APRICOT 11:Multicast Workshop
Understanding & Deploying
IP Multicast Networks
Srini Irigi, Stefan Olofsson, Greg Shepherd, SPG TME
Cisco Systems
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Today’s Agenda
Multicast Fundamentals
Multicast Service Models, Distribution Trees,
Forwarding
Multicast Protocol Basics
Layer2 Multicast
PIM Mechanics
SSM
MBGP
MSDP
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Fundamentals of IP Multicast
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Agenda
Why Multicast
Multicast Applications
Multicast Service Model
Multicast Distribution Trees
Multicast Forwarding
Multicast Protocol Basics
Geekometer
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Why Multicast?
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Multicast Advantages
Host
Router
Unicast
Host
Router
Multicast
Multicast Disadvantages
Multicast Is UDP Based!!!
Besteffort delivery: Drops are to be expected. Multicast
applications should not expect reliable delivery of data and should
be designed accordingly. Reliable Multicast is still an area for
much research. Expect to see more developments in this area.
No congestion avoidance: Lack of TCP windowing and “slowstart”
mechanisms can result in network congestion. If possible,
Multicast applications should attempt to detect and avoid
congestion conditions.
Duplicates: Some multicast protocol mechanisms (e.g. Asserts,
Registers and ShortestPath Tree Transitions) result in the
occasional generation of duplicate packets. Multicast applications
should be designed to expect occasional duplicate packets.
Outofsequence packets: Various network events can result in
packets arriving out of sequence. Multicast applications should be
designed to handle packets that arrive in some other sequence
than they were sent by the source.
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Multicast Service Model
IP Multicast Service Model
RFC 1112 (Host Ext. for Multicast Support)
Each multicast group identified by a classD IP address
Members of the group could be present anywhere in
the Internet
Members join and leave the group and indicate this to
the routers
Senders and receivers are distinct:
i.e., a sender need not be a member
Routers listen to all multicast addresses and use
multicast routing protocols to manage groups
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IP Multicast Packet
Source address
Unique unicast IP address of the packet source
Destination address
ClassD address range
Does NOT represent a unique unicast destination address
Used to represent a unique group of receivers
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IP Multicast Addressing
Multicast Group Addresses (224.0.0.0/4)
Range: 224.0.0.0.239.255.255.255
Old Class D address range.
Highorder 4 bits are 1110
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Multicast Address Ranges
LinkLocal Address Range
224.0.0.0.224.0.0.255
Global Address Range
224.0.1.0.238.255.255.255
Administratively Scoped Address Range
239.0.0.0.239.255.255.25
Scope Relative Address Range
Top 256 addresses of a Scoped Address Range
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LinkLocal Address Range
Assigned by IANA
224.0.0.0.224.0.0.255
Local wire multicast
TTL = 1
Examples:
224.0.0.5 = OSPF_DR’s
224.0.0.10 = EIGRP Hello’s
224.0.0.13 = All_PIM_Routers
224.0.0.22 = All_IGMPv3_Routers
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Global Address Range
Assigned by IANA
Address Range: 224.0.1.0.238.255.255.255
Generally intended for “global”
Internet scope multicast
Sometimes assigned to specific protocols
Example: AutoRP (224.0.1.39 and 224.0.1.40)
Problem:
IANA is coming under increasing pressure from companies
to assign them blocks of addresses for their applications or
content services
This was never the intent of this block!
GLOP Addressing or SSM should be used instead!
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Global Multicast Address Assignment
Dynamic Group Address Assignment
Historically accomplished using SDR application
Sessions announced over wellknown group(s)
Address collisions detected and resolved at session
creation time
Has problems scaling
Other techniques considered
Multicast Address SetClaim (MASC)
Hierarchical, dynamic address allocation scheme
Unlikely to be deployed
No really good dynamic assignment method available for Global
multicast
But is dynamic assignment really necessary with GLOP and SSM
available?
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Global Multicast Address Assignment
Static Group Address Assignment
RFC 3180.GLOP Addressing in 233/8
Group range: 233.0.0.0.233.255.255.255
Your AS number is inserted in middle two octets
Remaining loworder octet used for group assignment
EGLOP Addresses
Make use of private AS numbers
Assigned by a Registration Authority
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Global Multicast Address Assignment
Static Group Address Assignment
Source Specific Multicast
Address range: 232.0.0.0/8
Flows based on both Group and Source address
Two different content flows can share the same Group
address without interfering with each other
Provides virtually unlimited address space!
Preferred method for global onetomany multicast
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Private Multicast Address Assignment
Assigned from the private 239.0.0.0/8 range
May be subdivided into geographic scopes ranges
Administration responsibility can be by scope range
Question:
“What technology is most often used to manage private
multicast assignment?”
Answer:
A spreadsheet
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