Explaining Multicast Cisco Systems, Inc. All rights reserved. Cisco Academy

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4 Multicast Adoption Past, Present, and Future Research Community MBONE Early Adopters NASA, DOD, Cisco, Microsoft, Sprint Multicast ( ) Corporate Communication HP, IBM, Intel, Ford, BMW, Dupont E Learning 150 Universities in US, Hawaii, Oregon, USC, UCLA, Berkley Financials NASDAQ, NYSE, LIFE, Morgan, GS, Prudential MXU & Content Providers Fastweb, B2, Yahoo, BBC, CNN Surveillance Law Enforcement and Federal IPv6 Multicast NTT, Sony, Panasonic, Multicast VPN C&W, MCI, AT&T, TI, FT, DT, NTT Time 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 4

5 Why Multicast? Used when sending same data a to multiple receivers e Better bandwidth utilization Less host/router processing Used when addresses of receivers unknown Used when simultaneous s delivery er for a group of receivers is required (simulcast) 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 5

traffic redundancy Distributed applications: Makes multipoint

7 Multicast Advantages Enhanced efficiency: Controls network traffic and reduces server and CPU loads Optimized performance: Eliminates traffic redundancy Distributed applications: Makes multipoint applications possible 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 7

8 Other Multicast Advantages For the equivalent amount of multicast traffic, the sender needs much less processing power and bandwidth. Multicast packets do not impose as high a rate of bandwidth utilization as unicast packets, so there is a greater possibility that they will arrive almost simultaneously at the receivers Cisco Systems, Inc. All rights reserved. Cisco Academy 8

9 Multicast Disadvantages Multicast is UDP-based. Best-effort effort delivery Heavy drops in Voice traffic Moderate to Heavy drops in Video No congestion avoidance Duplicate packets may be generated Out-of-sequence delivery may occur Efficiency cy issues in filtering and in security 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 9

10 Types of Multicast Applications One-to-many A single host sending to two or more (n) receivers Many-to-many Audio or video distribution Push media Announcements Monitoring Any number of hosts sending to the same multicast group; hosts are also members of the group (sender = receiver) Many-to-one Collaboration Concurrent processing Distributed interactive simulations Any number of receivers sending data back to a source (via unicast or multicast) Resource discovery Data collection Auctions Polling 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 10

14 Multicast Addressing IPv4 Header Version IHL Type of Service Total Length Identification Flags Fragment Offset Time to Live Protocol Header Checksum Source Source Address (Class A, B, C) Destination Destination Address (Class D) Multicast Group Address Range Options Padding 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 14

15 IP Multicast Address Groups Local scope addresses, reserved by IANA for network protocol use to Global scope addresses are allocated dynamically throughout the Internet to Administratively scoped addresses are reserved for use inside of private domains to Cisco Systems, Inc. All rights reserved. Cisco Academy 15

16 Local Scope Addresses Well-known addresses assigned by IANA Reserved use: through (all multicast systems on subnet) (all routers on subnet) (all Distance Vector Multicast Routing Protocol (DVMRP) (all OSPF Routers on a subnet) (all OSPF DRs on a subnet) (all RIPv2 routers on a subnet) (all EIGRP routers on a subnet) (all PIMv2 routers) 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 16

17 Global Scope Addresses Transient addresses, assigned and reclaimed dynamically (within applications): Global scope range: X.X usually used in MBONE applications Some of these addresses have been registered with IANA, for example IP address has been reserved for Network Time Protocol (NTP). Applications that t use multicast t addresses in the / /32, /23, 22/23 and /32 ranges have been demonstrated to be vulnerable to exploitation, which has led to serious security problems. Addresses in the to range are reserved for Source Specific Multicast (SSM). SSM is an extension of Protocol Independent Multicast (PIM), which allows for an efficient data delivery mechanism in one-to-many communications Cisco Systems, Inc. All rights reserved. Cisco Academy 17

18 Administratively Scoped Addresses Transient addresses, assigned and reclaimed dynamically (within applications): Limited (local) scope: /8 00/8 for private IP multicast addresses (RFC-2365) Site-local scope: /16 Organization-local scope: to Cisco Systems, Inc. All rights reserved. Cisco Academy 18

20 IANA Ethernet MAC Address Range IANA owns a block of Ethernet MAC addresses that start with E00 in hexadecimal format. Half of this block is allocated for multicast addresses. The range from e through h e7f.ffff ffff is the available range of Ethernet MAC addresses for IP multicast e through e-7f-ff-ff00 ff ff 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 20

21 IANA Ethernet MAC Address Range Available range of MAC addresses for IP multicast : : : : : through : : : : : Within this range, these MAC addresses have the first 25 bits in common. The remaining 23 bits are available for mapping to the lower 23 bits of the IP multicast group address Cisco Systems, Inc. All rights reserved. Cisco Academy 21

23 Multicast Addressing IP Multicast MAC Address Mapping (FDDI & Ethernet) Be Aware of the 32:1 Address Overlap 32 - IP Multicast Addresses Multicast MAC Address (FDDI and Ethernet). 0x0100.5E Cisco Systems, Inc. All rights reserved. Cisco Academy 23

Madcap in MS Server Multicast Address Dynamic Client Allocation Protocol (MADCAP) allows a client workstation to

24 Madcap in MS Server Multicast Address Dynamic Client Allocation Protocol (MADCAP) allows a client workstation to lease a multicast address from a MADCAP server in a manner similar to how it leases an IP address from a DHCP server. When a MADCAP client workstation wants to lease a multicast address, first it must locate the nearest MADCAP Servers. This is accomplished by multicasting a MADCAP DISCOVER message to the MADCAP Scope Relative multicast address (-1) in the Site-Local scope, (for instance, ). (Note: This is why it is important to adhere to the conventions for the Site-Local scope defined in RFC 2365.) 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 24

25 How are Multicast Addresses Assigned? Static Global Group Address Assignment Temporary method to meet immediate needs Group range: Your AS number is inserted in middle two octets Remaining low-order octet used for group assignment For example, AS is written in hexadecimal format as "F23A." This value is separated into two parts, F2 and 3A and those numbers, converted to decimal would be 242 and 58. This would yield a multicast GLOP address of /24. Defined in RFC 2770 GLOP Addressing in 233/8 Manual address allocation by the admin is still the most common practice Cisco Systems, Inc. All rights reserved. Cisco Academy 25

26 Learning About Multicast Sessions Potential receivers have to learn about multicast streams or sessions available before a multicast t application is launched. Possibilities: Another multicast application sending to a well-known group whose members are all potential receivers Directory services Web page, Session Announcement Protocol (SAP) 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 26

sdr Session Directory The Session Directory y( (sd)) application acts as a guide,

A client application runs on a PC and lets the user know what content is available.

Announcement Protocol (SAP) to learn about the content.

(referred to in this course as SDR ), which is an applications tool that allows the

27 sdr Session Directory The Session Directory y( (sd)) application acts as a guide, displaying multicast content. A client application runs on a PC and lets the user know what content is available. This directory application uses either Session Description Protocol (SDP) or Session Announcement Protocol (SAP) to learn about the content. The original sd application served as a means to announce available sessions and to assist in creating new sessions. The initial sd tool was revised, resulting in the Session Description Protocol tool (referred to in this course as SDR ), which is an applications tool that allows the following: Session description and its announcement Transport of session announcement via well-known multicast groups ( ) Creation of new sessions 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 27

A Cisco IP/TV Example The SDR mechanisms are shown in this Cisco IP/TV example.

server ) Viewer (the receiver) The Viewers can either: Contact the Content Manager directly (by

periodic SAP announcements Cisco IP/TV uses SAP to transport the SDR sessions to the viewer.

28 A Cisco IP/TV Example The SDR mechanisms are shown in this Cisco IP/TV example. Cisco IP/TV generally has three components: Server (the source) Content Manager (the directory server ) Viewer (the receiver) The Viewers can either: Contact the Content Manager directly (by unicast) and request the list of available programs (sessions, streams) from it Listen to periodic SAP announcements Cisco IP/TV uses SAP to transport the SDR sessions to the viewer. The standard SDR format for session description is used Cisco Systems, Inc. All rights reserved. Cisco Academy 28

IGMP Overview IGMP Joining/Leaving Multicast Groups 2008

32 Controlling Multicasts IGMP IGMP Internet Group Management Protocol Used primarily by multicast hosts to signal their local multicast router they wish to join a specific multicast group IGMP IGMP Join/Leave Receiver 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 32

33 IGMP Multicasting on a single physical segment is simple. Multicast Traffic Sender Multicast Traffic Receiver The sender (server) specifies a destination multicast address and the receiving devices (clients) indicate that they want to receive these packets for a given multicast address (and port). The application at both ends handles this Cisco Systems, Inc. All rights reserved. Cisco Academy 33

34 IGMP Complications arise when multicasting is extended beyond a single physical network and multicast packets pass through routers. Multicast Traffic Multicast Traffic Sender IGMP Join/Leave Receiver Sending and receiving multicast traffic requires coordination from all devices participating in the multicast. Before multicast traffic can traverse the network, routers need to know which hosts (if any) on a specific physical network belong to a given multicast group Cisco Systems, Inc. All rights reserved. Cisco Academy 34

35 Internet Group Management Protocol (IGMP) How hosts tell routers about group membership Routers solicit group membership from directly connected hosts RFC 1112 specifies IGMPv1 Supported by Win95, Unix, etc. No way to expressly leave a multicast group. It s up to the router to timeout the group membership RFC 2236 specifies IGMPv2 Supported by Win98, 2k, latest Win95/UNIX updates Includes leave processing mechanism 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 35

36 Internet Group Management Protocol (IGMP) How hosts tell routers about group membership IGMP v3lite Host Signalling IGMP v3lite is a Cisco-developed transitional solution for application developers to immediately start programming SSM applications. It allows you to write and run SSM applications on hosts that do not yet support IGMPv3 in their operating system kernel. Applications must be compiled with the Host Side IGMP Library (HSIL) for IGMP v3lite. This software provides applications with a subset of the IGMPv3 applications programming interface (API) that is required to write SSM applications. HSIL was developed for Cisco by Talarian and is available from the following web page: RFC 3376 specifies IGMPv3 Supports "source filtering," which enables a multicast receiver host to signal to a router which groups it wants to receive multicast traffic from, and from which source(s) this traffic is expected. In addition, IGMPv3 supports the link local address , which is the destination IP address for IGMPv3 membership reports; all IGMPv3-capable multicast routers must listen to this address Cisco Systems, Inc. All rights reserved. Cisco Academy 36

37 IGMPv1 - RFC 1112 With IGMPv1, routers send periodic membership queries to the multicast address Hosts send membership reports to the group multicast address they want to join; hosts silently leave the multicast group. In IGMPv1, there is no election of an IGMP querier. If more than one router on the segment exists, all the routers send periodic IGMP queries. If there are multiple routers on a LAN, a designated router (DR) must be elected to avoid duplicating multicast traffic for connected hosts. PIM routers follow an election process to select a DR. The PIM router with the highest IP address becomes the DR. The DR is responsible for the following tasks: Sending PIM register and PIM Join and Prune messages toward the rendezvous point (RP) to inform it about host group membership. Sending IGMP host-query messages. Sending host-query messages by default every 60 seconds in order to keep the IGMP overhead on hosts and networks very low Cisco Systems, Inc. All rights reserved. Cisco Academy 37

38 IGMPv2 RFC 2236 Group-specific query Router sends query membership message to a single group rather than all hosts (reduces traffic). Leave group message Host sends leave message if it leaves the group and is the last member (reduces leave latency in comparison to v1). Query-interval response time The Query router sets the maximum Query-Response time (controls burstiness and fine-tunes nes leave e latencies). Querier election process IGMPv2 routers can elect the Query Router without relying on the multicast routing protocol Cisco Systems, Inc. All rights reserved. Cisco Academy 38

IGMPv2 Leaving a Group (Cont.) Hosts H2 and H3 are members of group 224.1.1.1. 1.

43 Slide 42 KA1 In the original slide the screen of computer H3 was a different color to bring it to the attention of the learner. Please change the screen color of computer H3 from the light teal color to a white. Karen Alderson, 10/19/2006

47 Unlike IGMPv1, inwhichthedr and the IGMP querier are typically the same router, inigmpv2 the two functions are decoupled. TheDR and the IGMP querier are selected based on different criteria and may be different routers on the same subnet. The DR is the router with the highest IP address on the subnet, whereas the IGMP querier is the router with the lowest IP address. Query messages are used to elect the IGMP querier as follows: 1. When IGMPv2 routers start, they each multicast a general query message to the all-systems group address of with their interface address in the source IP address field of the message. 2. When an IGMPv2 router receives a general query message, the router compares the source IP address in the message with its own interface address. The router with the lowest IP address on the subnet is elected the IGMP querier. 3. All routers (excluding the querier) start the query timer, whichis reset whenever a general query message is received from the IGMP querier. If the query timer expires, it is assumed that the IGMP querier has gone down, and the election process is performed again toelect anew IGMP querier. By default, the timer is two times the query interval Cisco Systems, Inc. All rights reserved. Cisco Academy 46

48 Routers Running IGMPv3 IGMPv3 adds support in Cisco IOS software for source filtering, which enables a multicast receiver host to signal to a router which groups it wants to receive multicast traffic from, and from which sources this traffic is expected. IGMPv3 supports applications that explicitly signal sources from which they want to receive traffic. With IGMPv3, receivers signal membership to a multicast group in the following two modes: INCLUDE mode - In this mode, the receiver announces membership to a group and provides a list of IP addresses (the INCLUDE list) fromwhich it wants to receive traffic. EXCLUDE mode - In this mode, the receiver announces membership to a group and provides a list of IP addresses (the EXCLUDE list) fromwhich it does not want to receive traffic Cisco Systems, Inc. All rights reserved. Cisco Academy 47

51 IGMPv3 Maintaining Maintaining State Router sends periodic queries: All IGMPv3 members respond. Reports contain multiple group state records Cisco Systems, Inc. All rights reserved. Cisco Academy 50

52 Multicast Listener Discovery Protocol RFC 2710 defines specifications for the Multicast Listener Discovery (MLD) protocol.mld is derived from IGMPv2 and is designed for IPv6. The operation of MLD is similar to IGMPv2. The major differences between IGMPv2 and MLD are as follows: All the multicast devices on a subnet use a special IPv6 link-local address as their source address in their communication to other multicast devices. The use of the link-local source address prevents the MLD packet from traveling beyond the local link. In MLD, when a host wants to leave a group, it sends a Done message. The Done message is similar to the IGMPv2 Leave message. It is addressed to the all-routers IPv6 link-local scope address, FF02::2. In MLD, the router Queries are called Multicast Listener Queries. The General Queries are addressed to the all-nodes IPv6 link-local scope address, FF02::1. When a router receives a Done message, itsendsa Multicast-Address-Specific Query. Its function is similar to IGMPv2 Group-Specific Query Cisco Systems, Inc. All rights reserved. Cisco Academy 51

Determining IGMP Version Running Determining which IGMP version is running on an interface. rtr-a>show ip igmp interface e0 Ethernet0 is up, line protocol is up Internet address is 1.

53 Determining IGMP Version Running Determining which IGMP version is running on an interface. rtr-a>show ip igmp interface e0 Ethernet0 is up, line protocol is up Internet address is , subnet mask is IGMP is enabled on interface Current IGMP version is 2 CGMP is disabled on interface IGMP query interval is 60 seconds IGMP querier timeout is 120 seconds IGMP max query response time is 10 seconds Inbound IGMP access group is not set Multicast routing is enabled on interface Multicast TTL threshold is 0 Multicast designated router (DR) is (this system) IGMP querying router is (this system) Multicast groups joined: Cisco Systems, Inc. All rights reserved. Cisco Academy 52

Static entries may sometimes be set to specify which ports receive which groups of multicast traffic.

55 Layer 2 Multicast Frame Switching Problem: Layer 2 flooding of multicast frames Typical Layer 2 switches treat multicast traffic as unknown or broadcast and must flood the frame to every port (in VLAN). Static entries may sometimes be set to specify which ports receive which groups of multicast traffic. Dynamic configuration of these entries may reduce administration Cisco Systems, Inc. All rights reserved. Cisco Academy 54

56 Layer 2 Multicast Switching Solutions 1. Cisco Group Management Protocol (CGMP): Simple, proprietary; routers and switches 2. IGMP snooping: With IGMP snooping, the switch intercepts IGMP messages from the host and updates the MAC table accordingly. To implement IGMP snooping without suffering switch performance loss, it is necessary to make the switch Layer 3-aware. This result is typically accomplished by using Layer 3 ASICs Cisco Systems, Inc. All rights reserved. Cisco Academy 55

CGMP packet contains: Type field: join or leave MAC address of the IGMP client Multicast MAC address of the group

57 Layer 2 Multicast Frame Switching CGMP Solution 1: CGMP Runs on switches and routers. CGMP packets sent by routers to switches at the CGMP multicast MAC address of cdd.dddd. CGMP packet contains: Type field: join or leave MAC address of the IGMP client Multicast MAC address of the group Switch uses CGMP packet information to add or remove an entry for a particular multicast MAC address Cisco Systems, Inc. All rights reserved. Cisco Academy 56

58 CGMP CGMP CGMP IGMP Non-Receiver CGMP Multicast Traffic Receiver When the router sees an IGMP packet, the router creates a CGMP packet. This CGMP packet contains the request type, either a join or a leave, the multicast group address, and the actual MAC address of the client (from the Source MAC address in the Ethernet frame). The packet is sent to a well-known address (0x0100.0cdd.dddd) to which all switches listen. Each switch then interprets the packet and creates the proper entries in a forwarding table. The important information in the CGMP messages is one or more pairs of MAC addresses: Group Destination Address (GDA) Unicast Source Address (USA) 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 57

59 CGMP Join The IGMP membership report is received by the Layer 2 switch and forwarded to the CGMP server for normal IGMP processing. The CGMP server, receives the membership report and translates the report into a CGMP join message. It sends the CGMP join message to the switch through the well-known CGMP multicast MAC address (0x0100.0cdd.dddd). When the Layer 2 switch receives the join message, it updates its forwarding table to include the MAC-equivalent of the group destination address and the applicable input and output switch ports Cisco Systems, Inc. All rights reserved. Cisco Academy 58

Effect on switch without Layer 3-aware Hardware/ASICs Must process all Layer 2 multicast packets Administration i ti load increased with

60 IGMP Snooping Solution 2: IGMP snooping Switches become IGMP-aware. IGMP packets are intercepted by the CPU or by special hardware ASICs. Switch examines contents of IGMP messages to learn which ports want what traffic. Effect on switch without Layer 3-aware Hardware/ASICs Must process all Layer 2 multicast packets Administration i ti load increased with multicast t traffic load Effect on switch with Layer 3-aware Hardware/ASICs Maintain high-throughput performance but cost of switch increases 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 59

IGMP Snooping H1 sends an IGMP Join message for 226.

SW1 receives the packet on its fa0/1 port and, noticing that it is an IGMP packet, forwards the packet

61 IGMP Snooping H1 sends an IGMP Join message for At Layer 2, H1 uses the multicast MAC address 0x0100.5e (the MAC for group ) as the destination address and uses its own BIA as the source address. SW1 receives the packet on its fa0/1 port and, noticing that it is an IGMP packet, forwards the packet to the switch CPU Cisco Systems, Inc. All rights reserved. Cisco Academy 60

62 IGMP Snooping H2 sends an IGMP Join message for AtLayer2, H2 uses the multicast MAC address 0x0100.5e as the destination address and uses its own BIA as the source address. SW1 receives the packet on its fa0/2 port, and its switching engine examines the packet. The process of analyzing the packet, as described in Step 1, is repeated and the CAM table entries are updated as shown Cisco Systems, Inc. All rights reserved. Cisco Academy 61

IGMP Snooping Router R1 forwards the group traffic. R1 is receiving multicast traffic for group 226.6.6.6 and starts forwarding the traffic to SW1.

63 IGMP Snooping Router R1 forwards the group traffic. R1 is receiving multicast traffic for group and starts forwarding the traffic to SW1. SW1 starts receiving the multicast traffic on its port fa0/8. The switching engine would examine the packet and determine that this is a non-igmp packet, search its CAM table, and determine that it should forward the packet on ports fa0/1 and fa0/ Cisco Systems, Inc. All rights reserved. Cisco Academy 62

64 IGMPv3 and IGMP Snooping Impact of IGMPv3 on IGMP Snooping IGMPv3 Reports are sent to a separate group ( ) reduces load on switch CPU No Report Suppression in IGMPv3 IGMP Snooping should not cause a serious performance problem once IGMPv3 is implemented Cisco Systems, Inc. All rights reserved. Cisco Academy 63

66 Multicast Protocol Basics Types of multicast distribution trees: Source distribution trees; also called shortest path trees (SPTs) Shared distribution trees; rooted at a meeting point in the network A core router serves as a rendezvous point (RP) 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 65

67 Multicast Distribution Trees Shortest Path or Source Distribution Tree Source 1 Notation: (S, G) S = Source G = Group Source 2 A B D F C E Receiver 1 Receiver Cisco Systems, Inc. All rights reserved. Cisco Academy 66

68 Multicast Distribution Trees Shortest Path or Source Distribution Tree Source 1 Notation: (S, G) S = Source G = Group Source 2 A B D F C E Receiver 1 Receiver Cisco Systems, Inc. All rights reserved. Cisco Academy 67

69 Multicast Distribution Trees Shared Distribution Tree Notation: (*, G) * = All Sources G = Group A B D (RP) F C E (RP) PIM Rendezvous Point Shared Tree Receiver 1 Receiver Cisco Systems, Inc. All rights reserved. Cisco Academy 68

70 Multicast Distribution Trees Shared Distribution Tree Source 1 Notation: (*, G) * = All Sources G = Group Source 2 A B D (RP) F C E (RP) PIM Rendezvous Point Shared Tree Source Tree Receiver 1 Receiver Cisco Systems, Inc. All rights reserved. Cisco Academy 69

71 Multicast Distribution Tree Identification (S,G) entries For this particular source sending to this particular group Traffic is forwarded through the shortest path from the source (*,G) entries For any (*) source sending to this group Traffic is forwarded d through h a meeting point for this group 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 70

72 Multicast Distribution Trees Characteristics of Distribution Trees Source or Shortest Path trees Uses more memory but optimal paths from source to all receivers; minimizes delay Shared trees Uses less memory but sub-optimal paths from source to all receivers; may introduce extra delay 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 71

74 Protocols for IP Multicast Routing PIM is used between routers so that they can track which multicast li packets to forward to each other and to their directly connected LANs Cisco Systems, Inc. All rights reserved. Cisco Academy 73

75 Protocol-Independent Multicast (PIM) PIM maintains the current IP multicast service mode of receiver-initiated initiated membership. PIM is not dependent on a specific unicast routing protocol. With PIM, routers maintain forwarding tables to forward multicast datagrams. PIM can operate in dense mode or sparse mode. Dense mode protocols flood multicast traffic to all parts of the network and prune the flows where there are no receivers using a periodic flood-and-prune mechanism. Sparse mode protocols use an explicit join mechanism where distribution trees are built on demand by explicit tree join messages sent by routers that have directly connected receivers Cisco Systems, Inc. All rights reserved. Cisco Academy 74

76 Multicast Tree Creation PIM Join/Prune Control Messages Used to create/remove Distribution Trees Shortest Path trees PIM control messages are sent toward the Source Shared trees PIM control messages are sent toward RP 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 75

77 Multicast Forwarding Multicast routing operation is the opposite of unicast routing. Unicast routing is concerned with where the packet is going. Multicast routing is concerned with where the packet comes from. Multicast routing uses Reverse Path Forwarding (RPF) to prevent forwarding loops Cisco Systems, Inc. All rights reserved. Cisco Academy 76

78 Reverse Path Forwarding (RPF) The RPF Calculation The multicast source address is checked against the unicast routing table. This determines the interface and upstream router in the direction of the source to which PIM Joins are sent. This interface becomes the Incoming or RPF interface. A router forwards a multicast datagram only if received on the RPF interface Cisco Systems, Inc. All rights reserved. Cisco Academy 77

79 Reverse Path Forwarding (RPF) RPF Calculation Based on Source Address. Best path to source found in Unicast Route Table. Determines where to send Joins. Joins continue towards Source to build multicast tree. Multicast data flows down tree. Unicast Route Table Network Interface /24 E0 E0 Join Join E2 E Cisco Systems, Inc. All rights reserved. Cisco Academy 78

Reverse Path Forwarding (RPF) RPF Calculation (cont.) Repeat for other receivers 10

Reverse Path Forwarding (RPF) RPF Calculation What if we have equal-cost paths? We can t use both. Tie-Breaker Use highest Next-Hop IP address. 10.1.1.1 1.1.1.1 E0 Join E1 1.

81 Reverse Path Forwarding (RPF) RPF Calculation What if we have equal-cost paths? We can t use both. Tie-Breaker Use highest Next-Hop IP address E0 Join E Unicast Route Table Network Intfc Nxt-Hop 10100/ /24 E /24 E E Cisco Systems, Inc. All rights reserved. Cisco Academy 80

82 Multicast Distribution Tree Creation PIM uses both source trees and RP-rooted shared trees to forward datagrams; the RPF check is performed differently for each, as follows: If a PIM router has source-tree state (that is, an (S,G) entry is present in the multicast routing table), the router performs the RPF check against the IP address of the sourceof the multicast packet. If a PIM router has shared-tree state t (and no explicit it source-tree state), it performs the RPF check on the RP's address (which is known when members join the group) Cisco Systems, Inc. All rights reserved. Cisco Academy 81

88 PIM Sparse Mode PIM-SM supports both source and shared trees. PIM-SM is based on an explicit pull model. PIM-SM uses an RP. Senders and receivers meet each other. Senders are registered with RP by their first-hop router. Receivers are joined to the shared tree (rooted at the RP) by their local DR Cisco Systems, Inc. All rights reserved. Cisco Academy 87

90 PIM-SM Sender Registration Source RP Traffic Flow Shared Tree Source Tree (S, G) Register (S, G) Join (unicast) Receiver (S, G) State created only along the Source Tree Cisco Systems, Inc. All rights reserved. Cisco Academy 89

91 PIM-SM Sender Registration Source RP Traffic Flow Shared Tree Source Tree (S, G) Register (S, G) Register-Stop (unicast) (unicast) Receiver (S, G) traffic begins arriving at the RP through the Source tree. RP sends a Register-Stop back to the first-hop router to stop the Register process Cisco Systems, Inc. All rights reserved. Cisco Academy 90

92 PIM-SM Sender Registration Source RP Traffic Flow Shared Tree Source Tree Source traffic flows natively along SPT to RP. From RP, traffic flows down the Shared Tree to Receivers. Receiver 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 91

93 PIM-SM SPT Switchover Source RP Traffic Flow Shared Tree Source Tree (S, G) Join Receiver Last-hop router joins the Source Tree. Additional (S, G) State is created along new part of the Source Tree Cisco Systems, Inc. All rights reserved. Cisco Academy 92

94 PIM-SM SPT Switchover Source RP Traffic Flow Shared Tree Source Tree (S, G)RP-bit Prune Receiver Traffic begins flowing down the new branch of the Source Tree. Additional (S, G) State is created along the Shared Tree to prune off (S, G) traffic Cisco Systems, Inc. All rights reserved. Cisco Academy 93

95 PIM-SM SPT Switchover Source RP Traffic Flow Shared Tree Source Tree Receiver (S, G) Traffic flow is now pruned off of the Shared Tree and is flowing to the Receiver through the Source Tree Cisco Systems, Inc. All rights reserved. Cisco Academy 94

96 PIM-SM SPT Switchover Source RP Traffic Flow Shared Tree Source Tree (S, G) Prune Receiver (S, G) traffic flow is no longer needed by the RP so it Prunes the flow of (S, G) traffic Cisco Systems, Inc. All rights reserved. Cisco Academy 95

97 PIM-SM SPT Switchover Source RP Traffic Flow Shared Tree Source Tree Receiver (S, G) Traffic flow is now only flowing to the Receiver through a single branch of the Source Tree Cisco Systems, Inc. All rights reserved. Cisco Academy 96

98 PIM-SM Evaluation Effective for Sparse or Dense distribution of multicast receivers Advantages: Traffic only sent down joined branches Can switch to optimal source-trees for high traffic sources dynamically Unicast routing protocol-independent Basis for inter-domain multicast routing 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 97

101 Enabling IP Multicast Routing router(config)# ip multicast-routing Enables multicast t routing. Enabling IP multicast routing allows the Cisco IOS software to forward multicast packets Cisco Systems, Inc. All rights reserved. Cisco Academy 100

102 Enabling PIM on an Interface router(config-if)# ip pim { sparse-mode sparse-dense-mode } Enables PIM SM on an interface; the sparse-dense-mode option enables mixed sparse-dense groups. Enabling PIM on an interface also enables IGMP operation on that interface. Recommended method is to use sparse-dense-mode option Cisco Systems, Inc. All rights reserved. Cisco Academy 101

103 Announcing the RP and the Group Range It Serves router(config)# ip pim send-rp-announce {interface type} scope {ttl} group-list {acl} Configures a router to be the RP for the local group as defined in the access list. The following example advertises the IP address of Ethernet t 0 as the RP for the administratively i ti scoped groups: router(config)# ip pim send-rp-announce ethernet0 scope 16 group-list 1 access-list 1 permit This router sends an Auto-RP message to , announcing the router as a candidate RP for the groups in the range described by the access list Cisco Systems, Inc. All rights reserved. Cisco Academy 102

104 Assigning the RP Mapping Agent router(config)# ip pim send-rp-discovery {interface type} scope {ttl} The RP mapping agent is the router that tells other routers which group-to-rp range to use. Such a role is necessary in the event of conflicts (such as overlapping group-to-rp ranges). Find a router whose connectivity is not likely to be interrupted and assign it the role of RP-mapping agent. All routers within ttl number of hops from the source router receive the Auto-RP Discovery messages Cisco Systems, Inc. All rights reserved. Cisco Academy 103

105 Dense Mode Cisco recommends that you use Protocol Independent Multicast (PIM) sparse mode, particularly Auto-RP, where possible and especially for new deployments. However, if dense mode is desired, configure the global command ip multicast-routing and the interface command ip pim sparse-dense-mode on each interface that needs to process multicast traffic. As of Cisco IOS Sotware Release 11.1, you can configure the interface commands ip pim dense-mode and ip pim sparse-mode simultaneously with the ip pim sparse-dense-mode command. In this mode, the interface is treatedt as dense-moded if the group is in densemode. If the group is in sparse-mode (for example, if an RP is known), the interface is treated as sparse-mode Cisco Systems, Inc. All rights reserved. Cisco Academy 104

106 Dense Mode Note: The "Source" in the examples throughout this document represents the source of multicast traffic, and "Receiver" represents the receiver of multicast traffic. ip multicast-routing interface ethernet0 ip address <address> <mask> ip pim sparse-dense-mode interface serial0 ip address <address> <mask> ip pim sparse-dense-mode ip multicast-routing interface serial0 ip address <address> <mask> ip pim sparse-dense-mode interface ethernet0 ip address <address> <mask> ip pim sparse-dense-mode 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 105

107 Sparse Mode with one RP In this example, Router A is the RP which is typically the closest router to the source. Static RP configuration requires that all routers in the PIM domain have the same ip pim rp-address commands configured. You can configure multiple RPs, but there can only be one RP per specific group. ip multicast-routing ip pim rp-address interface ethernet0 ip address <address> <mask> ip pim sparse-dense-mode d ip multicast-routing ip pim rp-address interface serial0 ip address <address> <mask> ip pim sparse-dense-mode d interface serial0 interface ethernet0 ip address ip address <address> <mask> ip pim sparse-dense dense-mode ip pim sparse-dense dense-mode 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 106

108 Sparse Mode with Multiple RPs In this example, Source-A sends to , , and Source-B sends to , , and You could have one router, either RP 1 or RP 2, betherp for all groups. However, if you want different RPs to handle different groups, you need to configure all routers to include which groups the RPs will serve. This type of static RP configuration requires that all routers in the PIM domain have the same ip pim rp-address address acl commands configured. You can also use Auto-RP in order to achieve the same setup, which is easier to configure Cisco Systems, Inc. All rights reserved. Cisco Academy 107

109 ip multicast-routing ip pim RP-address ippim RP-address access-list 2 permit access-list 2 permit access-list 2 permit access-list 3 permit access-list 3 permit access-list 3 permit ip multicast-routing ip pim RP-address ip pim RP-address access-list 2 permit access-list 2 permit access-list 2 permit access-list 3 permit access-list 3 permit access-list 3 permit ip multicast-routing ip pim RP-address ip pim RP-address access-list 2 permit access-list 2 permit access-list 2 permit access-list 3 permit access-list 3 permit access-list 3 permit Cisco Systems, Inc. All rights reserved. Cisco Academy 108

110 Auto-RP with one RP Auto-RP requires that you configure the RPs to announce their availability as RPs and mapping agents. The RPs use to send their announcements. The RP mapping agent listens to the announced packets from the RPs, then sends RP-to-group mappings in a discovery message that is sent to These discovery messages are used by the remaining routers for their RP-to-group map. You can use one RP thatt also serves as the mapping agent, or you can configure multiple RPs and multiple mapping agents for redundancy purposes Cisco Systems, Inc. All rights reserved. Cisco Academy 109

111 Auto-RP with one RP Note that when you choose an interface from which h to source RP announcements, Cisco recommends that you use an interface such as a loopback instead of a physical interface. The loopback interface must be PIM-enabled and advertised by an Interior Gateway Protocol (IGP), or it must be reachable with static routing Cisco Systems, Inc. All rights reserved. Cisco Academy 110

112 Auto-RP with one RP ip multicast-routing ip pim send-rp-announce loopback0 scope 16 (RP) ip pim send-rp-discovery scope 16 (Mapping agent) interface loopback0 ip address <address> <mask> ip pim sparse-dense-mode interface ethernet0 ip address <address> <mask> ip pim sparse-dense-mode ip multicast-routing interface ethernet0 ip address <address> <mask> ip pim sparse-dense-mode interface serial0 ip address <address> <mask> ip pim sparse-dense-mode interface serial0 ip address <address> <mask> ip pim sparse-dense-mode 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 111

113 Auto-RP with Multiple RPs The access lists in this example allow the RPs to be an RP only for the groups you want. If no access list is configured, therpsareavailableasanrpfor all groups. If two RPs announce their availability to be RPs for the same group(s), the mapping agent(s) resolve these conflicts with "the highest IP address wins" rule. When two RPs announce for that group, you can configure each router with a loopback address in order to influence which router is the RP for a particular group. Place the higher IP address on the preferred RP, then use the loopback interface as the source of the announce packets; for example, ip pim send-rp-announce loopback0. When multiple mapping agents are used, they each advertise the same group to RP mappings to the discovery group Cisco Systems, Inc. All rights reserved. Cisco Academy 112

114 Auto-RP with Multiple RPs ip multicast-routing interface loopback0 ip address <address> <mask> ip pim sparse-dense-mode ip pim send-rp-announce loopback0 scope 16 group-list 1 ip pim send-rp-discovery scope 16 access-list 1 permit Cisco Systems, Inc. All rights reserved. Cisco Academy 113

115 Auto-RP with Multiple RPs ip multicast-routing interface loopback0 ip address <address> <mask> ip pim sparse-dense-mode ip pim send-rp-announce loopback0 scope 16 group-list 1 ip pim send-rp-discovery scope 16 access-list 1 deny access-list 1 permit Cisco Systems, Inc. All rights reserved. Cisco Academy 114

116 Anycast RP MSDP Example The main purpose of an Anycast RP implementation is that the downstream multicast routers will see just one address for an RP. The example given shows how the loopback 0 interface of the RPs (RP1 and RP2) is configured with the same IP address. If this address is configured on all RPs as the address for the loopback 0 interface and then configured as the RP address, IP routing will converge on the closest RP. This address must be a host route - note the subnet mask/32. The downstream routers must be informed about the RP address. In Figure, the routers are configured statically with the ip pim rp-address global configuration command. This configuration could also be accomplished using the Auto-RP or bootstrap router (BSR) features Cisco Systems, Inc. All rights reserved. Cisco Academy 115

118 Inspecting Multicast Routing Table router# show ip mroute [group-address] [summary] [count] [active kbps] Displays the contents of the IP multicast routing table summary: Displays a one-line, abbreviated summary of each entry in the IP multicast routing table. count: Displays statistics about the group and source, including number of packets, packets per second, average packet size, and bits per second. active: Displays the rate at which active sources are sending to multicast t groups. Active sources are those sending at a rate specified in the kbps argument or higher. The kbps argument defaults to 4 kbps Cisco Systems, Inc. All rights reserved. Cisco Academy 117

119 show ip mroute NA-1#sh ip mroute IP Multicast Routing Table Flags: D - Dense, S - Sparse, B - Bidir Group, s - SSM Group, C - Connected L - Local, P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running, A - Advertised via MSDP, U - URD, I - Received Source Specific Host Report Outgoing interface flags: H - Hardware switched Timers: Uptime/Expires Interface state: Interface, Next-Hop or VCD, State/Mode (*, ), 00:07:54/00:02:59, RP , flags: S Incoming interface: Null, RPF nbr Outgoing interface list: Serial1/3, Forward/Sparse, 00:07:54/00:02:32 ( , ), 00:01:29/00:02:08, flags: TA Incoming interface: Serial1/4, RPF nbr Outgoing interface list: Serial1/3, Forward/Sparse, 00:00:57/00:02: Cisco Systems, Inc. All rights reserved. Cisco Academy 118

120 Finding PIM Neighbors router# show ip pim interface [type number] [count] Displays information about interfaces configured for PIM router# show ip pim neighbor [type number] Lists the PIM neighbors discovered by the router router# mrinfo [hostname address] Queries which neighboring g multicast routers are peering with the local router or router specified 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 119

121 show ip pim interface NA-2#show ip pim interface Address Interface Ver/ Nbr Query DR DR Mode Count Intvl Prior Serial0/0 v2/s Serial1/2 v2/s Serial1/3 v2/s Cisco Systems, Inc. All rights reserved. Cisco Academy 120

122 show ip pim neighbor NA-2#show ip pim neighbor PIM Neighbor Table Neighbor Interface Uptime/Expires Ver DR Address Priority Serial0/0 00:01:46/00:01:28 v2 None Serial1/2 00:01:05/00:01:40 v2 1 (BD) Serial1/3 00:01:56/00:01:18 v2 1 (BD) 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 121

123 Checking RP Information router(config)# show ip pim rp [group-name group-address mapping] Displays active RPs that are cached with associated multicast routing entries. Mapping displays all group-to-rp mappings that the router is aware of router(config)# show ip rpf {source address name } Displays how IP multicast routing does Reverse Path Forwarding (RPF). Source Address source address of the host for which RPF information is displayed Name name of the host for which RPF information is displayed 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 122

124 show ip pim rp P4-2#show ip pim rp Group: , RP: , uptime 00:00:20, expires never P4-2#show ip pim rp mapping PIM Group-to-RP Mappings Group(s) /32 RP (NA-1), v1 Info source: local, via Auto-RP Uptime: 00:00:21, expires: never Group(s) /32 RP (NA-1), v1 Info source: local, via Auto-RP Uptime: 00:00:21, expires: never Group(s): /4, Static RP: (NA-1) 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 123

125 show ip rpf (towards the RP) NA-2#show ip rpf RPF information for NA-1 ( ) RPF interface: Serial1/3 RPF neighbor:? ( ) RPF route/mask: / /32 RPF type: unicast (ospf 1) RPF recursion count: 0 Doing distance-preferred lookups across tables (towards the source) NA-2#show ip rpf RPF information for? ( ) RPF interface: Serial0/0 RPF neighbor:? ( ) RPF route/mask: /25 RPF type: unicast (ospf 1) RPF recursion count: 0 Doing distance-preferred lookups across tables 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 124

126 Checking the Group State router# show ip igmp interface [type number] Displays multicast-related information about an interface router# show ip igmp groups [group-address type number] Displays the multicast groups that are directly connected to the router and that were learned via IGMP 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 125

127 Configure a Router as a Group Member Router (config-if)# ip igmp join-group group address Configure a router to join a specific multicast group and enable IGMP on an interface. Router (config-if)# ip igmp static-group group-address Configures the router as a statically connected member of a group 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 126

128 show ip igmp interface rtr-a>show ip igmp interface e0 Ethernet0 is up, line protocol is up Internet address is , subnet mask is IGMP is enabled on interface Current IGMP version is 2 CGMP is disabled on interface IGMP query interval is 60 seconds IGMP querier timeout is 120 seconds IGMP max query response time is 10 seconds Inbound IGMP access group is not set Multicast routing is enabled on interface Multicast TTL threshold is 0 Multicast designated router (DR) is (this system) IGMP querying router is (this system) Multicast groups joined: Cisco Systems, Inc. All rights reserved. Cisco Academy 127

129 show ip igmp groups rtr-a>sh ip igmp groups IGMP Connected Group Membership Group Address Interface Uptime Expires Last Reporter Ethernet0 6d17h 00:01: Ethernet0 6d17h never Cisco Systems, Inc. All rights reserved. Cisco Academy 128

130 Verifying IGMP Snooping on a Switch switch> show multicast group [igmp] [mac_addr] [vlan_id] Displays information about multicast groups. If igmp keyword is used, only IGMP-learned information is shown. switch> show multicast router [igmp] [mod_num/port_num] [vlan_id] Displays information on dynamically learned and manually configured multicast router ports. If igmp keyword is used, only IGMP-learned information is shown Cisco Systems, Inc. All rights reserved. Cisco Academy 129

IP Multicasting: Explaining Multicast Cisco Systems, Inc. All rights reserved. Cisco Academy

IP Multicasting: Explaining Multicast 2008 Cisco Systems, Inc. All rights reserved. Cisco Academy 1 IP Multicast Distribute information to large audiences over an IP network 2008 Cisco Systems, Inc. All