Internet2 Multicast Workshop by v8F6UR


Multicast Workshop

            Engineering Workshops


 Greg Shepherd           Matt Davy
Beau Williamson          Yul Pyun
Marshall Eubanks        Stig Venaas
  Bill Nickless    Dave Devereaux-Weber
 Caren Litvanyi     University of Oregon
  Patrick Dorn      Columbia University
Leonard Giuliano        NYSERNet
 Alan Crosswell           OARnet
  Debbie Fligor       Cisco Systems
  Mitch Kutzko       Juniper Networks
                       Engineering Workshops

• Introductions
  – Instructors
  – Students
     • Juniper experts?
     • BGP experts?
• Finding things here & nearby…
  – Snacks, coffee
  – Restrooms
  – Restaurants
• Workshop schedule

                             Engineering Workshops

• What's in the binder?
  – Slides, with space for notes.
  – Labs. For labs 2-5 and 7, there are separate "answers"
    docs which are not included in the binder. These are
    distributed after, or sometimes during, the labs (they're
    labs, not tests). If you get stuck, please ask!
  – References: Cisco/JUNOS multicast commands, JUNOS
    RIB groups, JUNOS config editor,
    JUNOS CLI. For use during the labs.

                                     Engineering Workshops

•   Overview (cf. Interdomain Multicast Routing Ch. 1-3)
•   Multicast on the LAN (Ch. 2, sections 2.1-2.2)
•   Source-Specific Mcast (SSM) – Intra-domain (Ch. 4, 6)
•   Any-Source Mcast (ASM) – Intra-domain (Ch. 4)
•   SSM – Inter-domain (Ch. 7)
•   ASM – Inter-domain (Ch. 5)
•   Troubleshooting Methodology
•   Best Current Practices; Future of Multicast

                                    Engineering Workshops


       Engineering Workshops

           The Basic Idea
  Instead of sending a separate copy
of the data for each recipient, the source
 sends the data only once, and routers
     along the way to the destinations
         make copies as needed.

     Unicast does mass mailings;
      multicast does chain letters.

                         Engineering Workshops

          Unicast vs. Multicast
Unicast              Multicast

                          Engineering Workshops

                      The MBone
• The original multicast network was called the MBone. It used a
  simple routing protocol called DVMRP (Distance Vector Multicast
  Routing Protocol).
• As there were only isolated subnetworks that wanted to deal with
  DVMRP, the old MBone used tunnels to get multicast traffic
  between DVMRP subnetworks.
   – i.e., the multicast traffic was hidden and sent between the
     subnetworks via unicast.
• This mechanism was simple, but required manual administration
  and absolutely could not scale to the entire Internet.
• Worse, DVMRP requires substantial routing traffic behind
  the scenes and this grew with the size of the MBone.
   – Thus, the legend grew that multicast was a
     bandwidth hog.

                                         Engineering Workshops

                Multicast Grows Up
• Starting about 1997, the building blocks for a multicast-enabled
  Internet were put into place.
   –An efficient modern multicast routing protocol, Protocol
     Independent Multicast - Sparse Mode (PIM-SM), was deployed.
     (PIM also has Dense and Sparse-Dense modes, but these are
     not widely used.)
   –The mechanisms for multicast peering were established, using
     an extension to BGP called Multiprotocol BGP (MBGP), and
     peering became routine.
   –The service model was split into:
       • a one-to-many (or “broadcast”) part:
         a many-to-many part (e.g., for videoconferencing):
         Any-Source Multicast (ASM), and
       • Source-Specific Multicast (SSM).
• By 2001, these had completely replaced the old MBone.
                                         Engineering Workshops

           What capabilities does
           IP Multicast provide ?

• Cost-efficient distribution of data
• Timely distribution of data
• Robust distribution of data

“Data” here could be
  – Files
  – Streamed Audio or Video

                                 Engineering Workshops

      Cost Efficient Data Distribution
• This is the core of the streaming case.
   – Unicast streaming is just too expensive.
   – This is true either on the commodity Internet or
     on the Intranet.
   – Multicast is especially compelling for video.

                                 Engineering Workshops

       Timely Distribution of Data
• This is the argument for multicast in financial
• In unicast, it takes time to send packets
  separately to each receiver.
   – Even if cost is not a problem, time may be.
   – Example: A DS3 would take 2 days to
     distribute a 100 megabyte file to 10,000
     desktops. With multicast, this would take 18
   – Multicasting is compelling here if timely
     distribution is important.

                                Engineering Workshops

        Robust Distribution of Data
• In some streaming or data distribution cases, the
  problem is handling sudden large increases in
• Multicast was designed to handle sudden large
  increases in load.

                                Engineering Workshops

            Case Study: 9/11/2001
         Internet News “Melt-down”:
  Web Site Performance 9:00 AM to 10:00 AM

       Site                        % Users able to access                          0%                              0%                          0%                       18 %                          22 %

(source: Keynote’s Business Performance / Interactive Week 9/17/2001)

                                           Engineering Workshops

Internet News Performance on 9/11/2001
 • Of course, the “melt-down” was caused by the
   incredible demand for news after the attacks.
 • Unicast streaming web sites suffered similar problems,
   at least from anecdotal evidence
 • By contrast, multicast performed well
    – Large increase in traffic
    – Roughly 1 Gigabit per second saved at peak
    – Over time, the multicast peering mesh degraded,
       but this was NOT due to increased traffic

                                    Engineering Workshops

                     Eyewitness Accounts
We had a large plasma screen in the iLabs [at Networld+Interop] intended to demonstrate high
rate HDTV over I2. We came in Tuesday morning and were preparing for the first day of the
show when word came in about the initial plane crash into the towers. Our I2 Lead, Roy Hockett
was able to switch the stream to a CNN broadcast from UMich. We began attracting exhibitors to
the display even before the showfloor opened. Once the attendees were on the floor, the crowd
had grown to well over a hundred.
By this point, three things had happened. The crowds around the one display had grown so large
as to constitute a fire hazard, all the major news web sites had completely melted down, and
CNN was being multicast from several sources. We then started loading multicast tools on every
PC in the NOC, from the one driving the large video wall to people's individual laptops. By 10:30
(about half an hour after the floor opened) we had at least 3 large displays as well as a number
of normal monitors turned out towards the plexiglass walls.
Soon after, we had a good number of exhibitors come and ask how to get "the CNN viewer
                                          — Jim Martin, <>

More than 1,000 copies of StreamPlayerII, our multicast MPEG viewer, were downloaded or
handed out on disk between 9/11 and 9/12. We normally average 20 to 100 per day.
                                          — Rich Mavrogeanes <>

                                                              Engineering Workshops

Sudden increase in Multicast
traffic of at least 1000 group
    – Mostly viewing VBrick’s
   television broadcast
   – Measured viewership >830
   – But each measured point could
   have many individual viewers
   since they multicast locally
excess of 1 Gbps vs. unicast

                                     Crowds viewing the 9/11 multicasts at Networld+Interop

                                               Engineering Workshops

  How is Multicast Being Used Today?

•Network Video!
  •Netcast Events, TV over IP,
   Distance Learning, Collaboration
•Other applications
  •PTT “Push to talk” on 802.11 wireless VoIP
     •Nortel and Vocera both implement PTT with
•Some examples follow...

                                      Engineering Workshops

                 Video: Netcast Events
• Technical events
   – IETF, NANOG, Joint Techs
• Scientific events
   – Undersea exploration with Robert Ballard:
• Performance events
   – Digital Video Transport Service (
     provides relatively cheap & painless high-quality network video, and is
     increasingly popular
     for a wide variety of uses.
   – DVTS over multicast is ideal for netcasting performance events.
   – DancingQ performance event:

                                              Engineering Workshops

                     Video: TV over IP
• DV Guide:
• ResearchChannel:
• UW-Madison:
• Northwestern University
   – Cable TV via campus networks:
   – C-SPAN over the Internet2 Network:
• Several other campuses (Cornell, Columbia, Duke...) have TV-over-IP
  projects, or are considering them.
• Open Student Television Network
   – "the only 24/7 worldwide channel exclusively devoted to
      student-produced programming"

                                            Engineering Workshops

                Video: TV over IP
• Set-top boxes are available from several vendors,
• Some corporations, particularly in the financial
  sector, pay big bucks to have cable news
  multicast on their intranets.

                                   Engineering Workshops

          Video: Distance Learning
• University of Hawaii uses multicast in its Hawaii
  Interactive Television Service
  – Two-way interactive video and audio to all UH
    campuses and education centers
  – Each classroom can view and converse with at least
    two other sites, and listen to additional sites
  – Each campus can receive and transmit multiple
    classes simultaneously

                                  Engineering Workshops

Video: Distance Learning

                        U. of Hawaii
                       Interactive TV
                       Locations and
                         Staff Sites

                Engineering Workshops

               Video: Collaboration
Access Grid:
• "The Access Grid® is an ensemble
  of resources...used to support group-to-group interactions
  across the Grid."
• survey of AG multicast issues:
• Access Grid via VRVS:

                                     Engineering Workshops

                   Other Applications
• While it seems clear that the killer app for multicast
  will involve video, there are other things you can do
  with it...
   – radio:,
   – file distribution (a popular intranet ASM application)
   – NNTP

• Please keep us informed about your current and
  planned applications!
   – See

                                           Engineering Workshops

                Essential Multicast Terminology
                                 IP source = IP unicast addr
                                Ethernet source = MAC addr
            source                                                               receivers
                              IP destination = IP multicast addr
                                  Ethernet dest = MAC addr

         e.g., video server

                                 Multicast stream
source = origin of multicast stream
multicast address = an IP address in the Class D range ( –, used to
    refer to multiple recipients. A multicast address is also called a multicast group
    or channel.
multicast stream = stream of IP packets with multicast address for IP destination address. All
    multicast uses UDP or ICMP packets (Never TCP).
receiver(s) = recipient(s) of multicast stream
tree = the path taken by multicast data. Routing loops are not allowed, so there is always a unique
    series of branches between the root of the tree and the receivers.

                                                             Engineering Workshops

                  (S,G) notation
• For every multicast source there must be two
  pieces of information: the source IP address,
  S, and the group address, G.
  – These correspond to the sender and receiver
    addresses in unicast.
  – This is generally expressed as (S,G).
     • (,
  – Also commonly used is (*,G) - every source for
    a particular group. - (*,

                                  Engineering Workshops

             Essential Multicast Protocols
           Delivery tree
           Membership reports


                                  Multicast Routing                 Group Management
                                  Protocol (e.g. PIM-SM)            Protocol (e.g. IGMP)
 •   Group Management Protocol - enables hosts to dynamically join/leave multicast
     groups. Receivers send group membership reports to the nearest router.
 •   Multicast Routing Protocol - enables routers to build a delivery tree between the
     sender(s) and receivers of a multicast group.

                                                         Engineering Workshops

          Multicast Building Blocks
• The SENDERS send without worrying about receivers
   – Packets are sent to a multicast address (RFC 1700)
   – This is in the class D range
     ( -
• The RECEIVERS inform the routers what they want to
   – done via Internet Group Management Protocol (IGMP),
     version 2 (RFC 2236) or later
• The routers make sure the STREAMS make it to the
  correct receiving networks.
   – Multicast routing protocol: PIM-SM

                                  Engineering Workshops

         Multicast Protocol Summary
• Essential Protocols
   – PIM-SM - Protocol Independent Multicast - Sparse Mode is
     used to propagate forwarding state between routers.
   – IGMP - Internet Group Management Protocol is used by
     hosts and routers to tell each other about group
• Other Protocols (much more on these later in the
   – MBGP or MP-BGP - Multiprotocol Border Gateway Protocol
     is used to exchange routing information for inter-domain
     reverse-path forwarding (RPF) checking.
   – MSDP - Multicast Source Discovery Protocol is used to
     exchange active-source information.

                                      Engineering Workshops

             Multicast Addressing

• IPv4 Multicast Group Addresses
  – Class D Address Space
     • High order bits of 1st Octet = “1110”
  – Source sends to group address
  – Receivers receive traffic sent to group address

                                    Engineering Workshops

              CIDR Address Notation
• The multicast address block is to
• It is cumbersome to refer to address blocks in the above
  fashion. Address blocks are usually described using
  “CIDR notation”
   – This specifies the start of a block, and the number of bits THAT
      • In this shorthand, the multicast address space can be described as or, even more simply, as 224/4. The fixed part of the
        address is referred to as the prefix, and this block would be
        pronounced "two twenty four slash four."
   – Note that the LARGER the number after the slash, the
     LONGER the prefix and the SMALLER the address block.

                                            Engineering Workshops

                 Multicast Addressing
• RFC 3171
• Examples:
   – - (224.0.0/24) - reserved & not forwarded
       • - All local hosts
       • - All local routers
       • - DVMRP
       • - OSPF
       • - Designated Router OSPF
       • - RIP2
       • - PIM
       • - VRRP
       • – IGMP
    – - (232/8) - SSM
    – - (239/8) - Administrative Scoping
• “Ordinary” multicasts don’t have to request a multicast address
  from IANA.

                                                Engineering Workshops

• TTL value defines scope and limits distribution
   – IP multicast packet must have TTL > interface TTL or it is
   – No longer recommended as a reliable scoping mechanism
• Administratively Scoped Addresses – RFC 2365
   – Private address space
       • Similar to RFC 1918 unicast addresses
       • Not used for global Internet traffic
       • Used to limit “scope” of multicast traffic
       • Same addresses may be in used in different sub-networks for
         different multicast sessions
   – Examples
       • Site-local scope:
       • Organization-local scope:

                                          Engineering Workshops

         Multicast Address Allocation
• For a long time, this was a sore spot. There was no way
  to claim or register a Multicast Class D address like
  unicast address blocks can be registered.
   – For temporary teleconferences, this is not such a
     problem, but it does not fit well into a broadcast model.
• Now, there are two solutions:
   – For SSM, addresses don’t matter, as the broadcast
     address is really unique as long as the (S,G) pair is
   – For ASM, there is “GLOP”.

                                         Engineering Workshops

             Multicast Addressing
GLOP addresses
  – Provides globally available private Class D space
  – 233.x.x/24 per AS number
  – RFC 3180
  – Insert the 16-bit AS number into the middle two
     octets of the 233/8
  – Online GLOP calculator:
  – If you have an AS, you have multicast addresses.

                                  Engineering Workshops

             Expanding Multicast
             Address Assignment
• GLOP based address assignment has worked well.
   – Every organization gets the same amount of space, a
• What if you need more?
   – There is an (as yet unused) mechanism for requesting
     more GLOP space: RFC 3138.
   – Is this unused because of lack of demand, or because
     the mechanism is not fully implemented?
• What about 4-byte ASNs?
   – Policy proposal rejected by ARIN in 2007 for “eGLOP”
   – Current 7/2008: IETF draft-ietf-mboned-rfc3171bis-03

                                    Engineering Workshops

              Prefix-based Multicast
              Address Assignment
• Dave Thaler of Microsoft has proposed prefix-based
   – draft-ietf-mboned-ipv4-uni-based-mcast-05 (expired Aug 28,
• The idea is that every unicast address assignment you have is
  mapped into a multicast address range.
   – Take one of the unused multicast /8's
   – For a /N unicast assignment, the multicast address block
        • [/8] [/N][24 - N bits of available addresses]
   – So, a /24 provides a /32; a /16 provides a /24; a /8 provides
     a /16
• This would complement GLOP by giving larger organizations
  more addresses.
                                                Engineering Workshops

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