mboned Working Group P. Savola Internet Draft CSC/FUNET Expiration Date:
AugustSeptember 2004 B. Haberman Caspian Networks FebruaryMarch 2004 Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address draft-ietf-mboned-embeddedrp-01.txtdraft-ietf-mboned-embeddedrp-02.txt Status of this Memo This document is an Internet-Draft and is subject to 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. To view the list Internet-Draft Shadow Directories, see http://www.ietf.org/shadow.html. Abstract A very difficult deployment problem with global, interdomain IPv6 multicast using Protocol Independent Multicast - Sparse Mode (PIM-SM) has been identified.This memo defines an address allocation policy in which the address of the Rendezvous Point (RP) is encoded in thean IPv6 multicast group address. For PIM-SM,Protocol Independent Multicast - Sparse Mode (PIM-SM), this can be seen as a specification of a group-to-RP mapping mechanism. This allows an easy deployment of scalable inter-domain multicast, and simplifies the intra-domain multicast configuration as well. This memo updates the addressing format presented in RFC 3306. Table of Contents 1. Introduction ............................................... 23 1.1. Background ............................................. 3 1.2. Solution ............................................... 3 1.3. Assumptions and Scope .................................. 4 1.4. Keywords ............................................... 4 2. Unicast-Prefix-based Address Format ........................ 4 3. Modified Unicast-Prefix-based Address Format ............... 45 4. Embedding the Address of the RP in the Multicast Address ... 5 5. Examples ................................................... 67 5.1. Example 1 .............................................. 67 5.2. Example 2 .............................................. 7 5.3. Example 3 .............................................. 78 5.4. Example 4 .............................................. 78 6. Operational Considerations ................................. 78 6.1. RP Redundancy .......................................... 78 6.2. RP Deployment .......................................... 8 6.3. Guidelines for Assigning IPv6 Addresses to RPs ......... 89 6.4. Use as a Substitute for BSR ............................ 9 7. PIM-SM Protocol Modifications .............................. 8The Embedded-RP Group-to-RP Mapping Mechanism .............. 9 7.1. PIM-SM Group-to-RP Mapping ............................. 9 7.2. Overview of the Model .................................. 910 8. Scalability/UsabilityScalability Analysis ............................. 10....................................... 11 9. Acknowledgements ........................................... 1112 10. Security Considerations ................................... 1112 11. References ................................................ 13 11.1. Normative References .................................. 13 11.2. Informative References ................................ 13 Authors' Addresses ............................................. 14 A. Discussion about Design Tradeoffs .......................... 14 B. Changes .................................................... 15 B.1 Changes since -01 ....................................... 15 B.2 Changes since -00 ................................................................................. 15 Intellectual Property Statement ................................ 1516 Full Copyright Statement ....................................... 16 1. Introduction 1.1. Background As has been noticed [V6MISSUES], there exists a deployment problem with global, interdomain IPv6 multicast: PIM-SM [PIM-SM] RPs have no way of communicating the information about (active) multicast sources to other multicast domains, as there is noMulticast Source Discovery Protocol (MSDP) [MSDP] (at least yet).has not been, on purpose, specified for IPv6. Therefore the whole interdomain Any Source Multicast model is rendered unusable; Source-Specific Multicast (SSM) [SSM] avoids these problems but is not a complete solution for several reasons. Further, it has been noted that there are some problems with the support and deployment of mechanisms SSM would require:require [V6MISSUES]: it seems unlikely that SSM could be usable as the only interdomain multicast routing mechanism in the short term. 1.2. Solution This memo describes a multicast address allocation policy in which the address of the RP is encoded in the IPv6 multicast group address, and specifies a PIM-SM group-to-RP mapping to use the encoding, leveraging and extending theunicast-prefix -based addressing [RFC3306]. This mechanism not only provides a simple solution for IPv6 interdomain Any Source Multicast (ASM) but can be used as a simple solution for IPv6 intradomain ASM onwith scoped multicast addresses as well. It can also be used as an automatic RP discovery mechanism in those deployment scenarios which would have previously used the Bootstrap Router protocol (BSR) [BSR]. The solution consists of three elements: o A specification of a subrange of [RFC3306] IPv6 multicast group addresses defined by setting one previously unused bit of the Flags field to "1", o A specification of the mapping by which such a group address encodes the RP address that is to be used with this group, and o A specificationdescription of optional and mandatoryoperational procedures to operate ASM with PIM-SMPIM- SM on these IPv6 multicast groups. Addresses in the subrange will be called embedded RPembedded-RP addresses. This scheme obviates the need for inter-domainMSDP, and the routers are not required to include any multicast configuration, except when they act as an RP. This memo updates the addressing format presented in RFC 3306. 1.3. Assumptions and Scope In general, a 128-bit RP address can't be embedded into a 128-bit group address with space left to carry the group identity itself. An appropriate form of encoding is thus defined, and it is assumeddefined by requiring that the Interface-IDInterface-IDs of RPs in the embedded RPembedded-RP range can be assigned to be a specific value. If these assumptions can't be followed, either operational procedures and configuration must be slightly changed or this mechanism can not be used. The assignment of multicast addresses is outside the scope of this document; it is up to the RP and applications to ensure that group addresses are unique using some unspecified method. However, the mechanisms are very probably similar to ones used with [RFC3306]. Similarly, RP failure management methods, such as Anycast-RP, are out of scope for this document. These do not work without additional specification or deployment. This is covered briefly in Section 6.1. This memo updates the addressing format presented in RFC 3306.1.4. Keywords The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. Unicast-Prefix-based Address Format As described in [RFC3306], the multicast address format is as follows: | 8 | 4 | 4 | 8 | 8 | 64 | 32 | +--------+----+----+--------+--------+----------------+----------+ |11111111|flgs|scop|reserved| plen | network prefix | group ID | +--------+----+----+--------+--------+----------------+----------+ Where flgs are "0011". (The first two bits arehave been yet undefined, sent as zero and ignored on receipt.) 3. Modified Unicast-Prefix-based Address Format This memo specifies a modification to the unicast-prefix-based address format: 1. If the second high-order bit in "flgs" is set to 1, the address of the RP is embedded in the multicast address, as described in this memo. 2. If the second high-order bit in "flgs" is set to 1, interpret the last low-order 4 bits of "reserved" field as signifying the RP interface ID,ID ("RIID"), as described in this memo. In consequence, the address format becomes: | 8 | 4 | 4 | 4 | 4 | 8 | 64 | 32 | +--------+----+----+----+----+--------+----------------+----------+ |11111111|flgs|scop|rsvd|RIID| plen | network prefix | group ID | +--------+----+----+----+----+--------+----------------+----------+ +-+-+-+-+ flgs is a set of 4 flags: |0|R|P|T| +-+-+-+-+ R = 1 indicates a multicast address that embeds the address on the RP. Then P MUST BEbe set to 1, and consequently T MUST be set to 1, as specified in [RFC3306]. In the case that R = 1, the last 4 bits of the previously reserved field are interpreted as embedding the RP interface ID ("RIID"),ID, as specified in this memo. R = 0 indicates a multicast address that does not embed the address of the RP and follows the semantics defined in [ADDRARCH] and [RFC3306]. In this context, the value of "RIID" MUST be sent as zero and MUST be ignored on receipt. 4. Embedding the Address of the RP in the Multicast Address The address of the RP can only be embedded in unicast-prefix -based ASM addresses. ToThat is, to identify whether an address is a multicast address as specified in this memo and to be processed any further, it must satisfy all of the below: o it MUST be a multicast address and have R, P, and T flag bits set to 1 (that is, be part of the prefixes FF70::/12 or FFF0::/12), o "plen" MUST NOT be 0 (ie. not SSM), and o "plen" MUST NOT be greater than 64. The address of the RP can be obtained from a multicast address satisfying the above criteria by taking the two steps: 1. copy the first "plen" bits of the "network prefix" to a zeroed 128-bit address structure, and 2. replace the last 4 bits with the contents of "RIID". These two steps could be illustrated as follows: | 20 bits | 4 | 8 | 64 | 32 | +---------+----+----+----------------+----------+ |xtra bits|RIID|plen| network prefix | group ID | +---------+----+----+----------------+----------+ || \\ vvvvvvvvvvv || ``====> copy plen bits of "network prefix" || +------------+------------------------+ || | network pre| 0000000000000000000000 | || +------------+------------------------+ \\ ``=================> copy RIID to the last 4 bits +------------+---------------------+--+ | network pre| 0000000000000000000 |ID| +------------+---------------------+--+ One should note that there are several operational scenarios (see Example 2 below) when [RFC3306] statement "all non-significant bits of the network prefix field SHOULD be zero" is ignored. This is to allow multicast group address assignmentsallocations to third parties whichbe consistent with unicast prefixes, while the multicast addresses would still use the RP associated with the network prefix. "plen" higher than 64 MUST NOT be used as that would overlap with the upperhigh-order bits of multicast group-id. When processing an encoding to get the RP address, the multicast routers MUST perform at least the same address validity checks to the calculated RP address as to one received via other means (like BSR [BSR] or MSDP for IPv4), to avoid e.g.,IPv4). At least fe80::/10, ::/16, and ff00::/8 MUST be excluded. This is particularly important as the address being "::", "::1", or a link-local address.information is obtained from an untrusted source, i.e., any Internet user's input. One should note that the 4 bits reserved for "RIID" set the upper bound for RPs for the combination of scope, network prefix, and group ID -- without varying any of these, you can have 4 bits worth of different RPs. However, each of these is an IPv6 group address of its own (i.e., there can be only one RP per multicast address). 5. Examples Four examples of multicast address allocation and resulting group-to- RP mappings are described here, to better illustrate the possibilities provided by the encoding. 5.1. Example 1 The network administrator of 2001:DB8::/32 wants to set up an RP for the network and all of histhe customers. (S)he chooses network prefix=2001:DB8 and plen=32, and wants to use this addressing mechanism. The multicast addresses (s)he will be able to use are of the form: FF7x:y20:2001:DB8:zzzz:zzzz:<group-id> Where "x" is the multicast scope, "y" the interface ID of the RP address, and "zzzz:zzzz" will be freely assignable within the PIM-SM domain.to anyone. In this case, the address of the PIM-SMRP would be: 2001:DB8::y (and "y" could be anything from 01 to F);F, as 0 must not be used); the address 2001:DB8::y/128 is added on a router as a Loopbackloopback address and injected to the routing system. 5.2. Example 2 As in Example 1, the network administrator can also allocate multicast addresses like "FF7x:y20:2001:DB8:DEAD::/80" to some of his customers within the PIM-SM domain.customers. In this case the RP address would still be "2001:DB8::y". Note the second rule of deriving the RP address: the "plen" field in the multicast address, 0x20 = 32, refers to the length of "network prefix" field considered when obtaining the RP address. In this case, only the first 32 bits of the network prefix field, "2001:DB8" are preserved: the value of "plen" takes no stance on actual unicast/multicast prefix lengths allocated or used in the networks, here from 2001:DB8:DEAD::/48. In short, this distinction allows more flexible RP address configuration in the scenarios where it is desirable to have the group addresses to be consistent with the unicast prefix allocations. 5.3. Example 3 In the network of Examples 1 and 2, the network admin sets up addresses for use by their customers, but an organization wants to have their own PIM-SM domain; that's reasonable.domain. The organization can pick multicast addresses like "FF7x:y30:2001:DB8:BEEF::/80", and then their RP address would be "2001:DB8:BEEF::y". 5.4. Example 4 In the above networks, if the adminadministrator wants to specify the RP to be in a non-zero /64 subnet, (s)he could always use something like "FF7x:y40:2001:DB8:BEEF:FEED::/96", and then their RP address would be "2001:DB8:BEEF:FEED::y". There are still 32 bits of multicast group-id's to assign to customers and self. 6. Operational Considerations This desction describes the major operational considerations for those deploying this mechanism. 6.1. RP Redundancy A technique called "Anycast RP" is used within a PIM-SM domain to share an address and multicast state information between a set of RP's mainly for redundancy purposes. Typically, MSDP has been used for that as well [ANYCASTRP]. There are also other approaches, like using PIM for sharing this information [ANYPIMRP]. RP failover cannot be used with this specification without additional mechanisms or techniques such as MSDP, PIM-SM extensions, or anycasting"anycasting" (i.e., the shared-unicast model [ANYCAST]) the RP address in the IGP without state sharing (depending on the redundancy requirements, this may or may not be enough, though). However, the redundancy mechanisms are outside of the scope of this memo. 6.2. RP Deployment As there is no need to share inter-domain state with MSDP, each DR connecting multicast sources could act as an RP without scalability concerns about setting up and maintaining MSDP sessions. This might be particularly attractive when concerned about RP redundancy. In the case where the DR close to a major source for a group acts as the RP, a certain amount of fate-sharing properties can be obtained without using any RP failover mechanisms: if the DR goes down, the multicast transmission may not be all that interestingwork anymore in any case. Along the same lines, it's may also be desirable to distribute the RP responsibilities to multiple RPs. As long as different RPs serve different groups, this is is trivial: each group shouldcould map to a different RP (or enoughsufficiently many different RPs that the load on one RP is not a problem). However, load sharing one group faces the similar challenges as Anycast-RP. 6.3. Guidelines for Assigning IPv6 Addresses to RPs With this mechanism, the RP can be given basically any network prefix up to /64. The interface identifier will have to be manually configured to match "RIID". RIID = 0 SHOULD NOTmust not be used as using it would cause ambiguity with the Subnet-Router Anycast Address [ADDRARCH]. If an administrator wishes to use an RP address that does not conform to the addressing topology but is still from the network provider's prefix (e.g., an additional loopback address assigned on a router),router, as described in example 1 in Section 5.1), that address can be injected into the routing system via a host route. 6.4. Use as a Substitute for BSR With embedded-RP, use of BSR or other RP configuration mechanisms throughout the PIM domain is not necessary, as each group address specifies the RP to be used. 7. PIM-SM Protocol ModificationsThe Embedded-RP Group-to-RP Mapping Mechanism This section describes how PIM-SM is modified, i.e., howspecifies the group- to-RPgroup-to-RP mapping mechanism works for Embedded RP. 7.1. PIM-SM Group-to-RP Mapping The only PIM-SM modification required is implementing this mechanism as one group-to-RP mapping method. The implementation will have to recognize the address format and derive and use the RP address using the rules in Section 4. This information is used at least when performing RPF lookups andReverse Path Forwarding (RPF) lookups, when processing Join/Prune messages, or performing Register-encapsulation. To avoid loops and inconsistancies, the group-to-RP mapping specified in this memo MUST be used for all embedded RPembedded-RP groups (i.e., addresses with prefix FF70::/12 or FFF0::/12). It is worth noting that compared to the other group-to-RP mappings,mapping mechanisms, which can be precomputed, the embedded RPembedded-RP mapping must be redone for every new IPv6 group address which would map to a different RP. For efficiency, the results may be cached in an implementation-specific manner.manner, to avoid computation for every embedded-RP packet. This group-to-RP mapping mechanism must be supported by the DR adjacent to the senders and any router on the path from any receiver to the RP. Further, as the switch-over to Shortest Path Tree (SPT) is also possible, it must be supported on the path between the receivers and the senders as well. It also must be supported by any router on the path from any sender to the RP -- in case the RP issues a Register-Stop and Joins the sources. It should be noted that this approach removes the need to run inter- domain MSDP. Multicast distribution trees in foreign networks can be joined by issuing a PIM-SM Join/Prune/Register to the RP address encodedSo, in practice, the multicast address. Also, the addressing model described here could be used to replace or augment the intra-domain Bootstrap Routermechanism (BSR), as the RP- mappings canmust be derived fromsupported by all routers on any path between the application of multicast address assignmen policies.RP, receivers, and senders. 7.2. Overview of the Model This section gives a high level,high-level, non-normative overview of how Embedded RP operates, as specified in the previous section. The steps when a receiver wishes to join a group are: 1. A receiver finds out a group address from some means (e.g., SDR or a web page). 2. The receiver issues an MLD Report, joining the group. 3. The receiver's DR will initiate the PIM-SM Join process towards the RP embeddedencoded in the multicast address.address, irrespective of whether it is in the "local" or "remote" PIM domain. The steps when a sender wishes to send to a group are: 1. A sender finds out a group address from some means, whether inusing an existing group (e.g., SDR, web page) or in a new group (e.g., a call tounspecified method (e.g, by contacting the administrator for group assignment, use ofassignment or using a multicast address assignment protocol). 2. The sender sends to the group. 3. The sender's DR will send the packets unicast-encapsulated in PIM-SM Register-messages to the RP address encoded in the multicast address (in the special case that DR is the RP, such sending is only conceptual). In fact, all the messages go as specified in [PIM-SM] -- embedded RPembedded-RP just acts as a group-to-RP mapping mechanism; instead of obtaining the address of the RP from local configuration or configuration protocols (e.g., BSR), it is derived transparently from the encoded multicast address. 8. Scalability/UsabilityScalability Analysis Interdomain MSDP model for connecting PIM-SM domains is mostly hierarchical in configuration and deployment, but flat with regard to information distribution. The embedded RPembedded-RP inter-domain model behaves as if all of the Internet was a single PIM domain, with just one RP per group. So, the inter-domain multicast becomes a flat, RP- centered topology. The scaling issues are bedescribed below. Previously foreign sources sent the unicast-encapsulated data to their local RP, now they do so to the foreign RP responsible"responsible" for the specific group.group (i.e., the prefix where the group address was derived from). This is especially important with large multicast groups where there are a lot of heavy senders -- particularly if implementations do not handle unicast-decapsulation well. This model increases the amount of Internet-wide multicast state slightly: the backbone routers might end up with (*, G) and (S, G, rpt) state between receivers (and past receivers, for PIM Prunes) and the RP, in addition to (S, G) states between the receivers and senders. Certainly, the amount of inter-domain multicast traffic between sources and the embedded RP will increase compared tosenders, if SPT is used. However, the traditional ASM model with MSDP.also requires MSDP state to propagate everywhere in inter-domain, so the total amount of state is smaller. The embedded RPembedded-RP model is practically identical in both inter-domain and intra-domain cases to the traditional PIM-SM in intra-domain. On the other hand, PIM-SM has been deployed (in IPv4) in inter-domain using MSDP; compared to that inter-domain model, this specification simplifies the multicast routing by removing the RP for senders and receivers in foreign domains.domains, and eliminating the MSDP information distribution. As the address of the RP is tied to the multicast address, the RP failure management becomes more difficult, as failover or redundancy mechanisms (e.g., BSR, Anycast-RP with MSDP) cannot be used as-is. On the other hand, Anycast-RP using PIM could be used. This described briefly in Section 6.1. The PIM-SM specification states, "Any RP address configured or learned MUST be a domain-wide reachable address". What "reachable" precisely means is not clear, even without embedded RP.embedded-RP. This statement cannot be proven especially with the foreign RPs (oneas one can not even guarantee that the RP exists!).exists. Instead of configuring RPs and DRs with a manual process (configuring a non-existent RP was possible though rare), with this specification the hosts and users using multicast indirectly specify the RP themselves, lowering the expectancy of the RP reachability. This is a relatively significant problem but not much different from the current multicast deployment: e.g., MLDv2 (S,G) joins, whether ASM or SSM, yield the same result [PIMSEC]. Being able to join/send to remote RPs raises security concerns that are considered separately, but it has an advantage too: every group has a "home"responsible RP" which is able to control (to some extent) who are able to send to the group. A more extensive description and comparison of the inter-domain multicast routing models (traditional ASM with MSDP, embedded RP,embedded-RP, SSM) and their security properties has been described in [PIMSEC]. 9. Acknowledgements Jerome Durand commented on an early draft of this memo. Marshall Eubanks noted an issue regarding short plen values. Tom Pusateri noted problems with an earlier SPT-join approach. Rami Lehtonen pointed out issues with the scope of SA-state and provided extensive commentary. Nidhi Bhaskar gave the draft a thorough review. Toerless Eckert, Hugh Holbrook, and Dave Meyer provided very extensive feedback. The whole MboneD working group is also acknowledged for the continued support and comments. 10. Security Considerations The address of the RP is encoded in the multicast address. RPs may be a good target for Denial of Service attacksaddress -- and thus become more visible as they are asingle pointpoints of failure (excluding failover techniques) for a group. Infailure. Even though this way,does not significantly affect the target would be clearly visible. However, it could be argued that if interdomainmulticast was to be made to work e.g., with MSDP,routing security, it may expose the address would haveRP to be visible anyway (through viaother channels).kinds of attacks. The operators are encouraged to pay special attention to securing these routers. See Section 6.1 on considerations regarding failover and Section 6.2 on placement of RPs leading to a degree of fate-sharing properties. As any RP will have to accept PIM-SM Join/Prune/Register messages from any DR, this might cause a potential DoS attack scenario. However, this can be mitigated by the fact that the RP can discard all such messages for all multicast addresses that do not encode the address of the RP, and if deemed important, theRP. The implementation couldMAY also allow manual configuration of which multicast addresses or prefixes embedding the RP could be used, so that only the pre-agreed sources could use the RP.used. In a similar fashion, when a receiver joins to an RP, the DRs must accept similar PIM-SM messages back from RPs. One consequence of the embedded RP usage model is that it allows Internet-wide multicast state creation (from receiver(s) in another domain to the RP in another domain) compared to the domain wide state creation in the traditional ASM model.However, the traditional ASM model also requires MSDP state to propagate everywhere in inter- domain, so the total amount of statethis is smaller.not a considerable threat. One should observe that the embedded RPembedded-RP threat model is actually prettyrather similar to SSM; both mechanisms significantly reduce the threats at the sender side, but have new ones inside. On the receiver side, the threats are somewhat comparable, as any receiver can try toan attacker could do an MLDv2 (S,G) join anytowards a non-existent group or channel, andsource, which the local DR orRP cannot readily reject (e.g.,could not block based on the MSDP information) such joins. RPs become single points of failure as anycast-RP mechanism is not (at least immediately) available. However, some other forms of failover are still possible (see Section 6.1) and one can obtain some forms of fate-sharing properties with a proper placement of RPs (see Section 6.2).information. The implementation MUST perform at least the same address validity checks to the embedded RPembedded-RP address as to one received via other means (like BSR or MSDP), to avoidmeans; at least fe80::/10, ::/16, and ff00::/8 should be excluded. This is particularly important as the address being e.g., "::", "::1", or a link-local address.information is derived from the untrusted source (i.e., any user in the Internet), not from the local configuration. A more extensive description and comparison of the inter-domain multicast routing models (traditional ASM with MSDP, embedded RP,embedded-RP, SSM) and their security properties has been describeddone separately in [PIMSEC]. 11. References 11.1. Normative References [ADDRARCH] Hinden, R., Deering, S., "IP Version 6 Addressing Architecture", RFC3513, April 2003. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3306] Haberman, B., Thaler, D., "Unicast-Prefix-based IPv6 Multicast Addresses", RFC3306, August 2002. 11.2. Informative References [ANYCAST] Hagino, J., Ettikan, K., "An analysis of IPv6 anycast", work-in-progress, draft-ietf-ipngwg-ipv6-anycast-analysis-02.txt, June 2003. [ANYCASTRP] Kim, D. et al, "Anycast RP mechanism using PIM and MSDP", RFC 3446, January 2003. [ANYPIMRP] Farinacci, D., Cai, Y., "Anycast-RP using PIM", work-in-progress, draft-ietf-pim-anycast-rp-00.txt, November 2003. [BSR] Fenner, B., et al., "Bootstrap Router (BSR) Mechanism for PIM Sparse Mode", work-in-progress, draft-ietf-pim-sm- bsr-03.txt, February 2003. [MSDP] Meyer, D., Fenner, B, (Eds.), "Multicast Source Discovery Protocol (MSDP)", RFC 3618, October 2003. [PIMSEC] Savola, P., Lehtonen, R., Meyer, D., "PIM-SM Multicast Routing Security Issues and Enhancements", work-in-progress, draft-savola-mboned-mroutesec-00.txt, January 2004. [PIM-SM] Fenner, B. et al, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised), work-in-progress, draft-ietf-pim-sm-v2-new-08.txt, October 2003.draft-ietf-pim-sm-v2-new-09.txt, February 2004. [SSM] Holbrook, H. et al, "Source-Specific Multicast for IP", work-in-progress, draft-ietf-ssm-arch-04.txt, October 2003. [V6MISSUES] Savola, P., "IPv6 Multicast Deployment Issues", work-in-progress, draft-savola-v6ops-multicast- issues-02.txt, October 2003.issues-03.txt, February 2004. Authors' Addresses Pekka Savola CSC/FUNET Espoo, Finland EMail: email@example.com Brian Haberman Caspian Networks One Park Drive, Suite 300 Research Triangle Park, NC 27709 EMail: firstname.lastname@example.org Phone: +1-919-949-4828 A. Discussion about Design Tradeoffs One could argueIt has been argued that there should be more RPs thaninstead of allowing the 4-bit "RIID" allows for, especially if anycast-RP cannot be used. In that light, extending "RIID"operator to take full advantage of whole 8 bits would seem reasonable. However, this would use up all ofspecify RIID, the reserved bits, and leave no room for future flexibility. In case of large number of RPs, an operational workaroundvalue could be to split the PIM domain: for example, using two /33's instead of one /32 would gain another 16 (or 15, if zero ispre-determined (e.g., "1"). However, this has not used) RP addresses. Note that the limit of 4 bits worth of RPs just depends on the prefix the RPbeen adopted, as this eliminates address is derived from; one can use multiple prefixes in a domain, andassignment flexibility from the limit of 16 (or 15) RPs should never really be a problem.operator. Values 64 < "plen" < 96 would overlap with upper bits of the multicast group-id; due to this restriction, "plen" must not exceed 64 bits. This is in line with RFC 3306. The embedded RPembedded-RP addressing could be used to convey other information (other than RP address) as well, for example, what should be the RPT threshold for PIM-SM. These could bebe, whether feasible or not, encoded in the RP address somehow, or in the multicast group address. Whether this is a good idea is another thing.In any case, such modifications are beyond the scope of this memo. For the cases where the RPs do not exist or are unreachable, or too much state is being generated to reach in a resource exhaustion DoS attack, some forms of rate-limiting or other mechanisms could be deployed to mitigate the threats while trying not to disturb the legitimate usage. This has been described at more lengthHowever, as the threats are generic, they are considered out of scope and discussed separately in [PIMSEC]. The mechanism is not usable with Bidirectional PIM without protocol extensions, as pre-computing the Designated Forwarder is not possible. B. Changes since -00[[ RFC-Editor: please remove before publication ]] B.1 Changes since -01 o Lots of editorial cleanups and some reorganization, without technical changes. o Remove the specification that RIID=0 SHOULD NOT be accepted, but state that they "must not" be used (implementation vs. operational wording). o Specify that the RP address MUST NOT be of prefixes fe80::/10, ::/16, or ff00::/8. B.2 Changes since -00 o Lots of editorial cleanups, or cleanups without techinical changes. o Reinforce the notion of Embedded RP just being a group-to-RP mapping mechanism (causing substantive rewriting in section 7); highlight the fact that precomputing the group-to-RP mapping is not possible. o Add (a bit) more text on RP redundancy and deployment tradeoffs wrt. RPs becoming SPoF. o Clarify the usability/scalability issues in section 8. o Clarify the security issues in Sections 8, Security Considerations and Appendix A, mainly by referring to a separate document. o Add a MUST that embedded RPembedded-RP mappings must be honored by implementations. Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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