multiprotocol label switching (mpls) july 29, 2000tecon 2000 pramoda nallur alcatel internetworking...
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MultiProtocol Label Switching (MPLS)
July 29, 2000 TECON 2000
Pramoda Nallur
Alcatel Internetworking Division
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July 29, 2000 TECON 2000July 29, 2000 TECON 2000 2
Agenda
• MPLS - The Motivation
• How MPLS Works !
• MPLS Technology
• MPLS Application
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July 29, 2000 TECON 2000July 29, 2000 TECON 2000 3
MPLS - The Motivation
• IP Protocol Suite - the most predominant networking technology.
• Voice & Data convergence on a single network infrastructure.
• Continual increase in number of users.
• Demand for higher connection speeds.
• Increase in traffic volumes.• Ever-increasing number of ISP networks.
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July 29, 2000 TECON 2000July 29, 2000 TECON 2000 4
MPLS Working Groups and Standards
• Standardized by the IETF - currently in Draft stage.• MPLS recommendations are done by IP players for IP
services• MPLS core components are generic• MPLS doesn’t use specific technology process (e.g.
ATM/FR signaling protocol PNNI or ATM OAM flow)
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July 29, 2000 TECON 2000July 29, 2000 TECON 2000 5
MPLS and ISO model
PPP
Physical (Optical - Electrical) 1
2
IP 3
4
Applications7to5
FrameRelay
ATM (*)
TCP UDP
PPP FR ATM (*)
MPLS
(*) ATM overlay model (without addressing and P-NNI) is considered as an ISO layer 2 protocol.
IETF main goal is that when a layer is added, no modification is needed on the existing layers.All new protocol must be backward compatible
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Agenda
• Motivation for MPLS
• How MPLS Works !
• MPLS Technology
• MPLS Application
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July 29, 2000 TECON 2000July 29, 2000 TECON 2000 7
MPLS Architecture
Routing protocol OSPF OSPF OSPF
Attributes Precedence
Local tableLabel table Local table Local table
LSP Label swapping Label removalClassificationLabel assignment
IngressNode
CoreNode
EgressNode
Label SwitchLayer 2
Layer 1
Layer 2
Layer 1
Layer 2
Layer 1
Layer 2
Layer 1
Layer 2
Layer 1
FEC table Local table Local table Local table
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Label swapping
Label removal
ClassificationLabel assignment
Label swapping
Label removal
ClassificationLabel assignment
OSPF / RIP / IS-IS
Label Switch Path
Label table
IngressNode
CoreNode
EgressNode
Layer 2
Layer 1
Layer 2
Layer 1
Layer 2
Layer 1
Precedence
Label table Label table
Layer 2
Layer 1
Layer 2
Layer 1
FEC FEC FEC
MPLS process
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July 29, 2000 TECON 2000July 29, 2000 TECON 2000 9
MPLS Cloud
LSR
LER
LSR
LER
IP PacketIP Packet w/ Label
L3 RoutingL3 Routing
Label SwappingLabel Swapping
LER
LERLER
L3 RoutingL3 Routing
L3 Routing
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July 29, 2000 TECON 2000July 29, 2000 TECON 2000 10
MPLS Link Layers & Label Encapsulation
ATM FR Ethernet PPP
VPI VCI DLCI “Shim Label”
Layer2
“Shim header” …….
IP | PAYLOAD
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Agenda
• Motivation for MPLS
• How MPLS Works !
• MPLS Technology
• MPLS Application
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Some MPLS Terms...
• LER - Label Edge Router
• LSR - Label Switch Router
• FEC - Forward Equivalence Class
• Label - Associates a packet to a FEC
• Label Stack - Multiple labels containing information on how a packet is forwarded.
• Shim - Header containing a Label Stack
• Label Switch Path - path that a packet follows for a specific FEC
• LDP - Label Distribution Protocol, used to distribute Label information between MPLS-aware network devices
• Label Swapping - manipulation of labels to forward packets towards the destination.
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Ingress Label FEC Egress Label
6 138.120.6/24 - xxxx 9
Ingress Label AttributeFEC Egress LabelIngress Label FEC Egress Label
6 138.120.6/24 - xxxx 9
Attribute
A
6 138.120.6/24 - xxxx 12B
•FECs are manually initiated by the operator
•A FEC is associated at least one Label
•A packet can be mapped to a particular FEC based on the following criteria:•destination IP address,•source IP address,•TCP/UDP port,•in case of inter AS-MPLS, Source-AS and Dest-AS,•class of service, •application used,•…•any combination of the previous criteria.
FEC Classification
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What is a Label ?
• A short, fixed length, locally significant identifier used to identify a FEC.
• The label can be identified by the L2 technology identifier (e.g. VPI/VCI for ATM, DLCI for FR or MPLS label for PPP/Ethernet).
L2 Type L2 TypePort PortIngress Label Egress LabelFEC
ATM 1-1 12 (i.e. 4/65) F1 22 (i.e. 5/65)3-4ATM
ATM 1-1 15 (i.e. 0/25) F4 9 (i.e. 101) 5-1FR
Gig Eth 5-1 7 F1 22 (i.e. 4/65)3-4ATM
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MPLS Label Assignment Schemes
• Topology Driven – Label assignment in response to routing
protocols (OSPF and BGP) updates
• Control Driven – Label assignment in response to RSVP, CR-
LDP requests
• Traffic Driven – Label assignment in response to flow detection
& triggering
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The MPLS Shim Header• The Label (Shim Header) is represented as a sequence of
Label Stack Entry• Each Label Stack Entry is coded by 4 bytes (32 bits) as
described• 20 Bits is reserved for the Label Identifier (also named Label)
Label(20 bits)
Exp(3 bits)
S(1 bit)
TTL(8bits)
Label : Label value (0 to 15 are reserved for special use)
Exp : Experimental UseS : Bottom of Stack (set to 1 for the last entry in the label)
TTL : Time To Live
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Label Switched Path
5 12
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 138.120 312
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 138.120 x4
53
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 x 138.120
MPLS switch
MPLS switch
MPLS switch
MPLS switch1
2
3
1 2
3
1
2
3
41
2
3
138.120
192.168127.20
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MPLS switch
MPLS switch
MPLS switch
MPLS switch1
2
3
1 2
3
1
2
3
41
2
3
138.120
192.168127.20
138.120.6.12
138.120.6.12138.120.6.12
138.120.6.12 138.120.6.12
138.120.6.12
??138.120.6.12
Default3
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 x None
??138.120.6.12
??
138.120.6.12
Default Default
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 None 3
??
138.120.6.12 ??138.120.6.12
Default
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 None x4
??138.120.6.12
Hop by Hop IP forwarding
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5 12
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 138.120 312
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 138.120 x4
53
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 x 138.120
MPLS switch
MPLS switch
MPLS switch
MPLS switch1
2
3
1 2
3
1
2
3
41
2
3
138.120
192.168127.20
138.120.6.12
138.120.6.12
138.120.6.12
138.120.6.12 138.120.6.12
IP forwarding using LSP
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MPLS Label Distribution Protocol
• LDP - a set of procedures by which one LSR informs the other of the FEC-to-Label binding it has made.
• Currently, several protocols used as Label Distribution Protocol (LDP) are available:– RSVP-TE (MPLS extension)
– LDP and CR-LDP
– BGP-4 MPLS extensions
• Label Distribution schemes
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July 29, 2000 TECON 2000July 29, 2000 TECON 2000 21
Downstream stream on demand
Mapping 12Mapping 5
5 12
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 138.120 312
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 138.120 x4
53
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 x 138.120
Request 138.120Request 138.120
MPLS switch
MPLS switch
MPLS switch
MPLS switch1
2
3
1 2
3
1
2
3
41
2
3
138.120
192.168127.20
The label is requested by the upstream node and the downstream node defines the
label used.
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July 29, 2000 TECON 2000July 29, 2000 TECON 2000 22
Unsolicited Downstream
MPLS switch
MPLS switch
MPLS switch
MPLS switch1
2
3
1 2
3
1
2
3
41
2
3
138.120
192.168127.20
Mapping 12Mapping 5
5 1212
5
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 138.120 3
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 138.120 x4
3
IngressInterface
IngressLabel
FEC EgressInterface
EgressLabel
1 x 138.120
The downstream node defines the label and advertises it to the upstream node.
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Edge LSR Features
– Routing protocols
– FEC Classification
– Initiates LSP setup for Downstream On Demand method
– Adaptation of non-MPLS data to MPLS data
– Layer 2 translation for MPLS data
– Terminated MPLS-VPN
– At least one LDP protocol
– Edge LSR is counted into the TTL count as a regular router
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Core LSR Features– Routing protocols
– Propagates Downstream On Demand method (request and mapping)
– Layer 2 translation
– High speed label forwarding/switching
– At least one LDP protocol
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Agenda
• Motivation for MPLS
• How MPLS Works !
• MPLS Technology
• MPLS Application
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MPLS Advantages
• Simplified Forwarding• Efficient Explicit Routing• Traffic Engineering• QoS Routing• Mappings from IP Packet to Forwarding
Equivalence Class (FEC)• Partitioning of Functionality• Common Operation over Packet and Cell media
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MPLS - the Future
• Who will use MPLS?– Large-scale data networks used by Enterprises,
Carriers and ISPs.
• Why MPLS?– Delivers high speed L2 (really “Label”) switching
at low cost vs. traditional L3 routing – Provides Traffic Engineering - allows the user to
direct traffic based on network utilization and demand.
– Ease of provisioning QoS– Support for VPNs
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Explicitly Routed LSP
• End-to-End forwarding decision determined by ingress node.
• Enables Traffic Engineering
LER 1
LSR 2 LSR 3
LER 4
Forward toLSR 2LSR 3LSR 4LSR X
Overload !!
Overload !!
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MPLS Traffic Engineering
• MPLS Traffic Engineering (TE) provides high quality IP service.
• TE defines :– LSP Admission Control (LAC)
– IP traffic (policing or shaping)
– IP service prioritization
– Network capacity and growth capacity
• TE is primary done by external tools. This solution allows flexibility and customization.
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MPLS VPN : MPLS topology
Site A
138.120.8.0/24
VPN 2
Site B
138.120.6.0/24
VPN 2
ISP BackboneLSR LSR
LSR
LSR
LSR
LSR
Site A
138.120.8.0/24
VPN 1
Site B
138.120.6.0/24 VPN 1
LSP 32
LSP 47
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July 29, 2000 TECON 2000July 29, 2000 TECON 2000 31
MPLS - Some Major Vendors
• Alcatel
• Cisco
• Juniper Networks
• Nortel
• Lucent
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MPLS - More Information @
• MPLS Charter http://www.ietf.org/html.charters/mpls-charter.html
• MPLS Resource Centerhttp://www.mplsrc.com
• MPLS Forum http://www.mplsforum.org
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MPLS - An Analysis
UDP Rate (in Mbps)
Th
rou
ghp
ut
(in
Mb
ps)
TCP 1
UDP
TCP 2
TCP & UDP Flows without MPLS
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MPLS - An Analysis
UDP Rate (in Mbps)
Th
rou
ghp
ut
(in
Mb
ps)
TCP 1
UDP
TCP 2
TCP & UDP Flows with MPLS Trunks (LSPs)