Introduction to mpls and traffic engineering
This presentation is the property of its rightful owner.
Sponsored Links
1 / 45

Introduction to MPLS and Traffic Engineering PowerPoint PPT Presentation


  • 130 Views
  • Uploaded on
  • Presentation posted in: General

Introduction to MPLS and Traffic Engineering. Zartash Afzal Uzmi. Outline. Traditional IP Routing Forwarding and routing Problems with IP routing Motivations behind MPLS MPLS Terminology and Operation MPLS Label, LSR and LSP, LFIB Vs FIB Transport of an IP packet over MPLS

Download Presentation

Introduction to MPLS and Traffic Engineering

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Introduction to mpls and traffic engineering

Introduction to MPLS and Traffic Engineering

Zartash Afzal Uzmi


Outline

Outline

  • Traditional IP Routing

    • Forwarding and routing

    • Problems with IP routing

    • Motivations behind MPLS

  • MPLS Terminology and Operation

    • MPLS Label, LSR and LSP, LFIB Vs FIB

    • Transport of an IP packet over MPLS

    • More MPLS terminology

  • Traffic Engineering [with MPLS]

    • Nomenclature

    • Requirements

    • Examples

CS 573: Network Protocols and Standards


Outline1

Outline

  • Traditional IP Routing

    • Forwarding and routing

    • Problems with IP routing

    • Motivations behind MPLS

  • MPLS Terminology and Operation

    • MPLS Label, LSR and LSP, LFIB Vs FIB

    • Transport of an IP packet over MPLS

    • More MPLS terminology

  • Traffic Engineering [with MPLS]

    • Nomenclature

    • Requirements

    • Examples

CS 573: Network Protocols and Standards


Forwarding and routing

Forwarding and routing

  • Forwarding:

    • Passing a packet to the next hop router

  • Routing:

    • Computing the “best” path to the destination

  • IP routing – includes routing and forwarding

    • Each router makes the forwarding decision

    • Each router makes the routing decision

  • MPLS routing

    • Only one router (source) makes the routing decision

    • Intermediate routers make the forwarding decision

CS 573: Network Protocols and Standards


Ip versus mpls routing

IP versus MPLS routing

  • IP routing

    • Each IP datagram is routed independently

    • Routing and forwarding is destination-based

      • Routers look at the destination addresses

      • May lead to congestion in parts of the network

  • MPLS routing

    • A path is computed “in advance” and a “virtual circuit” is established from ingress to egress

    • An MPLS path from ingress to egress node is called a label switched path (LSP)

CS 573: Network Protocols and Standards


How ip routing works

How IP routing works

Searching Longest Prefix Match in FIB (Too Slow)

CS 573: Network Protocols and Standards


Problems with ip routing

Problems with IP routing

  • Too slow

    • IP lookup (longest prefix matching) “was” a major bottleneck in high performance routers

    • This was made worse by the fact that IP forwarding requires complex lookup operation at every hop along the path

  • Too rigid – no flexibility

    • Routing decisions are destination-based

  • Not scalable in some desirable applications

    • When mapping IP traffic onto ATM

CS 573: Network Protocols and Standards


Ip routing rigidity example

IP routing rigidity example

D

1

1

A

S

A

B

B

1

2

C

  • Packet 1: Destination A

  • Packet 2: Destination B

  • S computes shortest paths to A and B; finds D as next hop

  • Both packets will follow the same path

    • Leads to IP hotspots!

  • Solution?

    • Try to divert the traffic onto alternate paths

CS 573: Network Protocols and Standards


Ip routing rigidity example1

IP routing rigidity example

D

1

4

A

S

A

B

B

1

2

C

  • Increase the cost of link DA from 1 to 4

  • Traffic is diverted away from node D

  • A new IP hotspot is created!

  • Solution(?): Network Engineering

    • Put more bandwidth where the traffic is!

    • Leads to underutilized links; not suitable for large networks

CS 573: Network Protocols and Standards


Motivations behind mpls

Motivations behind MPLS

  • Avoid [slow] IP lookup

    • Led to the development of IP switching in 1996

  • Provide some scalability for IP over ATM

  • Evolve routing functionality

    • Control was too closely tied to forwarding

  • Evolution of routing functionality led to some other benefits

    • Explicit path routing

    • Provision of service differentiation (QoS)

CS 573: Network Protocols and Standards


Ip routing versus mpls routing

IP routing versus MPLS routing

Traditional IP Routing

Multiprotocol Label Switching (MPLS)

1

2

S

D

3

4

5

MPLS allows overriding shortest paths!

CS 573: Network Protocols and Standards


Outline2

Outline

  • Traditional IP Routing

    • Forwarding and routing

    • Problems with IP routing

    • Motivations behind MPLS

  • MPLS Terminology and Operation

    • MPLS Label, LSR and LSP, LFIB Vs FIB

    • Transport of an IP packet over MPLS

    • More MPLS terminology

  • Traffic Engineering [with MPLS]

    • Nomenclature

    • Requirements

    • Examples

CS 573: Network Protocols and Standards


Mpls label

MPLS label

  • To avoid IP lookup MPLS packets carry extra information called “Label”

  • Packet forwarding decision is made using label-based lookups

  • Labels have local significance only!

  • How routing along explicit path works?

Label

IP Datagram

CS 573: Network Protocols and Standards


Routing along explicit paths

Routing along explicit paths

  • Idea: Let the source make the complete routing decision

  • How is this accomplished?

    • Let the ingress attach a label to the IP packet and let intermediate routers make forwarding decisions only

  • On what basis should you choose different paths for different flows?

    • Define some constraints and hope that the constraints will take “some” traffic away from the hotspot!

    • Use CSPF instead of SPF (shortest path first)

CS 573: Network Protocols and Standards


Label lsp and lsr

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

Label | Exp|S| TTL

Label = 20 bits

Exp = Experimental, 3 bits

S = Bottom of stack, 1bit

TTL = Time to live, 8 bits

Label, LSP and LSR

  • Label

  • Router that supports MPLS is known as label switching router (LSR)

  • An “Edge” LSR is also known as LER (edge router)

  • Path which is followed using labels is called LSP

CS 573: Network Protocols and Standards


Lfib versus fib

LFIB versus FIB

  • Labels are searched in LFIB whereas normal IP Routing uses FIB to search longest prefix match for a destination IP address

  • Why switching based on labels is faster?

    • LFIB has fewer entries

    • Routing table FIB has larger number of entries???

    • In LFIB, label is an exact match

    • In FIB, IP is longest prefix match

CS 573: Network Protocols and Standards


Mpls flow progress

Mpls Flow Progress

D

R1

LSR4

R2

LSR1

D

destination

LSR6

LSR3

LSR2

R1 and R2 are

regular routers

LSR5

1 - R1 receives a packet for destination D connected to R2

CS 573: Network Protocols and Standards


Mpls flow progress1

Mpls Flow Progress

D

R1

LSR4

R2

LSR1

D

destination

LSR6

LSR3

LSR2

LSR5

2 - R1 determines the next hop as LSR1 and forwards the packet

(Makes a routing as well as a forwarding decision)

CS 573: Network Protocols and Standards


Mpls flow progress2

Mpls Flow Progress

R1

LSR4

R2

LSR1

31

D

D

destination

LSR6

LSR3

LSR2

LSR5

3 – LSR1 establishes a path to LSR6 and “PUSHES” a label

(Makes a routing as well as a forwarding decision)

CS 573: Network Protocols and Standards


Mpls flow progress3

Mpls Flow Progress

R1

LSR4

R2

LSR1

D

destination

LSR6

LSR3

17

D

LSR2

Labels have local

signifacance!

LSR5

4 – LSR3 just looks at the incoming label

LSR3 “SWAPS” with another label before forwarding

CS 573: Network Protocols and Standards


Mpls flow progress4

MPLS Flow Progress

R1

LSR4

R2

LSR1

D

destination

LSR6

LSR3

17

D

LSR2

Path within MPLS cloud

is pre-established:

LSP (label-switched path)

LSR5

5 – LSR6 looks at the incoming label

LSR6 “POPS” the label before forwarding to R2

CS 573: Network Protocols and Standards


Mpls and explicit routing recap

MPLS and explicit routing recap

  • Who establishes the LSPs in advance?

    • Ingress routers

  • How do ingress routers decide not to always take the shortest path?

    • Ingress routers use CSPF (constrained shortest path first) instead of SPF

    • Examples of constraints:

      • Do not use links left with less than 7Mb/s bandwidth

      • Do not use blue-colored links for this request

      • Use a path with delay less than 130ms

CS 573: Network Protocols and Standards


Introduction to mpls and traffic engineering

CSPF

  • What is the mechanism? (in typical cases!)

    • First prune all links not fulfilling constrains

    • Now find shortest path on the rest of the topology

  • Requires some reservation mechanism

  • Changing state of the network must also be recorded and propagated

    • For example, ingress needs to know how much bandwidth is left on links

    • The information is propagated by means of routing protocols and their extensions

CS 573: Network Protocols and Standards


More mpls terminology

Data

More MPLS terminology

Upstream

Downstream

172.68.10/24

LSR1

LSR2

CS 573: Network Protocols and Standards


Label advertisement

Use label 5 for destination 171.68.32/24

MPLS Data Packet

with label 5 travels

Label advertisement

  • Always downstream to upstream label advertisement and distribution

Downstream

Upstream

171.68.32/24

LSR2

LSR1

CS 573: Network Protocols and Standards


Label advertisement1

Sends label ONLY after

receiving request

Sends label

Without any Request

Request For label

Label advertisement

  • Label advertisement can be downstream unsolicited or downstream on-demand

Downstream

Upstream

171.68.32/24

LSR2

LSR1

Downstream

Upstream

171.68.32/24

LSR1

LSR2

CS 573: Network Protocols and Standards


Label distribution

Egress LSR

Ingress LSR

Label distribution

  • Label distribution can be ordered or unordered

  • First we see an example of ordered label distribution

Label

CS 573: Network Protocols and Standards


Label distribution1

Egress LSR

Ingress LSR

Label distribution

  • Label distribution can be ordered or unordered

  • Next we see an example of unordered label distribution

Label

Label

CS 573: Network Protocols and Standards


Label retention modes

Label retention modes

  • Label retention can be conservative or liberal

?

Destination

Label

LSR1

Label

CS 573: Network Protocols and Standards


Label operations

Label operations

  • Advertisement

    • Downstream unsolicited

    • Downstream on-demand

  • Distribution

    • Ordered

    • Unordered

  • Retention

    • Liberal

    • Conservative

CS 573: Network Protocols and Standards


Outline3

Outline

  • Traditional IP Routing

    • Forwarding and routing

    • Problems with IP routing

    • Motivations behind MPLS

  • MPLS Terminology and Operation

    • MPLS Label, LSR and LSP, LFIB Vs FIB

    • Transport of an IP packet over MPLS

    • More MPLS terminology

  • Traffic Engineering [with MPLS]

    • Nomenclature

    • Requirements

    • Examples

CS 573: Network Protocols and Standards


Traffic engineering

Traffic Engineering

Traffic Engineering with MPLS

(Application of CSPF)


What is traffic engineering

What is traffic engineering?

  • Performance optimization of operational networks

    • optimizing resource utilization

    • optimizing traffic performance

    • reliable network operation

  • How is traffic engineered?

    • measurement, modeling, characterization, and control of Internet traffic

  • Why?

    • high cost of network assets

    • service differentiation

CS 573: Network Protocols and Standards


Traffic engineering1

Traffic engineering

  • Recall the IP hotspot problem

  • The ability to move traffic away from the shortest path calculated by the IGP (such as OSPF) to a less congested path

  • IP: changing a metric will cause ALL the traffic to divert to the less congested path

  • MPLS: allows explicit routing (using CSPF) and setup of such explicitly computed LSPs

CS 573: Network Protocols and Standards


Mpls te how to do it

MPLS-TE: How to do it?

  • LSPs are set up by LSRs based on information they learn from routing protocols (IGPs)

  • This defeats the purpose!

    • If we were to use “shortest path”, IGP was okay

CS 573: Network Protocols and Standards


Mpls te how we actually do it

MPLS TE: How we actually do it?

  • MPLS TE Requires:

    • Enhancements to routing protocols

      • OSPF-TE

      • ISIS-TE

    • Enhancement to signaling protocols to allow explicit constraint based routing

      • RSVP-TE and CR-LDP

    • Constraint based routing

      • Explicit route selection

      • Recovery mechanisms defined

CS 573: Network Protocols and Standards


Signaling mechanisms

Signaling mechanisms

  • RSVP-TE

    • Extensions to RSVP for traffic engineering

  • BGP-4

    • Carrying label information in BGP-4

  • CR-LDP

    • A label distribution protocol that distributes labels determined based on constraint based routing

  • RSVP-TE and CR-LDP both do label distribution and path reservation – use any one of them!

CS 573: Network Protocols and Standards


Rsvp te

RSVP-TE

Basic flow of LSP set-up using RSVP

CS 573: Network Protocols and Standards


Rsvp te path message

RSVP-TE PATH Message

  • PATH message is used to establish state and request label assignment

  • R1 transmits a PATH message addressed to R9

CS 573: Network Protocols and Standards


Rsvp te resv message

RSVP-TE RESV Message

  • RESV is used to distribute labels after reserving resources

  • R9 transmits a RESV message, with label=3, to R8

  • R8 and R4 store “outbound” label and allocate an “inbound” label. They also transmits RESV with inbound label to upstream LSR

  • R1 binds label to forwarding equivalence class (FEC)

CS 573: Network Protocols and Standards


Rerouting lsp tunnels

Rerouting LSP tunnels

  • When a more “optimal” route/path becomes available

  • When a failure of a resource occurs along a TE LSP

  • Make-before-break mechanism

    • Adaptive, smooth rerouting and traffic transfer before tearing down the old LSP

    • Not disruptive to traffic

CS 573: Network Protocols and Standards


Recovering lsp tunnels

Recovering LSP tunnels

LSP Set-up

CS 573: Network Protocols and Standards


Protection lsp set up

Protection LSP set up

CS 573: Network Protocols and Standards


Protection lsp

Protection LSP

CS 573: Network Protocols and Standards


References

References

  • RFC 2702 “Requirements for Traffic Engineering Over MPLS”

  • RFC 3031 “Multiprotocol Label Switching Architecture”

  • RFC 3272 “Overview and Principles of Internet Traffic Engineering”

  • RFC 3346 “Applicability Statement for Traffic Engineering with MPLS”

  • MPLS Forum (http://www.mplsforum.org)

CS 573: Network Protocols and Standards


  • Login