1. MPLS and Traffic Engineering
Zartash Afzal Uzmi
Department of Computer Science
Lahore University of Management Sciences (LUMS)
MPLS and Traffic Engineering
December 08, 2003

2. MPLS and Traffic Engineering
Outline
Traditional IP Routing
IP Routing Operation and Problems
Motivation behind MPLS
MPLS Terminology and Operation
MPLS Label, LSR and LSP, LFIB Vs FIB
Transport of an IP packet over MPLS
Traffic Engineering [with MPLS]
Nomenclature
Requirements
Examples
MPLS and Traffic Engineering
December 08, 2003

3. Traditional IP Routing
IP forwarding is done independently at every hop
IP forwarding decisions are made using:
Destination IP address (in packet header!)
Routing table (updated by routing algorithms!)
Each IP router runs its own instance of the routing algorithm
Each IP router makes its own forwarding decisions
MPLS and Traffic Engineering
December 08, 2003

4. MPLS and Traffic Engineering
How IP Routing Works?
Searching Longest Prefix Match in FIB (Too Slow)
MPLS and Traffic Engineering
December 08, 2003

5. Problems with IP Routing
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
MPLS and Traffic Engineering
December 08, 2003

6. Motivation behind MPLS
Avoid [slow] IP lookup
Provide traffic differentiation (QoS)
Voice is really different from data!
Evolve routing functionality
Control was too closely tied to forwarding!
Simplify deployment of IPv6
MPLS and Traffic Engineering
December 08, 2003

7. MPLS and Traffic Engineering
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!
Label
IP Datagram
MPLS and Traffic Engineering
December 08, 2003

8. MPLS and Traffic Engineering
LSR and LSP
Router that supports MPLS is known as label switching router (LSR)
Path which is followed by using labels is called label switched path (LSP)
MPLS and Traffic Engineering
December 08, 2003

9. MPLS and Traffic Engineering
LFIB Vs 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 very large number of entries
In LFIB Label is an exact match
In FIB IP is longest prefix match
MPLS and Traffic Engineering
December 08, 2003

10. Transport of IP over MPLS
Label Pushing:
MPLS and Traffic Engineering
December 08, 2003

11. Transport of IP over MPLS
Label Swapping:
MPLS and Traffic Engineering
December 08, 2003

12. Transport of IP over MPLS
Label Swapping:
MPLS and Traffic Engineering
December 08, 2003

13. Transport of IP over MPLS
Label Popping:
MPLS and Traffic Engineering
December 08, 2003

14. Transport of IP over MPLS
MPLS and Traffic Engineering
December 08, 2003

15. 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
MPLS and Traffic Engineering
December 08, 2003

16. Hyperaggregation Problem
Routing Protocols Create A single "Shortest Path"
MPLS and Traffic Engineering
December 08, 2003

17. Hyperaggregation Problem
MPLS and Traffic Engineering
December 08, 2003

18. MPLS and Traffic Engineering
Nomenclature
Network Engineering
Put the bandwidth where the traffic is!
Physical cable deployment
Virtual connection provisioning
Traffic Engineering
Put the traffic where the bandwidth is!
Optimization of routes
Ability to “explicitly route” traffic
MPLS and Traffic Engineering
December 08, 2003

19. Traditional Traffic Engineering
Traffic sent to A or B follows path with lowest metrics! 1 2 A B C
MPLS and Traffic Engineering
December 08, 2003

20. Traditional Traffic Engineering
Demerits of IGP-based traffic engineering
Changing traffic metric causes ALL the traffic to shift to the new path
Can not shift traffic destined only for A or only for B to the new path (through C)
Result is under or over utilization of some links 1 4 2 A B C
MPLS and Traffic Engineering
December 08, 2003

21. Traffic Engineering: IGP vs. MPLS
Traditional TE (IGP based)
The ability to move traffic away from the shortest path calculated by the IGP to a less congested path
MPLS TE
Allows explicit routing and setup of LSPs
Provides recovery mechanisms failure
Enables Value added services
VPNs, SLAs, VoIP, etc.
MPLS and Traffic Engineering
December 08, 2003

22. MPLS and Traffic Engineering
MPLS TE: How we may do it?
MPLS and Traffic Engineering
December 08, 2003

23. MPLS and Traffic Engineering
MPLS TE: How we may 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
MPLS and Traffic Engineering
December 08, 2003

24. MPLS TE: How we actually do it?
MPLS TE Requires:
Enhancements to routing protocols
OSPF-TE and 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
MPLS and Traffic Engineering
December 08, 2003

25. MPLS and Traffic Engineering
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
MPLS and Traffic Engineering
December 08, 2003

26. MPLS and Traffic Engineering
RSVP-TE
Basic flow of LSP set-up using RSVP
MPLS and Traffic Engineering
December 08, 2003

27. MPLS and Traffic Engineering
RSVP-TE PATH Message
PATH message is used to establish state and request label assignment
R1 transmits a PATH message addressed to R9
MPLS and Traffic Engineering
December 08, 2003

28. MPLS and Traffic Engineering
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)
MPLS and Traffic Engineering
December 08, 2003

29. MPLS and Traffic Engineering
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
MPLS and Traffic Engineering
December 08, 2003

30. Recovering LSP Tunnels
LSP Set-up
MPLS and Traffic Engineering
December 08, 2003

31. MPLS and Traffic Engineering
Protection LSP set up
MPLS and Traffic Engineering
December 08, 2003

32. MPLS and Traffic Engineering
Protection LSP
MPLS and Traffic Engineering
December 08, 2003

33. MPLS and Traffic Engineering
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 (
MPLS and Traffic Engineering
December 08, 2003

34. Upstream and downstream LSR
/24
LSR1
LSR2
Data
MPLS and Traffic Engineering
December 08, 2003

35. MPLS and Traffic Engineering
How MPLS Works
Searching Longest Prefix Match in FIB (Too Slow)
Ingress LSR
Egress LSR
MPLS and Traffic Engineering
December 08, 2003

36. Label Distribution ALWAYS, Downstream to upstream label distribution
Use label 5 for destination /24
/24
MPLS Data Packet
with label 5 travel
LSR2
LSR1
MPLS and Traffic Engineering
December 08, 2003

37. Downstream Un-solicited
Send label
Without any Request
Upstream
Upstream
/24
LSR2
LSR1
MPLS and Traffic Engineering
December 08, 2003

38. Downstream On Demand (DoD)
Send label ONLY after
receiving request
Down Stream
Upstream
/24
Request For label
LSR2
LSR1
MPLS and Traffic Engineering
December 08, 2003

39. Ordered Label Distribution
Ingress LSR
Egress LSR
Label
MPLS and Traffic Engineering
December 08, 2003

40. Unordered Label Distribution
Ingress LSR
Egress LSR
Label
Label
MPLS and Traffic Engineering
December 08, 2003

41. MPLS and Traffic Engineering
Label Retention Modes
1. Liberal Retention Mode
2. Conservative Retention Mode ?
Destination
Label
LSR1
Label
MPLS and Traffic Engineering
December 08, 2003

42. Label Distribution Modes
Advertisement
Distribution
Downstream-on-Demand
Downstream-Unsolicited
Independent
Ordered
Retention
Liberal
Conservative
MPLS and Traffic Engineering
December 08, 2003

43. MPLS and Traffic Engineering
Hierarchical LSP
Ingress LSR for LSP3
LSP1
LSP2
LSP3
Ingress LSR for LSP1
Egress LSR for LSP1
Quiz -
MPLS and Traffic Engineering
December 08, 2003