The Internet Under Crisis Conditions Learning from September 11 (2003) / Chapter Skim
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5 Measuring the Internet
5 Measuring the Internet
Pages 61-70
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From page 61... ...
Network traffic loads measured in several ISP networks the day of the attacks were generally lighter than normal. However, demand on servers at the major news Web sites was unprecedented to such an extent that several of these systems were rendered inoperative for a period of hours.
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From page 62... ...
Answering these questions would require data from a large number of ISPs or from a carefully targeted sample of ISPs. These unanswered questions suggest that a more robust assessment of crisis events in the future will require new approaches to gathering network measurement data.
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From page 63... ...
Active probes are important because one can gain crucial insight into network conditions for a specific end-to-end path at a specific time, which may not be possible if one monitoring occurs at only a single point. Furthermore, active measurements generally do not require special participation by intermediate nodes, making them easy to deploy and execute.
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From page 64... ...
The subsections below describe several common passive measurement tools. Web Access Logs Logging access activity is a standard feature in Web server software that is usually enabled by content providers.
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From page 65... ...
A standard tool for logging individual packets is "tcpdump,"~ which uses packet filters to capture selected packet activity from the network interface. A typical log entry from tcpdump consists of a time stamp, the source/destination IP/ port numbers, the transport protocol name, details from the packet header, and details of the packet payload.
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From page 66... ...
Assessing the overall status of the network thus requires examining many, carefully selected BGP tables that in aggregate reflect the shape of the entire network.3 Simple Network Management Protocol The Simple Network Management Protocol (SNMP) 4 iS an important component in the daily operation of large-scale networks.
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From page 67... ...
An alternative approach would be to mandate reporting by ISPs to an agency such as the Federal Communications Commission (indeed, reports of certain types of outages in the public telephone network must be so filed under present rules)
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From page 68... ...
Global Network Monitoring A thorough analysis of Internet behavior during crisis events requires clean, consistent data from a number of vantage points across all network layers. In a general sense, this means that the following data are required from sufficient numbers and types of protocols, networks, geographic points, and time scales: · Application and service-level data such as Web server logs, · End-to-end connectivity, delay, and loss data such as those gathered by active probes, · Packet traffic data such as IP flow or router Management Information Base logs, and · Global interdomain routing data.
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From page 69... ...
Targeted Measurement During a Crisis Effective assessment of Internet behavior during a crisis would be greatly enhanced by the ability to adjust the scope of what is being measured in accordance with the specific situation. This kind of targeted assessment would be facilitated by the establishment of a general repository of contact information for network operators, content providers, and groups that run network-monitoring infrastructures.
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