Multicast Overview. IP Multicasting: Explaining Multicast. Lesson Cisco Systems, Inc. All rights reserved. Cisco Public. BSCI Module 7 Lesson 1

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1 IP Multicasting: Explaining Multicast BSCI Module 7 Lesson 1 BSCI Module 7 Lesson Cisco Systems, Inc. All rights reserved. Cisco Public 1 Multicast Overview BSCI Module 7 2 1

2 IP Multicast Distribute information to large audiences over an IP network BSCI Module 7 3 Multicast Adoption Past, Present, and Future Research Community MBONE Early Adopters NASA, DOD, Cisco, Microsoft, Sprint Financials NASDAQ, NYSE, LIFE, Morgan, GS, Prudential Multicast ( ) Corporate Communication HP, IBM, Intel, Ford, BMW, Dupont E Learning 150 Universities in US, Hawaii, Oregon, USC, UCLA, Berkley MXU & Content Providers Fastweb, B2, Yahoo, BBC, CNN Multicast Deployment Surveillance Law Enforcement and Federal IPv6 Multicast NTT, Sony, Panasonic, Multicast VPN C&W, MCI, AT&T, TI, FT, DT, NTT 1986 z z z Time BSCI Module 7 4 2

3 Why Multicast? Used when sending same data to multiple receivers Better bandwidth utilization Less host/router processing Used when addresses of receivers unknown Used when simultaneous delivery for a group of receivers is required (simulcast) BSCI Module 7 5 Unicast vs. Multicast BSCI Module 7 6 3

4 Multicast Advantages Enhanced efficiency: Controls network traffic and reduces server and CPU loads Optimized performance: Eliminates traffic redundancy Distributed applications: Makes multipoint applications possible BSCI Module 7 7 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. BSCI Module 7 8 4

5 Multicast Disadvantages Multicast is UDP-based. Best-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 issues in filtering and in security BSCI Module 7 9 Types of Multicast Applications One-to-many A single host sending to two or more (n) receivers Many-to-many Any number of hosts sending to the same multicast group; hosts are also members of the group (sender = receiver) Many-to-one Any number of receivers sending data back to a source (via unicast or multicast) BSCI Module

6 IP Multicast Applications Live TV and Radio Broadcast to the Desktop Multicast File Transfer Data and File Replication Distance Learning Corporate Broadcasts Training Whiteboard/Collaboration Real-Time Data Delivery Financial Videoconferencing Video-on-Demand BSCI Module 7 11 Self Check 1. List some advantages of multicast transmission over unicast transmission. 2. How does the best effort delivery nature of UDP impact multicast transmissions? 3. What are the 3 basic types of multicast applications? 4. Give examples of one-to-many. 5. What model is used when a host can be a sender as well as a receiver simultaneously? BSCI Module

7 Multicast Addressing BSCI Module 7 13 IP Multicast Address Structure IP group addresses: Class D address (high-order three bits are set) Range from through BSCI Module

8 Multicast Addressing IPv4 Header Version IHL Type of Service Total Length Identification Flags Fragment Offset Source Address can never be Class D Multicast Group Address Time to Live Protocol Header Checksum Source Source Address (Class A, B, C) Destination Destination Address (Class D) Multicast Group Address Range Options Padding BSCI Module 7 15 IP Multicast Address Groups Local scope addresses to Global scope addresses to Administratively scoped addresses to BSCI Module

9 Local Scope Addresses Well-known addresses assigned by IANA Reserved use: through (all multicast systems on subnet) (all routers on subnet) (all DVMRP routers) (all PIMv2 routers) , , , and used by unicast routing protocols BSCI Module 7 17 Global Scope Addresses Transient addresses, assigned and reclaimed dynamically (within applications): Global range: X.X usually used in MBONE applications Part of a global scope recently used for new protocols and temporary usage BSCI Module

10 Administratively Scoped Addresses Transient addresses, assigned and reclaimed dynamically (within applications): Limited (local) scope: /8 for private IP multicast addresses (RFC-2365) Site-local scope: /16 Organization-local scope: to BSCI Module 7 19 Layer 2 Multicast Addressing IEEE MAC Address Format BSCI Module

11 IANA Ethernet MAC Address Range Available range of MAC addresses for IP multicast e through e-7f-ff-ff BSCI Module 7 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. BSCI Module

12 Ethernet MAC Address Mapping BSCI Module 7 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 BSCI Module

13 Madcap in MS Server BSCI Module 7 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 Defined in RFC 2770 GLOP Addressing in 233/8 Manual address allocation by the admin is still the most common practice. BSCI Module

14 Learning About Multicast Sessions Potential receivers have to learn about multicast streams or sessions available before a multicast 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) BSCI Module 7 27 sdr Session Directory BSCI Module

15 A Cisco IP/TV Example Cisco IP/TV application Clients (viewers) use program listing Contact the server directly Listen to SAP announcements BSCI Module 7 29 Self Check 1. What is the address range for multicast addresses? 2. What are Local Scope Addresses? 3. What is Mbone? 4. What is the 32-to-1 overlap? 5. What is MADCAP? BSCI Module

16 IP Multicasting: IGMP and Layer 2 Issues BSCI Module 7 Lesson 2 BSCI Module 7 Lesson Cisco Systems, Inc. All rights reserved. Cisco Public 31 IGMP Overview BSCI Module

17 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 on Windows 95 RFC 2236 specifies IGMPv2 Supported on latest service pack for Windows and most UNIX systems RFC 3376 specifies IGMPv3 Supported in Window XP and various UNIX systems BSCI Module 7 33 IGMPv2 RFC 2236 Group-specific query Router sends query membership message to a single group rather than all hosts at (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 leave latencies). Querier election process IGMPv2 routers can elect the Query Router without relying on the multicast routing protocol. BSCI Module

18 IGMPv2 Joining a Group Join Group BSCI Module 7 35 IGMPv2 Leaving a Group IGMPv2 has explicit Leave Group messages, which reduces overall leave latency. BSCI Module

19 IGMPv2 Leaving a Group (Cont.) Hosts H2 and H3 are members of group H2 sends a leave message. BSCI Module 7 37 IGMPv2 Leaving a Group (Cont.) 2. Router sends group-specific query. BSCI Module

20 IGMPv2 Leaving a Group (Cont.) 3. A remaining member host sends report, so group remains active. BSCI Module 7 39 IGMPv2 Leaving a Group (Cont.) BSCI Module

21 IGMPv2 Leaving a Group (Cont.) BSCI Module 7 41 IGMPv3 Joining a Group Joining member sends IGMPv3 report to immediately upon joining. BSCI Module

22 IGMPv3 Joining Specific Source(s) IGMPv3 Report contains desired sources in the Include list. Only Included sources are joined. BSCI Module 7 43 IGMPv3 Maintaining State Router sends periodic queries: All IGMPv3 members respond. Reports contain multiple group state records. BSCI Module

23 Self Check 1. What is the primary purpose of IGMP? 2. When 2 IGMP routers are located on the same Ethernet segment, which router will be the designated querier? 3. What does the ICMPv2 Query router doe when it receives a Leave Message? BSCI Module 7 45 IGMP Layer 2 Issues BSCI Module

24 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: BSCI Module 7 47 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. BSCI Module

25 Layer 2 Multicast Switching Solutions Cisco Group Management Protocol (CGMP): Simple, proprietary; routers and switches IGMP snooping: Complex, standardized, proprietary implementations; switches only BSCI Module 7 49 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. BSCI Module

26 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 load increased with multicast traffic load Effect on switch with Layer 3-aware Hardware/ASICs Maintain high-throughput performance but cost of switch increases BSCI Module 7 51 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. BSCI Module

27 Self Check 1. What command is used to determine the version of IGMP active on an interface? 2. How does a typical layer 2 switch treat multicast traffic? 3. What is CGMP? 4. What type of switch is recommending for use with IGMP snooping? BSCI Module 7 53 Resources Wikipedia IP Multicast article Webopedia Mbone article BSCI Module

28 Resources Wikipedia IGMP article Multicast in a Campus Network: CGMP and IGMP Snooping IP Multicast Glossary of Terms bca26.html BSCI Module 7 55 IP Multicasting: Multicast Routing Protocols and Verification BSCI Module 7 Lesson 3 & 4 BSCI Module 7 Lesson Cisco Systems, Inc. All rights reserved. Cisco Public 56 28

29 Multicast Distribution Trees BSCI Module 7 57 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) BSCI Module

30 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 2 BSCI Module 7 59 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 2 BSCI Module

31 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 2 BSCI Module 7 61 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 2 BSCI Module

32 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 BSCI Module 7 63 Multicast Routing BSCI Module

33 Protocols for IP Multicast Routing PIM is used between routers so that they can track which multicast packets to forward to each other and to their directly connected LANs. BSCI Module 7 65 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 BSCI Module

34 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. BSCI Module 7 67 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. BSCI Module

35 Reverse Path Forwarding (RPF) RPF Calculation Based on Source Address. Best path to source found in Unicast Route Table. Join Determines where to send Joins. Joins continue towards Source to build multicast tree. Multicast data flows down tree. E0 Join E2 E1 Unicast Route Table Network Interface /24 E0 BSCI Module 7 69 Reverse Path Forwarding (RPF) RPF Calculation (cont.) Repeat for other receivers Join Join E0 E1 E2 BSCI Module

36 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 Unicast Route Table Network Intfc Nxt-Hop /24 E /24 E E0 Join E1 E BSCI Module 7 71 Multicast Distribution Tree Creation Shared Tree Example BSCI Module

37 PIM Dense Mode Operation BSCI Module 7 73 PIM-DM Flood and Prune Initial Flooding BSCI Module

38 PIM-DM Flood and Prune (Cont.) BSCI Module 7 75 PIM-DM Flood and Prune (Cont.) Results After Pruning BSCI Module

39 PIM Sparse Mode Operation BSCI Module 7 77 PIM Sparse Mode PIM-SM works with any of the underlying unicast routing protocols. 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. BSCI Module

40 PIM-SM Shared Tree Join RP (*, G) Join Shared Tree (*, G) State created only along the Shared Tree. Receiver BSCI Module 7 79 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. BSCI Module

41 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. BSCI Module 7 81 PIM-SM Sender Registration Source RP Traffic Flow Shared Tree Source Tree Receiver Source traffic flows natively along SPT to RP. From RP, traffic flows down the Shared Tree to Receivers. BSCI Module

42 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. BSCI Module 7 83 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 along the Shared Tree to prune off (S, G) traffic. BSCI Module

43 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. BSCI Module 7 85 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. BSCI Module

44 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. BSCI Module 7 87 The default behavior of PIM-SM is that routers with directly connected members will join the Shortest Path Tree as soon as they detect a new multicast source. PIM-SM Frequently Forgotten Fact BSCI Module 7 Lesson Cisco Systems, Inc. All rights reserved. Cisco Public 88 44

45 Multiple RPs with Auto RP PIM Sparse-Dense-Mode BSCI Module 7 89 IP Multicasting: Multicast Configuration and Verification BSCI Module 7 Lesson 4 BSCI Module 7 Lesson Cisco Systems, Inc. All rights reserved. Cisco Public 90 45

46 Multicast Configuration BSCI Module 7 91 Enabling IP Multicast Routing router(config)# ip multicast-routing Enables multicast routing. Enabling IP multicast routing allows the Cisco IOS software to forward multicast packets. BSCI Module

47 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. BSCI Module 7 93 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 0 as the RP for the administratively scoped groups: router(config)# ip pim send-rp-announce ethernet0 scope 16 group-list 1 access-list 1 permit BSCI Module

48 Verifying Multicast Configuration BSCI Module 7 95 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 groups. Active sources are those sending at a rate specified in the kbps argument or higher. The kbps argument defaults to 4 kbps. BSCI Module

49 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, 00:00:57/00:02:02 BSCI Module 7 97 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 BSCI Module

50 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) BSCI Module 7 99 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) BSCI Module

51 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 BSCI Module 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: BSCI Module

52 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. BSCI Module Verifying IGMP Snooping Example BSCI Module

53 Verifying IGMP Snooping Example (Cont.) Switch> show multicast router igmp Port Vlan /1 10 Total Number of Entries = 1 '*' - Configured '+' - RGMP-capable Switch> show multicast group igmp VLAN Dest MAC/Route Des [CoS] Destination Ports or VCs / [Protocol Type] e / e /1-2 Total Number of Entries = 2 BSCI Module Verifying IGMP Snooping Example (Cont.) Switch> show igmp statistics 10 IGMP enabled IGMP statistics for vlan 10: IGMP statistics for vlan 10: Transmit: General Queries: 0 Group Specific Queries: 0 Reports: 0 Leaves: 0 Receive: General Queries: 1 Group Specific Queries: 0 Reports: 2 Leaves: 0 Total Valid pkts: 4 Total Invalid pkts: 0 Other pkts: 1 MAC-Based General Queries: 0 Failures to add GDA to EARL: 0 Topology Notifications: 0 BSCI Module

54 Q and A BSCI Module BSCI Module