Transcript Title Subtitle - Aalborg Universitet
MPLS Tutorial Bilel N. Jamoussi, Ph.D.
Senior Network Architect Carrier Data Networks [email protected]
Tutorial Outline
• • • • • • •
Overview Label Encapsulations Label Distribution Protocols MPLS and ATM IETF Status Nortel Networks Activity Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 2
MPLS Motivations
• • •
Flexibility (L2/L3 Integration)
— Media Support: ATM, FR, Ethernet, PPP — Operate IP over Multiservice ATM — More than destination-based Forwarding •
IP Traffic Engineering
— Constraint-based Routing
IP-VPN
— Tunneling mechanism
VOIP
— Connection-oriented Paths and QoS
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 3
All Nodes Run Standard IP Routing
47.3
3 Dest 47.1
47.2
47.3
Out 1 2 3 1 3 2 Dest 47.1
47.2
47.3
Out 1 2 3 1 2 3 Dest 47.1
47.2
47.3
Out 1 2 3 2 1 47.1
47.2
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 4
IP Destination Lookup at Each Hop
47.3
3 IP 47.1.1.1
3 Dest 47.1
47.2
47.3
Out 1 2 3 1 IP 47.1.1.1
2 Dest 47.1
47.2
47.3
Out 1 2 3 1 2 IP 47.1.1.1
Dest 47.1
47.2
47.3
Out 1 2 3 2 1 47.1
IP 47.1.1.1
47.2
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 5
Multiprotocol Label Switching (MPLS)
Edge Label Switch Router (LSR) Label Switch Router Label Switch Router Edge Label Switch Router (LSR) IP Packet IP Packet Label
Layer 3 Routing
IP Packet IP Packet Label
Layer 2 Forwarding
IP Packet Label
Layer 3 Routing
MPLS involves routing at the edges, switching in the core INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 6
MPLS Terminology
LDP: Label Distribution Protocol FEC: Forwarding Equivalence Class LSP: Label Switched Path LSR: Label Switching Router LER: Label Edge Router (Note that LER is a Nortel Networks term describing the edge LSR function) INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 7
Forwarding Equivalence Classes
LSR LSP FEC FEC
Packets are destined for different address prefixes, but can be mapped to common egress router, treated as equivalent FEC
• • • 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 an FEC at each hop (i.e., L3 lookup); in MPLS, it is only done once at the network ingress
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 8
Label Switched Path — Concept
Incoming Packets Classified, Labeled Label Switched Path (LSP) Set Up Across Network Interior Nodes Forwarded Along LSP Based on Labels Egress Node Removes Label Before Forwarding Two types of Label Switched Paths:
• •
Hop-by-hop Explicit Routing INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 9
MPLS Label Distribution
Intf In 3 Dest Intf Out 47.1 1 Label Out 0.50
1 47.3
3 2 3 Intf In 3 Label In 0.50
Dest Intf Out 47.1 1 Label Out 0.40
Intf In 3 Request: 47.1
3 Label In 0.40
Dest Intf Out 47.1 1 1 47.1
2 1 Mapping: 0.40
2 47.2
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 10
Label Switched Path (LSP)
Intf In 3 Dest Intf Out 47.1 1 Label Out 0.50
1 47.3
3 2 IP 47.1.1.1
3 Intf In 3 Label In 0.50
Dest Intf Out 47.1 1 Label Out 0.40
2 1 Intf In 3 3 Label In 0.40
Dest Intf Out 47.1 1 1 2 47.2
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 11
LSPs: Explicit Routing
Explicit Routing LSR A LSR B LSR C LSR D
Forward to LSR B LSR C LSR D LSR E •
Ingress node (or egress node) determines path from ingress to egress
•
Operator has routing flexibility (policy-based, QoS-based)
•
Required for MPLS traffic engineering
•
Two signaling options proposed in the standards: RSVP, CR-LDP LSR E INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 12
Traffic Engineered Path
Intf In 3 3 Dest 47.1.1
47.1
Intf Out 2 1 Label Out 1.33
0.50
3 Intf In 3 Label In 0.50
Dest Intf Out 47.1 1 Label Out 0.40
1 1 2 47.3
3 2 IP 47.1.1.1
Intf In 3 3 Label In 0.40
Dest Intf Out 47.1 1 1 2 47.2
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 13
Tutorial Outline
• • • • • • •
Overview Label Encapsulations Label Distribution Protocols MPLS & ATM IETF Status Nortel Networks Activity Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 14
Label Encapsulation
MPLS
ATM
L2 Label
VPI VCI FR DLCI Ethernet
“
Shim” PPP
MPLS Encapsulation is specified over various media types
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 15
MPLS Link Layers
•
MPLS is intended to run over multiple link layers
•
Specifications for the following link layers currently exist:
• ATM: label contained in VCI/VPI field of ATM header • Frame Relay: label contained in DLCI field in FR header • PPP/LAN: uses ‘shim’ header inserted between L2 and L3 headers •
Fields and functionality may vary between different link layers
— ATM/FR have to adapt to existing structure — PPP/LAN header has more freedom to incorporate useful features (CoS, TTL) •
Translation between link-layers types must be supported MPLS intended to be “multiprotocol” below as well as above INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 16
MPLS Encapsulation — ATM
ATM LSR constrained by the cell format imposed by existing ATM standards 5 Octets ATM Header Format VPI VCI PT CLP HEC Option 1 Option 2 Option 3 Label Label Combined Label ATM VPI (Tunnel) Label ATM SAR ATM Header ATM Payload n
•••
1 Generic Label Encap.
(PPP/LAN format)
48 Bytes 48 Bytes • • •
AAL 5 PDU Frame (nx48 bytes) Network Layer Header and Packet (e.g., IP) AAL5 Trailer
• • •
Top one or two labels are contained in the VPI/VCI fields of ATM header
— one in each or single label in combined field, negotiated by LDP
Further fields in stack are encoded with ‘shim’ header in PPP/LAN format
— must be at least one, with bottom label distinguished with ‘explicit NULL’
TTL is carried in top label in stack, as a proxy for ATM header (that lacks TTL) INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 17
MPLS Encapsulation — Frame Relay
Q.922
Header n Generic Encap.
(PPP/LAN Format)
•••
1 DLCI C/ R E A DLCI FE CN BE CN D E E A Layer 3 Header and Packet DLCI Size = 10, 17, 23 Bytes
•
Current label value carried in DLCI field of Frame Relay header
•
Can use either 2 or 4 octet Q.922 address (10, 17, 23 bytes)
•
Generic encapsulation contains n labels for stack of depth n
— top label contains TTL (which FR header lacks), ‘explicit NULL’ label value
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 18
MPLS Encapsulation — PPP & LAN Data Links
MPLS ‘Shim’ Headers (1-n) n
•••
1 Layer 2 Header (e.g., PPP, 802.3) Network Layer Header and Packet (e.g., IP) 4 Octets Label Stack Entry Format Label Exp.
S TTL
Label: Label Value, 20 bits (0-16 reserved) Exp.: Experimental, 3 bits (was Class of Service) S: TTL: Bottom of Stack, 1 bit (1 = last entry in label stack) Time to Live, 8 bits •
Network layer must be inferable from value of bottom label of the stack
• •
TTL must be set to the value of the IP TTL field when packet is first labeled When last label is popped off stack, MPLS TTL to be copied to IP TTL field
•
Pushing multiple labels may cause length of frame to exceed layer-2 MTU
— LSR must support “Max. IP Datagram Size for Labeling” parameter — any unlabeled datagram greater in size than this parameter is to be fragmented
MPLS on PPP links and LANs uses ‘Shim’ Header Inserted Between Layer 2 and Layer 3 Headers INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 19
Tutorial Outline
• • • • • • •
Overview Label Encapsulations Label Distribution Protocols MPLS & ATM IETF Status Nortel Networks Activity Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 20
Label Distribution Protocols
• • • • •
Overview of Hop-by-hop and Explicit Label Distribution Protocol (LDP) Constraint-based Routing LDP (CR-LDP) Extensions to RSVP Extensions to BGP INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 21
LSPs: Hop-by-Hop vs. Explicit Routing
Hop-by-Hop Routing LSR A MPLS will form label switched paths by one of two methods — hop-by-hop routing or explicit routing LSR B LSR D LSR C LSR E
Forward to LSR B Forward to LSR C Forward to LSR D Forward to LSR E • •
Each node runs layer 3 routing protocol Routing decisions made independently at each node Explicit Routing LSR A LSR B LSR D LSR C
Forward to LSR B LSR C LSR D LSR E • •
Also known as ‘source routing’ or ‘traffic steering’ Ingress node (or egress node) determines path from ingress to egress INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
Forward to LSR ...
LSR E
MPLS Tutorial 22
Comparison — Hop-by-Hop vs. Explicit Routing
Hop-by-Hop Routing Explicit Routing
• Distributes topology awareness • Centralized topology awareness (in ingress node) • No path setup/tear-down/refresh required • Path setup/tear-down/refresh required • Automates routing using industry standard protocols (e.g., OSPF, ISIS) • Requires manual provisioning or creation of new routing protocol • Loop detection/prevention required • Reroute on failure impacted by convergence time of routing protocol • Backup paths may be preprovisioned for rapid restoration • Existing routing protocols are destination prefix-based • Operator has routing flexibility (policy-based, QoS-based) • Easily used for traffic engineering • Difficult to perform traffic engineering, QoS-based routing Explicit routing shows great promise for traffic engineering, at the cost of operator involvement (or new routing protocols)
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 23
Explicit Routing — MPLS vs. Traditional Routing
LSR A LSR D LSR E LSR B LSR C
Forward to LSR B LSR C LSR D LSR E •
Connectionless nature of IP implies that routing is based on information in each packet header
•
Source routing is possible, but path must be contained in each IP header
— lengthy paths increase size of IP header, make it variable size, increase overhead — some gigabit routers require ‘slow path’ option-based routing of IP packets •
Source routing has not been widely adopted in IP and is seen as impractical
— some network operators may filter source-routed packets for security reasons •
MPLS enables the use of source routing by its connection-oriented capabilities
— paths can be explicitly set up through the network — the ‘label’ now can represent the explicitly routed path •
Loose and strict source routing can be supported MPLS makes the use of source routing in the Internet practical INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 24
Label Distribution Protocol (LDP)
—
Purpose
Label distribution ensures that adjacent routers have a common view of FEC <-> label bindings Routing Table: Addr-prefix Next Hop 47.0.0.0/8 LSR2 Routing Table: Addr-prefix Next Hop 47.0.0.0/8 LSR3
LSR1 LSR2 LSR3
IP Packet 47.80.55.3
Label Information Base: Label-In FEC Label-Out XX 47.0.0.0/8 17 For 47.0.0.0/8 use label ‘17’ Label Information Base: Label-In FEC Label-Out 17 47.0.0.0/8 XX
Step 3: LSR inserts label value into forwarding base Step 2: LSR communicates binding to adjacent LSR Step 1: LSR creates binding between FEC and label value
Common understanding of which FEC the label is referring to!
Label distribution can either piggyback on top of an existing routing protocol, or a dedicated label distribution protocol (LDP) can be created
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 25
Label Distribution — Methods
Label Distribution can take place using one of two possible methods
Downstream Label Distribution
LSR1 LSR2
Downstream-on-Demand Label Distribution
LSR1 LSR2 Label-FEC Binding
• LSR2 and LSR1 are said to have an “LDP adjacency” (LSR2 being the downstream LSR) • 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
Request for Binding 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
Both methods are supported, even in the same network at the same time.
For any single adjacency, LDP negotiation must agree on a common method.
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 26
Distribution Control: Ordered vs. Independent
Next Hop (for FEC)
MPLS path forms as associations are made between FEC next-hops and incoming and outgoing labels
Incoming Label Outgoing Label
Definition Independent LSP Control
• 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
Ordered LSP Control
• 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
Example
• Cisco’s Tag Switching • IBM’s ARIS
Comparison
• 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 INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 27
Label Retention Methods
Binding
LSR2
for LSR5
LSR1 An LSR may receive label bindings from multiple LSRs
Binding for LSR5
Some bindings may come from LSRs that are not the valid next-hop for that FEC
Binding for LSR5
LSR4 LSR3 Conservative Label Retention Liberal Label Retention LSR2
Label Bindings for LSR5
LSR1 LSR3 LSR4’s Label
LSR3’s Label LSR2’s Label
LSR4 Valid Next Hop
• 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
LSR5
Label Bindings for LSR5
LSR4’s Label
LSR3’s Label LSR2’s Label
LSR1 LSR2 LSR3 LSR4 Valid Next Hop
• 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 INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 28
LSPs: Hop-by-Hop
Hop-by-Hop Routing LSR B LSR A LSR C LSR D LSR E
Forward to LSR B Forward to LSR C Forward to LSR D Forward to LSR E • •
Each node runs layer 3 routing protocol Routing decisions made independently at each node
Forward to LSR ...
•
Distributes topology awareness
•
Automates routing using industry standard protocols (e.g., OSPF, ISIS)
•
Difficult to perform traffic engineering INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 29
Outline
• • • •
CR-LDP Solution overview CR-LDP update CR-LDP QoS Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 30
ER-LSP Setup using CR-LDP
1. Label Request message. It contains ER path < B,C,D>.
6. When LER A receives label mapping, the ER established.
LER A 2. Request message processed and next node determined. Path list modified to
LSR B 5. LSR C receives label to use for sending data to LER D. Label table updated.
LSR C 3. Request message terminates.
4. Label mapping message originates.
LER D Ingress ER Label Switched Path Egress
•
Simple — part of the MPLS LDP protocol
• • •
Robust — signaling built upon reliable TCP layer Scalable — no need to refresh LSP state Interoperable — proven multivendor interoperability INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 31
MPLS Traffic Engineering
•
Traffic Engineering requires a solution to route LSPs according to various constraints
•
Solution has to be:
— Scalable — Reliable •
CRLDP use LDP messages to signal these various constraints INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 32
Constraint-based LSP Setup using LDP
• •
Uses LDP Messages & TLVs
— LDP runs on a reliable transport (TCP) •
Does NOT require hop-by-hop
— DOD-O can be used for loose segments •
Introduces additional TLVs to the base LDP specification to signal ER, and other “constraints” TLVs for error handling & diagnostics INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 33
Why CR-LDP?
• • •
Runs on TCP Hard State Reliable Scalable QoS Support ATM-like, FR-like, & Diffserv
— More apt to integrate/migrate in existing FR and ATM networks and to support emerging diffserev-based POS gigabit routers • •
Demonstrated interoperability Simple protocol based on LDP, output of MPLS WG INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 34
Latest CRLDP Revision
• •
Constraint-based routing overview section CR-TLV is broken in separate TLVs
— Explicit route, route pinning, pre-emption •
ER-Hop TLV encoding consistent with LDP
— 2-byte type, 2-byte length, variable length content •
Traffic TLVs and QoS INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 35
CR-LDP TLVs
•
CR-LSP FEC Element
— An opaque FEC element type 0x04 value (0 octet) • •
LSPID TLV
— A CRLSP unique identifier within an MPLS network.
•
ER-Hop Type (4) LSPID TLV
— The LSPID is used to identify the tunnel ingress point as the next hop in the ER.
Resource Class (Color) TLV
— 32 bit mask indicating which of the 32 "administrative groups" or "colors" of links the CRLSP can traverse.
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 36
CR-LDP Label Request Message
U F Label Request Message Length Message ID TLV Return Message ID TLV FEC TLV LSPID TLV ER-TLV Traffic Parameters TLV Pinning TLV "Resource Class" TLV Pre-emption TLV Optional INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 37
CRLDP Traffic and QoS
• • •
In the crldp-00 draft three service classes (delay sensitive, throughput sensitive and best effort) were defined.
This is inflexible and it's hard to map existing and new applications onto these service definitions.
In crldp-01 only CRLSP traffic and QoS parameters of a CRLSP are defined. These describe the characteristics of the CRLSP.
Loosely routed segment Unlabeled IP CRLDP MPLS domain INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA HBH only MPLS domain
MPLS Tutorial 38
Traffic Parameters TLV
U F Traf. Param. TLV Flags Frequency Length Reserved Peak Data Rate (PDR) Weight Peak Burst Size (PBS) Committed Data Rate (CDR) Committed Burst Size (CBS) Excess Burst Size (EBS) 32 bit fields are short IEEE floating point numbers Any parameter may be used or not used by selecting appropriate values Flags control “negotiability” of parameters Frequency constrains the variable delay that may be introduced Weight of the CRLSP in the “relative share” Peak rate (PDR+PBS) maximum rate at which traffic should be sent to the CRLSP Committed rate (CDR+CBS) the rate that the MPLS domain commits to be available to the CRLSP Excess Burst Size (EBS) to measure the extent by which the traffic sent on a CRLSP exceeds the committed rate INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 39
CRLSP characteristics not edge functions
• •
The approach is like diffserv’s separation of PHB from edge The parameters describe the “path behavior” of the CRLSP, i.e., the CRLSP’s characteristics
• •
Dropping behavior is not signaled
— Dropping may be controlled by DS packet markings
CRLSP characteristics may be combined with edge functions (which are undefined in CRLDP) to create services
— Edge functions can perform packet marking — Example services are in an appendix
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 40
Peak Rate
• • • • •
The maximum rate at which traffic should be sent to the CRLSP Defined by a token bucket with parameters
— Peak data rate (PDR) — Peak burst size (PBS)
Useful for resource allocation If a network uses the peak rate for resource allocation then its edge function should regulate the peak rate May be unused by setting PDR or PBS or both to positive infinity INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 41
Committed Rate
• • • • •
The rate that the MPLS domain commits to be available to the CRLSP Defined by a token bucket with parameters
— Committed data rate (CDR) — Committed burst size (CBS)
Committed rate is the bandwidth that should be reserved for the CRLSP CDR = 0 makes sense; CDR = +
less so CBS describes the burstiness with which traffic may be sent to the CRLSP INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 42
Excess Burst Size
• •
Measure the extent by which the traffic sent on a CRLSP exceeds the committed rate Defined as an additional limit on the committed rate’s token bucket
• • •
Can be useful for resource reservation If a network uses the excess burst size for resource allocation then its edge function should regulate the parameter and perhaps mark or drop packets EBS = 0 and EBS = +
both make sense INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 43
Frequency
• • • • •
Specifies how frequently the committed rate should be given to CRLSP Defined in terms of “granularity” of allocation of rate Constrains the variable delay that the network may introduce Constrains the amount of buffering that an LSR may use Values:
— Very frequently: no more than one packet may be buffered — Frequently: only a few packets may be buffered — Unspecified: any amount of buffering is acceptable
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 44
Weight
• • • •
Specifies the CRLSP’s weight in the “relative share algorithm” Implied but not stated:
— CRLSPs with a larger weight get a bigger relative share of the “excess bandwidth”
Values:
— 0 — the weight is not specified — 1-255 — weights; larger numbers are larger weights
The definition of “relative share” is network specific INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 45
Negotiation Flags
Res F6 F5 F4 F3 F2 F1
If a parameter is flagged as negotiable then LSRs may replace the parameter value with a smaller value in the label request message. LSRs descover the negotiated values in the label mapping message. Label request - possible downward negotiation Label mapping - no negotiation
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 46
ER-LSP Setup Using RSVP
1. Path message. It contains ER path < B,C,D>.
5. When LER A receives Resv, the ER established.
LER A 6. ResvConf message (o).
LSR B 2. New path state. Path message sent to next node.
4. New reservation state. Resv message propagated upstream.
LSR C 3. Resv message originates. Contain the label to use and the required traffic/QoS para.
Per-hop Path and Resv refresh unless suppressed.
LER D
•
More complex — signaling in addition to MPLS LDP protocol
•
Unreliable — signaling built upon UDP
•
Scalability concerns — Significant number of refresh messages to process
•
Interoperability concerns — IETF draft underspecified, no proven interoperability INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 47
BGP Extensions
•
A mechanism to exchange label binding information among BGP peers by adding (piggybacking) the label mapping information on the BGP route update INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 48
Tutorial Outline
• • • • • • •
Overview Label Encapsulations Label Distribution Protocols MPLS & ATM IETF Status Nortel Networks Activity Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 49
MPLS & ATM
•
Various Modes of Operation
— Label-controlled ATM — Tunneling through ATM — Ships in the night with ATM •
ATM Merge
— VC merge — VP merge
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 50
MPLS & ATM
Several models for running MPLS on ATM:
1. Label-Controlled ATM: • Use ATM hardware for label switching • Replace ATM Forum SW by IP/MPLS IP Routing MPLS ATM HW
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 51
Label-Controlled ATM
• Label switching is used to forward network-layer packets • It combines the fast, simple forwarding technique of ATM with network layer routing and control of the TCP/IP protocol suite Label Switching Router
Switched path topology formed using network layer routing (i.e., TCP/IP technique) Network Layer Routing (e.g., OSPF, BGP4) Forwarding Table
Forwarding Table B 17 C 05 • Label
Port
A C IP Packet 05 Label IP Packet 17 B D
Packets forwarded by swapping short, fixed-length labels (i.e., ATM technique)
ATM Label Switching is the combination of L3 routing and L2 ATM switching
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 52
2. MPLS Over ATM
VP MPLS L S R ATM Network L S R MPLS Two Models VC Internet Draft:
VCID notification over ATM Link
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 53
3. Ships in the Night
L S R ATM SW MPLS ATM L S R ATM SW •
ATM Forum and MPLS control planes both run on the same hardware but are isolated from each other, i.e., they do not interact.
•
This allows a single device to simultaneously operate as both an MPLS LSR and an ATM switch.
•
Important for migrating MPLS into an ATM network.
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 54
Ships in the Night Requirements
•
Resource Management
— VPI.VCI Space Partitioning — Traffic management – – Bandwidth Reservation Admission Control – – Queuing & Scheduling Shaping/Policing — Processing Capacity
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 55
Bandwidth Management
A. Full Sharing MPLS Pool 1 • MPLS • ATM ATM Available B. Protocol Partition Pool 1 • 50% • ATM MPLS Available Pool 2 • 50% • rt-VBR ATM Available • •
Bandwidth Guarantees Flexibility INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
C. Service Partition Pool 1 • 50% • rt-VBR • COS2 MPLS ATM Available Pool 2 • 50% • nrt-VBR • COS1 MPLS ATM Available MPLS Tutorial 56
ATM Merge
• •
Multipoint-to-point capability Motivation
— Stream Merge to achieve scalability in MPLS: – – O(n) VCs with Merge as opposed to O(n2) for full mesh Less labels required — Reduce number of receive VCs on terminals •
Alternatives
— Frame-based VC Merge — Cell-based VP Merge
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 57
Stream Merge
Input cell streams
1 1 2 2 2 3 3 1 in out 1 7 2 3 6 9 6 7 9 6 7 9 6 7
Non-VC merging (Nin–Nout) Input cell streams
1 1 2 2 2 3 3 1 in out 1 2 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 3 7 No Cell Interleaving
VC merging (Nin-1out)
7 7 AAL5 Cell Interleaving Problem 7
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 58
VC-Merge: Output Module
Reassembly buffers Merge Output buffer
Passport is VC-Merge Capable
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 59
VP-Merge
VCI=1 VCI=2 VCI=3
Option 1
: Dynamic VCI Mapping VPI=1 No Cell Interleaving Problem Since VCI is Unique VCI=1 VCI=2 VPI=2 VCI=3 VPI=3
Option 2
: Root Assigned VCI –merge multiple VPs into one VP –use separate VCIs within VPs to distinguish frames –less efficient use of VPI/VCI space, needs support of SVP
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 60
Tutorial Outline
• • • • • • •
Overview Label Encapsulations Label Distribution Protocols MPLS & ATM IETF Status Nortel Networks Activity Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 61
Proposed Standard RFCs
• • •
MPLS Label Stack Encoding
•
Use of Label Switching on Frame Relay Networks Specification
MPLS Tutorial 62
Last Call
• •
Gone through Last Call:
— Label Distribution Protocol
Going to last call:
— Constraint-based Label Distribution Protocol — Extensions to RSVP for LSP Tunnels — RSVP Refresh Reduction Extensions
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 63
Tutorial Outline
• • • • • • •
Overview Label Encapsulations Label Distribution Protocols MPLS & ATM IETF Status Nortel Networks Activity Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 64
Nortel’s Activity
• •
IETF Interoperability Demonstration
— CR-LDP •
Implementation
— Traffic Engineering — VPN
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 65
Progress: Consensus Plus Running Code
• • • • •
14 vendors & ISPs collaborated on CRLDP MPLS WG document in Orlando CRLDP is included by reference in the LDP Specification LDP Spec has gone through last call Demonstrated interoperability among three Vendors’ implementations in November ’98
• •
CRLDP is simple, stable, robust, and easily extendible CR-LDP WG document is going to last call INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 66
Leading Key MPLS Standards
• • • • •
Label Distribution Protocol (LDP)
— Loa Andersson & Andre Fredette
Constraint-based Routing LDP (CR-LDP)
— Bilel Jamoussi, Andre Fredette, Loa Andersson, Osama Abould Magd, & Peter Ashwood-Smith
QoS Resource Management in MPLS-Based Networks
— Osama Aboul-Magd & Bilel Jamoussi with Jerry Ash, AT&T
MPLS using ATM VP Switching
— Bilel Jamoussi & Nancy Feldman, IBM
Explicit Tree Routing
— Swee Loke
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 67
Hosting MPLS Multivendor Interoperability Demo
• • • • •
MPLS over ATM Protocol implemented according to:
— CRLSP over LDP Spec.
— Explicit Routing (ER) — Bw Reservation — QoS signaling
VC-Merge Ships in the Night Has been Tested for Interoperability with Bay BN router, Ericsson & GDC INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 68
Demo Description
• • • •
Demo of five node network
— Three MPLS LSRs based on ATM switches: – Ericsson AXI537, GDC Apex, Nortel Networks Passport — Two Nortel Networks MPLS LERs based on BN/ARE routers
MPLS/IP links are OC3 ATM IP/Ethernet links are 10baseT All LERs/LSRs capable of LDP and CR-LDP functions INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 69
Demo Interoperability Network
LSR 3 Ericsson AXD311 A4 A3 A2 LSR 2 Nortel Networks Passport A0 A1 PC2 PC1 E22 LER 2 Nortel Networks BN/ARE A51 A5 A6 LSR 1 GDC APEX A4 A8
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
A51 A41 LER 1 Nortel Networks BN/ARE E22 MPLS Tutorial 70
Experience Gained
•
Clear intent and structure of LDP
— Fast implementation — Simple implementation •
LDP flexibility
— Made implementing CR-LDP easy — Frame format flexibility helped
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 71
Promoting Open Standard
www.nortelnetworks.com/mpls
C Source code of LDP/CRLDP message and TLV processing According to the latest Specs: LDP:
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 72
Passport 6400/7400/15000 MPLS
•
Q399
— Passport 6400/7400/15000 LSR over ATM – – Strict ER Hop-by-hop – – – QoS mapping Failure handling and recovery Interoperability with BN router — Passport 6400/7400/15000 LER – Support for terminating and initiating LSPs – – – FEC configuration QoS-based mapping of traffic onto LSPs MVR over MPLS •
Q499
— MPLS over Frame Relay
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 73
Passport 6400/7400/15000 as an LSR
• •
BN router can do the LER capability Passport current edge switch position in the network makes it an LSR candidate
•
Passport can intemperate with Cisco at edge based on MPLS Standard LDP
LER LSR LER FEC LDP
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 74
Passport 6400/7400/15000 as an LER
•
Provides ability to interface to legacy non-MPLS literate routers and take advantage of MPLS in the network
•
Provides support for MPLS as a transport for MVR
LER LSR LER FEC LDP
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 75
MPLS interconnecting MVRs
• • •
LSPs established between CVRs Label Stacking between VRn and CVRx BGP or LDP sessions established to distribute reachability and Label INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 76
Tutorial Outline
• • • • • • •
Overview Label Encapsulations Label Distribution Protocols MPLS & ATM IETF Status Nortel Networks Activity Summary INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 77
• • • • • • •
Summary of Motivations for MPLS
Simplified forwarding based on exact match of fixed-length label
– Initial drive for MPLS was based on existance of cheap, fast ATM switches
Separation of routing and forwarding in IP networks
– Facilitates evolution of routing techniques by fixing the forwarding method – New routing functionality can be deployed without changing the forwarding techniques of every router in the Internet
Facilitates the integration of ATM and IP
– Allows carriers to leverage their large investment of ATM equipment – Eliminates the adjacency problem of VC-mesh over ATM
Enables the use of explicit routing/source routing in IP networks
– Can be easily used for such things as traffic management, QoS routing
Promotes the partitioning of functionality within the network
– Move granular processing of packets to edge; restrict core to packet forwarding – Assists in maintaining scalability of IP protocols in large networks
Improved routing scalability through stacking of labels
– Removes the need for full routing tables from interior routers in transit domain; only routes to border routers are required
Applicability to both cell and packet link-layers
– Can be deployed on both cell (e.g., ATM) and packet (e.g., FR, Ethernet) media – Common management and techniques simplifies engineering Many drivers exist for MPLS above and beyond high-speed forwarding
INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 78
IP and ATM Integration
IP over ATM VCs IP over MPLS
•
ATM cloud invisible to Layer 3 Routing
•
Full mesh of VCs within ATM cloud
•
Many adjacencies between edge routers
•
Topology change generates many route updates
•
Routing algorithm made more complex
•
ATM network visible to Layer 3 Routing
•
Singe adjacency possible with edge router
•
Hierachical network design possible
•
Reduces route update traffic and power needed to process them MPLS eliminates the “n-squared” problem of IP over ATM VCs INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 79
Traffic Engineering
Demand
B C A D Traffic engineering is the process of mapping traffic demand onto a network
Network Topology
Purpose of traffic engineering:
• • • • •
Maximize utilization of links and nodes throughout the network Engineer links to achieve required delay, grade-of-service Spread the network traffic across network links, minimize impact of single failure Ensure available spare-link capacity for rerouting traffic on failure Meet policy requirements imposed by the network operator Traffic engineering key to optimizing cost/performance INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 80
Traffic Engineering Alternatives
Current methods of traffic engineering: Manipulating routing metrics Use PVCs over an ATM backbone Overprovision bandwidth Difficult to manage Not scalable Not economical MPLS provides a new method to do traffic engineering (traffic steering)
Example Network:
Ingress node explicitly routes traffic over uncongested path Congested Node Potential benefits of MPLS for traffic engineering: - Allows explicitly routed paths No “n-squared” problem - Per FEC traffic monitoring - Backup paths may be configured Chosen by Traffic Eng.
(least congestion) Chosen by routing protocol (least cost) operator control scalable granularity of feedback redundancy/restoration MPLS combines benefits of ATM and IP-layer traffic engineering INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 81
MPLS Traffic Engineering Methods
•
MPLS can use the source routing capability to steer traffic on desired path
•
Operator may manually configure these in each LSR along the desired path — Analogous to setting up PVCs in ATM switches
•
Ingress LSR may be configured with the path, RSVP used to set up LSP — Some vendors have extended RSVP for MPLS path setup
•
Ingress LSR may be configured with the path, LDP used to set up LSP — Many vendors believe RSVP not suited
•
Ingress LSR may be configured with one or more LSRs along the desired path, hop-by-hop routing may be used to set up the rest of the path — A.k.a loose source routing, less configuration required
•
If desired for control, route discovered by hop-by-hop routing can be frozen — A.k.a “route pinning”
•
In the future, constraint-based routing will offload traffic engineering tasks from the operator to the network itself INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 82
MPLS: Scalability Through Routing Hierarchy
AS1 AS2 BR2 AS3 TR1 BR1 TR2 BR3 TR4 TR3
Ingress router receives packet Packet labeled based on egress router
BR4
Forwarding in the interior based on IGP route Egress border router pops label and fwds.
• • • • •
Border routers BR1-4 run an EGP, providing inter-domain routing Interior transit routers TR1-4 run an IGP, providing intra-domain routing
•
Normal layer 3 forwarding requires interior routers to carry full routing tables — Transit router must be able to identify the correct destination ASBR (BR1-4) Carrying full routing tables in all routers limits scalability of interior routing — Slower convergence, larger routing tables, poorer fault isolation MPLS enables ingress node to identify egress router, label packet based on interior route Interior LSRs would only require enough information to forward packet to egress MPLS increases scalability by partitioning exterior routing from interior routing INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 83
MPLS: Partitioning Routing and Forwarding
Routing Forwarding
OSPF, IS-IS, BGP, RIP MPLS
Forwarding Table
Based on: Classful Addr. Prefix?
Classless Addr. Prefix?
Multicast Addr.?
Port No.?
ToS Field?
Based on: Exact Match on Fixed-Length Label
• • • •
Current network has multiple forwarding paradigms
— Class-ful longest prefix match (Class A,B,C boundaries) — Classless longest prefix match (variable boundaries) — Multicast (exact match on source and destination) — Type-of-service (longest prefix. match on addr. + exact match on ToS)
As new routing methods change, new route lookup algorithms are required
— Introduction of CIDR
Next generation routers will be based on hardware for route lookup
— Changes will require new hardware with new algorithm
MPLS has a consistent algorithm for all types of forwarding; partitions routing/forwarding
— Minimizes impact of the introduction of new forwarding methods
MPLS introduces flexibility through consistent forwarding paradigm INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 84
Upper Layer Consistency Across Link Layers
Ethernet PPP (SONET, DS-3 etc.) ATM Frame Relay
•
MPLS is “multiprotocol” below (link layer) as well as above (network layer)
•
Provides for consistent operations, engineering across multiple technologies
•
Allows operators to leverage existing infrastructure
•
Co-existence with other protocols is provided for
—
e.g., “Ships in the Night” operation with ATM, muxing over PPP MPLS positioned as end-to-end forwarding paradigm INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 85
Summary
• •
MPLS is a promising emerging technology Basic functionality (Encapsulation and basic Label Distribution) has been defined by the IETF
•
Nortel Networks is taking an active role in defining key aspects of MPLS standard and providing support of MPLS on the Bay and Nortel Networks platforms INFORM ’99 - APRIL 11 - 16, 1999 - LAS VEGAS, NEVADA
MPLS Tutorial 86