Richard Mortier, Microsoft Research, Guest Lecture on Network ...

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  • Two types: link-state (OSPF), distance/path-vector (BGP) IP options Loose source routing, strict source routing, record route Can be treated separately, ignored, dropped
  • Layer violation Control protocol encapsulated by controlled protocol...
  • Note advantages: unlike routers and netflow
  • Annotations state what’s happening; italics are outcomes; boxes are hosts (which generate packets); blue arrowed circles are routers (which generate routeing protocol info)
  • Netflow: sample flows in middle of net (partial info about any flow); enma, sample flows at edges (complete info about some flows)
  • imperative; Complex, hard to control, independent of (eg) SNMP and other management tools
  • imperative; Complex, hard to control, independent of (eg) SNMP and other management tools

Transcript

  • 1. Network Management Richard Mortier Microsoft Research, Cambridge (Guest lecture, Digital Communications II)
  • 2. Overview
    • Introduction
    • Abstractions
    • IP network components
    • IP network management protocols
    • Pulling it all together
    • An alternative approach
  • 3. Overview
    • Introduction
      • What’s it all about then?
    • Abstractions
    • IP network components
    • IP network management protocols
    • Pulling it all together
    • An alternative approach
  • 4. What is network management ?
    • One point-of-view: a large field full of acronyms
      • EMS, TMN, NE, CMIP, CMISE, OSS, AN.1, TL1, EML, FCAPS, ITU, ...
      • (Don’t ask me what all of those mean, I don’t care!)
    • From question.com:
      • In 1989, a random of the journalistic persuasion asked hacker Paul Boutin “What do you think will be the biggest problem in computing in the 90s?” Paul's straight-faced response: “There are only 17,000 three-letter acronyms.” (To be exact, there are 26^3 = 17,576.)
    • Will ignore most of them 
  • 5. What is network management ?
    • Computer networks are considered to have three operating timescales
      • Data : packet forwarding [ μs, ms ]
      • Control : flows/connections [ secs, mins ]
      • Management : aggregates, networks [ hours,days ]
    • … so we’re concerned with “the network” rather than particular devices
    • Standardization is key!
  • 6. Overview
    • Introduction
    • Abstractions
      • ISO FCAPS, TMN EMS, ATM
    • IP network components
    • IP network management protocols
    • Pulling it all together
    • An alternative approach
  • 7. ISO FCAPS: functional separation
    • F ault
      • Recognize, isolate, correct, log faults
    • C onfiguration
      • Collect, store, track configurations
    • A ccounting
      • Collect statistics, bill users, enforce quotas
    • P erformance
      • Monitor trends, set thresholds, trigger alarms
    • S ecurity
      • Identify, secure, manage risks
  • 8. TMN EMS: administrative separation
    • Telecommunications Management Network
    • Element Management System
    • “ ...simple but elegant...” (!)
      • (my emphasis)
    • NEL: network elements (switches, transmission systems)
    • EML: element management (devices, links)
    • NML: network management (capacity, congestion)
    • SML: service management (SLAs, time-to-market)
    • BML: business management (RoI, market share, blah)
  • 9. The B-ISDN reference model
    • Asynchronous Transfer Mode “cube”
      • See IAP lectures, maybe 
    • Plane management…
      • The whole network
    • … vs layer management
      • Specific layers
    • Topology
    • Configuration
    • Fault
    • Operations
    • Accounting
    • Performance
    management plane user plane control plane higher layers ATM layer physical layer plane management higher layers ATM adaptation layer layer management
  • 10. Network management
    • Models of general communication networks
      • Tend to be quite abstract and exceedingly tedious!
      • Many practitioners still seem excited about OO programming, WIMP interfaces, etc
      • … probably because implementation is hard due to so many excessively long and complex standards!
    • My view: basic “need-to-know” requirements are
      • What should be happening? [ c ]
      • What is happening? [ f, p, a ]
      • What shouldn’t be happening? [ f, s ]
      • What will be happening? [ p, a ]
  • 11. Network management
    • We’ll concentrate on IP networks
      • Still acronym city: ICMP, SNMP, MIB, RFC 
      • Sample size: 10 2 routers, 10 5 hosts
    • We’ll concentrate on the network core
      • Routers, not hosts
    • We’ll ignore “service management”
      • DNS, AD, file stores, etc
  • 12. Overview
    • Introduction
    • Abstractions
    • IP network components
      • IP primer, router configuration
    • IP network management protocols
    • Pulling it all together
    • An alternative approach
  • 13. IP primer (you probably know all this)
    • Destination-routed packets – no connections
      • Time-to-live field: allow removal of looping packets
    • Routers forward packets based on routeing tables
      • Tables populated by routeing protocols
    • Routers and protocols operate independently
      • … although protocols aim to build consistent state
    • RFCs ~= standards
      • Often much looser semantics than e.g. ISO, ITU standards
      • Compare for example OSPF [RFC2327] and IS-IS [RFC1142, RFC1195], two link-state routeing protocols
  • 14. So, how do you build an IP network?
    • Buy (lease) routers
    • Buy (lease) fibre
    • Connect them all together
    • Configure routers appropriately
    • Configure end-systems appropriately
    • Assume you’ve done 1–3 and someone else is doing 5…
  • 15. Router configuration
    • Initialization
      • Name the router, setup boot options, setup authentication options
    • Configure interfaces
      • Loopback, ethernet, fibre, ATM
      • Subnet/mask, filters, static routes
      • Shutdown (or not), queueing options, full/half duplex
    • Configure routeing protocols (OSPF, BGP, IS-IS, …)
        • Process number, addresses to accept routes from, networks to advertise
    • Access lists, filters, ...
      • Numeric id, permit/deny, subnet/mask, protocol, port
    • Route-maps, matching routes rather than data traffic
    • Other configuration aspects: traps, syslog, etc
  • 16. Router configuration fragments hostname FOOBAR ! boot system flash slot0:a-boot-image.bin boot system flash bootflash: logging buffered 100000 debugging logging console informational aaa new-model aaa authentication login default tacacs local aaa authentication login consoleport none aaa authentication ppp default if-needed tacacs aaa authorization network tacacs ! ip tftp source-interface Loopback0 no ip domain-lookup ip name-server 10.34.56.78 ! ip multicast-routing ip dvmrp route-limit 7000 ip cef distributed interface Loopback0 description router-1.network.corp.com ip address 10.65.21.43 255.255.255.255 ! interface FastEthernet0/0/0 description Link to New York ip address 10.65.43.21 255.255.255.128 ip access-group 175 in ip helper-address 10.65.12.34 ip pim sparse-mode ip cgmp ip dvmrp accept-filter 98 neighbor-list 99 full-duplex ! interface FastEthernet4/0/0 no ip address ip access-group 183 in ip pim sparse-mode ip cgmp shutdown full-duplex router ospf 2 log-adjacency-changes passive-interface FastEthernet0/0/0 passive-interface FastEthernet0/1/0 passive-interface FastEthernet1/0/0 passive-interface FastEthernet1/1/0 passive-interface FastEthernet2/0/0 passive-interface FastEthernet2/1/0 passive-interface FastEthernet3/0/0 network 10.65.23.45 0.0.0.255 area 1.0.0.0 network 10.65.34.56 0.0.0.255 area 1.0.0.0 network 10.65.43.0 0.0.0.127 area 1.0.0.0 access-list 24 remark Mcast ACL access-list 24 permit 239.255.255.254 access-list 24 permit 224.0.1.111 access-list 24 permit 239.192.0.0 0.3.255.255 access-list 24 permit 232.192.0.0 0.3.255.255 access-list 24 permit 224.0.0.0 0.0.0.255 access-list 1011 deny 0000.0000.0000 ffff.ffff.ffff ffff.ffff.ffff 0000.0000.0000 0xD1 2 eq 0x42 access-list 1011 permit 0000.0000.0000 ffff.ffff.ffff 0000.0000.0000 ffff.ffff.ffff tftp-server slot1:some-other-image.bin tacacs-server host 10.65.0.2 tacacs-server key xxxxxxxx rmon event 1 trap Trap1 description "CPU Utilization>75%" owner config rmon event 2 trap Trap2 description "CPU Utilization>95%" owner config
  • 17.
    • Lots of quite large and fragile text files
      • 00s/000s routers, 00s/000s lines per config
      • Errors are hard to find and have non-obvious results
      • Router configuration also editable on-line
    • How to keep track of them all?
      • Naming schemes, directory hierarchies, CVS
      • ssh upload and atomic commit to router
      • Perhaps even a database
    • State of the art is pretty basic
      • Few tools to check consistency
      • Generally generate configurations from templates and have human-intensive process to control access to running configs
    • Topic of current research [Feamster et al]
    Router configuration this counts as quite advanced!
  • 18. Overview
    • Introduction
    • Abstractions
    • IP network components
    • IP network management protocols
      • ICMP, SNMP, Netflow
    • Pulling it all together
    • An alternative approach
  • 19. ICMP
    • Internet Control Message Protocol [RFC792]
      • IP protocol #1
      • In-band “control”
    • Variety of message types
      • echo/echo reply [ PING (packet internet groper) ]
      • time exceeded [ TRACEROUTE ]
      • destination unreachable, redirect
      • source quench
  • 20. Ping (Packet INternet Groper)
    • Test for liveness
      • … also used to measure (round-trip) latency
    • Send ICMP echo
    • Valid IP host [RFC1122, RFC1123] must reply with ICMP echo response
    • Subnet PING?
      • Useful but often not available/deprecated
      • “ ACK” implosion could be a problem
      • RFCs ~= standards
  • 21. Traceroute
    • Which route do my packets take to their destination?
      • Send UDP packets with increasing time-to-live values
      • Compliant IP host must respond with ICMP “time exceeded”
      • Triggers each host along path to so respond
    • Not quite that simple
      • One router, many IP addresses: which source address?
        • Router control processor, inbound or outbound interface
      • Routes often asymmetric, so return path != outbound path
      • Routes change
    • Do we want full-mesh host-host routes anyway?!
      • Size of data set, amount of probe traffic
      • This is topology, what about load on links?
  • 22. SNMP
    • Protocol to manage information tables at devices
    • Provides get, set, trap, notify operations
      • get , set : read, write values
      • trap : signal a condition (e.g. threshold exceeded)
      • notify : reliable trap
    • Complexity mostly in the MIB design
      • Some standard tables, but many vendor specific
      • Non-critical, so often tables populated incorrectly
      • Many tens of MIBs (thousands of lines) per device
      • Different versions, different data, different semantics
        • Yet another configuration tracking problem
      • Inter-relationships between MIBs
  • 23. IPFIX
    • IETF working group
      • Export of flow based data out of IP network devices
      • Developing suitable protocol based on Cisco NetFlow™ v9
      • [RFC3954, RFC3955]
    • Statistics reporting
      • Setup template
      • Send data records matching template
    • Many variables
      • Packet/flow counters, rule matches, quite flexible
  • 24. Overview
    • Introduction
    • Abstractions
    • IP network components
    • IP network management protocols
    • Pulling it all together
      • Network mapping, statistics gathering, control
    • An alternative approach
  • 25. An hypothetical NMS
    • GUI around ICMP (ping, traceroute), SNMP, etc
    • Recursive host discovery
      • Broadcast ping, ARP, default gateway: start somewhere
      • Recursively SNMP query for known hosts/connected networks
      • Ping known hosts to test liveness
      • Iterate
    • Display topology: allow “drill-down” to particular devices
    • Configure and monitor known devices
      • Trap, Netflow™, syslog message destinations
      • Counter thresholds, CPU utilization threshold, fault reporting
      • Particular faults or fault patterns
      • Interface statistics and graphs
  • 26. A real NOC (Network Operations Centre) [ from AT&T ]
  • 27. An hypothetical NMS
    • All very straightforward? No, not really
      • A lot of software engineering: corner cases, traceroute interpretation, NATs, etc
      • MIBs may contain rubbish
      • Can only view inside your network anyway
    • Efficiency
      • Rate pacing discovery traffic: ping implosion/explosion
      • SNMP overloading router CPUs
    • Tunnelled, encrypted protocols becoming prevalent
    • Using NMSs also not straightforward
      • How to setup “correct” thresholds?
      • How to decide when something “bad” has happened?
      • How to present (or even interpret) reams and reams of data?
  • 28. Overview
    • Introduction
    • Abstractions
    • IP network components
    • IP network management protocols
    • Pulling it all together
    • An alternative approach
      • From the edges…
  • 29.
    • Edge-based network management platform
      • Collect flow information from hosts, and
      • Combine with topology information from routeing protocols
    • Enable visualization, analysis, simulation, control
    • Avoid problems of not-quite-standard interfaces
      • Management support is typically ‘non-critical’ (i.e. buggy  ) and not extensively tested for inter-operability
    • Do the work where resources are plentiful
      • Hosts have lots of cycles and little traffic (relatively)
    • Protocol visibility: see into tunnels, IPSec, etc
    ENMA
  • 30. System outline Control Packets Flows Routeing protocol Topology Visualize Simulate Simulator Distributed database Traffic matrix Set of routes srcs dsts routes
  • 31.
    • Pictures of current topology and traffic
      • Routes+flows+forwarding rules  BIG PICTURE
    • In fact, where did my traffic go yesterday?
      • Keep historical data for capacity planning, etc
    • A platform for anomaly detection
      • Historical data suggests “normality,” live monitoring allows anomalies to be detected
    Where is my traffic going today?
  • 32. Where might my traffic go tomorrow?
    • Plug into a simulator back-end
      • Discrete event simulator, flow allocation solver
    • Run multiple ‘what-if’ scenarios
      • … failures
      • … reconfigurations
      • … technology deployments
    • E.g. “What happens if we coalesce all the Exchange servers in one data-centre?”
  • 33. Where should my traffic be going?
    • Close the loop: compute link weights to implement policy goals
      • Recompute on order of hours/days
    • Allows more dynamic policies
      • Modify network configuration to track e.g. time of day load changes
    • Make network more efficient (~cheaper)?
  • 34. Where are we now?
    • Three major components
      • Flow collection
      • Route collection
      • Distributed database
    • Building prototypes, simulating system
  • 35. Data collection
    • Flow collection
      • Hosts track active flows
        • Using low overhead event posting infrastructure, ETW
        • Built prototype device driver provider & user-space consumer
      • Used packet traces for feasibility study on (client, server)
        • Peaks at (165, 5667) live and (39, 567) active flows per sec
    • Route collection
      • OSPF is link-state: passively collect link state adverts
      • Extension of my work at Sprint (for IS-IS and BGP); also been done at AT&T (NSDI’04 paper)
  • 36. The distributed database
    • Logically contains
      • Traffic flow matrix (bandwidths), {srcs} × {dsts}
      • … each entry annotated with current route from src to dst
        • N.B. src/dst might be e.g. (IP end-point, application)
    • Large dynamic data set suggests aggregation
    • Related work
      • { distributed, continuous query, temporal } databases
      • Sensor networks
    • Potential starting points: Astrolabe or SDIMS (SIGCOMM’04)
      • Where/what/how much to aggregate?
        • Is data read- or write-dominated?
        • Which is more dynamic, flow or topology data?
        • Can the system successfully self-tune?
  • 37. The distributed database
    • Construct traffic matrix from flow monitoring
      • Hosts can supply flows they source and sink
      • Only need a subset of this data to get complete traffic matrix
    • Construct topology from route collection
      • OSPF supplies topology -> routes
    • Wish to be able to answer queries like
      • “ Who are the top-10 traffic generators?”
        • Easy to aggregate, don’t care about topology
      • “ What is the load on link l ?”
        • Can aggregate from hosts, but need to know routes
      • “ What happens if we remove links {l…m} ?”
        • Interaction between traffic matrix, topology, even flow control
  • 38. The distributed database
    • Building simulation model
      • OSPF data gives topology, event list, routes
      • Simple load model to start with (load ~ # subnets)
      • Precedence matrix (from SPF) reduces flow-data query set
    • Can we do as well/better than e.g. NetFlow?
      • Accuracy/coverage trade-off
    • How should we distribute the DB?
      • Just OSPF data? Just flow data? A mixture?
    • How many levels of aggregation?
      • How many nodes do queries touch?
    • What sort of API is suitable?
      • Example queries for sample applications
  • 39. Summary
    • Introduction
      • What is network management?
    • Abstractions
      • ISO FCAPS, TMN EMS, ATM
    • IP network components
      • IP, routers, configurations
    • IP network management protocols
      • ICMP, SNMP, etc
    • Pulling it all together
      • Outline of a network management system
    • An alternative approach: from the edges
  • 40. The end
    • Questions
    • Answers?
    • http:// www.cisco.com /
    • http://www.routergod.com/
    • http://www.ietf.org/
    • http:// ipmon.sprintlabs.com/pyrt /
    • http:// www.nanog.org /
  • 41. Backup slides
    • Internet routeing
    • OSPF
    • BGP
  • 42. Internet routeing
    • Q: how to get a packet from node to destination?
    • A1: advertise all reachable destinations and apply a consistent cost function ( distance vector)
    • A2: learn network topology and compute consistent shortest paths ( link state )
      • Each node (1) discovers and advertises adjacencies ; (2) builds link state database ; (3) computes shortest paths
    • A1, A2: Forward to next-hop using longest-prefix-match
  • 43. OSPF (~link state routeing)
    • Q: how to route given packet from any node to destination?
    • A: learn network topology; compute shortest paths
    • For each node
      • Discover adjacencies (~ immediate neighbours ) ; advertise
      • Build link state database (~ network topology )
      • Compute shortest paths to all destination prefixes
      • Forward to next-hop using longest-prefix-match (~ most specific route )
  • 44. BGP (~path vector routeing)
    • Q: how to route given packet from any node to destination?
    • A: neighbours tell you destinations they can reach; pick cheapest option
    • For each node
      • Receive (destination, cost, next-hop) for all destinations known to neighbour
      • Longest-prefix-match among next-hops for given destination
      • Advertise selected (destination, cost+  , next-hop ' ) for all known destinations
    • Selection process is complicated
    • Routes can be modified/hidden at all three stages
      • General mechanism for application of policy