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Cross-layer Visibility as a Service Ramana Rao Kompella Albert Greenberg, Jennifer Rexford Alex C. Snoeren, Jennifer Yates 1 Layering in the current Internet OVERLAYS MPLS IP Ethernet Optics Fiber-spans Fiber 2 Layering is a mixed blessing Layering allows us to contain complexity Each layer evolves independently without affecting any other layer Allows us to focus on one layer at a time There are associated challenges too… Routine operational tasks need associations across layers Example: mapping an IP link to optical circuit, overlay link to an IP path Lack of accurate cross-layer associations can affect the reliability of the network 3 Intended planned maintenance Seattle Planned maintenance on optics Boston Denver San Francisco Chicago New York St Louis Los Angeles Dallas Orlando 4 Intended planned maintenance Optical component is on circuit id A LA to San Traffic from LA to Lookup database to Francisco link is Dallas is rerouted congested map circuit id A to IP via Denver Planned maintenancelink can Denver induce faults if Due to mis-association, San Francisco accurate associationsincorrectly are maps it to LA not maintained to Dallas Los Angeles Increase OSPF weight Dallas High on LA to Dallas link OSPF Disconnect component weight Causes failure X 5 Customer Fault Tolerance New York Internet Shared optical element Customer diversity Customer in NJ information requires INTRA-CARRIER Philadelphia accurate cross-layer DIVERSITY Sprint associations, sometimes Level 3domains across New York Internet Going through same conduit or Holland tunnel ? Customer in NJ INTER-CARRIER DIVERSITY 6 Fault diagnosis Seattle Because of a bug, IP forwarding path changed, but MPLS did not ! Boston Denver San Francisco Los Angeles Chicago Diagnosing faults requires accurate cross-layer St Louis associations X Dallas New York Orlando MPLS circuit between LA and New York What happened ?!! 7 Why is it hard ? Can’t the operators maintain associations in a centralized fashion ? Maintain database as links are provisioned Update as and when interfaces are re-homed Hard due to flux in topology Churn because of dynamic topology changes Human errors during re-homing interfaces Operational realities – separation of concerns 8 How it is done today ? A combination of non-standard databases Human-generated inventory data Measurement data obtained from probes Configuration state from network elements Policies implemented in network elements Higher complexity and overhead No compatibility across ASes Difficult to evolve a network Difficult to integrate two networks after acquisition Difficult to incorporate third-party tools 9 Why not concentrate on restoration? Advantages of lower-layer restoration Hides lower-layer failures from impacting upper layers Obviates to some extent need for cross-layer visibility Cross-layer visibility still important Lower-layer restoration more expensive than IP restoration Subtle performance changes (e.g., RTT) need diagnosis 10 Why not fatten the interfaces ? Fattening interfaces to make layers aware of the entire topologies above and below Layers discover and propagate mappings automatically Management system can query the network to obtain mappings Fattening results in high complexity Interoperability is a big challenge – long design and test cycles Wider interfaces impact security 11 Architecture for cross-layer visibility BOW-TIE OVERLAYS Backbone planning MPLS Cross-layer Policy Server IP Ethernet Optics DB Fiberspans Ping Trace-route Customer diversity Backbone maintenance Fault diagnosis Fiber IP HOUR-GLASS MANAGEMENT APPLICATIONS 12 Standardize what goes in ! OVERLAYS Standardize what goes in (e.g. IP topologies) MPLS IP Optics FIBER, FIBERSPAN Facilitates interaction between ISP policy servers AS1 OVERLAYS MPLS IP Optics FIBER, FIBERSPAN AS2 13 Advantages of the bow-tie Topology, routing information and other associations can be queried for maintenance, diversity, and fault diagnosis Cooperation across ASes to present better visibility across domains Policies easily enforced through the server Lower overhead on network elements Caching of common queries possible Historical questions can be answered 14 Evolution path to improve accuracy A lot of room for improvement Architecture accommodates evolution so that accuracy can be improved over time Evolution path for individual layers Fiber & Fiber-spans Optical components IP links MPLS and overlay paths 15 Fiber & Fiberspans Automated mechanisms [sebos02] FIBER GPS OPTICAL TAPS / RFID DB FIBER Inject labels through fibers or use RFID GPS to determine the location of fibers Transmit this information to the DB More coverage results in better accuracy but expensive 16 Optical components Manual mechanisms Basic consistency checks Automatic correlation mechanisms such as [kompella05nsdi] to output errors Automatic mechanisms Neighbor discovery for active optical devices Configuration state from “intelligent” optical networks (that support dynamic restoration) 17 Optical components Configuration state during restoration Neighbor discovery through periodic broadcasts at optical layer Intelligent Optical Network ROUTER B ROUTER A DB 18 Other layers IP layer Periodically obtain configuration information to construct topology Automatically collect up/down messages to provide up-to-date view MPLS and overlay paths Static paths obtained from configuration Dynamic paths obtained by monitoring signaling messages 19 Summary Accurate associations critical to many operational tasks A bow-tie architecture for cross-layer visibility Provides the cross-layer associations as a service to various applications Allows better cooperation among ASes through standardizing what goes into the database Policy controlled export of these associations Lower overhead on network elements Allows for innovation while containing complexity 20 Future research directions Design automated mechanisms at each layer to improve cross-layer visibility What frequency should information be obtained? How do we resolve conflicts (minimal edits) in the database? Identify higher-level models that we need to standardize Devise incentives for cooperation among ASes Define a language to specify policies 21 Questions ? 22