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Traffic Engineering

Traffic Engineering
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Dr.NeerajMittal,India,Teacher
Published Date:19-07-2017
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Traffic Engineering Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Overview  Introductions:course description & calendar  Answers to frequently asked questions  Prerequisites  Informal Quiz Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2Without Traffic Engineering Cars: SFO-LAX SAN-SMF LAX-SFO SMF-SAN No Traffic Engineering analogy to Human Drivers Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3Traffic Engineering: Analogy Cars: SFO-LAX SAN-SMF LAX-SFO SMF-SAN Traffic Engineering analogy Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4Motivation  TE: “…that aspect of Internet network engineering dealing with the issue of performance evaluation and performance optimization of operational IP networks …’’  90’s approach to TE was by changing link weights in IGP (OSPF, IS-IS) or EGP (BGP-4)  Performance limited by the shortest/policy path nature  Assumptions: Quasi-static traffic, knowledge of demand matrix B B B 11 11 1 4 2 22 A A D D D EE E 1 2 A 1 1 2 2 Links AB and BD are overloaded C C C LiC nk an s AC not a dnd o t C hD is a w re ov ith O eS rlPF oaded Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5Fundamental Requirements  Need the ability to:  Map traffic to an LSP  Monitor and measure traffic  Specify explicit path of an LSP Partial explicit route Full explicit route  Characterize an LSP Bandwidth Priority/ Preemption Affinity (Link Colors)  Reroute or select an alternate LSP Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6Traffic Engineering Steps  First, determine how to lay out traffic on the physical topology Measure traffic (e.g., city-pair-wise) Crunch numbers  Second, do something to convince the packets to follow your plan Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7Traffic Engineering Options  BGP – play with communities, filtering  IGP – play with metrics Linear programming can help  Source routing ATM MPLS Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8Routing Solution to Traffic Engineering R2 R3 R1  Construct routes for traffic streams within a service provider in such a way, as to avoid causing some parts of the provider’s network to be over-utilized, while others parts remain under-utilized (I.e. load-balance) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 9Linear Programming  TE among N cities: N² city pairs  Set up N² by N² matrix for LP  Matrix multiplication/inversion is O(M³) for M x M matrix; simplex is O(M³) matrix operations 12  So, LP problem is O(N )  Also can’t deal with “looped routes” Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 10The “Overlay” Solution L3 L3 L3 L3 L2 L2 L3 L2 L3 L3 L3 L2 L2 L2 L3 L3 L3 L3 Physical Logical  Routing at layer 2 (ATM or FR) is used for traffic engineering  Analogy to direct highways between SFO-LAX & SAN-SMF. Nobody enters the highway in between. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11Traffic engineering with overlay R2 R3 R1 PVC for R2 to R3 traffic PVC for R1 to R3 traffic Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12Connectionless Routing Today  Internet connectionless routing protocols originally designed to find one route Eg: shortest route or policy route)  Connectionless routing relies upon a global consistency criterion (GCC) The GCC is constructed using globally known identifiers (Eg: ASNs, link weights) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 13DV: Global Consistency Criterion  The subset of a shortest path is also the shortest path between the two intermediate nodes.  If the shortest path from node i to node j, with distance D(i,j) passes through neighbor k, with link cost c(i,k), then: D(i,j) = c(i,k) + D(k,j)  D(i,) is a distance vector at node i. j i k Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14Link State (LS): Global Consistency Criterion  The link state (Dijkstra) approach is iterative, but it pivots around destinations j, and their predecessors k = p(j)  Alternative version of the consistency condition: D(i,j) = D(i,k) + c(k,j) j i k  Each node i collects all link states c(,) first and runs the complete Dijkstra algorithm locally. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15Path-Vector: BGP’s Consistency Criterion Policy-based routing: Arbitrary preference among a menu of available routes (based upon routes’ attributes) 135.207.0.0/16 ASPATH = 3 2 1 AS 1 AS 3 AS 4 AS 2 135.207.0.0/16 IP Packet Dest = 135.207.44.66  Consistency: If AS2 announces a route, it is actively using the route, and will honor forwarding requests on that route Acknowledgement: Based upon Dr. Tim Griffin’s SIGCOMM Tutorial Slides Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16Limitations of Today’s Connectionless TE  Traffic mapping coupled with route availability Changing parameters changes routes AND changes the traffic mapped to the routes  Priority rules only: LOCAL-PREF, MED, longest-prefix match Cannot split traffic to same destination among two paths Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17Signaled Approach (eg: MPLS)  Nice features: In MPLS, choice of a route (and its setup) is orthogonal to the problem of traffic mapping onto the route Signaling maps global IDs (addresses, path- specification) to local IDs (labels) Nice label stacking, tunneling features Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18Label-Switched Forwarding  San Francisco prepends MPLS header to the IP packet  MPLS label is swapped at each hop along the LSP  Forwarding is done based on a label table Seattle New York (Egress) IP 0 IP 1321 5 San IP 120 Francisco 1321 (Ingress) 120 Miami IP Label Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19What Does MPLS Offer?  Tunnels Drop a packet in, and out it comes at the other end without being IP routed  Explicit (source) routing (circuits)  Label stack 2-label stack: “outer” label defines the tunnel; “inner” label de-multiplexes  Layer 2 independence Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20