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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Hyperaggregation Problem MPLS and Traffic Engineering December 08, 2003

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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 (http://www.mplsforum.org) MPLS and Traffic Engineering December 08, 2003

Upstream and downstream LSR 172.68.10/24 LSR1 LSR2 Data MPLS and Traffic Engineering December 08, 2003

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

Label Distribution ALWAYS, Downstream to upstream label distribution Use label 5 for destination 171.68.32/24 171.68.32/24 MPLS Data Packet with label 5 travel LSR2 LSR1 MPLS and Traffic Engineering December 08, 2003

Downstream Un-solicited Send label Without any Request Upstream Upstream 171.68.32/24 LSR2 LSR1 MPLS and Traffic Engineering December 08, 2003

Downstream On Demand (DoD) Send label ONLY after receiving request Down Stream Upstream 171.68.32/24 Request For label LSR2 LSR1 MPLS and Traffic Engineering December 08, 2003

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

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

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

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

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