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2000/05/15 2
Topics
Introduction History and motivation MPLS mechanisms
MPLS protocols RSVP-TE/CR-LDP
MPLS applications VPNSs, traffic engineering, restoration
Generalized MPLS
2000/05/15 Shirl Grant NLANR Engineering Services
3
WHY MPLS ?
Ultra fast forwarding Use switching instead of
routing IP Traffic Engineering
Constraint-based routing Virtual Private Networks
Controllable tunneling mechanism
Protection and restoration
2000/05/15 4
IP Forwarding Table
47.1.*.*
47.2.*.*47.3.*.*
Dest Out
47.1 147.2 2
47.3 3
1
23
Dest Out
47.1 147.2 2
47.3 3
Dest Out
47.1 147.2 2
47.3 3
1
23
1
2
3
2000/05/15 5
Hop-by-Hop IP Forwarding
47.1
47.247.3
IP 47.1.1.1
Dest Out
47.1 147.2 2
47.3 3
1
23
Dest Out
47.1 147.2 2
47.3 3
1
2
1
2
3
IP 47.1.1.1
IP 47.1.1.1IP 47.1.1.1
Dest Out
47.1 147.2 2
47.3 3
2000/05/15 6
Routing Lookup
Longest prefix match is (was) expensive. Label matching is much less expensive.
10 Gbps 10 Gbps
20M packets/sec
Switchfabric
Control CPU
I/F I/F
9.*.*.* 14.1.2.1 29.1.*.* 67.1.2.2 49.2.*.* 71.1.2.3 69.1.1.* 113.1.2.1 89.2.1.* 113.1.2.1 89.1.1.1 71.1.2.3 69.1.1.2 14.1.2.1 29.2.1.1 71.1.2.3 6
Prefix Next Hop Interface
2000/05/15 7
IntfIn
LabelIn
Dest IntfOut
3 0.40 47.1 1
IntfIn
LabelIn
Dest IntfOut
LabelOut
3 0.50 47.1 1 0.40
MPLS Labels
47.1
47.247.3
1
2
31
2
1
2
3
3IntfIn
Dest IntfOut
LabelOut
3 47.1 1 0.50 Mapping: 0.40
Request: 47.1
Mapping: 0.50
Request: 47.1
2000/05/15 8
Label Switched Path
IntfIn
LabelIn
Dest IntfOut
3 0.40 47.1 1
IntfIn
LabelIn
Dest IntfOut
LabelOut
3 0.50 47.1 1 0.40
47.1
47.247.3
1
2
31
2
1
2
3
3IntfIn
Dest IntfOut
LabelOut
3 47.1 1 0.50
IP 47.1.1.1
IP 47.1.1.1
2000/05/15 9
Forwarding Equivalence Classes
FEC = “A subset of packets that are all treated the same way by a router” The concept of FECs provides for a great deal of flexibility and scalability In conventional routing, a packet is assigned to a FEC at each hop (i.e. L3
look-up), in MPLS it is only done once at the network ingress
Packets are destined for different address prefixes, but can be mapped to common pathPackets are destined for different address prefixes, but can be mapped to common path
IP1
IP2
IP1
IP2
LSRLSRLER LER
LSP
IP1 #L1
IP2 #L1
IP1 #L2
IP2 #L2
IP1 #L3
IP2 #L3
2000/05/15 10
MPLS Terminology
LDP: Label Distribution Protocol LSP: Label Switched Path FEC: Forwarding Equivalence Class LSR: Label Switching Router LER: Label Edge Router
2000/05/15 11
Label Distribution Methods
LSR1 LSR2
Downstream Label Distribution
Label-FEC Binding
• LSR2 discovers a ‘next hop’ for a particular FEC
• LSR2 generates a label for the FEC and communicates the binding to LSR1
• LSR1 inserts the binding into its forwarding tables
• If LSR2 is the next hop for the FEC, LSR1 can use that label knowing that its meaning is understood
LSR1 LSR2
Downstream-on-Demand Label Distribution
Label-FEC Binding
• LSR1 recognizes LSR2 as its next-hop for an FEC
• A request is made to LSR2 for a binding between the FEC and a label
• If LSR2 recognizes the FEC and has a next hop for it, it creates a binding and replies to LSR1
• Both LSRs then have a common understanding
Request for Binding
Both methods are supported, even in the same network at the same time
2000/05/15 12
Distribution Control
Independent LSP ControlIndependent LSP Control Ordered LSP ControlOrdered LSP Control
Next Hop(for FEC)
OutgoingLabel
IncomingLabel
• Each LSR makes independent decision on when to generate labels and communicate them to upstream peers
• Communicate label-FEC binding to peers once next-hop has been recognized
• LSP is formed as incoming and outgoing labels are spliced together
• Label-FEC binding is communicated to peers if: - LSR is the ‘egress’ LSR to particular FEC - label binding has been received from
upstream LSR
• LSP formation ‘flows’ from egress to ingress
DefinitionDefinition
ComparisonComparison • Labels can be exchanged with less delay• Does not depend on availability of egress node• Granularity may not be consistent across the nodes
at the start• May require separate loop detection/mitigation
method
• Requires more delay before packets can be forwarded along the LSP
• Depends on availability of egress node• Mechanism for consistent granularity and freedom
from loops• Used for explicit routing and multicast
Both methods are supported in the standard and can be fully interoperable
2000/05/15 13
Label Retention Methods
Liberal Label Retention Conservative Label Retention
LSR1
LSR2
LSR3
LSR4
Label Bindingsfor LSR5
Valid Next Hop
LSR4’s LabelLSR3’s LabelLSR2’s Label
LSR1
LSR2
LSR3
LSR4
Label Bindingsfor LSR5
Valid Next Hop
LSR4’s LabelLSR3’s LabelLSR2’s Label
• LSR maintains bindings received from LSRs other than the valid next hop
• If the next-hop changes, it may begin using these bindings immediately
• May allow more rapid adaptation to routing changes
• Requires an LSR to maintain many more labels
• LSR only maintains bindings received from valid next hop
• If the next-hop changes, binding must be requested from new next hop
• Restricts adaptation to changes in routing
• Fewer labels must be maintained by LSR
Label Retention method trades off between label capacity and speed of adaptation to routing changes
2000/05/15 14
Label Encapsulation
ATM FR Ethernet PPP
MPLS Encapsulation is specified over various media types. Top labels may use existing format, lower label(s) use a new “shim” label format.
VPI VCI DLCI “Shim Label”
L2
Label
“Shim Label” …….
IP | PAYLOAD
2000/05/15 15
Label Format
Exp field used to identify the class of service Stack bit is used identify the last label in the
label stack TTL field is used as a time-to-live counter. Special
processing rules are used to mimic IP TTL semantics.
Label 20 bits
Exp 3 bits
Stack1 bit
TTL8 bits
2000/05/15 16
Label Distribution Protocols
Label Distribution Protocol (LDP) Constraint-based Routing LDP (CR-
LDP) Extensions to RSVP Extensions to BGP
2000/05/15 17
LDP:Label Distribution Protocol
Label distribution ensures that adjacent routers havea common view of FEC <-> label bindings
Routing Table:
Addr-prefix Next Hop47.0.0.0/8 LSR2
Routing Table:
Addr-prefix Next Hop47.0.0.0/8 LSR2
LSR1 LSR2 LSR3
IP Packet 47.80.55.3
Routing Table:
Addr-prefix Next Hop47.0.0.0/8 LSR3
Routing Table:
Addr-prefix Next Hop47.0.0.0/8 LSR3
For 47.0.0.0/8use label ‘17’
Label Information Base:
Label-In FEC Label-Out17 47.0.0.0/8 XX
Label Information Base:
Label-In FEC Label-Out17 47.0.0.0/8 XX
Label Information Base:
Label-In FEC Label-OutXX 47.0.0.0/8 17
Label Information Base:
Label-In FEC Label-OutXX 47.0.0.0/8 17
Step 1: LSR creates bindingbetween FEC and label value
Step 2: LSR communicatesbinding to adjacent LSR
Step 3: LSR inserts labelvalue into forwarding base
Common understanding of which FEC the label is referring to!
2000/05/15 18
LDP: Basic Characteristics
Provides LSR discovery mechanisms to enable LSR peers to find each other and establish communication
Defines four classes of messages DISCOVERY: deals with finding neighboring LSRs ADJACENCY: deals with initialization, keep alive, and shutdown of
sessions LABEL ADVERTISEMENT: deals with label binding advertisements,
request, withdrawal, and release NOTIFICATION: deals with advisory information and signal error
information Runs over TCP for for reliable delivery of messages,
except for discovery, which uses UDP and IP multicast Designed to be extensible, using messages specified as
TLVs (type, value, length) encoded objects.
2000/05/15 19
LDP Messages
INITIALIZATION KEEPALIVE LABEL MAPPING LABEL WITHDRAWAL LABEL RELEASE LABEL REQUEST
2000/05/15 20
IntfIn
LabelIn
Dest IntfOut
3 0.40 47.1 1
IntfIn
LabelIn
Dest IntfOut
LabelOut
3 0.50 47.1 1 0.40
47.1
47.247.3
1
2
31
2
1
2
3
3
IntfIn
Dest IntfOut
LabelOut
3 47.1.1 2 1.333 47.1 1 0.50
IP 47.1.1.1
IP 47.1.1.1
Explicitly Routed LSP
2000/05/15 21
ER LSP - Advantages
Operator has routing flexibility policy-based, QoS-based
Can use routes other than shortest path
Can compute routes based on constraints in exactly the same manner as ATM based on distributed topology database.(traffic engineering)
2000/05/15 22
ER LSP - discord!
Two signaling options proposed in the standards: CR-LDP, RSVP extensions:
CR-LDP = LDP + Explicit Route RSVP ext = Traditional RSVP + Explicit
Route +Scalability Extensions Market will probably have to resolve it Survival of the fittest not such a bad
thing.
2000/05/15 24
Integrated Services Internet
Applications specify traffic and service specs Tspec: traffic specs including peak rate, maximum
packet size, burst size, and mean rate Rspec: service spec, specifically service rate
Two classes of service defined Guaranteed service: satisfies hard guarantees on
bandwidth and delay Controlled load service: provides service similar to that
in “unloaded network” RSVP was extended to RSVP-TE support signaling
RSVP was further extend to add MPLS support
2000/05/15 25
Differentiated Services Internet
IP packets carry 6-bit service code points (DSCP) Potentially support 64-different classes of services
Routers map DSCP to per-hop-behavior (PHB) PHBs can be standard or local Standard PHBs include
Default: No special treatment or best effort Expedited forwarding (EF): Low delay and loss Assured forwarding (AF): Multiple classes, each class with multiple
drop priorities LSRs don’t sort based on IP headers, hence DSCPs need to
be mapped to EXP field in MPLS shim header Exp field is only 3-bit wide – can support only 8 DSCPs/PHBs Labels can be used if more than 8 PHBs need to be supported Same approach can be used for link layers which do not use
Shim headers, e.g. ATM
2000/05/15 26
Traffic Engineering with RSVP
Sender
Receiver
PATH {Tspec}
RESV{Rspec}
PATH {Tspec}
PATH {Tspec} PATH
{Tspec}
RESV{Rspec}
RESV{Rspec}
RESV{Rspec}
2000/05/15 27
Label Distribution with RSVP-TE
PATH {Tspec}
RESV{Rspec}
{Label = 5}
RESV{Rspec}
{Label = 10}
Sender
PATH {Tspec}
RESV{Rspec}
PATH {Tspec}
PATH {Tspec} PATH
{Tspec}
RESV{Rspec}
2000/05/15 29
MPLS ProtectionEnd-to-end Path Protection
A
C
BD
E
F
Backup LSP
Primary LSP
Backup and primary LSPs should be route diverse
2000/05/15 30
MPLS ProtectionFast Reroute
LSR A
LSR F
LSR E
LSR D
LSR C
LSR B
Detour to avoid AB
Detour to avoid BC
Detour to avoid CD
Detour to avoid DE
Detour to avoid link DE
Detour around node or link failures Example LSP shown traverses (A, B, C, D, E, F)
Each detour avoids Immediate downstream node & link towards it Except for last detour: only avoids link DE
2000/05/15 31
Detour Merging
LSR A
LSR F
LSR E
LSR D
LSR C
LSR B
Detour to avoid AB
Detour to avoid BC
Merged detour to avoid AB and BC
Reduces state maintained Improves resource utilization
2000/05/15 32
MPLS Protection Types
1+1: Backup LSP established in advance, resources dedicated, data simultaneously sent on both primary and backup
Switchover performed only by egress LSR Fastest, but most resource intensive
1:1 : Same as 1+1 with the difference that data is not sent on the backup
Requires failure notification to the ingress LSR to start transmitting on backup
Notification may be send to egress also Resources in the backup may be used by other traffic
Low priority traffic (e.g., plain IP traffic), shared by other backup paths
2000/05/15 33
MPLS VPN: The Problem
10.1/16
10.1/16
10.2/16
10.2/16
10.3/16
10.3/16
Provider NetworkCustomer 1
Site 1
Customer 1Site 2
Customer 1Site 3
Customer 2Site 3
Customer 2Site 1
Customer 2Site 2
2000/05/15 34
MPLS VPN: The Model
10.1/16
10.1/16
10.2/16
10.2/16
10.3/16
10.3/16
Customer 1Site 1
Customer 2Site 1
Customer 2Site 3
Customer 1Site 3
Customer 2Site 2
Customer 1Site 2
Customer 1Virtual Network
Customer 2Virtual Network
2000/05/15 35
MPLS VPN: The Solution
10.1/16
10.1/16
10.2/16
10.2/16
10.3/16
10.3/16
Customer 1Site 1
Customer 1Site 2
Customer 1Site 3
Customer 2Site 3
Customer 2Site 1
Customer 2Site 2
VRF 1
VRF 1
VRF 1
VRF 2
VRF 2
VRF 2
MPLS LSP
MPLS LSP
2000/05/15 36
Unified Control Plane
UNI - User-to-Network InterfaceI-NNI - Internal Network-to-Network InterfaceE-NNI - External Network-to-Network Interface
Optical Network
Optical subnet
Optical subnet
Optical subnet
UNI
UNI
E-NNIE-NNI
E-NNI
I-NNI
ATM Network IP Network
IP Network
ATM Network
ATM Network
ATM Network
ATM NetworkIP Network
ATM Network
ATM Network
2000/05/15 37
GMPLS: Generalized MPLS
GMPLS Handles Nodes With Diverse Capabilities. Packet Switch Capable (PSC) Time Division Multiplexing Capable (TDM) Lambda Switch Capable (LSC) Fiber Switch Capable (FSC)
Each Node Is Treated As an MPLS Label-switching Router (LSR) Lightpaths/TDM Circuits Are Considered Similar to Label-Switched Paths
(LSPs) Selection of s and OXC ports are considered similar to selection of labels
FSC Cloud
LSCCloud
TDM Cloud
PSC Cloud