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Network Monitoring for Internet Traffic Engineering

Network Monitoring for Internet Traffic Engineering. Jennifer Rexford AT&T Labs – Research Florham Park, NJ 07932 http://www.research.att.com/~jrex. Tracking the AT&T IP Backbone. Traffic Modem records for each WorldNet dial connection SNMP link and loss statistics for every link

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Network Monitoring for Internet Traffic Engineering

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  1. Network Monitoring for Internet Traffic Engineering Jennifer Rexford AT&T Labs – Research Florham Park, NJ 07932 http://www.research.att.com/~jrex

  2. Tracking the AT&T IP Backbone • Traffic • Modem records for each WorldNet dial connection • SNMP link and loss statistics for every link • Flow-level measurement on selective peering links • Packet-level measurement on two edge links • Performance • Active probes of performance for each pair of cities • Network state • Configuration file from each router • Fault data from each router (alarms and polling) • BGP routing tables for routers connecting to peers • BGP update messages from two core routers

  3. Outline • ISP backbone networks • Service provider backbone • Routing protocols • Network model for traffic engineering • Topology, capacity, and routing configuration • Destinations reachable via neighboring domains • Populating the model • Static snapshot (config files, forwarding tables) • Real-time view (OSPF monitor, iBGP monitor) • Integration in traffic engineering tool

  4. Internet Service Provider Backbone modem banks, business customers, web/e-mail servers neighboring providers Backbone routers Gateway routers Access routers

  5. Border Gateway Protocol (BGP) • ASes exchange info about who they can reach • Update messages exchanged over a TCP connection • Local policies for path selection (which to use?) • Local policies for route propagation (who to tell?) • Policies configured by the AS’s network operator “I can reach 12.34.158.0/23 via AS 1” “I can reach 12.34.158.0/23” 2 3 1 flow of traffic 12.34.158.5 AS = Autonomous System

  6. Interior Gateway Protocol (Within an AS) • Routers flood information to learn the topology • Routers determine “next hop” to reach other routers • Path selection based on link weights (shortest path) • Link weights configured by the network operator 2 1 3 1 3 2 5 1 3 4 Path cost = 8

  7. Traffic Engineering in an ISP Backbone • Network topology • Connectivity and capacity of routers and links • Configurable policies for resource allocation • Path selection, buffer management, and link scheduling • Traffic demands • Expected/offered load between points in the network • Performance objective • Balanced load, low latency, service level agreements … • Question: Given the topology and traffic demands, which configuration parameters should be used? This talk focuses on the topology and configuration part.

  8. Our Approach: Measure, Model, and Control • Monitor the network to collect the various inputs • Model the network-wide path-selection process • Build tools on top of the data and the model Routing configuration Topology Distributed routing protocols Offered traffic BGP updates Flow of traffic through the network

  9. Network Topology • Router • Loopback IP address (e.g., 12.123.37.250) • IP addresses of interfaces • Link • Network address (e.g., 12.125.133.88/30) • Capacity (e.g., 10 Mbps, 622 Mbps) 12.125.133.88/30 12.123.37.250 12.7.108.3 12.125.133.89 12.125.133.90

  10. Core link OSPF weight per interface OSPF area Edge link Set of destination prefixes Core and Edge Links area 9 1024 512 {12.34.158.0/23, 192.0.2.0/24}

  11. Populating the Model: Daily Snapshot • Router configuration files • Router name, OS version, IP address, running processes • Individual interfaces and their location in the router • Set of commands applied against the router • Processing the configuration data • Parsing the commands applied to each router • Identifying all of the outgoing interfaces at the router • Finding each pair of interfaces that forms a core link • Populates part of the model • Router, links, and link capacities • Identification of edge and core links • OSPF weights and areas for core links

  12. Example: Router Configuration File • Language with hundreds of different commands • Cisco IOS is a de facto standard config language • Sections for interfaces, routing protocols, filters, etc. version 12.0 hostname MyRouter ! interface Loopback0 ip address 12.123.37.250 255.255.255.255 ! interface Serial9/1/0/4:0 description MyT1Customer bandwidth 1536 ip address 12.125.133.89 255.255.255.252 ip access-group 10 in ! interface POS6/0 description MyBackboneLink ip address 12.123.36.73 255.255.255.252 ip ospf cost 1024 ! router ospf network 12.123.36.72 0.0.0.3 area 9 network 12.123.37.250 0.0.0.0 area 9 ! access-list 10 permit 12.125.133.88 0.0.0.3 access-list 10 permit 135.205.0.0 0.0.255.255 ip route 135.205.0.0 255.255.0.0 Serial9/1/0/4:0

  13. Daily Snaphot: Continued • Router forwarding tables • Next-hop interface(s) for each destination prefix • Processing the forwarding tables • Identify next hops associated with edge interfaces • Ignore entries where next hop is a core interface • Extract the associated destination prefixes • Populates part of the model • Set of prefixes reachable via each edge link • Or, set of edge links associated with each prefix

  14. Example: Forwarding Table (“show ip cef”) Prefix Next Hop Interface 4.20.90.120/29 12.123.28.134 POS7/0 12.123.28.130 POS6/0 4.20.90.128/29 12.123.28.130 POS6/0 4.24.7.104/30 12.123.28.134 POS7/0 4.36.100.0/23 192.205.32.126 ATM5/0.1 6.0.0.0/8 12.123.28.134 POS7/0 12.123.28.130 POS6/0 9.2.0.0/16 192.205.32.126 ATM5/0.1 9.3.4.0/24 12.123.28.130 POS6/0 9.3.5.0/24 12.123.28.130 POS6/0 9.20.0.0/17 192.205.32.178 POS0/3

  15. Locating the Set of Egress Links for Prefix d Prefix d: exit links {i, k} i Table entry: (d, i) k d Table entry: (d, k)

  16. Populating the Model: Real-Time View • OSPF monitor • Up/down status of routers and their interfaces • OSPF weight and area for each interface • Acquiring the real-time view • Software router (GateD) that implements OSPF routing • Physical adjacency with an operational router • Copy of all flooded link-state advertisements Route monitor Router OSPF messages Router Router Work by A. Shaikh and A. Greenberg

  17. Real-Time View (Continued) • iBGP monitor • Destination prefixes associated with each edge link • Frequency of changes, attributes of routes, etc. • Acquiring the real-time view • Software router (Zebra) that implements BGP routing • Logical adjacency (TCP) with operational routers • “Best route” for each prefix from each vantage point Route monitor Router BGP messages BGP messages Router Router Work with T. Griffin and D. Caldwell

  18. Toolkit for Traffic Engineerng • Other components of traffic engineering • Traffic measurements at destination prefix level • Path computation based on OSPF weights/areas • Network visualization to display flow of traffic • Optimization algorithm for selecting good weights Optimization Visualization Routing model Traffic model Network model

  19. Combining With Traffic Measurements Peering point Color/size of node: proportional to traffic to this router (highto low) Color/size of link: proportional to traffic carried (high to low)

  20. Conclusions • Summary • Network model for traffic engineering (TE) • Populating the model from existing data sets • Real-time monitoring of OSPF and BGP messages • Integration of the network model in a TE tool • Ongoing work • Extensions to support changes to BGP policies • Analysis of the real-time OSPF and BGP data • Improved support for measurement on routers • Driving goal • Accurate, timely, network-wide view of topology, routing, and traffic data

  21. To Learn More... • Network overview and routing model • “Traffic engineering for IP networks” (http://www.research.att.com/~jrex/papers/ieeenet00.ps) • Measurement infrastructure • "Measurement and analysis of IP network usage and behavior”(http://www.research.att.com/~jrex/papers/ieeecomm00.ps) • Topology and configuration • “IP network configuration for intradomain traffic engineering” (http://www.research.att.com/~jrex/papers/ieeenet01.ps) • Traffic demands • “Deriving traffic demands for operational IP networks: Methodology and experiences” (http://www.research.att.com/~jrex/papers/sigcomm00.ps) • OSPF monitor • “An OSPF topology server: Design and evaluation”

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