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Wide Area Ethernet Services Using GELS Architecture

Wide Area Ethernet Services Using GELS Architecture. Zartash Afzal Uzmi Department of Computer Science School of Science and Engineering Lahore University of Management Sciences (LUMS) Lahore, Pakistan. What we are going to talk about?. Given A network of nodes and communication links

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Wide Area Ethernet Services Using GELS Architecture

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  1. Wide Area Ethernet Services Using GELS Architecture Zartash Afzal Uzmi Department of Computer Science School of Science and Engineering Lahore University of Management Sciences (LUMS) Lahore, Pakistan

  2. What we are going to talk about? Given • A network of nodes and communication links Problem “Optimally” place traffic on the given network Options (1) use 25+ years old STP in the network (2) use a newly proposed GELS architecture Question • Is it feasible and/or better to use newly proposed GELS architecture instead of traditional (STP) solution? AICCSA 2008: Wide Area Ethernet Services Using GELS

  3. What is GELS? • GMPLS control for Ethernet label switching • Ethernet uses IEEE 802.3 data plane • Control plane • Current (old): STP and its variants • Proposed: GMPLS (proposed by GELS!) • To evaluate GELS, we need to understand: • STP and its variants such as Rapid STP (RSTP) • GMPLS (generalized MPLS!) AICCSA 2008: Wide Area Ethernet Services Using GELS

  4. Tutorial Agenda • PART-I • Introduction to MPLS and MPLS Terminology • Setting up a simulated MPLS network (Hands-on) • PART-II • Introduction to STP for Bridges • PART-III • GMPLS and the GELS Architecture • Comparison of GELS with Rapid STP (Hands-on) • PART-IV • Restoration and Protection Routing with MPLS • PART-V • Comparison of GELS with RSTP (Hands-on) AICCSA 2008: Wide Area Ethernet Services Using GELS

  5. PART-I Introduction to MPLS and MPLS Terminology Setting up a simulated MPLS Network

  6. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  7. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  8. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  9. 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) AICCSA 2008: Wide Area Ethernet Services Using GELS

  10. How IP routing works Searching Longest Prefix Match in FIB (Too Slow) AICCSA 2008: Wide Area Ethernet Services Using GELS

  11. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  12. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  13. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  14. 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) AICCSA 2008: Wide Area Ethernet Services Using GELS

  15. IP routing versus MPLS routing Traditional IP Routing 1 2 S D 3 4 5 AICCSA 2008: Wide Area Ethernet Services Using GELS

  16. IP routing versus MPLS routing Traditional IP Routing 1 2 S D 3 4 5 AICCSA 2008: Wide Area Ethernet Services Using GELS

  17. IP routing versus MPLS routing Traditional IP Routing 1 2 S D 3 4 5 AICCSA 2008: Wide Area Ethernet Services Using GELS

  18. IP routing versus MPLS routing Multiprotocol Label Switching (MPLS) 1 2 S D 3 4 5 AICCSA 2008: Wide Area Ethernet Services Using GELS

  19. IP routing versus MPLS routing Multiprotocol Label Switching (MPLS) 1 2 S D 3 4 5 MPLS allows overriding shortest paths! AICCSA 2008: Wide Area Ethernet Services Using GELS

  20. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  21. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  22. 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) AICCSA 2008: Wide Area Ethernet Services Using GELS

  23. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  24. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  25. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  26. 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) AICCSA 2008: Wide Area Ethernet Services Using GELS

  27. 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) AICCSA 2008: Wide Area Ethernet Services Using GELS

  28. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  29. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  30. MPLS and explicit routing recap • Who establishes the LSPs in advance? • Ingress routers (usually!) • 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  31. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  32. More MPLS terminology Upstream Downstream 172.68.10/24 LSR1 LSR2 AICCSA 2008: Wide Area Ethernet Services Using GELS

  33. Data More MPLS terminology Upstream Downstream 172.68.10/24 LSR1 LSR2 AICCSA 2008: Wide Area Ethernet Services Using GELS

  34. Label advertisement • Always downstream to upstream label advertisement and distribution Downstream Upstream 171.68.32/24 LSR2 LSR1 AICCSA 2008: Wide Area Ethernet Services Using GELS

  35. Use label 5 for destination 171.68.32/24 Label advertisement • Always downstream to upstream label advertisement and distribution Downstream Upstream 171.68.32/24 LSR2 LSR1 AICCSA 2008: Wide Area Ethernet Services Using GELS

  36. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  37. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  38. Sends label Without any Request 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  39. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  40. 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 AICCSA 2008: Wide Area Ethernet Services Using GELS

  41. Setting up a simulated MPLS Network • Need a simulator • TOTEM with additional modules • Need a network • Use famous European and NA networks • Need a traffic matrix • Bandwidth for input-output pairs • Place traffic matrix on the network using TOTEM simulator! AICCSA 2008: Wide Area Ethernet Services Using GELS

  42. PART-II Introduction to STP for Bridges

  43. Transparent Bridging Ethernet LAN Segment … stations Bridge For stations, the two topologies are the same  transparent bridging AICCSA 2008: Wide Area Ethernet Services Using GELS

  44. Transparent Bridge Functions • Promiscuous Listening • Every packet passed up to software • Store and Forward • Based on a forwarding database • Filtering • Also based on forwarding database AICCSA 2008: Wide Area Ethernet Services Using GELS

  45. Example 1: Learning and Forwarding • Transmission order • A  D • Ports 2, 3 • D  A • Port 1 • Q  A • Filtered • Z  C • Ports 1, 3 Port 1 Port 3 B Port 2 A Q D M Z C AICCSA 2008: Wide Area Ethernet Services Using GELS

  46. Example 2: Two Bridges Port 1 Port 2 Port 1 Port 2 B1 B2 A Q D M K T What are the Station Caches after “complete” learning? AICCSA 2008: Wide Area Ethernet Services Using GELS

  47. Topologies with Loops • Problems • Frames proliferate • Learning process unstable • Multicast traffic loops forever A LAN 1 B1 B2 B3 LAN 2 AICCSA 2008: Wide Area Ethernet Services Using GELS

  48. Spanning Tree Algorithm • A distributed Algorithm • Elects a single bridge to be the root bridge • Calculates the distance of the shortest path from each bridge to the root bridge (cost) • For each LAN segment , elects a “designated” bridge from among the bridges residing on that segment • The designated bridge for a LAN segment is the one closest to the root bridge • And… AICCSA 2008: Wide Area Ethernet Services Using GELS

  49. Spanning Tree Algorithm • For each bridge • Selects ports to be included in spanning tree • The ports selected are: • The root port --- the port that gives the best path from this bridge to the root • The designated ports --- ports connected to a segment on which this bridge is designated • Ports included in the spanning tree are placed in the forwarding state • All other ports are placed in the blocked state AICCSA 2008: Wide Area Ethernet Services Using GELS

  50. Forwarding frames along the spanning treeForward and Blocked States of Ports • Data traffic (from various stations) is forwarded to and from the ports selected in the spanning tree • Incoming data traffic is always discarded (this is different from filtering frames. Why?) and is never forwarded on the blocked ports AICCSA 2008: Wide Area Ethernet Services Using GELS

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