mboned Working Group P. Savola Internet Draft CSC/FUNET Expiration Date:
AprilAugust 2004 B. Haberman Caspian Networks October 2003February 2004 Embedding the Rendezvous Point (RP) Address of RPin an IPv6 Multicast Address draft-ietf-mboned-embeddedrp-00.txtdraft-ietf-mboned-embeddedrp-01.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 There exists a hugeA very difficult deployment problem with global, interdomain IPv6 multicast:multicast using Protocol Independent Multicast - Sparse Mode (PIM-SM) Rendezvous Points (RPs) have no way of communicating the information about multicast sources to other multicast domains, as there is no Multicast Source Discovery Protocol (MSDP), and the whole interdomain Any Source Multicast (ASM) model is rendered unusable; Source Specific Multicast (SSM) avoids these problems but is not considered readily deployable at the moment.has been identified. This memo defines a PIM-SM group- to-RP mappingan address allocation policy in which encodesthe address of the RPRendezvous Point (RP) is encoded in the IPv6 multicast group address. In consequence, there wouldFor PIM-SM, this can be no need for interdomain MSDP,seen as a specification of a group-to-RP mapping mechanism. This allows an easy deployment of scalable inter-domain multicast, and evensimplifies the intra-domain RPmulticast configuration could be simplified.as well. This memo updates the addressing format presented in RFC 3306. Table of Contents 1. Introduction ............................................... 2 2. Unicast-Prefix-based Address Format ........................ 4 3. Modified Unicast-Prefix-based Address Format ............... 4 4. Embedding the Address of the RP in the Multicast Address ... 5 5. Examples ................................................... 6 5.1. Example 1 .............................................. 6 5.2. Example 2 .............................................. 67 5.3. Example 3 .............................................. 67 5.4. Example 4 .............................................. 7 6. Operational Requirements ...................................Considerations ................................. 7 6.1. Anycast-RP .............................................RP Redundancy .......................................... 7 6.2. RP Deployment .......................................... 8 6.3. Guidelines for Assigning IPv6 Addresses to RPs ......... 78 7. RequiredPIM-SM Protocol Modifications .............................. 78 7.1. PIM-SM Group-to-RP Mapping ............................. 9 7.2. Overview of the Model .................................. 9 8. Scalability/Usability Analysis ............................. 910 9. Acknowledgements ........................................... 11 10. Security Considerations ................................... 11 11. References ................................................ 1213 11.1. Normative References .................................. 1213 11.2. Informative References ................................ 1213 Authors' Addresses ............................................. 1314 A. Discussion about Design Tradeoffs .......................... 1314 B. Changes since -00 .......................................... 15 Intellectual Property Statement ................................ 1415 Full Copyright Statement ....................................... 1516 1. Introduction As has been noticed [V6MISSUES], there exists a hugedeployment problem with global, interdomain IPv6 multicast: PIM-SM [PIM-SM] RPs have no way of communicating the information about multicast sources to other multicast domains, as there is no MSDP [MSDP], andMulticast Source Discovery Protocol (MSDP) [MSDP] (at least yet). Therefore the whole interdomain Any Source Multicast model is rendered unusable; SSMSource-Specific Multicast (SSM) [SSM] avoids these problems. Itproblems but is not a complete solution for several reasons. Further, it has been noted that there are some problems with SSM deploymentthe support and support:deployment of mechanisms SSM would require: it seems unlikely that SSM could be usable as the only interdomain multicast routing mechanism in the short term. This memo proposesdescribes a fix to interdomainmulticast routing, and provides an additional method for the RP discovery with the intra-domain case. This document proposes a solution to the group-to-RP mapping problemaddress allocation policy in which leverages and extends [RFC3306] by encodingthe RPaddress of the RP is encoded in the IPv6 multicast group intoaddress, and specifies a PIM-SM group-to-RP mapping to use the group address itself.encoding, leveraging and extending the unicast-prefix -based addressing [RFC3306]. This mechanism not only provides a simple solution for IPv6 interdomain ASMAny Source Multicast (ASM) but can be used as a simple solution for IPv6 intradomain ASM on scoped addresses,addresses as well. The use as a substitute for Bootstrap Router protocol (BSR) [BSR] isIt can also possible.be used in those deployment scenarios which would have previously used the Bootstrap Router protocol (BSR) [BSR]. The solution consists of two elements applicable tothree elements: o A specification of a subrange of [RFC3306] IPv6 multicast group addresses which aredefined by setting one previously unused bit of the Flags field to "1":"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 specification of optional and mandatory procedures to operate ASM with PIM-SM on these IPv6 multicast groups. Addresses in thisthe subrange will be called embedded-RPembedded RP addresses. If used inThis scheme obviates the interdomain, a mechanism similar to MSDP is not requiredneed for these addressesinter-domain MSDP, and RP configuration for these addresses can be as simple as zero configuration forthe routers supporting this specification. It is self-evident thatare not required to include any multicast configuration, except when they act as an RP. In general, a 128 bit128-bit RP address can in general notcan't be embedded into a 128-bit group address with space left to carry athe group identity itself. An appropriate form of encoding is thus defined, and it is assumed that the Interface-ID of RPs in the embedded-RPembedded RP range can be assigned to be a specific values.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; however,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. 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 are yet undefinedundefined, sent as zero and thus zero.)ignored on receipt.) 3. Modified Unicast-Prefix-based Address Format This memo proposesspecifies 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" wasis 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: | 8 | 4 | 4 | 4 | 4 | 8 | 64 | 32 | +--------+----+----+----+----+--------+----------------+----------+ |11111111|flgs|scop|rsvd|RPad||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 ofon the PIM-SMRP. Then P MUST BE 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 ("RPad")are interpreted as embedding the RP interface ID of the RP,("RIID"), as specified in this memo. R = 0 indicates a multicast address that does not embed the address of the PIM-SMRP and follows the semantics defined in [ADDRARCH] and [RFC3306]. In this context, the value of "RPad" has no meaning."RIID" MUST be 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. 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::/12prefixes FF70::/12 or FFF::/12),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 followingtwo steps: 1. takecopy the last 96first "plen" bits of the multicast"network prefix" to a zeroed 128-bit address add 32 zero bits at the end, 2. zero the last 128-"plen" bits,structure, and 3.2. replace the last 4 bits with the contents of "RPad"."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 -- and why the second step, above, is necessary.ignored. This is to allow multicast address assignments to third parties which still use your RP; see example 2 below.the RP associated with the network prefix. "plen" higher than 64 MUST NOT be used as that would overlap with the upper bits of multicast group-id. The implementationWhen 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.e.g., the address being "::""::", "::1", or "::1".a link-local address. One should note that the 4 bits reserved for "RPad""RIID" set the upper bound for RPs per multicast group address; notfor the numbercombination of RPs in a subnet, PIM-SM domain or large-scale network.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 3FFE:FFFF::/322001:DB8::/32 wants to set up an RP for the network and all of his customers. He(S)he chooses network prefix=3FFE:FFFFprefix=2001:DB8 and plen=32, and wants to use this addressing mechanism. The multicast addresses he(s)he will be able to use are of the form: FF7x:y20:3FFE:FFFF:zzzz:zzzz:<group-id>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. In this case, the address of the PIM-SM RP would be: 3FFE:FFFF::y2001:DB8::y (and "y" could be anything from 0 to F); the address 3FFE:FFFF::y/1282001:DB8::y/128 is added as a Loopback address and injected to the routing system. 5.2. Example 2 As above,in Example 1, the network administrator can also allocate multicast addresses like "FF7x:y20:3FFE:FFFF:DEAD::/80""FF7x:y20:2001:DB8:DEAD::/80" to some of his customers within the PIM-SM domain. In this case the RP address would still be "3FFE:FFFF::y"."2001:DB8::y". Note the second rule of deriving the RP address: the "plen" field in the multicast address, (hex)200x20 = 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, "3FFE:FFFF""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 3FFE:FFFF:DEAD::/48.2001:DB8:DEAD::/48. 5.3. Example 3 In the above network,network of Examples 1 and 2, the network admin sets up addresses as above,for use by their customers, but an organization wants to have their own PIM-SM domain; that's reasonable. The organization can pick multicast addresses like "FF7x:y30:3FFE:FFFF:BEEF::/80","FF7x:y30:2001:DB8:BEEF::/80", and then their RP address would be "3FFE:FFFF:BEEF::y"."2001:DB8: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(s)he could always use something like "FF7x:y40:3FFE:FFFF:BEEF:FEED::/96","FF7x:y40:2001:DB8:BEEF:FEED::/96", and then their RP address would be "3FFE:FFFF:BEEF:FEED::y"."2001:DB8:BEEF:FEED::y". There are still 32 bits of multicast group-id's to assign to customers and self. 6. Operational RequirementsConsiderations This desction describes the major operational considerations for those deploying this mechanism. 6.1. Anycast-RP One should note that MSDPRP Redundancy A technique called "Anycast RP" is also used, in additionused within a PIM-SM domain to interdomain connections between RPs, in anycast-RP [ANYCASTRP] -technique, for sharing theshare an address and multicast state information between different RPs in one PIM-SM domain. However, therea set of RP's mainly for redundancy purposes. Typically, MSDP has been used for that as well [ANYCASTRP]. There are also other propositions,approaches, like [ANYPIMRP]. Anycast-RP mechanism is incompatible with this addressing method unless MSDP is specified and implemented. Alternatively, another methodusing PIM for sharing statethis information could be used. Anycast-RP and other possible[ANYPIMRP]. RP failover cannot be used with this specification without additional mechanisms or techniques such as MSDP, PIM-SM extensions, or anycasting 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. Guidelines for Assigning IPv6 AddressesRP Deployment As there is no need to RPs With this mechanism, theshare inter-domain state with MSDP, each DR connecting multicast sources could act as an RP without scalability concerns about 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 given basicallyobtained without using any networkRP failover mechanisms: if the DR goes down, the multicast transmission may not be all that interesting 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 should map to a different RP (or enough 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 "RPad". RPad"RIID". RIID = 0 SHOULD 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.(e.g., an additional loopback address assigned on a router), that address can be injected into the routing system via a host route. 7. RequiredPIM-SM Protocol Modifications The use of multicast addresses with embedded RP addresses requires additionalThis section describes how PIM-SM processing. Namely, ais modified, i.e., how the group- to-RP mapping mechanism works for Embedded RP. 7.1. PIM-SM routerGroup-to-RP Mapping The only PIM-SM modification required is implementing this mechanism as one group-to-RP mapping method. The implementation will need to be ablehave to recognize the encodingaddress format and derive and use the RP address from the addressusing the rules in section 4Section 4. This information is used at least when performing RPF lookups and to be able to usewhen processing Join/Prune messages, or performing Register-encapsulation. To avoid loops and inconsistancies, the embedded RP, instead of its own for multicast addressesgroup-to-RP mapping specified in this specified range. The three key places where these modifications arememo MUST be used are the Designated Routers (DRs) onfor all embedded RP groups (i.e., with prefix FF70::/12 or FFF0::/12). It is worth noting that compared to the receiver/sender networks,other group-to-RP mappings, which can be precomputed, the backbone networks, andembedded RP mapping must be redone for every new IPv6 group address which would map to a different RP. For efficiency, the RPsresults may be cached in an implementation-specific manner. This group-to-RP mapping mechanism must be supported by the domain whereDR adjacent to senders and any router on the embdedded address has been derivedpath from (see figure below). Forany receiver to the foreign DRs (rtrR1, rtrR23, and rtrR4), this means sending PIM-SM Join/Prune/Register messages towards the foreign RP (rtrRP_S). Naturally, PIM-SM Register-Stop and other messages mustRP. It also must be allowed from the foreign RP. DRs in the local PIM-SM domain (rtrS) do the same. For the RP (rtrRP_S), this means being able to recognize and validate PIM-SM messages which use RP-embedded addressing originated fromsupported by any DR at all. For the other routers on the path (rtrBB), this means recognizing and validating that the Join/Prune PIM-SM messages using the embedded RP addressing arerouter on the rightpath towards the RP they think is in charge of the particular address. nodeS - rtrS - rtrRP_S - rtrBB -----+--- rtrR1 - node1 | | | node2_S ---------+ | +-- rtrR23 - node2 | | | +---- node3 | +------------ rtrR4 - node4 In addition, the administration of the PIM-SM domains MAY have an option to manually override the RP selection for the embedded RP multicast addresses: the default policy SHOULD be to use the embedded RP. The extraction of the RP informationfrom any sender to the multicast address should be done during forwarding state creation. That is, if no state exists for the multicast address, PIM-SM must take the embeddedRP information into account when creating forwarding state. Unless otherwise dictated by the administrative policy, this would result-- in a receiver's DR initiating a PIM-SM Join towardscase the foreignRP orissues a source's DR sending PIM-SM Register messages towardsRegister-Stop and Joins the foreign RP.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 encoded in the multicast address. Also, the addressing model described here could be used to replace or augment the intra-domain Bootstrap Router mechanism (BSR), as the RP- mappings can be communicated byderived from the application of multicast address assignment. 7.1.assignmen policies. 7.2. Overview of the Model This section gives a 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.(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 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.(e.g., SDR, web page) or in a new group (e.g.(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-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 both cases,fact, all the messages thengo onas specified in [PIM-SM] and other specifications (e.g. Register-Stop and/or SPT Join); there is no difference in them except for-- embedded RP just acts as a group-to-RP mapping mechanism; instead of obtaining the fact thataddress of the RP addressfrom local configuration or configuration protocols (e.g., BSR), it is derived transparently from the encoded multicast address. Sometimes, some information, using conventional mechanisms, about another RP exists in the PIM-SM domain. The embedded RP SHOULD be used by default, but there MAY be an option to switch the preference. This is because especially when performing PIM-SM forwarding in the transit networks, the routers must have the same notion of the RP, or else the messages may be dropped. 8. Scalability/Usability Analysis Interdomain MSDP model for connecting8. Scalability/Usability Analysis Interdomain MSDP model for connecting PIM-SM domains is mostly hierarchical.hierarchical in configuration and deployment, but flat with regard to information distribution. The "embeddedembedded 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 robustinter-domain model behaves as the number of third parties is minimized. A good scalability analysis is needed. In some cases (especiallyif e.g. every home user is employing site- local multicast), some degreeall of hierarchy would be highly desirable, for scalability (e.g. to takethe advantage of shared multicast state) and administrative point-of-view. Being able to join/send to remote RPs has security considerations that are considered below, but it has an advantage too: every group hasInternet was a "home RP" which is able to control (to some extent) who are able to send to thesingle PIM domain, with just one RP per group. One should note that the model presented here simplifiesSo, the PIM-SMinter-domain multicast routing model slightly by removing the RP for senders and receivers in foreign domains. One scalability consideration shouldbecomes a flat, RP- centered topology. The scaling issues are be noted: previouslydescribed below. 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 (*, 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- domaininter-domain multicast traffic between sources and the embedded-RPembedded RP will increase compared to the ASM model with MSDP; however, the domain responsible for theMSDP. The embedded RP model is expectedpractically identical in both inter-domain and intra-domain cases to be ablethe traditional PIM-SM in intra-domain. On the other hand, PIM-SM has been deployed (in IPv4) in inter-domain using MSDP; compared to handle this.that inter-domain model, this specification simplifies the multicast routing by removing the RP for senders and receivers in foreign domains. As the address of the RP is tied to the multicast address, inthe case ofRP failure PIM-SM BSRmanagement becomes more difficult, as failover or redundancy mechanisms (e.g., BSR, Anycast-RP with MSDP) cannot pick a new RP; the failover mechanisms, if used, for backup RPs are different, and typically would depend on sharing one address. The failover techniques are outside of the scope of this memo.be used as-is. 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 this"reachable" precisely means is not clear, even without embedded-RP. However, typically thisembedded RP. This statement cannot be proven especially with the foreign RPs (typically one(one can not even guarantee that the RP exists!). The bottom line is that while traditionally the configurationInstead of configuring RPs and DRs was typicallywith a manual process, and e.g. configuringprocess (configuring a non-existantnon-existent RP was possible, but herepossible though rare), with this specification the hosts and users which useusing multicast indirectly specify the RP.RP themselves, lowering the expectancy of the RP reachability. 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 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, 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 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 PIM-SMRP is embeddedencoded 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 to work e.g.e.g., with MSDP, the address would have to be visible anyway (through via other channels, which may be more easily securable).channels). 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 embedencode 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, so that only the pre-agreed sources could use the RP. 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 MSDPtraditional ASM model. However, the traditional ASM model also requires MSDP state to propagate everywhere in inter- domain, so the total amount of state is smaller. One should observe that the embedded RP threat model is actually pretty similar to SSM; both mechanisms significantly reduce the threats at the sender side, but have new ones in the receiver side, as any receiver can try to join any non-existantnon-existent group or channel, and the local DR or RP cannot readily reject such joins (based(e.g., based on MSDP information).information) such joins. RPs maybecome a bit moresingle points of failure as anycast-RP mechanism is not (at least immediately) available. This can be partially mitigated by the fact thatHowever, some other forms of failover are still possible,possible (see Section 6.1) and there should be less need to store state asone can obtain some forms of fate-sharing properties with MSDP.a proper placement of RPs (see Section 6.2). The implementation MUST perform at least the same address validity checks to the embedded RP address as to one received via other means (like BSR or MSDP), to avoid the address being e.g. "::"e.g., "::", "::1", or "::1".a link-local address. A more extensive description and comparison of the inter-domain multicast routing models (traditional ASM with MSDP, embedded RP, SSM) and their security properties has been described 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 [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-farinacci-pim-anycast-rp-00.txt, Januarydraft-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 SourcSource Discovery Protocol (MSDP)", work-in-progress, draft-ietf-msdp-spec-20.txt, MayRFC 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. [SSM] Holbrook, H. et al, "Source-Specific Multicast for IP", work-in-progress, draft-ietf-ssm-arch-03.txt, Maydraft-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. Authors' Addresses Pekka Savola CSC/FUNET Espoo, Finland EMail: firstname.lastname@example.org Brian Haberman Caspian Networks One Park Drive, Suite 300 Research Triangle Park, NC 27709 EMail: email@example.com Phone: +1-919-949-4828 A. Discussion about Design Tradeoffs 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 should be more RPs than the 4-bit "RPad""RIID" allows for, especially if anycast-RP cannot be used. In that light, extending "RPad""RIID" 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 (or 15, if zero is not used) RP addresses. Note that the limit of 4 bits worth of RPs just depends on the prefix the RP address is derived from; one can use multiple prefixes in a domain, and the limit of 16 (or 15) RPs should never really be a problem. 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, whether in the backbone or in the sender's domain, is where the regular PIM-SM RP would be X, and the embedded RP address would be Y. This could e.g. be a result of a default all- multicast-to-one-RP group mapping, or a local policy decision. The embedded RP SHOULD be used by default, but there MAY be an option to change this preference.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 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 be encoded in the RP address somehow, or in the multicast group address. However,Whether this is a good idea is another thing. In any case, such modifications are beyond the scope of this memo. Some kindFor 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 functions, ICMP message responses,or similarother mechanisms could be defined for the case of when the RP embedded indeployed to mitigate the address isthreats while trying not willingto serve fordisturb the specific group (or doesn't even exist). Typically this would resultlegitimate usage. This has been described at more length in the datagrams getting blackholed or rejected[PIMSEC]. The mechanism is not usable with ICMP. In particular, a case for "rejection" or "source quench" -like messages would be inBidirectional PIM without protocol extensions, as pre-computing the case that a source keeps transmitting a huge amount of data, which is sent to a foreign RP using Register message butDesignated Forwarder is discarded ifnot possible. B. Changes since -00 [[ RFC-Editor: please remove before publication ]] o Lots of editorial cleanups, or cleanups without techinical changes. o Reinforce the notion of Embedded RP doesn't allowjust being a group-to-RP mapping mechanism (causing substantive rewriting in section 7); highlight the source host to transmit:fact that precomputing the group-to-RP mapping is not possible. o Add (a bit) more text on RP should be able to indicate toredundancy and deployment tradeoffs wrt. RPs becoming SPoF. o Clarify the DR, "please limitusability/scalability issues in section 8. o Clarify the amount of Register messages", or "this source sending to my group is bogus". Note that such "kiss- of-death" packets have an authentication problem; spoofing them could resultsecurity issues in an entirely different kind of Denial of Service, for legitimate sources. One possibility here would be to specify some form of "return routability" check for DRsSections 8, Security Considerations and RPs; for example, ifAppendix A, mainly by referring to a DR receives packets fromseparate document. o Add a host to group G G (resulting inMUST that embedded RP address R), the DR would send only a limited amount of packets to R until it has heard back from R (a "positive acknowledgement"). It is not clear whether this needs tomappings must be considered or specified in more detail. Could this model work with bidir-PIM? Is it feasible? Not sure, not familiar enough with bidir-PIM.honored by implementations. 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