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
• Juniper experts?
• BGP experts?
• Finding things here & nearby…
– Snacks, coffee
• Workshop schedule
• 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.
• 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
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.
Unicast vs. Multicast
• The original multicast network was called the MBone. It used a
simple routing protocol called DVMRP (Distance Vector Multicast
• 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
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.
What capabilities does
IP Multicast provide ?
• Cost-efficient distribution of data
• Timely distribution of data
• Robust distribution of data
“Data” here could be
– Streamed Audio or Video
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.
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.
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.
Case Study: 9/11/2001
Internet News “Melt-down”:
Web Site Performance 9:00 AM to 10:00 AM
Site % Users able to access
USAToday.com 18 %
MSNBC.com 22 %
(source: Keynote’s Business Performance / Interactive Week 9/17/2001)
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
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, <firstname.lastname@example.org>
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 <email@example.com>
Sudden increase in Multicast
traffic of at least 1000 group
– Mostly viewing VBrick’s
– Measured viewership >830
– But each measured point could
have many individual viewers
since they multicast locally
BANDWIDTH SAVED: in
excess of 1 Gbps vs. unicast
Crowds viewing the 9/11 multicasts at Networld+Interop
How is Multicast Being Used Today?
•Netcast Events, TV over IP,
Distance Learning, Collaboration
•PTT “Push to talk” on 802.11 wireless VoIP
•Nortel and Vocera both implement PTT with
•Some examples follow...
Video: Netcast Events
• Technical events
– IETF, NANOG, Joint Techs
• Scientific events
– Undersea exploration with Robert Ballard: www.explorethesea.com
• Performance events
– Digital Video Transport Service (http://apps.internet2.edu/dvts.html)
provides relatively cheap & painless high-quality network video, and is
for a wide variety of uses.
– DVTS over multicast is ideal for netcasting performance events.
– DancingQ performance event: http://arts.internet2.edu/dancingq.html
Video: TV over IP
• DV Guide: http://dvguide.arts.usf.edu
• ResearchChannel: www.researchchannel.org/tech/i2wg.asp
• UW-Madison: http://datn.wisc.edu
• 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
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.
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
Video: Distance Learning
U. of Hawaii
• www.accessgrid.org: "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:
• While it seems clear that the killer app for multicast
will involve video, there are other things you can do
– radio: www.onthei.com, www.kexp.org
– file distribution (a popular intranet ASM application)
• Please keep us informed about your current and
– See https://mail.internet2.edu/wws/arc/wg-multicast
Essential Multicast Terminology
IP source = IP unicast addr
Ethernet source = MAC addr
IP destination = IP multicast addr
Ethernet dest = MAC addr
e.g., video server
source = origin of multicast stream
multicast address = an IP address in the Class D range (188.8.131.52 – 184.108.40.206), used to
refer to multiple recipients. A multicast address is also called a multicast group
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.
• 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).
• (220.127.116.11, 18.104.22.168)
– Also commonly used is (*,G) - every source for
a particular group. - (*,22.214.171.124)
Essential Multicast Protocols
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.
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
(126.96.36.199 - 188.8.131.52)
• 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
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.
• 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
CIDR Address Notation
• The multicast address block is 184.108.40.206 to 220.127.116.11
• It is cumbersome to refer to address blocks in the above
fashion. Address blocks are usually described using
– This specifies the start of a block, and the number of bits THAT
• In this shorthand, the multicast address space can be described as
18.104.22.168/4 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.
• RFC 3171
– 22.214.171.124 - 126.96.36.199 (224.0.0/24) - reserved & not forwarded
• 188.8.131.52 - All local hosts
• 184.108.40.206 - All local routers
• 220.127.116.11 - DVMRP
• 18.104.22.168 - OSPF
• 22.214.171.124 - Designated Router OSPF
• 126.96.36.199 - RIP2
• 188.8.131.52 - PIM
• 184.108.40.206 - VRRP
• 220.127.116.11 – IGMP
– 18.104.22.168 - 22.214.171.124 (232/8) - SSM
– 126.96.36.199 - 188.8.131.52 (239/8) - Administrative Scoping
• “Ordinary” multicasts don’t have to request a multicast address
• 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
• Site-local scope: 184.108.40.206/16
• Organization-local scope: 220.127.116.11/14
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”.
– 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.
• 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
• 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
• This would complement GLOP by giving larger organizations