is
necessary for the so-called "turnaround rules" - when the RP uses (S,G)
joins to stop encapsulation, and then (S,G) prunes to prevent traffic
from unnecessarily reaching the RP.

4.1.5.  (S,G,rpt) State

For every source/group pair (S,G) for which a router also has (*,G)
state, it also keeps the following state:

     (S,G,rpt) state:

          For each interface:

               Local Membership:
                    State: One of {"NoInfo", "Exclude"}

               PIM (S,G,rpt) Join/Prune State:

                    o State: One of {"NoInfo", "Pruned", "PrunePending"}

                    o Prune Pending Timer (PPT)

                    o Join/Prune Expiry Timer (ET)

          Not interface specific:




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               Upstream (S,G,rpt) Join/Prune State:

                    o State: One of {"NotJoined(*,G)",
                      "NotPruned(S,G,rpt)", "Pruned(S,G,rpt)"}