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Measurement in the Internet. Outline. Internet topology Bandwidth estimation Tomography Workload characterization Routing dynamics. Why study Internet topology?. General understanding of growth of Internet Fragility/robustness to failures and attacks

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Presentation Transcript
  • Internet topology
  • Bandwidth estimation
  • Tomography
  • Workload characterization
  • Routing dynamics
why study internet topology
Why study Internet topology?
  • General understanding of growth of Internet
  • Fragility/robustness to failures and attacks
  • Are there feasible design principles to:
    • improve robustness
    • reduce deployment/growth costs
    • make maintenance/support easier
    • improve performance for users/customers
  • Realistic input to simulators
topology misleading word
"topology" - misleading word
  • Unlabelled graph links do not capture the problem.
  • BGP routing behavior is determined by policies, not just connectivity.
    • Peers, customers and providers are very different.
  • Bandwidth, latency, and congestion at the router level matters.
    • A small ISP peering link is not the same as a large ISP backbone link.
scales hierarchies of topology
Scales/Hierarchies of topology
  • Routing/BGP connectivity of ASes or ARDs
    • What are the connectivity patterns between organizations? Are there cluster patterns?
  • Geographic/logical clusters within large organizations (particularly ISPs)
  • Router-level
  • Switches, hubs, firewalls, hosts

Tracing route to []

over a maximum of 30 hops:

1 <10 ms <10 ms 10 ms

2 <10 ms <10 ms <10 ms []

3 40 ms 30 ms 90 ms []

4 <10 ms <10 ms 10 ms []

5 <10 ms <10 ms 10 ms []

6 <10 ms <10 ms 10 ms []

7 <10 ms <10 ms 10 ms []

8 <10 ms <10 ms 10 ms []

9 30 ms 30 ms 30 ms []

10 30 ms 30 ms 40 ms []

11 40 ms 40 ms 40 ms []

12 60 ms 70 ms 70 ms []

13 80 ms 80 ms 80 ms []

14 70 ms 80 ms 80 ms []

15 80 ms 81 ms 80 ms []

16 80 ms 80 ms 80 ms []

17 80 ms 80 ms 80 ms []

18 * * * Request timed out.

how traceroute works
How traceroute works
  • All IP packets have a Time-To-Live (TTL) field specifying the number of routerhops the packet is allowed to be in the network.
  • When an IP device (router or host) receives a packet:
    • if the packet is for the device, the device processes the packet
    • otherwise, decrement the TTL
      • if TTL > 0, forward packet towards destination
      • if TTL = 0, drop this data packet and send error packet back to source
how traceroute works1
How traceroute works
  • traceroutetries to measure the forward-path (one direction only) from source to destination
  • each router hop on the path is found one at a time
  • source sends a packet with TTL 1 and waits for an error from the router 1 hop away, use the source IP address of error as the identity of this hop
  • source repeats with larger TTLs until it reaches the destination (or gives up)
how traceroute works2






How traceroute works
  • However, there are multiple potential choices for the IP address in the message from an intermediary hop.
  • Every interface on a router has a different IP address.
  • AI - input interface to A from source
  • AO - output interface towards destination from A
  • AR - return path interface towards source from A
traceroute to topology
traceroute to topology
  • Apply traceroute methodology from multiple sources to multiple destinations to discover links.
  • Number of sources and destinations necessary not clearly known.
    • There are diminishing returns of discovering new links, but not always clear if they are important or not.
    • We know that it is bad in some cases, but how bad is it?
traceroute and routers
traceroute and routers
  • traceroute only finds interface IP addresses, so we need a way to collapse those on the same router
  • load-balancing and non-atomicity can lead to false links
big questions for topology
Big questions for topology
  • We know we can't see all backup and peering links.
    • How much might we really be off?
    • What set of possible "actual networks" could lead to what has been measured, and can we assign probabilities?
    • How much does it matter for different problems?
  • Are there ways of targetting measurement to improve coverage?
  • How do we understand the network with partial link characteristic or traffic information?
why bandwidth estimation
Why bandwidth estimation?
  • Not all link bandwidths and utilizations are the same.
  • Realistic inputs to simulators and models.
  • End hosts and routers may want to make intelligent decisions based on more knowledge about the network.
bandwidth estimation
Bandwidth estimation
  • Capacity vs. available bandwidth
  • Network does not directly expose this information.
  • May be variable over short-time scales.
  • Cross-traffic can cause confusion.
  • Convolution of forward-path and return-paths in some techniques.
bandwidth estimation1
Bandwidth estimation
  • Link techniques try to find bandwidth for each link (hop) along a path.
  • Path techniques try to find to the bandwidth along the entire path.
  • Typically large numbers of probes needed, due to variability in measurements.
  • Two forms of this problem
    • given edge measurements infer something about the inside state of the network (link speeds, bandwidth, congestion)
    • given internal state of the network infer something about the traffic entering/exiting the network
  • What measurements yield the most information?
  • How much might results be off?
why study workload characterization
Why study workload characterization?
  • Capacity planning
  • Understanding trends in network usage to predict deployment needs
  • Interactions between applications and protocols
  • Input for new protocol design
  • Predicting effects from network changes
  • Detecting anomalous behavior
why study routing dynamics
Why study routing dynamics?
  • Is global reachability goal of Internet met?
  • How fragile is the routing system to failures or attacks?
  • How much does policy effect performance?