Chapter 5 Introducing SDN Control in MPLS Networks - High ...

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177In essence, this usage model is simply IP-routing-with-labels, and is a holdover fromthe days when it was faster to do a lookup on a fixed 20-bit label than a variable length IPaddresses. Today, it has found use in MPLS-VPNs, where the MPLS label-stack is usedto deliver full mesh connectivity with address-space isolation. The outer label identifiesthe destination-router (PE) and the inner label identifies the VPN VRF instance. The pathto the PE router is determined via IP routing, and forwarding is performed using theouter-label. We will discuss this MPLS use-case in the SDN context in Sec. 5.4.5.1.2 MPLS Flow ModelIn the flow-based usage-model, LSPs are actually set-up in the network by head-endrouters (also called Label Edge Routers). Packets are classified into FECs. All packets inthe same FEC are forwarded equivalently via an LSP whose path can be determinedindependent from regular IP routing (Fig. 5.4). Path calculation is done dynamically bythe head-end router or offline by a management system. And it is typically signaledexplicitly from the head-end to all other routers (LSRs) along the path using a signalingprotocol like RSVP. Label distribution is therefore typically downstream-on-demand andordered [106]. Importantly in this usage model LSRs do not make independent routing/forwarding decisions on packets. Once an LSP is set-up and the LER has mapped an FECto an LSP, packets are forwarded as part of flows (FEC+LSP).(a)(b)Fig. 5.4 MPLS Flow Model
178 CHAPTER 5. INTRODUCING SDN CONTROL IN MPLS NETWORKSThe MPLS flow-model is used to provide MLPS based Traffic Engineering. Carrierswidely use MPLS-TE today to achieve a) more deterministic behavior in IP networks;and b) greater efficiency in the utilization of network resources. In MPLS-TE the LSPsare more commonly known as TE-LSPs or tunnels. Traffic engineering is accomplishedby routing the tunnels over under-utilized links in the network, and then routing IP trafficthrough those tunnels. MPLS-TE provides admission-control for TE-LSPs (tunnels) viabandwidth-reservation and constrained SPF routing. Additionally, there are a number of‘features’ that MPLS-TE provides to ease the management, operation, and utility oftunnels. Such features include: Auto-Route, Auto-Bandwidth, tunnel-priorities, DS-TE,load-balancing, explicit-routes, re-optimization timers and so on. We will discuss thisuse-case in the SDN context in more detail in this chapter.5.2 MPLS and AbstractionsThe primary objective of this section is to show how MPLS compares to our controlarchitecture. We show that while the MPLS definition of flows is not exactly the same asour definition, it is close enough to be applicable. But while MPLS retains and makes useof a map, it completely misses out on the map-abstraction. We discuss a few examples ofwhat the map-abstraction brings to MPLS networks.5.2.1 MPLS and the Flow-AbstractionWe mentioned before that MPLS has the concept of flows. In the following discussionwe compare MPLS based-flows to the SDN based flow-abstraction from Sec 2.1.1. Weconclude that MPLS based flows (FEC+LSP) are not as generic and flexible as the SDNflow-abstraction in terms of the ‘match’-definitions and forwarding-actions. Neither dothey support vendor-neutral switch-APIs. † But nonetheless, flows exist in MPLS basedWANs.† For example, the API into the FEC table is called Policy Based Routing (PBR) in Cisco routers, and FilterBased Forwarding in Juniper routers. Naturally the CLI commands are different.
Page 1: Chapter 5Introducing SDN Control in
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Page 10 and 11: 181routers make decisions on LSP pa
Page 12 and 13: 183benefits of the map-abstraction
Page 14 and 15: 185all upgraded at the same time. M
Page 16 and 17: 187However the tunnel’s reserved
Page 18 and 19: 189Admission-Control: The MPLS cont
Page 20 and 21: 191This latter point can best be ex
Page 22 and 23: 193different customer’s traffic d
Page 24 and 25: 195the start of the tunnel, to the
Page 26 and 27: 197forwarding traffic-type (or clas
Page 28 and 29: 199controller, as well as link-stat
Page 30 and 31: 201netdev-linux module that abstrac
Page 32 and 33: 203packet-flow routing. The other t
Page 34 and 35: 205In Fig. 5.14 we show two tunnels
Page 36 and 37: 207forced to route along a less-uti
Page 38 and 39: 209tunnel carries both video and Vo
Page 40 and 41: 211former include (i) our implement
Page 42 and 43: 213these backup tunnels usually do
Page 44 and 45: 215annotated fiber topology, on whi
Page 46: 217of magnitude fewer than implemen

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