Access Chandan-L2 L3 Multicast
Transcript of Access Chandan-L2 L3 Multicast
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2006 Cisco Systems, Inc. All rights reserved.CiscoConfidentialPresentation_ID 1
Comparing Layer 2 andLayer 3 Metro Ethernet
Access Rings for MulticastTraffic
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2006 Cisco Systems, Inc. All rights reserved.CiscoConfidentialPresentation_ID 2
Abstract Currently the Service Providers are implementing Metro Ethernet across the cities,
and are looking at mainly two options
1. Having Layer 2 based rings or
2. Layer 3 / MPLS control plane based.
The primary services that Service Providers will implement are
1. Residential : HSI, IPTV, VoIP
2. Business: Layer 2, Layer 3 point to point and also multipoint to multipoint.
The session will discuss advantages and disadvantages that Layer 3 / IP basedmulticast provides as compared to a Layer 2 based approach for a ringconfiguration.
The session will describe how basic multicast streams / flows behave when therings are based on layer2 or layer3. The session would also look at how the twoimplementations differ in responding to fibre cuts / ring failures / node failure.
Finally we conclude with the importance that services have in developing a flexiblemetro ethernet architecture.
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Agenda
Network and Service Rollout scenarios
Layer 2 and Layer 3 solution
Failure Scenarios Comparison
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Ethernet DSL Services Considerations
Service Transport TopologyService
GovernanceApplication
Elements IP Edge Element
Internet Access P2MP, Unicast Subscriber Policy Server,
Portal BRAS
VoIP Telepony P2P, Unicast Application Call Control Server BRAS, Aggregation
Node
VoD P2MP, Unicast Application Video Middleware Aggregation Node
TV Broadcast P2MP, Multicast Application Video Middleware Aggregation Node
MPLS VPN partial MP, Unicast Subscriber None MPLS PE
Ethernet VirtualLines P2P Subscriber None Aggregation Node
Ethernet VirtualLANs MP Subscriber None
Aggregation,Distribution Node,MPLS PE
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Current Architecture Options Driven by the Services and SLAs
Internet
IP/MPLS
U-PE
SONET/SDH
Ring
10/100/
1000 Mbps
10/100/
1
000Mbps
Metro D
N-PE
N-PE
N-PE
P P
PP
Hub &
Spoke
Metro C
10/100/
1000 Mbps
U-PE
DWDM/
CDWM
Metro B
U-PE
GE Ring
Metro A U-PE
PE-AGG
GE
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Access / Aggregation Network Control Plane Options
Layer 3 - IP, MPLS
Distributed L3 Service Edge
Layer 2 MPLSEoMPLS/ H-VPLS
Centralised L3 Service EdgeTransparent Ethernet Services
EoMPLS
DSL
Access Node
DistributionNode
BRAS
MPLS PE
SCE
Business
Corporate
Residential
STB
AggregationNode
AggregationNode
Core NetworkIP / MPLS
VoD
Content Network
TV SIP
Business
Corporate
Business
Corporate
AggregationNode
EthernetAccess Node
Aggregation NetworkMPLS, Ethernet, IP
DistributionNode
Access L2/3 Edge
VoD
Content Network
TV SIP
Layer 2 Bridged EthernetIEEE 802.1q / 802.1ad
802.1q
Centralised L3 Service EdgeTransparent Ethernet Services
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Layer 2 based Ring
architectures
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TV/VoD Distribution MechanismsEthernet Layer 2 Aggregation Network
IGMP snooping
DR
Querier Router
PIM
L2L2
L2L2
L2 L2
IGMP/PIM snooping
IEEE 802.1q
RSTP
Multicast
Unicast and multicast IEEE 802.1qbridging
Forwarding with IEEE bridging relies on
flooding Consistent with the logical STP derived topology
Flooding for unicast is constrained by MAC
learning
Flooding for multicast is constrained by PIM orIGMP snooping
Subscriber STBs isolation needs to be secured
across the entire multicast VLAN
Redundant topologies solved by RSTP Convergence is in range of seconds
L3 multicast might be delivered inefficiently, as
STP is multicast unaware
Multicast convergence dependent on L3 Only one Multicast Router can inject traffic
Redundant Multicast Routers; Failover between
Multicast Routers could potentially take 120s
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TV/VoD Distribution MechanismsMPLS Layer 2 Aggregation Network
IGMP snooping
Designated Router
Querier Router
PIM
PW PW
PWPW
PW PW
IGMP/PIM snooping
MPLS
Overlay Topology:
VPLS, EoMPLS PW
VSI
VSI
VSI
VSI
VSI
VSI
Multicast
Overlay bridged H-VPLS topology Each VPLS node runs a bridged VSI (Virtual
Forwarding Instance
All physical links and bridges are replaced by
EoMPLS tunnels terminating into VFIs
Including the PW between the two switches that
connect to the multicast routers
Topology protection may be addressed at
different levels: MPLS TE FRR:
Protects the VPLS pseudo-wires
Does not protect the VPLS VFIs (the VFIs)
Can lead to 50 ms convergence but ONLY
in case of link failure
STP must be used to avoid the discontinuous
subnet
Still results into several seconds of STPconvergence in case of node failure
The H-VPLS overlay topology implies the
same considerations related to bridged
multicast distribution
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Layer 3 based Ring
architectures
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IP Multicast and Unicast TV and VoD
L3 control plane is now leveraged to run IPmulticasting (potentially together with MPLS)
Forwarding topology created at network layer
Both P2MP and MP2MP services are available toupper layers
No discontiguous subnet problems
Supports multiple injection points
Multiple active trees can co-exist
Dynamic topology driven by PIM
Enables anycasting
Node and service injection point failures solved atthis layer
Enables multicast (receiver driven) distributionmodel
Optimal forwarding
P2MP trees (TV) with PIM SSM
Predictable sub-second convergence (Ciscospecific)
Layer 3 BUS
Multicast
PIM
PIM
PIM
PIM
PIM
PIM
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TV / VoD distribution mechanisms with Layer3 / IP control plane
1PIM-SM
L3
L3L3
L3
L3L3
2 3
4
LocalAd Server or Multilingual Server
IP Multicast Implementation
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Failure Scenarios
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TV Multicast Distribution Failure CasesEthernet/MPLS La er 2 A re ation Network
Topology failures Link
Addressed by MPLS FRR with 50ms convergenceor by STP with1-3s convergence
Node
Addressed only by STP
Otherwise recovered by the DR failover Inconsistency: the layer 2 topology depends onlayer 3 topology convergence
Functional element failures
Querier Router failure
Requires Querier re-election, around 120 s
Designated Router failure Relies on DR failover, that (ex. Cisco) can be veryfast (sub second)
Source and other Headend failures
Anycast-Source possible if they are routed to theDR/QR
Conclusion:
Video Multicast redundancy has functional
DR
Querier Router
PIM
Multicast
Failure
Layer 2 BUS
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The Discontiguous Subnet ProblemFailure scenarios: Box Failure
Assume: R1 IGMP querier: IfR2 does not see IGMP-queries from R1 any more itusually starts being aquerier after 2 x query-
interval (default 120s) Requires significant tuning/
enhancements on PIMrouters to achieve fastfailover (> 50 ms!)
L2 Access Problem ispushed to the L3 Edge
IGMP
R1
R2
MPLS-FRR, backup LSP
PW
PW
PW
PW PW PIM
Logical view
R1
R2
IGMP
DN2
DN1
AN1
AN2
AN3
AN4
IGMP query
IGMP query
VSI
VSI
VSI
VSI
VSI
VSI
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The Discontiguous Subnet ProblemFailure scenarios: Box Failure (II)
Layer-2 subnet is partitionedinto two pieces
Violation of the fundamentalrule that an L2 segmentmust be contiguous
Usually there is unicastcontrol traffic in the multicastVLAN (e.g. RTCP, HTTP,MiddleWare traffic)
Unicast control traffic couldbe blackholed
R1
R2PW
PW
PW
PW PW
Logical view
R1
R2
DN2
DN1AN1
AN2
AN3
AN4
?
VSI
VSI
VSI
VSI
VSI
VSI
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Packet Duplication
N-PE 1 N-PE 2
U-PE A U-PE C
U-PE B
N-PE 1 N-PE 2
U-PE A U-PE C
U-PE B
Traffic-Flow from N-PE1 to U-PE B:Traffic traverses link twice
Ring-VPLSImplementation
1 PIM-SSM
L3
L3L3
L3
L3L3
2 3
4
IP MulticastImplementation
PW/FRR
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Conclusion and
Comparison
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Final Words
Is it Layer 2 or Layer 3 or may be Hybrid ?
There are quite a lot of advantages of Layer 2, cheaper, easier tomaintain
Layer 2 may be the best solution for various other services likeERS, EWS etc..
However as we clearly see there are some clear advantages ofLayer 3 specially for Video traffic
We see these two continue in hybrid way whereas the TV trafficwill be L3 primarily and the other traffic may continue on Layer 2pseudo wires or plane Layer 2 itself.
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Aggregation Network Models
Ethernet/IP Requires a STP operational domain for the
Layer 2 BUS transport
Provides optimal layer 2 multipoint transportthat is topology independent
Supports virtualised Layer 2 services thru
native 802.1q and 802.1ad bridges The scalability of the L2 Service BUS is
dependent on the aggregation network
Service recovery, in average of seconds, isimplemented with RSTP and Fast IGP
convergence
Possibility to aggregate other accessservices as: Mobile RAN, Legacy ATM/FR/
TDM with L2TPV3
Allows different or common administrativedomains for the aggregation and core network
Supports virtualized Layer 2 and 3 services thruMPLS based VPNs
Supports Traffic Engineering thru MPLS TE
mechanisms Service recovery, as low as 50ms, is
implemented with MPLS FRR and Fast IGPconvergence
The scalability for Layer 2 Service BUS isdependent on the network element
Flexibility for aggregating other access servicesas: Mobile RAN, Legacy ATM/FR/TDM with
MPLS AToM
MPLS/IP
S
imilarities
Charac
teristics
Similar Layer 2 and Layer 3 BUS mechanisms Support point to point and multipoint layer 2 and layer 3 transport Support the same residential, business and wholesale broadband services
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