RFC 8220
Protocol Independent Multicast (PIM) over Virtual Private LAN Service (VPLS)
Pages: 43
Informational
Informational
Part 2 of 2 – Pages 24 to 43
2.7. Bidirectional PIM (BIDIR-PIM)
Bidirectional PIM (BIDIR-PIM) is a variation of PIM-SM. The main differences between PIM-SM and BIDIR-PIM are as follows: o There are no source-based trees, and SSM is not supported (i.e., no (S,G) states) in BIDIR-PIM. o Multicast traffic can flow up the shared tree in BIDIR-PIM. o To avoid forwarding loops, one router on each link is elected as the Designated Forwarder (DF) for each RP in BIDIR-PIM. The main advantage of BIDIR-PIM is that it scales well for many-to-many applications. However, the lack of source-based trees means that multicast traffic is forced to remain on the shared tree. As described in RFC 5015 [BIDIR-PIM], parts of a BIDIR-PIM-enabled network may forward traffic without exchanging Join/Prune messages -- for instance, between DFs and the Rendezvous Point Link (RPL). As the described procedures for PIM snooping rely on the presence of Join/Prune messages, enabling PIM snooping on BIDIR-PIM networks could break the BIDIR-PIM functionality. Deploying PIM snooping on BIDIR-PIM-enabled networks will require some further study. Some thoughts on this topic are discussed in Appendix A.2.8. Interaction with IGMP Snooping
Whenever IGMP snooping is enabled in conjunction with PIM snooping in the same VPLS instance, the PE SHOULD follow these rules: o To maintain the list of multicast routers and ports on which they are attached, the PE SHOULD NOT use the rules described in RFC 4541 [IGMP-SNOOP] but SHOULD rely on the neighbors discovered by PIM snooping. This list SHOULD then be used to apply the first forwarding rule (rule 1) listed in Section 2.1.1 of RFC 4541 [IGMP-SNOOP].
o If the PE supports proxy reporting, an IGMP membership learned
only on a port to which a PIM neighbor is attached (i.e., not
learned elsewhere) SHOULD NOT be included in the summarized
upstream report sent to that port.
2.9. PIM-DM
The key characteristic of PIM-DM is flood-and-prune behavior.
Shortest-path trees are built as a multicast source starts
transmitting.
2.9.1. Building PIM-DM States
PIM-DM states are built by snooping on the PIM-DM Join, Prune, Graft,
and State Refresh messages received on ACs/PWs and State Refresh
messages sent on ACs/PWs. By snooping on these PIM-DM messages, a PE
builds the following states per (S,G,N) where S is the address of the
multicast source, G is the group address, and N is the upstream
neighbor to which Prunes/Grafts are sent by downstream CEs:
Per PIM(S,G,N):
Port PIM(S,G,N) Prune State:
* DownstreamPState(S,G,N,Port): One of {"NoInfo" (NI),
"Pruned" (P), "Prune-Pending" (PP)}
* Prune-Pending Timer (PPT)
* Prune Timer (PT)
* Upstream Port (valid if the PIM(S,G,N) Prune state is "Pruned")
2.9.2. PIM-DM Downstream Per-Port PIM(S,G,N) State Machine
The downstream per-port PIM(S,G,N) state machine is as defined in
Section 4.4.2 of RFC 3973 [PIM-DM], with a few changes relevant to
PIM snooping. When reading Section 4.4.2 of RFC 3973 [PIM-DM],
please be aware that, for the purposes of PIM snooping, the
downstream states are built per (S,G,N,Downstream-Port) in PIM
snooping and not per (Downstream-Interface,S,G) as in a PIM-DM
router. As noted in Section 2.9.1, the states (DownstreamPState) and
timers (PPT and PT) are per (S,G,N,Port).
2.9.3. Triggering Assert Election in PIM-DM
Since PIM-DM is a flood-and-prune protocol, traffic is flooded to all routers unless explicitly pruned. Since PIM-DM routers do not prune on non-RPF interfaces, PEs should typically not receive Prunes on Port(RPF-Neighbor). So, the asserting routers should typically be in pim_oiflist(S,G). In most cases, Assert election should occur naturally without any special handling, since data traffic will be forwarded to the asserting routers. However, there are some scenarios where a Prune might be received on a port that is also an upstream port. If we prune the port from pim_oiflist(S,G), then it would not be possible for the asserting routers to determine if traffic arrived on their downstream port. This can be fixed by adding pim_iifs(S,G) to pim_oiflist(S,G) so that data traffic flows to the upstream ports.2.10. PIM Proxy
As noted earlier, PIM snooping will work correctly only if Join suppression is disabled in the VPLS. If Join suppression is enabled in the VPLS, then PEs MUST do PIM relay/proxying for VPLS multicast to work correctly. This section applies specifically to full proxying and not to relay.2.10.1. Upstream PIM Proxy Behavior
A PIM proxying PE consumes Join/Prune messages and regenerates PIM Join/Prune messages to be sent upstream by implementing the Upstream FSM as specified in Section 4.5.4 of RFC 7761 [PIM-SM]. This is the only difference from PIM relay. The source IP address in PIM packets sent upstream SHOULD be the address of a PIM downstream neighbor in the corresponding Join/Prune state. The chosen address MUST NOT be the Upstream Neighbor field to be encoded in the packet. The Layer 2 encapsulation for the selected source IP address MUST be the encapsulation recorded in the PIM Neighbor Database for that IP address.2.11. Directly Connected Multicast Source
PIM snooping/relay/proxying could be enabled on a LAN that connects a multicast source and a PIM First-Hop Router (FHR). As the FHR will not send any downstream Join/Prune messages, we will not be able to establish any forwarding states for that source. Therefore, if there is a source in the CE network that connects directly into the VPLS instance, then multicast traffic from that source MUST be sent to all PIM routers on the VPLS instance in addition to the IGMP
receivers in the VPLS. If there is already (S,G) or (*,G) snooping
state that is formed on any PE, this will not happen per the current
forwarding rules and guidelines. So, in order to determine if
traffic needs to be flooded to all routers, a PE must be able to
determine if the traffic came from a host on that LAN. There are
three ways to address this problem:
o The PE would have to do IPv4 ARP snooping and/or IPv6 Neighbor
Discovery snooping to determine if a source is directly connected.
o Another option is to configure all PEs to indicate that there are
CE sources that are directly connected to the VPLS instance and
disallow snooping for the groups for which the source is going to
send traffic. This way, traffic from that source to those groups
will always be flooded within the provider network.
o A third option is to require that sources of CE multicast traffic
must be behind a router.
This document recommends the third option -- sources of traffic must
be behind a router.
2.12. Data-Forwarding Rules
First, we define the rules that are common to PIM-SM and PIM-DM PEs.
Forwarding rules for each protocol type are specified in the
subsections below.
If there is no matching forwarding state, then the PE SHOULD discard
the packet, i.e., the UserDefinedPortList (Sections 2.12.1 and
2.12.2) SHOULD be empty.
The following general rules MUST be followed when forwarding
multicast traffic in a VPLS:
o Traffic arriving on a port MUST NOT be forwarded back onto the
same port.
o Due to VPLS split-horizon rules, traffic ingressing on a PW
MUST NOT be forwarded to any other PW.
2.12.1. PIM-SM Data-Forwarding Rules
Per the rules in RFC 7761 [PIM-SM] and per the additional rules specified in this document, OutgoingPortList(*,G) = immediate_olist(*,G) (+) UpstreamPorts(*,G) (+) Port(PimDR) OutgoingPortList(S,G) = inherited_olist(S,G) (+) UpstreamPorts(S,G) (+) (UpstreamPorts(*,G) (-) UpstreamPorts(S,G,rpt)) (+) Port(PimDR) RFC 7761 [PIM-SM] specifies how immediate_olist(*,G) and inherited_olist(S,G) are built. PimDR is the IP address of the PIM DR in the VPLS. The PIM-SM snooping data-forwarding rules are defined below in pseudocode: BEGIN iif is the incoming port of the multicast packet. S is the source IP address of the multicast packet. G is the destination IP address of the multicast packet. If there is (S,G) state on the PE Then OutgoingPortList = OutgoingPortList(S,G) Else if there is (*,G) state on the PE Then OutgoingPortList = OutgoingPortList(*,G) Else OutgoingPortList = UserDefinedPortList Endif If iif is an AC Then OutgoingPortList = OutgoingPortList (-) iif Else ## iif is a PW OutgoingPortList = OutgoingPortList (-) PWPorts Endif Forward the packet to OutgoingPortList. END
First, if there is (S,G) state on the PE, then the set of outgoing ports is OutgoingPortList(S,G). Otherwise, if there is (*,G) state on the PE, then the set of outgoing ports is OutgoingPortList(*,G). The packet is forwarded to the selected set of outgoing ports while observing the general rules above in Section 2.12.2.12.2. PIM-DM Data-Forwarding Rules
The PIM-DM snooping data-forwarding rules are defined below in pseudocode: BEGIN iif is the incoming port of the multicast packet. S is the source IP address of the multicast packet. G is the destination IP address of the multicast packet. If there is (S,G) state on the PE Then OutgoingPortList = olist(S,G) Else OutgoingPortList = UserDefinedPortList Endif If iif is an AC Then OutgoingPortList = OutgoingPortList (-) iif Else ## iif is a PW OutgoingPortList = OutgoingPortList (-) PWPorts Endif Forward the packet to OutgoingPortList. END If there is forwarding state for (S,G), then forward the packet to olist(S,G) while observing the general rules above in Section 2.12. RFC 3973 [PIM-DM] specifies how olist(S,G) is constructed.3. IANA Considerations
This document does not require any IANA actions.
4. Security Considerations
Security considerations provided in the VPLS solution documents (i.e., RFC 4762 [VPLS-LDP] and RFC 4761 [VPLS-BGP]) apply to this document as well.5. References
5.1. Normative References
[BIDIR-PIM] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, "Bidirectional Protocol Independent Multicast (BIDIR-PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, <https://www.rfc-editor.org/info/rfc5015>. [JOIN-ATTR] Boers, A., Wijnands, I., and E. Rosen, "The Protocol Independent Multicast (PIM) Join Attribute Format", RFC 5384, DOI 10.17487/RFC5384, November 2008, <https://www.rfc-editor.org/info/rfc5384>. [PIM-DM] Adams, A., Nicholas, J., and W. Siadak, "Protocol Independent Multicast - Dense Mode (PIM-DM): Protocol Specification (Revised)", RFC 3973, DOI 10.17487/RFC3973, January 2005, <https://www.rfc-editor.org/info/rfc3973>. [PIM-SM] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 2016, <https://www.rfc-editor.org/info/rfc7761>. [PIM-SSM] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, <https://www.rfc-editor.org/info/rfc4607>. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RPF-VECTOR] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path Forwarding (RPF) Vector TLV", RFC 5496, DOI 10.17487/RFC5496, March 2009, <https://www.rfc-editor.org/info/rfc5496>.5.2. Informative References
[IGMP-SNOOP] Christensen, M., Kimball, K., and F. Solensky, "Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, <https://www.rfc-editor.org/info/rfc4541>. [VPLS-BGP] Kompella, K., Ed., and Y. Rekhter, Ed., "Virtual Private LAN Service (VPLS) Using BGP for Auto-Discovery and Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007, <https://www.rfc-editor.org/info/rfc4761>. [VPLS-LDP] Lasserre, M., Ed., and V. Kompella, Ed., "Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC 4762, DOI 10.17487/RFC4762, January 2007, <https://www.rfc-editor.org/info/rfc4762>. [VPLS-MCAST] Aggarwal, R., Ed., Kamite, Y., Fang, L., Rekhter, Y., and C. Kodeboniya, "Multicast in Virtual Private LAN Service (VPLS)", RFC 7117, DOI 10.17487/RFC7117, February 2014, <https://www.rfc-editor.org/info/rfc7117>. [VPLS-MCAST-REQ] Kamite, Y., Ed., Wada, Y., Serbest, Y., Morin, T., and L. Fang, "Requirements for Multicast Support in Virtual Private LAN Services", RFC 5501, DOI 10.17487/RFC5501, March 2009, <https://www.rfc-editor.org/info/rfc5501>.
Appendix A. BIDIR-PIM Considerations
This appendix describes some guidelines that may be used to preserve BIDIR-PIM functionality in combination with PIM snooping. In order to preserve BIDIR-PIM snooping, routers need to set up forwarding states so that: o on the RPL, all traffic is forwarded to all Port(N) ports. o on any other interface, traffic is always forwarded to the DF. The information needed to set up these states may be obtained by: o determining the mapping between the group (range) and the RP. o snooping and storing DF election information. o determining where the RPL is. This could be achieved by static configuration or by combining the information mentioned in the two bullet items above.A.1. BIDIR-PIM Data-Forwarding Rules
The BIDIR-PIM snooping data-forwarding rules are defined below in pseudocode: BEGIN iif is the incoming port of the multicast packet. G is the destination IP address of the multicast packet. If there is forwarding state for G Then OutgoingPortList = olist(G) Else OutgoingPortList = UserDefinedPortList Endif If iif is an AC Then OutgoingPortList = OutgoingPortList (-) iif Else ## iif is a PW OutgoingPortList = OutgoingPortList (-) PWPorts Endif Forward the packet to OutgoingPortList. END
If there is forwarding state for G, then forward the packet to olist(G) while observing the general rules above in Section 2.12. RFC 5015 [BIDIR-PIM] specifies how olist(G) is constructed.Appendix B. Example Network Scenario
Let us consider the scenario in Figure 3. +------+ AC3 +------+ | PE2 |-----| CE3 | /| | +------+ / +------+ | / | | / | | /PW12 | | / | /---\ / |PW23 | S | / | \---/ / | | / | | / | | +------+ / +------+ | +------+ | PE1 |/ PW13 | PE3 | +------+ | CE1 |-----| |-------------| |-----| CE4 | +------+ AC1 +------+ +------+ AC4 +------+ | |AC2 +------+ | CE2 | +------+ Figure 3: An Example Network for Triggering an Assert In the examples below, JT(Port,S,G,N) is the downstream Join Expiry Timer on the specified Port for the (S,G) with upstream neighbor N.B.1. PIM Snooping Example
In the network depicted in Figure 3, S is the source of a multicast stream (S,G). CE1 and CE2 both have two ECMP routes to reach the source. 1. CE1 sends a Join(S,G) with UpstreamNeighbors(S,G) = CE3. 2. PE1 snoops on the Join(S,G) and builds forwarding state, since it is received on an AC. It also floods the Join(S,G) in the VPLS. PE2 snoops on the Join(S,G) and builds forwarding state, since
the Join(S,G)is targeting a neighbor residing on an AC. PE3
does not create forwarding state for (S,G) because this is a
PW-only Join and there is neither an existing (*,G) state with an
AC in UpstreamPorts(*,G) nor an existing (S,G) state with an AC
in UpstreamPorts(S,G). Both PE2 and PE3 will also flood the
Join(S,G) in the VPLS.
The resulting states at the PEs are as follows:
PE1 states:
JT(AC1,S,G,CE3) = JP_HoldTime
UpstreamNeighbors(S,G) = { CE3 }
UpstreamPorts(S,G) = { PW12 }
OutgoingPortList(S,G) = { AC1, PW12 }
PE2 states:
JT(PW12,S,G,CE3) = JP_HoldTime
UpstreamNeighbors(S,G) = { CE3 }
UpstreamPorts(S,G) = { AC3 }
OutgoingPortList(S,G) = { PW12, AC3 }
PE3 states:
No (S,G) state
3. The multicast stream (S,G) flows along CE3 -> PE2 -> PE1 -> CE1.
4. Now CE2 sends a Join(S,G) with UpstreamNeighbors(S,G) = CE4.
5. All PEs snoop on the Join(S,G), build forwarding state, and flood
the Join(S,G) in the VPLS. Note that for PE2, even though this
is a PW-only Join, forwarding state is built on this Join(S,G),
since PE2 has an existing (S,G) state with an AC in
UpstreamPorts(S,G).
The resulting states at the PEs are as follows:
PE1 states:
JT(AC1,S,G,CE3) = active
JT(AC2,S,G,CE4) = JP_HoldTime
UpstreamNeighbors(S,G) = { CE3, CE4 }
UpstreamPorts(S,G) = { PW12, PW13 }
OutgoingPortList(S,G) = { AC1, PW12, AC2, PW13 }
PE2 states:
JT(PW12,S,G,CE4) = JP_HoldTime
JT(PW12,S,G,CE3) = active
UpstreamNeighbors(S,G) = { CE3, CE4 }
UpstreamPorts(S,G) = { AC3, PW23 }
OutgoingPortList(S,G) = { PW12, AC3, PW23 }
PE3 states:
JT(PW13,S,G,CE4) = JP_HoldTime
UpstreamNeighbors(S,G) = { CE4 }
UpstreamPorts(S,G) = { AC4 }
OutgoingPortList(S,G) = { PW13, AC4 }
6. The multicast stream (S,G) flows into the VPLS from two of the
CEs -- CE3 and CE4. PE2 forwards the stream received from CE3 to
PW23, and PE3 forwards the stream to AC4. This helps the CE
routers to trigger Assert election. Let us say that CE3 becomes
the Assert winner.
7. CE3 sends an Assert message to the VPLS. The PEs flood the
Assert message without examining it.
8. CE4 stops sending the multicast stream to the VPLS.
9. CE2 notices an RPF change due to the Assert and sends a
Prune(S,G) with upstream neighbor = CE4. CE2 also sends a
Join(S,G) with upstream neighbor = CE3.
10. All the PEs start a Prune-Pending timer on the ports on which
they received the Prune(S,G). When the Prune-Pending timer
expires, all PEs will remove the downstream (S,G,CE4) states.
The resulting states at the PEs are as follows:
PE1 states:
JT(AC1,S,G,CE3) = active
UpstreamNeighbors(S,G) = { CE3 }
UpstreamPorts(S,G) = { PW12 }
OutgoingPortList(S,G) = { AC1, AC2, PW12 }
PE2 states:
JT(PW12,S,G,CE3) = active
UpstreamNeighbors(S,G) = { CE3 }
UpstreamPorts(S,G) = { AC3 }
OutgoingPortList(S,G) = { PW12, AC3 }
PE3 states:
JT(PW13,S,G,CE3) = JP_HoldTime
UpstreamNeighbors(S,G) = { CE3 }
UpstreamPorts(S,G) = { PW23 }
OutgoingPortList(S,G) = { PW13, PW23 }
Note that at this point at PE3, since there is no AC in
OutgoingPortList(S,G) and no (*,G) or (S,G) state with an AC in
UpstreamPorts(*,G) or UpstreamPorts(S,G), respectively, the
existing (S,G) state at PE3 can also be removed. So, finally:
PE3 states:
No (S,G) state
Note that at the end of the Assert election, there should be no
duplicate traffic forwarded downstream, and traffic should flow only
on the desired path. Also note that there are no unnecessary (S,G)
states on PE3 after the Assert election.
B.2. PIM Proxy Example with (S,G) / (*,G) Interaction
In the same network, let us assume that CE4 is the upstream neighbor
towards the RP for G.
JPST(S,G,N) is the JP sending timer for the (S,G) with upstream
neighbor N.
1. CE1 sends a Join(S,G) with UpstreamNeighbors(S,G) = CE3.
2. PE1 consumes the Join(S,G) and builds forwarding state, since the
Join(S,G) is received on an AC.
PE2 consumes the Join(S,G) and builds forwarding state, since the
Join(S,G) is targeting a neighbor residing on an AC.
PE3 consumes the Join(S,G) but does not create forwarding state
for (S,G), since this is a PW-only Join and there is neither an
existing (*,G) state with an AC in UpstreamPorts(*,G) nor an
existing (S,G) state with an AC in UpstreamPorts(S,G).
The resulting states at the PEs are as follows:
PE1 states:
JT(AC1,S,G,CE3) = JP_HoldTime
JPST(S,G,CE3) = t_periodic
UpstreamNeighbors(S,G) = { CE3 }
UpstreamPorts(S,G) = { PW12 }
OutgoingPortList(S,G) = { AC1, PW12 }
PE2 states:
JT(PW12,S,G,CE3) = JP_HoldTime
JPST(S,G,CE3) = t_periodic
UpstreamNeighbors(S,G) = { CE3 }
UpstreamPorts(S,G) = { AC3 }
OutgoingPortList(S,G) = { PW12, AC3 }
PE3 states:
No (S,G) state
Joins are triggered as follows:
PE1 triggers a Join(S,G) targeting CE3. Since the Join(S,G) was
received on an AC and is targeting a neighbor that is residing
across a PW, the triggered Join(S,G) is sent on all PWs.
PE2 triggers a Join(S,G) targeting CE3. Since the Join(S,G) is
targeting a neighbor residing on an AC, it only sends the Join
on AC3.
PE3 ignores the Join(S,G), since this is a PW-only Join and there
is neither an existing (*,G) state with an AC in
UpstreamPorts(*,G) nor an existing (S,G) state with an AC in
UpstreamPorts(S,G).
3. The multicast stream (S,G) flows along CE3 -> PE2 -> PE1 -> CE1.
4. Now let us say that CE2 sends a Join(*,G) with
UpstreamNeighbors(*,G) = CE4.
5. PE1 consumes the Join(*,G) and builds forwarding state, since the
Join(*,G) is received on an AC.
PE2 consumes the Join(*,G); although this is a PW-only Join,
forwarding state is built on this Join(*,G), since PE2 has an
existing (S,G) state with an AC in UpstreamPorts(S,G). However,
since this is a PW-only Join, PE2 only adds the PW towards PE3
(PW23) into UpstreamPorts(*,G) and hence into
OutgoingPortList(*,G). It does not add the PW towards PE1 (PW12)
into OutgoingPortList(*,G).
PE3 consumes the Join(*,G) and builds forwarding state, since the
Join(*,G) is targeting a neighbor residing on an AC.
The resulting states at the PEs are as follows:
PE1 states:
JT(AC1,*,G,CE4) = JP_HoldTime
JPST(*,G,CE4) = t_periodic
UpstreamNeighbors(*,G) = { CE4 }
UpstreamPorts(*,G) = { PW13 }
OutgoingPortList(*,G) = { AC2, PW13 }
JT(AC1,S,G,CE3) = active
JPST(S,G,CE3) = active
UpstreamNeighbors(S,G) = { CE3 }
UpstreamPorts(S,G) = { PW12 }
OutgoingPortList(S,G) = { AC1, PW12, PW13 }
PE2 states:
JT(PW12,*,G,CE4) = JP_HoldTime
UpstreamNeighbors(*,G) = { CE4 }
UpstreamPorts(G) = { PW23 }
OutgoingPortList(*,G) = { PW23 }
JT(PW12,S,G,CE3) = active
JPST(S,G,CE3) = active
UpstreamNeighbors(S,G) = { CE3 }
UpstreamPorts(S,G) = { AC3 }
OutgoingPortList(S,G) = { PW12, AC3, PW23 }
PE3 states:
JT(PW13,*,G,CE4) = JP_HoldTime
JPST(*,G,CE4) = t_periodic
UpstreamNeighbors(*,G) = { CE4 }
UpstreamPorts(*,G) = { AC4 }
OutgoingPortList(*,G) = { PW13, AC4 }
Joins are triggered as follows:
PE1 triggers a Join(*,G) targeting CE4. Since the Join(*,G) was
received on an AC and is targeting a neighbor that is residing
across a PW, the triggered Join(S,G) is sent on all PWs.
PE2 does not trigger a Join(*,G) based on this Join, since this
is a PW-only Join.
PE3 triggers a Join(*,G) targeting CE4. Since the Join(*,G) is
targeting a neighbor residing on an AC, it only sends the Join
on AC4.
6. If traffic is not flowing yet (i.e., step 3 is delayed so that it
occurs after step 6) and in the interim JPST(S,G,CE3) on PE1
expires, causing it to send a refresh Join(S,G) targeting CE3,
since the refresh Join(S,G) is targeting a neighbor that is
residing across a PW, the refresh Join(S,G) is sent on all PWs.
7. Note that PE1 refreshes its JT based on reception of refresh
Joins from CE1 and CE2.
PE2 consumes the Join(S,G) and refreshes the JT(PW12,S,G,CE3)
timer.
PE3 consumes the Join(S,G). It also builds forwarding state on
this Join(S,G), even though this is a PW-only Join, since now PE2
has an existing (*,G) state with an AC in UpstreamPorts(*,G).
However, since this is a PW-only Join, PE3 only adds the PW
towards PE2 (PW23) into UpstreamPorts(S,G) and hence into
OutgoingPortList(S,G). It does not add the PW towards PE1 (PW13)
into OutgoingPortList(S,G).
PE3 states:
JT(PW13,*,G,CE4) = active
JPST(S,G,CE4) = active
UpstreamNeighbors(*,G) = { CE4 }
UpstreamPorts(*,G) = { AC4 }
OutgoingPortList(*,G) = { PW13, AC4 }
JT(PW13,S,G,CE3) = JP_HoldTime
UpstreamNeighbors(*,G) = { CE3 }
UpstreamPorts(*,G) = { PW23 }
OutgoingPortList(*,G) = { PW13, AC4, PW23 }
Joins are triggered as follows:
PE2 already has (S,G) state, so it does not trigger a Join(S,G)
based on reception of this refresh Join.
PE3 does not trigger a Join(S,G) based on this Join, since this
is a PW-only Join.
8. The multicast stream (S,G) flows into the VPLS from two of the
CEs -- CE3 and CE4. PE2 forwards the stream received from CE3 to
PW12 and PW23. At the same time, PE3 forwards the stream
received from CE4 to PW13 and PW23.
The stream received over PW12 and PW13 is forwarded by PE1 to AC1
and AC2.
The stream received by PE3 over PW23 is forwarded to AC4. The
stream received by PE2 over PW23 is forwarded to AC3. Either of
these helps the CE routers to trigger Assert election.
9. CE3 and/or CE4 send(s) Assert message(s) to the VPLS. The PEs
flood the Assert message(s) without examining it.
10. CE3 becomes the (S,G) Assert winner, and CE4 stops sending the
multicast stream to the VPLS.
11. CE2 notices an RPF change due to the Assert and sends a
Prune(S,G,rpt) with upstream neighbor = CE4.
12. PE1 consumes the Prune(S,G,rpt), and since
PruneDesired(S,G,Rpt,CE4) is TRUE, it triggers a Prune(S,G,rpt)
to CE4. Since the Prune is targeting a neighbor across a PW, it
is sent on all PWs.
PE2 consumes the Prune(S,G,rpt) and does not trigger any Prune
based on this Prune(S,G,rpt), since this was a PW-only Prune.
PE3 consumes the Prune(S,G,rpt), and since
PruneDesired(S,G,rpt,CE4) is TRUE, it sends the Prune(S,G,rpt)
on AC4.
PE1 states:
JT(AC2,*,G,CE4) = active
JPST(*,G,CE4) = active
UpstreamNeighbors(*,G) = { CE4 }
UpstreamPorts(*,G) = { PW13 }
OutgoingPortList(*,G) = { AC2, PW13 }
JT(AC2,S,G,CE4) = JP_HoldTime with S,G,rpt prune flag
JPST(S,G,CE4) = none, since this is sent along
with the Join(*,G) to CE4 based
on JPST(*,G,CE4) expiry
UpstreamPorts(S,G,rpt) = { PW13 }
UpstreamNeighbors(S,G,rpt) = { CE4 }
JT(AC1,S,G,CE3) = active
JPST(S,G,CE3) = active
UpstreamNeighbors(S,G) = { CE3 }
UpstreamPorts(S,G) = { PW12 }
OutgoingPortList(S,G) = { AC1, PW12, AC2 }
PE2 states:
JT(PW12,*,G,CE4) = active
UpstreamNeighbors(*,G) = { CE4 }
UpstreamPorts(*,G) = { PW23 }
OutgoingPortList(*,G) = { PW23 }
JT(PW12,S,G,CE4) = JP_HoldTime with S,G,rpt prune flag
JPST(S,G,CE4) = none, since this was created
off a PW-only Prune
UpstreamPorts(S,G,rpt) = { PW23 }
UpstreamNeighbors(S,G,rpt) = { CE4 }
JT(PW12,S,G,CE3) = active
JPST(S,G,CE3) = active
UpstreamNeighbors(S,G) = { CE3 }
UpstreamPorts(S,G) = { AC3 }
OutgoingPortList(*,G) = { PW12, AC3 }
PE3 states:
JT(PW13,*,G,CE4) = active
JPST(*,G,CE4) = active
UpstreamNeighbors(*,G) = { CE4 }
UpstreamPorts(*,G) = { AC4 }
OutgoingPortList(*,G) = { PW13, AC4 }
JT(PW13,S,G,CE4) = JP_HoldTime with S,G,rpt prune flag
JPST(S,G,CE4) = none, since this is sent along
with the Join(*,G) to CE4 based
on JPST(*,G,CE4) expiry
UpstreamNeighbors(S,G,rpt) = { CE4 }
UpstreamPorts(S,G,rpt) = { AC4 }
JT(PW13,S,G,CE3) = active
JPST(S,G,CE3) = none, since this state is
created by a PW-only Join
UpstreamNeighbors(S,G) = { CE3 }
UpstreamPorts(S,G) = { PW23 }
OutgoingPortList(S,G) = { PW23 }
Even in this example, at the end of the (S,G) / (*,G) Assert
election, there should be no duplicate traffic forwarded downstream,
and traffic should flow only to the desired CEs.
However, we don't have duplicate traffic because one of the CEs stops
sending traffic due to the Assert, not because we don't have any
forwarding state in the PEs to do this forwarding.
Acknowledgements
Many members of the former L2VPN and PIM working groups have contributed to, and provided valuable comments and feedback on, this document, including Vach Kompella, Shane Amante, Sunil Khandekar, Rob Nath, Marc Lasserre, Yuji Kamite, Yiqun Cai, Ali Sajassi, Jozef Raets, Himanshu Shah (Ciena), and Himanshu Shah (Cisco).Contributors
Yetik Serbest and Suresh Boddapati coauthored earlier draft versions of this document. Karl (Xiangrong) Cai and Princy Elizabeth made significant contributions to bring the specification to its current state, especially in the area of Join forwarding rules.
Authors' Addresses
Olivier Dornon Nokia Copernicuslaan 50 B-2018 Antwerp Belgium Email: olivier.dornon@nokia.com Jayant Kotalwar Nokia 701 East Middlefield Rd. Mountain View, CA 94043 United States of America Email: jayant.kotalwar@nokia.com Venu Hemige Nokia Email: vhemige@gmail.com Ray Qiu mistnet.io Email: ray@mistnet.io Jeffrey Zhang Juniper Networks, Inc. 10 Technology Park Drive Westford, MA 01886 United States of America Email: zzhang@juniper.net