PIM WG Zheng. Zhang Internet-Draft Fangwei. Hu Intended status: Standards Track BenChong. Xu Expires: June 8, 2017 ZTE Corporation December 5, 2016 PIM DR Improvement draft-ietf-pim-dr-improvement-02.txt Abstract PIM is worldly deployed multicast protocol. This document will improve the stability of PIM protocol, decrease the lost of multicast packets when the PIM DR (Designed Router) is down. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on June 8, 2017. Copyright Notice Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Zhang, et al. Expires June 8, 2017 [Page 1] Internet-Draft PIM DR Improvement December 2016 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. PIM hello message format . . . . . . . . . . . . . . . . . . 3 3.1. DR Address Option format . . . . . . . . . . . . . . . . 3 3.2. BDR Address Option format . . . . . . . . . . . . . . . . 4 4. The Protocol Treatment . . . . . . . . . . . . . . . . . . . 4 4.1. Election Algorithm . . . . . . . . . . . . . . . . . . . 5 4.2. Sending Hello Messages . . . . . . . . . . . . . . . . . 6 4.3. Receiving Hello Messages . . . . . . . . . . . . . . . . 6 4.4. The treatment . . . . . . . . . . . . . . . . . . . . . . 7 5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 8 6. Deployment suggestion . . . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 9. Normative References . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction Multicast technology is used widely. Many modern technology use PIM technology, such as IPTV, Net-Meeting, and so on. There are many events that will influence the quality of multicast services. The change of unicast routes will cause the lost of multicast packets. The change of DR cause the lost of multicast packets too. When a DR on a share-media LAN is down, other routers will elect a new DR until the expiration of Hello-Holdtime. The default value of Hello-Holdtime is 105 seconds. Although the value of Hello-Holdtime can be changed by manual, when the DR is down, there are still many multicast packets will be lost. The quality of IPTV and Net-Meeting will be influenced. \ / \ / ------- ------- | A | | B | ------- ------- | DR | | | ------- ------- | SW |-----------------------------| SW | ------- ------- | | Figure 1: An example of multicast network Zhang, et al. Expires June 8, 2017 [Page 2] Internet-Draft PIM DR Improvement December 2016 For example, there were two routers on one Ethernet. RouterA was elected to DR. When RouterA is down, the multicast packets are discarded until the RouterB is elected to DR and RouterB imports the multicast flows successfully. We suppose that there is only a RouterA in the Ethernet at first in Figure 1. RouterA is the DR which is responsible for forwarding multicast flows. When RouterB connects the Ethernet, RouterB will be elected to DR because a higher priority. So RouterA will stop forwarding multicast packets. The multicast flows will not recover until RouterB joins the multicast group after it is elected to DR. 2. Terminology Backup Designated Router (BDR): A shared-media LAN like Ethernet may have multiple PIM-SM routers connected to it. Except for DR, a router which will act on behalf of directly connected hosts with respect to the PIM-SM protocol. But BDR will not forward the flows. When DR is down, the BDR will forward multicast flows immediately. A single BDR is elected per interface like the DR. 3. PIM hello message format In [RFC4601] and [RFC7761], the PIM hello message format was defined. In this document, we define two new option values which are including Type, Length, and Value. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ | Hello message format | | | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ | OptionType + OptionLength | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ | OptionValue | | | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Figure 2: Hello message format 3.1. DR Address Option format o OptionType : The value is TBD. o OptionLength: If the network is support IPv4, the OptionLength is 4 octets. If the network is support IPv6, the OptionLength is 16 octets. Zhang, et al. Expires June 8, 2017 [Page 3] Internet-Draft PIM DR Improvement December 2016 o OptionValue: The OptionValue is IP address of DR. If the network is support IPv4, the value is IPv4 address of DR. If the network is support IPv6, the value is IPv6 address of DR. 3.2. BDR Address Option format o OptionType : The value is TBD. o OptionLength: If the network is support IPv4, the OptionLength is 4 octets. If the network is support IPv6, the OptionLength is 16 octets. o OptionValue: The OptionValue is IP address of BDR. If the network is support IPv4, the value is IPv4 address of BDR. If the network is support IPv6, the value is IPv6 address of BDR. 4. The Protocol Treatment A new router starts to send hello messages with the values of DR and BDR are all set to 0 after its interface is enabled in PIM on a share-media LAN. When the router receives hello messages from other routers on the same share-media LAN, the router will check if the value of DR is filled. If the value of DR is filled with IP address of router which is sending hello messages, the router will store the IP address as the DR address of this interface. Then the new router compare the priority and IP address itself to the stored IP address of DR and BDR according to the algorithm of [RFC4601] and [RFC7761]. If the new router notices that it is better to be DR than the existed DR or BDR. The router will make itself the BDR, and send new hello messages with its IP address as BDR and existed DR. If the router notices that the existed DR has the highest priority in the share-media LAN, but the existed BDR is set to 0x0 in the received hello messages, or the existed BDR is not better than the new router, the new router will elect itself to BDR. If the router notices that it is not better to be DR than existed DR and BDR, the router will respect the existed DR and BDR. When the new router becomes the new BDR, the router will join the existed multicast groups, import multicast flows from upstream routers. But the BDR MUST not forward the multicast flows to avoid the duplicate multicast packets in the share-media LAN. The new router will monitor the DR. The method that BDR monitors the DR may be BFD technology or other ways that can be used to detect link/node failure quickly. When the DR becomes unavailable because of the down or other reasons, the BDR will forward multicast flows immediately. Zhang, et al. Expires June 8, 2017 [Page 4] Internet-Draft PIM DR Improvement December 2016 4.1. Election Algorithm The DR and BDR election is according the rules defined below, the algorithm is similar to the DR election definition in [RFC2328]. (1) Note the current values for the network's Designated Router and Backup Designated Router. This is used later for comparison purposes. (2) Calculate the new Backup Designated Router for the network as follows. Those routers that have not declared themselves to be Designated Router are eligible to become Backup Designated Router. The one which have the highest priority will be chosen to be Backup Designed Router. In case of a tie, the one having the highest Router ID is chosen. (3) Calculate the new Designated Router for the network as follows. If one or more of the routers have declared themselves Designated Router (i.e., they are currently listing themselves as Designated Router in their Hello Packets) the one having highest Router Priority is declared to be Designated Router. In case of a tie, the one having the highest Router ID is chosen. If no routers have declared themselves Designated Router, assign the Designated Router to be the same as the newly elected Backup Designated Router. (4) If Router X is now newly the Designated Router or newly the Backup Designated Router, or is now no longer the Designated Router or no longer the Backup Designated Router, repeat steps 2 and 3, and then proceed to step 5. For example, if Router X is now the Designated Router, when step 2 is repeated X will no longer be eligible for Backup Designated Router election. Among other things, this will ensure that no router will declare itself both Backup Designated Router and Designated Router. (5) As a result of these calculations, the router itself may now be Designated Router or Backup Designated Router. The reason behind the election algorithm's complexity is the desire for the DR stability. The above procedure may elect the same router to be both Designated Router and Backup Designated Router, although that router will never be the calculating router (Router X) itself. The elected Designated Router may not be the router having the highest Router Priority. If Router X is not itself eligible to become Designated Router, it is possible that neither a Backup Designated Router nor a Designated Router will be selected in the above procedure. Note also that if Router X is the only attached router that is eligible to become Zhang, et al. Expires June 8, 2017 [Page 5] Internet-Draft PIM DR Improvement December 2016 Designated Router, it will select itself as Designated Router and there will be no Backup Designated Router for the network. 4.2. Sending Hello Messages According to Section 4.3.1 in [RFC4601] and [RFC7761], when a new router's interface is enabled in PIM protocol, the router send hello messages with the values of DR and BDR are filled with 0x0. Then the interface is in waiting state and start the hold-timer which is like the neighbor hold-timer. When the hold-timer is expired, the interface will elect the DR and BDR according to the DR election rules. When a new router sets itself BDR after receive hello messages from other routers, the router send hello messages with the value of DR is set to the IP address of existed DR and the value of BDR is set to the IP address of the router itself. When a existed BDR sets itself non DR and non BDR after receive hello messages from other routers, the router will send hello messages with the value of DR is set to existed DR and the value of BDR is set to new BDR. DR newcomer \ / ----- ----- ----- | A | | B | | C | ----- ----- ----- | | | | | | ------------------------------------------- LAN Figure 3 For example, there is a stable LAN that include RouterA and RouterB. RouterA is the DR which has the best priority. RouterC is a newcomer. RouterC sends hello packet with the DR and BDR is all set to zero. If RouterC cannot send hello packet with the DR/BDR capability, Router C may send the hello packet according the rule defined in[RFC4601] and [RFC7761]. 4.3. Receiving Hello Messages When the values of DR and BDR which are carried by hello messages are received is all set to 0x0, the router MUST elect the DR due to the algorithm of [RFC4601] and [RFC7761] after the hold-timer expires. And elect a new BDR which are the best choice except DR. Zhang, et al. Expires June 8, 2017 [Page 6] Internet-Draft PIM DR Improvement December 2016 In case the value of DR which is carried by received hello messages is not 0x0, and the value of BDR is set to 0x0, when the hold-timer expires there is no hello packet from other router is received, the router will elect itself to BDR. In case the values of DR and BDR that are carried by received hello messages are all larger than 0x0. The router will mark the existed DR, and compare itself and the BDR in message. When the router notice that it is better to be DR than existed BDR. The router will elect itself to the BDR. When a router receives a new hello message with the values of DR and BDR are set to 0x0. The router will compare the new router with existed information. If the router noticed that the new router is better to be DR than itself, or the new router is better to be BDR than the existed BDR, the router will set the BDR to the new router. As illustrated in Figure 3, after RouterC sends hello packet, RouterC will not elect the DR until hold-timer expired. During the period, RouterC should receive the hello packets from RouterA and RouterB. RouterC accepts the result that RouterA is the DR. In case RouterC has the lowest priority than RouterA and RouterB, RouterC will also accept that Router B is the BDR. In case RouterC has the intermediate priority among the three routers, RouterC will treat itself as new BDR after the hold-timer expired. In case RouterC has the highest priority among the three routers, RouterC will treat RouterA which is the existed DR as DR, and RouterC will treat itself as new BDR. If the network administrator thinks that RouterC should be new DR, the DR changing should be triggered manually. Exception: During the hold-timer period, RouterC receives only the hello packet from RouterA. When the hold-timer expired, RouterC treats RouterA as DR. and RouterC treats itself as BDR. In case RouterC only receives the hello packet from RouterB during the hold- timer period, RouterC will compare the priority between RouterB and itself to elect the new DR. In these situations, some interfaces or links go wrong in the LAN. 4.4. The treatment When all the routers on a shared-media LAN are start to work on the same time, the election result of DR is same as [RFC4601] and [RFC7761]. And all the routers will elect a BDR which is suboptimum to DR. The routers in the network will store the DR and BDR. The hello messages sent by all the routers are same with the value of DR and BDR are all set. Zhang, et al. Expires June 8, 2017 [Page 7] Internet-Draft PIM DR Improvement December 2016 When a new router start to work on a shared-media LAN and receive hello messages from other routers that the value of DR is set. The new router will not change the existed DR even if it is superior to the existed DR. If the new router is superior to existed BDR, the new router will replace the existed BDR. When the routers receive hello message from a new router, the routers will compare the new router and all the other routers on the LAN. If the new router is superior to existed BDR, the new router will be new BDR. Then the old BDR will send prune message to upstream routers. As a result, the BDR is the one which has the highest priority except DR. Once the DR is elected, the DR will not change until it fails or manually adjustment. After the DR and BDR are elected, the routers in the network will store the address of DR and BDR. 5. Compatibility If the LAN is a hybrid network that there are some routers which have DR/BDR capability and the other routers which have not DR/BDR capability. In order to avoid duplicated multicast flows in the LAN, all the routers should go backward to use the algorithm defined in [RFC4601] and [RFC7761]. 6. Deployment suggestion If there are two and more routers on a share-media LAN, and the multicast services is sensitive to the lost of multicast packets, the function of DR and BDR defined in this document should be deployed. 7. Security Considerations For general PIM Security Considerations. 8. IANA Considerations IANA is requested to allocate OptionTypes in TLVs of hello message. Include DR and BDR. 9. Normative References [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, April 1998, . Zhang, et al. Expires June 8, 2017 [Page 8] Internet-Draft PIM DR Improvement December 2016 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", RFC 4601, DOI 10.17487/RFC4601, August 2006, . [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 2016, . Authors' Addresses Zheng(Sandy) Zhang ZTE Corporation No. 50 Software Ave, Yuhuatai Distinct Nanjing China Email: zhang.zheng@zte.com.cn Fangwei Hu ZTE Corporation No.889 Bibo Rd Shanghai China Email: hu.fangwei@zte.com.cn BenChong Xu ZTE Corporation No. 68 Zijinghua Road, Yuhuatai Distinct Nanjing China Email: xu.benchong@zte.com.cn Zhang, et al. Expires June 8, 2017 [Page 9]