Internet Engineering Task Force P. Savola Internet Draft CSC/FUNET Expiration Date: September 2003 B. Haberman Caspian Networks March 2003 Embedding the Address of RP in IPv6 Multicast Address draft-savola-mboned-mcast-rpaddr-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 As has been noticed, there is exists a huge deployment problem with global, interdomain IPv6 multicast: PIM Renzesvous Points (RPs) have no way of communicating the information about multicast sources to other multicast domains, as there is no MSDP, and the whole interdomain Any Source Multicast model is rendered unusable; SSM avoids these problems. This memo outlines a way to embed the address of the RP in the multicast address, solving the interdomain multicast problem. The problem is three-fold: specify an address format, adjust the operational procedures and configuration if necessary, and modify PIM implementations of those who want to join or send to a group (Designated Routers) or provide one (Rendezvous Points). In consequence, there would be no need for interdomain MSDP. Savola & Haberman [Expires September 2003] [Page 1] Internet Draft draft-savola-mboned-mcast-rpaddr-02.txt March 2003 Table of Contents 1. Introduction ............................................... 2 2. Unicast-Prefix-based Address Format ........................ 3 3. Modified Unicast-Prefix-based Address Format ............... 3 4. Embedding the Address of the RP in the Multicast Address ... 4 5. Examples ................................................... 5 5.1. Example 1 .............................................. 5 5.2. Example 2 .............................................. 5 5.3. Example 3 .............................................. 6 5.4. Example 4 .............................................. 6 6. Operational Requirements ................................... 6 6.1. Anycast-RP ............................................. 6 6.2. Guidelines for Assigning IPv6 Addresses to RPs ......... 6 7. Required PIM Modifications ................................. 7 7.1. Overview of the Model .................................. 8 8. Scalability/Usability Analysis ............................. 8 9. Acknowledgements ........................................... 9 10. Security Considerations ................................... 10 11. References ................................................ 11 11.1. Normative References .................................. 11 11.2. Informative References ................................ 11 Authors' Addresses ............................................. 11 A. Open Issues/Discussion ..................................... 12 1. Introduction As has been noticed [V6MISSUES], there is exists a huge deployment problem with global, interdomain IPv6 multicast: PIM [PIM] RPs have no way of communicating the information about multicast sources to other multicast domains, as there is no MSDP [MSDP], and the whole interdomain Any Source Multicast model is rendered unusable; SSM [SSM] avoids there problems. This memo outlines a way to embed the address of the RP in the multicast address, solving the interdomain multicast problem. The problem is three-fold: specify an address format, adjust the operational procedures and configuration if necessary, and modify PIM implementations of DR's where receivers/senders are expected use the multicast addressing as described in this memo. In consequence, there would be no need for interdomain MSDP. The solution is founded upon unicast-prefix-based IPv6 multicast addressing [UNIPRFXM] and making some assumptions about IPv6 address assignment for the RPs in the PIM domain. Savola & Haberman [Expires September 2003] [Page 2] Internet Draft draft-savola-mboned-mcast-rpaddr-02.txt March 2003 Further, a change in how interdomain PIM operates with these addresses is presented: multicast receivers' and senders' DR's join or send to (respectively) the RP embedded in the address -- not their locally configured RP. It is self-evident that one can't embed, in the general case, two 128-bit addresses in one 128-bit address. In this memo, some assumptions on how this could be done are made. If these assumptions can't be followed, either operational procedures and configuration must be slightly changed or this mechanism not be used. The assignment of multicast addresses is outside the scope of this document; however, the mechanisms are very probably similar to ones used with [UNIPRFXM]. 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 [UNIPRFXM], 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 are yet undefined and thus zero.) 3. Modified Unicast-Prefix-based Address Format This memo proposes 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" was set to 1, interpret the last low-order 4 bits of "reserved" field as signifying the RP interface ID, as described in this memo. In consequence, the address format becomes: Savola & Haberman [Expires September 2003] [Page 3] Internet Draft draft-savola-mboned-mcast-rpaddr-02.txt March 2003 | 8 | 4 | 4 | 4 | 4 | 8 | 64 | 32 | +--------+----+----+----+----+--------+----------------+----------+ |11111111|flgs|scop|rsvd|RPad| 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 of the PIM RP. Then P MUST BE set to 1, and consequently T MUST be set to 1, as specified in [UNIPRFXM]. In the case that R = 1, the last 4 bits of previously reserved field ("RPad") are interpreted as embedding the interface ID of the RP, as specified in this memo. R = 0 indicates a multicast address that does not embed the address of the PIM RP and follows the semantics defined in [ADDRARCH] and [UNIPRFXM]. In this context, the value of "RPad" has no meaning. 4. Embedding the Address of the RP in the Multicast Address The address of the RP can only be embedded in unicast-prefix -based addresses, but the scheme could be extended to other forms of multicast addresses as well. Further, the mechanism cannot be combined with SSM, as SSM has no RP's. 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 prefix FF7::/12 or FFF::/12) o "plen" MUST NOT be 0 (ie. not SSM) o "plen" MUST NOT be greater than 96 The address of the RP can be obtained from a multicast address satisfying the above criteria by taking the following steps: 1. take the last 96 bits of the multicast address add 32 zero bits at the end, 2. zero the last 128-"plen" bits, and Savola & Haberman [Expires September 2003] [Page 4] Internet Draft draft-savola-mboned-mcast-rpaddr-02.txt March 2003 3. replace the last 4 bits with the contents of "RPad". One should note that there are several operational scenarios when [UNIPRFXM] statement "All non-significant bits of the network prefix field SHOULD be zero" is ignored. This is to allow multicast address assignments to third parties which still use your RP; see example 2 below. "Plen" higher than 64 SHOULD NOT be used as that would overlap with the upper bits of multicast group-id. The implementation MUST perform at least the same address validity checks to the calculated RP address as to one received via other means (like MSDP), to avoid e.g. the address being "::" or "::1". One should note that the 4 bits reserved for "RPad" set the upper bound for RP's per multicast group address; not the number of RP's in a subnet, PIM domain or large-scale network. 5. Examples 5.1. Example 1 The network administrator of 3FFE:FFFF::/32 wants to set up an RP for the network and all of his customers. He chooses network prefix=3FFE:FFFF and plen=32, and wants to use this addressing mechanism. The multicast addresses he will be able to use are of the form: FF7x:y20:3FFE:FFFF:zzzz:zzzz: Where "x" is the multicast scope, "y" the interface ID of the RP address, and "zzzz:zzzz" will be freely assignable within the PIM domain. In this case, the address of the PIM RP would be: 3FFE:FFFF::y (and "y" could be anything from 0 to F); the address 3FFE:FFFF::y/128 is added as a Loopback address and injected to the routing system. 5.2. Example 2 As above, the network administrator can also allocate multicast addresses like "FF7x:y20:3FFE:FFFF:DEAD::/80" to some of his customers within the PIM domain. In this case the RP address would still be "3FFE:FFFF::y" (note the prefix length rule: "plen" does not need to have anything to do with real unicast/multicast address prefix lengths). Savola & Haberman [Expires September 2003] [Page 5] Internet Draft draft-savola-mboned-mcast-rpaddr-02.txt March 2003 5.3. Example 3 In the above network, the network admin sets up addresses as above, but an organization wants to have their own PIM domain; that's reasonable. The organization can pick multicast addresses like "FF7x:y30:3FFE:FFFF:BEEF::/80", and then their RP address would be "3FFE:FFFF:BEEF::y". 5.4. Example 4 In the above networks, if the admin wants to specify the RP to be in a non-zero /64 subnet, he could always use something like "FF7x:y40:3FFE:FFFF:BEEF:FEED::/96", and then their RP address would be "3FFE:FFFF:BEEF:FEED::y". There are still 32 bits of multicast group-id's to assign to customers and self. 6. Operational Requirements 6.1. Anycast-RP One should note that MSDP is also used, in addition to interdomain connections between RPs, in anycast-RP [ANYCASTRP] -technique, for sharing the state information between different RPs in one PIM domain. However, there are other propositions, like [ANYPIMRP]. Anycast-RP mechanism is incompatible with this addressing method unless MSDP is specified and implemented. Alternatively, another method for sharing state information could be used. Anycast-RP and other possible RP failover mechanisms are outside of the scope of this memo. 6.2. Guidelines for Assigning IPv6 Addresses to RPs With this mechanism, the RP can be given basically any network prefix up to /64 (and even beyond, by using the upper bits of multicast group-id). The interface identifier will have to be manually configured to match "RPad". If an administrator wishes to use an RP address that does not conform to the addressing topology, that address can be injected into the routing system via a host route. This RP address SHOULD be assigned out of the network's prefix in order to ensure aggregation at the border. Savola & Haberman [Expires September 2003] [Page 6] Internet Draft draft-savola-mboned-mcast-rpaddr-02.txt March 2003 7. Required PIM Modifications The use of multicast addresses with embedded RP addresses requires additional PIM processing. Namely, a PIM router will need to be able to recognize the encoding and derive the RP address from the address using the rules in section 4 and to be able to use the embedded RP, instead of its own for multicast addresses in this specified range. The two key places where these modifications are used are the Designated Routers (DRs) on the receiver/sender networks and the RPs in the domain where the embdedded address has been derived from (see figure below). For the foreign DR's (rtrR1, rtrR23, and rtrR4), this means sending PIM Join/Prune/Register messages towards the foreign RP (rtrRP_S). Naturally, PIM Register-Stop and other messages must also be allowed from the foreign RP. DR's in the local PIM domain (rtrS) do the same, but the RP used should the same as with regular Any-Source Multicast (ASM); however, see the appendix for more. For the RP (rtrRP_S), this means being able to recognize and validate PIM messages which use RP-embedded addressing originated from any DR at all. In particular, there is no need to have all routers (like rtrBB) on the path modified: this is a major benefit for quick deployment. nodeS - rtrS - rtrRP_S - rtrBB -----+--- rtrR1 - node1 | | | node2_S ---------+ | +-- rtrR23 - node2 | | | +---- node3 | +------------ rtrR4 - node4 In addition, the administration of the PIM domain will require a policy decision on where the PIM messages to the encoded RP be sent; this is typically assumed to everywhere unless explicitly configured otherwise. The extraction of the RP information from the multicast address should be done during forwarding state creation. That is, if no state exists for the multicast address, PIM must take the embedded RP information into account when creating forwarding state. Depending on administrative policy, this would result in a receiver's DR initiating a PIM Join towards the foreign RP or a source's DR sending PIM Register messages towards the foreign RP. Savola & Haberman [Expires September 2003] [Page 7] Internet Draft draft-savola-mboned-mcast-rpaddr-02.txt March 2003 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 Join/Prune/Register to the RP address encoded in the multicast address. 7.1. Overview of the Model 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 Join process towards the RP embedded in the multicast address. The steps when a sender wishes to send to a group are: 1. A sender finds out a group address from some means, whether in an existing group (e.g. SDR, web page) or in a new group (e.g. a call to the administrator for group assignment, use of 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 unicast-encapsulated in PIM 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 both cases, the messages then go on as specified in [PIM] and other specifications (e.g. Register-Stop and/or SPT Join); there is no difference in them except for the fact that the RP address is derived from the multicast address. When sending or receiving, there is a special case when the DR is in local domain, and information about RP to be used with the group is available with conventional mechanisms, and that differs from the RP embedded in the address; see the appendix for more information. 8. Scalability/Usability Analysis Interdomain MSDP model for connecting PIM domains is mostly hierarchical. The "embedded RP address" changes this to a mostly flat, sender-centered, full-mesh virtual topology. This may or may not cause some effects; it may or may not be desirable. At the very least, it makes many things much more robust as the number of third parties is minimized. A good scalability analysis is needed. Savola & Haberman [Expires September 2003] [Page 8] Internet Draft draft-savola-mboned-mcast-rpaddr-02.txt March 2003 In some cases (especially if e.g. every home user is employing site- local multicast), some degree of hierarchy would be highly desirable, for scalability (e.g. take the advantage of shared multicast state) and administrative point-of-view. Being able to join/send to remote RP's has security considerations that are considered below, but it has an advantage too: every group has a "home RP" which is able to control (to some extent) who are able to send to the group. One should note that the model presented here simplifies the PIM multicast routing model slightly by removing the RP for senders and receivers in foreign domains. One scalability consideration should be noted: previously foreign sources sent the unicast-encapsulated data to their local RP, now they do so to the foreign RP responsible for the specific group. 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 at least temporary (*, G) and (S, G, rpt) state 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 to the ASM model with MSDP; however, the domain responsible for the RP is expected to be able to handle this. As the address of the RP is tied to the multicast address, in the case of RP failure, PIM BSR mechanisms cannot pick a new RP; the failover mechanisms, if used, for backup RP's are different, and typically would depend on sharing one address. The failover techniques are outside of the scope of this memo. 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 earlier SPT-join approach. Rami Lehtonen pointed out issues with the scope of SA-state and provided extensive commentary. The whole MboneD working group is also acknowledged for the continued support and comments. Savola & Haberman [Expires September 2003] [Page 9] Internet Draft draft-savola-mboned-mcast-rpaddr-02.txt March 2003 10. Security Considerations The address of the PIM RP is embedded in the multicast address. RPs may be a good target for Denial of Service attacks -- as they are a single point of failure (excluding failover techniques) for a group. In this way, the target would be clearly visible. However, it could be argued that if interdomain multicast was to be made work e.g. with MSDP, the address would have to be visible anyway (through via other channels, which may be more easily securable). As any RP will have to accept PIM Join/Prune/Register messages from any DR's, 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 embed the address of the RP, and if deemed important, the implementation could also allow manual configuration of which multicast addresses or prefixes embedding the RP could be used; however, at least with addresses, this would increase the need for coordination between multicast sources and administration. In a similar fashion, DR's must accept similar PIM messages back from the foreign RP's for which a receiver in DR's network has joined. One consequence of the 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 MSDP model. RPs may become a bit more single points of failure as anycast-RP mechanism is not (at least immediately) available. This can be partially mitigated by the fact that some other forms of failover are still possible, and there should be less need to store state as with MSDP. The implementation MUST perform at least the same address validity checks to the embedded RP address as to one received via other means (like MSDP), to avoid the address being e.g. "::" or "::1". TBD: the implications (if any) with regard to embedding the RP address in the packets (e.g. packet laundering and DoS do not seem possible due to the way multicast works, but more analysis is needed). Savola & Haberman [Expires September 2003] [Page 10] Internet Draft draft-savola-mboned-mcast-rpaddr-02.txt March 2003 11. References 11.1. Normative References [ADDRARCH] Hinden, R., Deering, S., "IP Version 6 Addressing Architecture", RFC2373, July 1998. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [UNIPRFXM] Haberman, B., Thaler, D., "Unicast-Prefix-based IPv6 Multicast Addresses", RFC3306, August 2002. 11.2. Informative References [ANYCASTRP] Kim, D. et al, "Anycast RP mechanism using PIM and MSDP", work-in-progress, draft-ietf-mboned-anycast- rp-08.txt, May 2001. [ANYPIMRP] Farinacci, D., Cai, Y., "Anycast-RP using PIM", work-in-progress, draft-farinacci-pim-anycast-rp-00.txt, January 2003. [MSDP] Meyer, D., Fenner, B, (Eds.), "Multicast Sourc Discovery Protocol (MSDP)", work-in-progress, draft-ietf-msdp-spec-14.txt, November 2002. [PIM] Fenner, B. et al, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised), work-in-progress, draft-ietf-pim-sm-v2-new-06.txt, December 2002. [SSM] Holbrook, H. et al, "Source-Specific Multicast for IP", work-in-progress, draft-ietf-ssm-arch-02.txt, February 2003. [V6MISSUES] Savola, P., "IPv6 Multicast Deployment Issues", work-in-progress, draft-savola-v6ops-multicast- issues-01.txt, November 2002. Authors' Addresses Pekka Savola CSC/FUNET Espoo, Finland EMail: psavola@funet.fi Brian Haberman Savola & Haberman [Expires September 2003] [Page 11] Internet Draft draft-savola-mboned-mcast-rpaddr-02.txt March 2003 Caspian Networks One Park Drive Suite 400 Research Triangle Park, NC 27709 EMail: bkhabs@nc.rr.com Phone: +1-919-949-4828 A. Open Issues/Discussion The initial thought was to use only SPT join from local RP/DR to foreign RP, rather than a full PIM Join to foreign RP. However, this turned out to be problematic, as this kind of SPT joins where disregarded because the path had not been set up before sending them. A full join to foreign PIM domain is a much clearer approach. One could argue that there can be more RPs than the 4-bit "RPad" allows for, especially if anycast-RP cannot be used. In that light, extending "RPad" to take full advantage of whole 8 bits would seem reasonable. However, this would use up all of the reserved bits, and leave no room for future flexibility. In case of large number of RPs, an operational workaround could be to split the PIM domain: for example, using two /33's instead of one /32 would gain another 16 RP addresses. Some hierarchy (e.g. two-level, "ISP/customer") for RPs could possibly be added if necessary, but that would be torturing one 128 bits even more. One particular case with a sender in the local domain is where regular ASM RP would be X, and the embedded RP address would be Y. This would typically be due to a misconfiguration, but the DR SHOULD be conservative and use the configured address X. However, the simplest approach, and one which would typically be least surprising, would be the one where one would always use the embedded RP address by default. Any other thoughts on that? 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