MultiProtocol Label Switching (MPLS)
Agenda
• • • • MPLS - The Motivation How MPLS Works ! MPLS Technology MPLS Application
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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.
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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)
MPLS and ISO model
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 Applications 7 to 5
TCP IP MPLS Frame FR Relay
UDP
4 3
PPP PPP
ATM (*) ATM (*)
2
Physical (Optical - Electrical)
1
(*) ATM overlay model (without addressing and P-NNI) is considered as an ISO layer 2 protocol.
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MPLS
• is a data-carrying mechanism that belongs to the family of packet-switched networks. • is generally considered to lie between traditional definitions of Layer 2 (data link layer) and Layer 3 (network layer), and thus is often referred to as a "Layer 2.5" protocol.
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Agenda
• • • • Motivation for MPLS How MPLS Works ! MPLS Technology MPLS Application
July 29, 2000 TECON 2000
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MPLS Architecture
LSP Routing protocol FEC table Attributes
Classification Label assignment Label swapping Label removal
OSPF
OSPF
OSPF
Local table
Local table
Local table
Precedence
Label table Label Switch
Local table
Local table
Local table
Layer 2
Layer 2
Layer 2
Layer 1 Ingress Node
Layer 1 Core Node
Layer 1 Egress Node
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MPLS process
Label Switch Path OSPF / RIP / IS-IS
Label removal
FEC FEC FEC
Label swapping
Classification Label assignment
Precedence
Label table
Label table
Label table
Layer 2
Layer 2
Layer 2
Layer 1 Ingress Node
Layer 1 Core Node
Layer 1 Egress Node
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MPLS Cloud
LER L3 Routing LER LER
L3 Routing
LER L3 Routing
IP Packet IP Packet w/ Label
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L3 Routing LSR Label Swapping LSR Label Swapping LER
L3 Routing
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MPLS Link Layers & Label Encapsulation
Layer2
ATM
VPI VCI
FR DLCI
Ethernet
PPP
“Shim Label”
“Shim header” ……. IP | PAYLOAD
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Agenda
• • • • Motivation for MPLS How MPLS Works ! MPLS Technology MPLS Application
July 29, 2000 TECON 2000
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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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FEC Classification
•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.
Ingress Label
6
FEC
138.120.6/24 - xxxx
Egress Label
9
•FECs are manually initiated by the operator
•A FEC is associated at least one Label
Ingress Label Ingress Label FEC FEC Attribute Egress Label Attribute Egress Label
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138.120.6/24 - xxxx 138.120.6/24 - xxxx
A B
9 12 14
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
Port Ingress Label FEC
L2 Type ATM
Egress Label Port
ATM
ATM Gig Eth
1-1
1-1 5-1
12 (i.e. 4/65)
15 (i.e. 0/25) 7
F1
F4 F1
22 (i.e. 5/65)3-4
9 (i.e. 101) 5-1 22 (i.e. 4/65)3-4
FR
ATM
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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, CRLDP 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)
Label : Exp : S: TTL :
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Exp (3 bits)
S (1 bit)
TTL (8bits)
Label value (0 to 15 are reserved for special use) Experimental Use Bottom of Stack (set to 1 for the last entry in the label) Time To Live
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Label Switched Path
Ingress Ingress Interface Label
FEC Egress Egress Interface Label
138.120 3 12
Ingress Ingress Interface Label
1
FEC Egress Egress Interface Label 138.120
12
4
x
1
5
MPLS switch
1 3
4
1 2 3 1 2 2 3
138.120
127.20
MPLS switch
1 3 2
MPLS switch
192.168
MPLS switch
Ingress Ingress Interface Label
1 x
FEC Egress Egress Interface Label 5 3 138.120
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Hop by Hop IP forwarding
Ingress Ingress Interface Label
1 Default FEC Egress Egress Interface Label None 3 Default Ingress Ingress Interface Label FEC Egress Egress Interface Label
1
Default
None
4
x
??
1
MPLS switch
3
??
1 2 2
4 3
138.120
138.120.6.12
127.20
MPLS switch
1 3 2 1
2
3
MPLS switch
192.168
138.120.6.12
??
Ingress Ingress Interface Label
1 x
MPLS switch
FEC Egress Egress Interface Label None 3 Default
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July 29, 2000 TECON 2000
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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Downstream stream on demand
Ingress Ingress Interface Label
1 5
FEC Egress Egress Interface Label
138.120 3 12
Ingress Ingress Interface Label 1
FEC Egress Egress Interface Label
12
138.120
4
x
MPLS switch
1 3
4
1 2 3 1 2 2
138.120
127.20
MPLS switch
1 3 2
3
MPLS switch
192.168
MPLS switch
Ingress Ingress Interface Label
1 x
FEC Egress Egress Interface Label
138.120 3 5
The label is requested by the upstream node and the downstream node defines the label used.
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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 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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SWAP PUSH POP
• In a swap operation the label is swapped with a new label, and the packet is forwarded along the path associated with the new label. • In a push operation a new label is pushed on top of the existing label, effectively "encapsulating" the packet in another layer of MPLS. This allows hierarchical routing of MPLS packets. • In a pop operation the label is removed from the packet, which may reveal an inner label below. This process is called "decapsulation". If the popped label was the last on the label stack, the packet "leaves" the MPLS tunnel. This is usually done by the egress router, but see PHP below.
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Agenda
• • • • Motivation for MPLS How MPLS Works ! MPLS Technology MPLS Application
July 29, 2000 TECON 2000
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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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MPLS VPN : MPLS topology
VPN 2
138.120.6.0/24
LSR
138.120.8.0/24
Site B
VPN 1
Site A
ISP Backbone
LSR
LSP 47
LSR LSR
LSR
LSP 32
LSR
Site A
138.120.8.0/24
Site B
138.120.6.0/24
VPN 2
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VPN 1
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MPLS - Some Major Vendors
• • • • • Alcatel Cisco Juniper Networks Nortel Lucent
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