Internet Draft Network Working Group Dino Farinacci Internet Draft Procket Networks, Inc. Expiration Date: May 2001 Yakov Rekhter Eric C. Rosen Ted Qian Cisco Systems, Inc. November 2000 Using PIM to Distribute MPLS Labels for Multicast Routes draft-farinacci-mpls-multicast-03.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document specifies a method of distributing MPLS labels [MPLS- ARCH, MPLS-MUL-FR] for multicast routes. The labels are distributed in the same PIM messages that are used to create the corresponding routes. The method is media-type independent, and therefore works for multi-access/multicast capable LANs, point-to-point links, and NBMA networks. Farinacci, et al. [Page 1] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 Table of Contents 1 Overview ........................................... 2 2 Label Distribution for PIM-SM ...................... 3 2.1 Piggybacking Labels with Multicast Routes .......... 3 2.2 LANs with Multiple Downstream Nodes ................ 5 2.2.1 Partitioning the Label Space ....................... 5 2.2.1.1 Partitioning Procedure ............................. 5 2.2.1.2 Effect of Partition in Layer 2 Topology ............ 6 2.2.1.3 Effect of Exceeding the Label Range ................ 7 2.2.2 Assigning the Labels ............................... 7 2.3 Labels for Point-to-Point Links .................... 8 2.4 Labels for NBMA Networks ........................... 8 2.5 When NOT to Send a Labelled Multicast Packet ....... 9 2.6 No Conflict between Unicast and Multicast Labels ... 9 2.7 Supporting Bidirectional PIM ....................... 9 2.8 ATM-LSRs without Multipoint-to-Multipoint .......... 10 2.8.1 Label Request/Binding .............................. 10 2.8.2 Steady State Maintenance ........................... 11 2.8.3 Label Distribution and LSP Control ................. 12 3 Modifications to PIMv2 ............................. 12 3.1 Join/Prune Packets ................................. 12 3.2 Hello Packets ...................................... 13 4 Label Distribution for PIM-DM ...................... 15 5 Security Considerations ............................ 16 6 Acknowledgments .................................... 16 7 References ......................................... 17 1. Overview PIM [PIMv1, PIMv2] is used to combine MPLS label distribution with the distribution of (*,G) join state, (S,G) join state, or (S,G)RPT- bit prune state. Labels and multicast routes are sent together in one message. This design has the following goals: o If an interface attaches to a network with data-link broadcast capability, an LSR should never have to send more than one copy of a given multicast data packet out that interface. However, it is NOT a goal for that LSR to be able to send the same packet, with the same label, out multiple interfaces. Farinacci, et al. [Page 2] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 o When an interface supports data link multicasting, it must be possible for the receiver of a labeled packet to interpret the label without knowing who the transmitter is. o When a LAN contains multiple label distribution peers, it should be possible to use data link multicast to distribute the label distribution control packets themselves. Other aspects of label distribution methodology should remain as consistent with unicast label distribution as possible. o Multicast label distribution procedures should not depend on the media type. (However, it has been necessary to compromise this goal in the case of ATM-LSRs which do not have multipoint-to- multipoint capability, see section 2.8.) o Once the label for a particular multicast tree on a given LAN has been assigned, unicast routing changes should not cause redistribution or reassignment of the label for that group on that LAN. o When a multicast routing table change requires a label distribution change, the latency between the two should be minimized, both to improve performance and to minimize the possibility of race conditions. o The procedures should work with either dense-mode or sparse mode operation. 2. Label Distribution for PIM-SM 2.1. Piggybacking Labels with Multicast Routes An LSR that supports multicast sends PIM Join/Prune messages on behalf of hosts that join groups. It sends Join/Prune messages to upstream neighboring LSRs toward the RP for the shared-tree (*,G) or toward a source for a source-tree (S,G). Labels are distributed by being associated with addresses in the join list or the prune list. In particular: 1. If an LSR Rd, joins the shared tree for a group, the Join/Prune message it sends upstream will contain the group address followed by a join-list. The join-list will contain an element which contains the address of the RP. This element will also contain a a label, and this label can be used by the upstream LSR Ru, when it sends multicast data down the shared tree. Intuitively, this label represents the route downstream from the current node along the shared tree. Farinacci, et al. [Page 3] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 Note that if Rd joins the shared tree for group G, but Ru happens to have (S,G) state for some S, then Ru must merge its (*,G) output interface list into its (S,G) output interface list. This is necessary in order to ensure that Rd will receive packets sent from S to G, even though Ru only gets these packets on the source tree. In this case, when Ru receives an (S,G) packet, it should forward it to Rd using the same label that Rd assigned for (*,G) packets, EXCEPT IN THE CASE where Ru is an ATM-LSR which does not support multipoint- to-multipoint connections(see section 2.8). 2. If an LSR Rd, joins a source tree for a group, the Join/Prune message it sends upstream will contain the group address followed by a join-list. The join-list will contain an element which contains the address of the source. This element will also contain a label, and this label can be used by the upstream LSR Ru, when it sends multicast data down the source tree. Intuitively, this label represents the route downstream from the current node along the specified source tree. 3. Suppose an LSR Rd, has (S,G)RPT-bit state with a null output interface list. This indicates that all of its downstream neighbors on the shared tree for G have pruned source S from the shared tree. Rd sends a Join/Prune message upstream (on the shared tree), containing the group address followed by a prune-list. The prune-list contains an element which contains the address of the source. In this case, no label is included in the element. Similarly, if an LSR has (S,G)SPT-bit state, and also has (*,G) state with a non-null output interface list, and the input interface for (*,G) is different than the input interface for (S,G), it will send a Join/Prune message upstream on the shared tree, with S in the prune-list, and will not include a label. 4. Suppose an LSR Rd, as the result of receiving, from a downstream neighbor on the shared tree, a Join/Prune message such as described in 3, creates (S,G)RPT-bit state with a non- null output interface list. In this case, it may send a Join/Prune message upstream on the shared tree, containing the group address followed by a prune-list. An element of the prune list will contain the address S and a corresponding label. However, a special bit (the "Label Only" bit, or "L- bit") in the element will be set indicating to the upstream LSR that the source S is not really to be pruned from the shared tree. The result is that the upstream LSR Ru, will still send packets from S to G to Rd, and will label those packets as specified. When Rd receives such packets, it forwards them Farinacci, et al. [Page 4] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 according to the output interface list of the (S,G)RPT-bit entry. Intuitively, this label represents a route along the shared tree, but only for packets from the specified source. 5. An LSR which receives a Join/Prune message as described in 4 may send a corresponding Join/Prune message (with the L-bit set) to its upstream LSR on the shared tree. Again, this label represents a route along the shared tree, but only for packets from the specified source. Rules 3-5 above ensure that if a source is pruned off the shared tree at some point, any packets from that source which is sent down the shared tree will have a label that implicitly identifies the source. Thus if those packets encounter a node with (S,G)RPT-bit state, they will be sent according to the output interface list of the (S,G)RPT- bit entry, NOT according to the output interface list of the (*,G) entry. 2.2. LANs with Multiple Downstream Nodes 2.2.1. Partitioning the Label Space Only one copy of a given multicast data packet is sent downstream. On a LAN, this packet will be received by all the LSRs on the LAN. The label it carries is used, by the receiving LSRs, to find the packet's multicast distribution tree. The label it carries must have a unique association, on that LAN, with a multicast distribution tree. Therefore, once an LSR assigns a label to a particular multicast distribution tree on a particular LAN, all other LSRs on that LAN are prohibited from making any other use of that label. The prohibition remains in effect as long as the distribution tree in question exists. In order to meet this requirement, the LSRs on a LAN must divide up the label space, such that each LSR has a particular unique range of labels which it may distribute. 2.2.1.1. Partitioning Procedure Each multicast LSR on a LAN is configured with the total number of labels (N) that may be used to represent multicast distribution trees on the LAN. It is also configured with an approximate count (R) of the routers on the LAN. The router divides the multicast label space into a number of equal-sized ranges, where the size of a range is Farinacci, et al. [Page 5] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 T/R. Each router will randomly select one of these ranges. When a multicast LSR boots up or enables the LAN interface to do multicast routing, it will advertise in PIM Hello messages the total number of multicast labels, the router count, and the label range it randomly selects. The lower range label value and the higher range label value accompany the advertisement. If the total number of multicast labels for the LAN is not configured consistently on all LSRs connected to a LAN, the smallest number advertised by any LSR will be used. If the router count is not configured consistently on all LSRs connected to a LAN, the smallest router count value advertised by any LSR will be used. If there is another LSR that has selected the same range, then the following procedures are used to determine which of the two LSRs would be able to keep its range, and which would be required to allocate another label range. If DR election priority is included in the Hello messages at both LSRs, and the priority values are not equal, then the LSR with the lower DR election priority is required to allocate another label range. Otherwise, the LSR with the lower IP address on the LAN is required to allocate another label range. In both cases the label range is allocated randomly. If as a result of these procedures a LSR has to allocate another label range, then the LSR has to withdraw its label bindings from its currently allocated range, and then (after it allocates another range) reallocate its bindings. A LSR can be configured to use more than one label range if one believes it will be an upstream LSR for many flows. It just inserts additional advertisements in the same PIM Hello message. The label table size and router-count should be the same in all advertisements contained in a message. 2.2.1.2. Effect of Partition in Layer 2 Topology When a subnet partitions (due to, say, the failure of a layer 2 switch) and new multicast LSRs come up, they will allocate label ranges that are unique to their partition. When the partition heals, there may be conflicts. Once the PIM Hellos messages are received by LSRs on the other side of the partition, they will determine there is a label range allocation conflict and immediately perform the tie breaking rules described above. Farinacci, et al. [Page 6] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 2.2.1.3. Effect of Exceeding the Label Range When a LSR cannot allocate a label range because all ranges within the label table size have been allocated, it will not participate in binding labels to multicast routes. Packets for these routes will not be label switched. However, the LSR is still capable of label switching a packet as either an upstream or downstream LSR on that LAN. This is the case when another router is binding labels for the multicast route and has an allocated a label range successfully. 2.2.2. Assigning the Labels Since PIM Join/Prune messages are multicast on a LAN, other downstream LSRs that are interested in the group will hear the message. They must cache the binding of multicast routing table state and label state together. Since the upstream LSR is going to forward data packets using the advertised label, they must be ready to accept the data packet with that advertised label. The first downstream LSR that joins a group is the label assigner on that LAN for that multicast route. All other downstream LSRs that send PIM Join/Prune messages will use the same label that the assigner selected. A LSR that sends a PIM Join/Prune message with a label of 0 means that it doesn't know the label for the associated multicast routing table entry. When this occurs, the assigner can trigger a PIM Join/Prune message making the label known. When the label assigner leaves the group, the label that it assigned still remains active. The next highest IP addressed downstream LSR becomes the owner of that label and may change it if it sees fit. However, it is not required to change it. All downstream LSRs can continue to use the assignment in their Join messages. If two systems simultaneously join a distribution tree for the first time (they do not have state for that tree), and each chooses a different label value, the highest IP addressed downstream LSR's label will be used by the upstream LSR. The lower addressed LSR will hear the higher addressed LSR's Join too and will also use it's label. If the label assigner crashes, the highest IP addressed downstream LSR assigns a new label to the multicast routes, which were assigned by the crashing LSR, and triggers a Join message so all other LSRs on the LAN to use the new label. When a LAN partitions due to a layer-2 switch failure, it follows the same logic for the case when a LSR stops joining for a group. When Farinacci, et al. [Page 7] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 the partition heals, there may be an RPF neighbor change in one of the partitions. When there is an RPF neighbor change and the downstream routers trigger joins to their new RPF neighbor with a different label assignment than the other partition is using, one of two resolutions occur: 1) The LSR which is the allocator in the partition of the new RPF neighbor will trigger a join if it has a higher IP address than the allocator in the other region. The downstream routers in the other partition use the new label assignment immediately. 2) If the LSR which is the allocator in the partition of the new RPF neighbor has a lower IP address, all downstream routers and the new RPF neighbor will switch to the label assigned by the allocator in the other partition. If an RPF change occurs (the topology changed so the upstream LSR is different), the PIM protocol spec indicates that a PIM Join may be triggered to get on the new distribution tree as soon as possible. In this case, if the label assigner becomes the upstream LSR, then the new highest IP addressed downstream LSR may become the label assigner. It may change the label if it sees fit. Otherwise, the same label is used. 2.3. Labels for Point-to-Point Links The procedure of section 2.2 works on point-to-point links because there is only one downstream LSR on the link which always becomes the label assigner. 2.4. Labels for NBMA Networks On NBMA networks, all PIM routers are known to each other through pseudo-broadcast mechanisms provided by the data-link layer. However, PIM Join messages are unicast to the upstream LSR. Therefore, other downstream LSRs will not hear the label assigner's advertisement. Therefore we treat an NBMA network with one upstream and n downstream LSRs as n point-to-point links, from the upstream LSR to each of the downstream LSRs. Each downstream LSR then assigns its own label, and the upstream LSR must replicate the multicast data packets. Therefore the procedure of section 2.2 applies. Note that this is not incompatible with the use of native point-to- multipoint capabilities at the data link layer. Farinacci, et al. [Page 8] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 2.5. When NOT to Send a Labelled Multicast Packet PIM Hello messages, sent periodically by all PIM-capable routers, will indicate if the router is MPLS-capable. An upstream router on a LAN will therefore know if all routers on the same LAN are LSRs or not. If there are ANY MPLS-incapable routers which are interested in a particular group, the upstream router will transmit to the LAN only unlabelled multicast data packets for that group. If there are any group members on a LAN, only unlabelled multicast data for that group will be transmitted onto that LAN. Routers that support non-PIM multicast are assumed, for the purposes of this procedure, to be MPLS-incapable. 2.6. No Conflict between Unicast and Multicast Labels Frame based MPLS uses different data-link layer code-points [MPLS- ENCAPS] to distinguish multicast labeled packets from unicast labeled packets. Therefore, the assignment of labels for unicast routes is completely independent from the assignment of labels for multicast routes. For example, the same label value could be allocated for a unicast route and for a multicast route, without any possibility of ambiguity. MPLS on a label switching controlled ATM (LC-ATM) interface uses VPI/VCI as the top label [MPLS-ATM]. There is no VPI/VCI range specifically reserved for multicast or for unicast. 2.7. Supporting Bidirectional PIM We consider support of Bidirectional PIM [PIM-BIDIR] only in LSRs which are not ATM-LSRs. In the absence of an ATM multipoint-to- multipoint capability, bidirectional PIM over ATM will not have the favorable scaling properties that make it interesting. On links which are not sender-only links, support for Bidirectional PIM is straightforward. Labels are assigned in the usual manner by downstream LSRs. However, a label can be used in either direction (i.e., can be carried by packets traveling either upstream or downstream). On a given link, the label is bound to the same multicast route (*,G) or (S,G) in both directions. As long as the procedures of section 2.2 are always used to partition the label space (even on point-to-point links), it is possible to use the same label in both directions. Sender-only links present a bit more of a difficulty since PIM Farinacci, et al. [Page 9] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 Join/Prune messages are not generally sent on those links. In order to assign labels to these links, a downstream node on a sender only link should send a PIM Join message, as if it were going to join the tree, but should set the newly defined "label only" bit (L-bit). In essence, these nodes will contain (*,G) state, and will associate the (*,G) state with a label that is distributed upstream. However, there will be no output interface list associated with the (*,G) state, and packets will just be forwarded towards the RP. 2.8. ATM-LSRs without Multipoint-to-Multipoint Multipoint-to-multipoint capability is a feature of an ATM switch that allows an outgoing VC to appear in one or more cross-connect (e.g., two incoming VCs cross-connecting to the the same set of outgoing VCs) without causing cell interleaving. The procedure described in this section applies to ATM-LSRs that do NOT have multipoint-to-multipoint capability. 2.8.1. Label Request/Binding When LSR Ru receives an (S,G) join from LSR Rd, Ru, which did not have the (S,G) state, must create the (S,G) state and populate it with the oifs from (*,G). When LSR Ru receives an (*,G) join from LSR Rd, if the (S,G) state already exists on Ru, the oif must be added to the (S,G)'s oif list as well. At LSR Ru, for each oif that is copied from a (*,G) to an (S,G), the associated label/VCI is not replicated. Instead, the oif moves into a Label Needed state, and an (S,G) L-bit Join/Request is sent out of the interface to the Rd. The Encoded-Unicast-Upstream Neighbor Address field in such Join is set to the address of Rd. Source address in the join list employs the Label Address encoding with the next t-bit (section 3.1) in the label field set and the L-bit set. Since this is a source specific Join Request along the shared tree, the R bit is set and W bit is clear. In addition, the current multicast route timer (section 3.1) is set to the time remaining on the (S,G) Entry-Timer at Ru. Rd, upon receiving such Join, fills in the label field with the next t-bit cleared, and then sends the (S,G) L-bit R-bit Join/Binding back out of the RPF interface toward the RP. (S,G) L-bit Join/Request received from non-RPF interface towards RP must be discarded. At Ru, the incoming label for (S,G) is then cross-connected with labels in the (S,G) L-bit R-bit join received from Rd. LSR Rd, that receives an (S,G) L-bit R-bit Join/Request via the RPF towards the RP, must create an (S,G) L-bit state if it doesn't Farinacci, et al. [Page 10] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 already exist, and must initializes the (S,G)'s Entry-Timer with the the current multicast route timer encoded in the source address. If Rd is capable of multipoint-to-multipoint connection, label replication follows the procedure described in section 2.1. Otherwise, it follows the procedure described in this section. The L-bit on an (S,G) indicates that the state is created by an (S,G) L-bit R-bit Join/Request, and periodic Joins that it sends must have the L-bit set. 2.8.2. Steady State Maintenance An (S,G) entry is removed upon expiration of its Entry-Timer. The timer may be updated upon receiving an (S,G) L-bit R-bit Join/Request from the RPF interface towards the RP. If the "Current Multicast Route Timer" is greater than the remaining timer value of the Entry- Timer, the timer value is increased to the "Current Multicast Route Timer" specified in the L-bit R-bit Join/Request. The time may also be updated by other event such as receiving (S,G) Join from any downstream oif peers. Note, (S,G) L-bit Join from downstream oif doesn't reset the Entry-Timer. In the event that an upstream router no longer needs a (S,G) label from its downstream peer (e.g., switching back to a share tree), the (S,G) state eventually expires since the (S,G) Entry-Timer is NOT updated by the receipt of L-bit Join/Bindings. It simply stops sending periodic L-bit R-bit Join/Request out of that oif upon expiration of the (S,G) state. This eventually causes the (S,G)'s Entry-Timer to expire in the downstream router and the state removal. Sending a (S,G) L-bit R-bit Join/Request out of an oif is triggered by the receipt of a (*,G) Join from the same oif. For each (S,G) that exists, an (S,G) L-bit R-bit Join/Request is sent down the oif in a Label Needed state. Regular (S,G) Join received with the L-bit cleared removes the Label Needed state on the oif, and also clears the L-bit state on the (S,G) entry. Joins triggered by the expiration of the Join Timer on such (S,G)contain cleared L-bit. This mechanism accommodates the situation where an upstream LSR that needs a label and a downstream DR receiver which decides that traffic exceeds the threshold both initiate the source tree, and part of the shared and source tree overlaps. Farinacci, et al. [Page 11] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 2.8.3. Label Distribution and LSP Control The procedures of section 2.8 use MPLS Downstream on Demand procedures with Independent LSP control [MPLS-ARCH]. The Downstream on Demand procedures are needed whenever two incoming VCs corresponding to the same FEC cannot be merged into a single outgoing VC. In the absence of multipoint-to-multipoint capability, this applies to multicast distribution trees. Independent LSP control is needed so that different downstream branches of a multicast distribution tree can join the tree independently. The fact that one particular downstream branch of the tree is slow to respond to the control messages does not then prevent or even delay other more responsive downstream branches from joining the tree. 3. Modifications to PIMv2 3.1. Join/Prune Packets PIMv2 has a packet format for each address type it may support when encoding both multicast and unicast addresses. We will define a new address type called "Label Address" for unicast address encoding. The label will accompany the source address in the Encoded Source Address format as specified in [PIMv2]. The label value will be in a 32-bit quantity following the source address. We also take one bit from the PIMv2 reserved field to be the "label only" bit (shown below as the "L-bit"). So, for example, an IPv4 Label Address format would look like: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Rsrvd |L|S|W|R| Mask Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |a|t| Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Current Multicast Route Timer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Label If the a-bit is clear, the low-order 20 bits are a label value (as Farinacci, et al. [Page 12] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 described in [MPLS-ATM]) assigned by the LSR sending the Join/Prune message. All other bits should be set to 0 by the sender and should be ignored by the receiver. If the a-bit is set, the low-order 28 bits are a label value in the VPI/VCI format of (as described in [MPLS-ATM]) assigned by the LSR sending the Join/Prune message. If the t-bit is set, the VPI/VCI label value should be ignored by the receiver since this represents a label request by an ATM-LSR. All other bits should be set to 0 by the sender and should be ignored by the receiver. Current Multicast Route Timer The sender of a Join/Prune message inserts the current time left before expiration for the multicast route table entry described by the Source Address (either the (S,G) or (*,G) entry). This is needed so all routers on a common multi-access subnet can time-out the entry close to the same time without each other recreating the state when the source goes inactive. Refer to [PIMv2] for other field descriptions not specified here. 3.2. Hello Packets The PIM Hello message will carry 2 new OptionTypes (called "Label Parameters" and "VCI Capability") as specified in [PIMv2]. A router that sends a PIM Hello with the Label Parameters option is regarded as being label-capable. This Option can appear multiple times in a Hello packet if a LSR wants to allocate multiple ranges. When this option appears multiple times in the Hello message, the Label Table Size and Router Count must be the same for each Label Parameters Option supplied in the message. When sent on point-to-point links, this option should have Router Count, Lower Label Range, and Upper Label Range set to 0. These fields are ignored on receipt. When sent on LC-ATM links, the first Label Parameter option carries the VPI range and the second one carries the VCI range. Farinacci, et al. [Page 13] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 Label Parameters TLV 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OptionType = 17 | OptionLength = 16 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Total Number of Multicast Labels for this LAN | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lower Label Range | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Upper Label Range | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ OptionType "Label Parameters" Set to value 17 decimal. OptionLength The option is 16 bytes in length. Total Number of Multicast Labels The total number of multicast labels the sending router can support on the interface the Hello is sent on. Router Count The approximate maximum number of routers that may be connected to the subnet the Hello is sent on. Lower Label Range The lower label value in the label range. This value, randomly selected by the sending router in the case of non LC-ATM link or supplied by the ATM driver in the case of LC-ATM link, must be less than the Upper Label Range value. Upper Label Range The upper label value in the label range. This value, randomly selected by the sending router in the case of non LC-ATM link or supplied by the ATM driver in the case of LC-ATM link, must be greater than the Lower Label Range value. Farinacci, et al. [Page 14] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 VCI Capability TLV 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OptionType = 23 | OptionLength = 5 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Priority | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved |D| +-+-+-+-+-+-+-+-+ OptionType "VCI Capability" Set to value 23 decimal. OptionLength The option is 5 bytes in length. Priority Peering ATM-LSRs exchange the priority value for VC space odd-even determination when at least one side supports unidirectional VC. An ATM-LSR with a higher priority value may assign only odd- numbered VC and ATM-LSR with a lower priority value may assign even-numbered VC. The value should be ignored if the LC-ATM link is bidirectional. D Bit When the D bit is clear, VCI capability is bidirectional. When it is set, VCI capability is unidirectional. Bidirectional capability indicates an ATM-LSR issuing this option can, within a single VPI, support binding of the same VCI to different routes on the different directions of the link. Unidirectional capability indicates an ATM-LSR issuing this option can, within a single VPI, a single VCI may appear in one binding only. In such systems when a VCI has been bound in one direction on the link it may not be used in the other. 4. Label Distribution for PIM-DM In dense-mode PIM, there is no downstream Join message traveling upstream to perform the binding of multicast routes with labels. However, since we don't want a separate algorithm for dense-mode groups, we extend this basic design for dense-mode PIM. When a downstream LSR creates (S,G) state from the receipt of 1) data, or 2) Join/Prune or Graft messages, it will start a periodic Farinacci, et al. [Page 15] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 timer to send Join messages with label assignment information present. The messages look no different and are treated on receipt no differently than in the sparse-mode case. The periodic Join message will be multicast on the LAN with an upstream target address of 0.0.0.0. All multicast LSRs on the LAN must know the group operates in dense-mode. This is accomplished using standard PIM mechanisms. 5. Security Considerations The security considerations for MPLS in general and label distribution in particular are discussed in [MPLS-ARCH] and [LDP] respectively. Security considerations for PIM are discussed in [PIMv2]. The use of IPSEC for securing the PIM messages, as suggested in [PIMv2], provides adequate security for this application. 6. Acknowledgments The authors would like to thank Yiqun Cai for his overall help on this draft. We thank Fred Baker for his comments on an earlier version. We also thank the authors of [MPLS-MUL-FR] for their critique of an earlier version. 9.0 Author's Addresses Dino Farinacci Procket Networks, Inc. 3850 North First Street San Jose, CA 95134 Email: dino@procket.com Yakov Rekhter Cisco Systems, Inc. 170 Tasman Drive San Jose, CA, 95134 Email: yakov@cisco.com Farinacci, et al. [Page 16] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 Eric C. Rosen Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA, 01824 Email: erosen@cisco.com Ted Qian Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA, 01824 Email: tqian@cisco.com 7. References [LDP] "LDP Specification", draft-ietf-mpls-ldp-7.txt, Andersson, Doolan, Feldman, Fredette, Thomas, June 2000. [MPLS-ARCH] "Multiprotocol Label Switching Architecture", draft- ietf-mpls-arch-06.txt, Rosen, Viswanathan, Callon, August 1999. [PIMv1] "Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol" Specification", RFC 2362, Estrin, Farinacci, Helmy, Thaler, Deering, Handley, Jacobson, Liu, Sharma, Wei, June 1998. [PIMv2] "Protocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification", draft-ietf-pim-v2-sm-01.txt, Wei, et. al., November, 1999. [PIM-BIDIR] "Bi-directional Protocol Independent Multicast",, Handley, Kouvelas, and Vicisano, March 2000. [MPLS-ENCAPS] "MPLS Label Stack Encoding", , Rosen, Rekhter, Farinacci, Tappan, Fedorkow, Li, Conta, September 1999. [MPLS-MUL-FR] "Framework for IP Multicast in MPLS", , Ooms, Sales, Livens, Acharya, Griffoul, Ansari, May 2000. [MPLS-ATM] "MPLS using LDP and ATM VC Switching", , Davie, Lawrence, McCloghrie, Rekhter, Rosen, Swallow, Doolan, June 2000. Farinacci, et al. [Page 17] Internet Draft draft-farinacci-mpls-multicast-03.txt November 2000 Farinacci, et al. [Page 18]