Network Training - VITEC
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Transcript of Network Training - VITEC
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Networking FundamentalsKobi Levy, March 2012
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Agenda
Why Multicast?
Multicast VS Unicast
Multicast forwarding
IGMPv1 vs IGMPv2
IGMP Snooping
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Why Multicast?
Used when sending same data to multiple receivers
Better bandwidth utilization
Less host/router processing
Used when receivers addresses unknown
Used when simultaneous delivery for a group of receivers is requir(simulcast)
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Multicast Vs Unicast
Pure Unicast: Send the same copy of data multiple times
Web Technologies: Webcastingpush the same data to multipl
Traditionally, receivers subscribed to data and pulled itperiodically
The underlying transport for those Technologies has bee
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Multicast Vs Unicast
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Host
Router
Unicast
Host
Router
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Multicast Vs Unicast
The sender (source) sends one copy of a single packet addressedreceivers - multicast group
Multicast routers replicate and forward the packet to all the branchreceivers (may) exist
Receivers express their interest in multicast traffic by sending contto routers
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Multicast advantages
Enhanced Efficiency: Controls network traffic and reduces server a
Optimized Performance: Eliminates traffic redundancy
Distributed Applications: Makes multipoint applications possible
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Example: Audio StreamingAll clients listening to the same 8-Kbps audio
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0.2
0.4
0.6
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Traffic
Mbps
1 20 40 60 80 100
Multicast
Unicast
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Multicast advantages
Fewer resources required bandwidth and host processing power
Almost simultaneous delivery is assured (one packet is simultaneoforwarded across the networks)
Foundation for a whole range of new applications not possible in th
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Multicast disadvantages
Multicast is UDP based.
Best Effort Delivery:Drops are to be expected. Multicast applications must nodelivery of data and should be designed accordingly. Reliable multicast will address
No Congestion Avoidance:Lack of TCP windowing and slow-start mechanetwork congestion. If possible, multicast applications should attempt to detect and conditions.
Duplicates:Some multicast protocol mechanisms result in the occasional generatpackets. Multicast applications should be designed to expect occasional duplicate pa
Out of sequence delivery:Network topology changes affect the order of delivapplication must properly address the issue.
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Multicast applications
One-to-many: A single host sending to two or more (n) receive
Many-to-many: Any number of hosts sending to the same mugroup hosts are also members of the group (sender = receiver)
Other: e.g. many-to-one: Any number of receivers sending data source (via unicast or multicast)
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Typical Multicast Network
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Source Source segment
First-hop router
Last-hop router
Multicastdistributiontree
Receiversegment
Multicast data flow
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Multicast Forwarding
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Multicast Forwarding
Multicast routing works the opposite way 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 to prevent forwar
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Multicast Forwarding
Dense Mode
Uses the push model
Traffic Flooded throughout network
Pruned back where it is unwanted
Flood and prune behavior (typically every three minutes)
Sparse Mode Uses the pull model
Traffic sent only to where it is requested
Explicit join behavior
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Dense Mode
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Initial Flooding
Source
Receiver
Multicast Packets
(S, G) state created ineveryrouter in the network!
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Dense Mode
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Pruning Unwanted Traffic
Source
Receiver
Multicast Packets
Prune Messages
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Dense Mode
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Source
Results after Pruning
Receiver
Multicast Packets
Flood and Prune processrepeats every three minutes!!!
(S, G) state still exists ineveryrouter in the network!
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Multicast Forwarding
Dense Mode
Uses the push model
Traffic Flooded throughout network
Pruned back where it is unwanted
Flood and prune behavior (typically every three minutes)
Sparse Mode Uses the pull model
Traffic sent only to where it is requested
Explicit join behavior
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Sparse Mode
Protocol Independent works with any of the underlying unicast roprotocols
Supports both source and shared trees
Based on an explicit pull model
Uses a rendezvous point (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 de(DR)
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PIM-SM Shared Tree Join
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Receiver
RP
(*, G) Join
Shared Tree
(*, G) State created onlyalong the Shared Tree.
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PIM-SM Sender Registration
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Receiver
RP
(S, G) Join
Source
Shared Tree
(S, G) Register (unicast)
Source Tree
(S, G) State created onlyalong the Source Tree.Traffic Flow
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PIM-SM Sender Registration
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Receiver
RPSource
Shared Tree
Source TreeRP sends a Register-Stopback to the first-hop routerto stop the Registerprocess.(S, G) Register-Stop (unicast)
Traffic Flow
(S, G) Register (unicast)
(S, G) traffic begins arrivingat the RP via the Sourcetree.
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IGMP
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IGMP
Internet Group management protocol (IGMP),
a multicasting protocol in the internet protocols family,
is used by IP hosts to report their host group memberships to any
immediately neighboring multicast routers. IGMP messages are
encapsulated in IP datagrams, with an IP protocol number of 2.
IGMP has versions IGMP v1, v2 and v3.
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IGMP v1
IGMPv1: Hosts can join multicast groups.
There were no leave messages. Routers were using a time-out
Based mechanism to discover the groups that are of no interest
To the members.
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IGMP v2
IGMPv2: Leave messages were added to the protocol.
Allow group membership termination to be quickly reported to
The routing protocol, which is important for high-bandwidth
Multicast groups and/or subnets with highly volatile group membersh
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IGMP v3
IGMPv3: Major revision of the protocol.
It allows hosts to specify the list of hosts from which they want to
Receive traffic from. Traffic from other hosts is blocked inside the
Network. It also allows hosts to block inside the network packets
That come from sources that sent unwanted traffic.
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IGMP Snooping
IGMP snooping is designed to prevent hosts on a local network from traffic for a multicast group they have not explicitly joined.
It provides switches with a mechanism to prune multicast traffic from not contain a multicast listener (an IGMP client).
A switch will, by default, flood multicast traffic to all the ports in a broaMulticast can cause unnecessary load on host devices by requiring thprocess packets they have not solicited.
When purposefully exploited this is known as one variation of a deniaattack.
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IGMP Snooping
IGMP snooping allows a switch to only forward multicast traffic to thehave solicited them.
Essentially, IGMP snooping is a layer 2 optimization for the layer 3 IG
IGMP snooping takes place internally on switches and is not a protoc
Snooping is therefore especially useful for bandwidth-intensive IP muapplications such as IPTV.
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