NET0183 Networks and Communications

NET0183 Networks and Communications by Dr Andy Brooks

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NET0183 Networks and CommunicationsLecture 10

Basic Internet Measurements

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NET0183 Networks and Communications by Dr Andy Brooks

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Internet Protocol address (IP address)

• A computer on the Internet has a unique 32-bit identifier called its IP address.

• IP addresses are described for convenience in dotted decimal notation where each 8-bits are given in decimal (0 to 255).

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basic terminology

NET0183 Networks and Communications by Dr Andy Brooks

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NET0183 Networks and Communications by Dr Andy Brooks

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Windows: ipconfig

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An address mask or subnet mask has one bits to mark the network prefix and zero bits to mark the host portion. Here the network prefix is 130.208.225.

NET0183 Networks and Communications by Dr Andy Brooks

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Windows: Control Panel -> Network connections -> Local Area Network->

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Dynamic Host Configuration Protocol (DHCP)Andy asks: Under DHCP does a computer’s IP address change from one session to the next? Is the default gateway the computer which connects the local network to the Internet?

NET0183 Networks and Communications by Dr Andy Brooks

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There are five kinds of geographical location which characterize a website.

1. Where are the website´s users located?2. Where is the website´s legal owner located?3. Where is the website´s maintainer located?4. Where is the hardware located? 5. To where does the website content refer?

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A website about Denmark could be hosted on a server in Iceland which is maintained by someone in Ireland for a website owner in Norway. Since the site is in Scottish Gaelic, all the users are located in Scotland.

Location can be imprecise. For example, the location of a web server might be known only at a city level rather than a building and street level.

NET0183 Networks and Communications by Dr Andy Brooks

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Where is the hardware located?

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city level onlyMay not be correct.May not be accurate.

NET0183 Networks and Communications by Dr Andy Brooks

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Who registered the domain name?http://www.domaintools.com/

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www.unak.is

May not be correct.May not be accurate.

NET0183 Networks and Communications by Dr Andy Brooks

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What do users in Iceland do?http://www.alexa.com/

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Facebook

Google

mbl.is May not be correct.May not be accurate.

NET0183 Networks and Communications by Dr Andy Brooks

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Measuring time distance

• It is possible to measure the time it takes to transmit and receive data between two nodes.– latency (or delay)

• If latency is large, then this implies a larger physical distance between the two nodes.

• Different hardware and different network configurations have an influence on latency.

• The relationship between physical distance and time distance is not always linear, however.

• Latency can increase in the presence of network congestion in the same way average traffic speed reduces when a road network becomes congested.

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latency/biðtími

NET0183 Networks and Communications by Dr Andy Brooks

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ping

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<networking, tool> (ping, originally contrived to match submariners' term for the sound of a returned sonar pulse) A program written in 1983 by Mike Muuss (who also wrote TTCP) used to test reachability of destinations by sending them one, or repeated, ICMP echo requests and waiting for replies. Since ping works at the IP level its server-side is often implemented entirely within the operating system kernel and is thus the lowest level test of whether a remote host is alive. Ping will often respond even when higher level, TCP-based services cannot.

Sadly, Mike Muuss was killed in a road accident on 2000-11-20.

The term is also used as a verb: "Ping host X to see if it is up." The Unix command "ping" can be used to do this and to measure round-trip delays. ICMP Internet Control Message Protocol

NET0183 Networks and Communications by Dr Andy Brooks

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Windows: ping www.hi.is

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Average = 6ms

NET0183 Networks and Communications by Dr Andy Brooks

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Windows: ping www.bbc.co.uk

Average = 46ms

NET0183 Networks and Communications by Dr Andy Brooks

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Western Europe

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Andy asks:Is the hardware for www.hi.is in Reykjavik?Is the hardware for www.bbc.co.uk in London?

46/6 = 7.6666Is London 7.666 times further away than Reykjavik is from Akureyri?

http://www.distance-calculator.co.uk/“The approximate distance as the crow flies from London to Akureyri is 1168.16 miles.”“Distance between Reykjavik and Akureyri is 154 miles or 247.79 Kilometers.” (by road?)

1168/154 = 7.5844

Andy comments: When making calculations like this we need to be clear about how the physical distance measure is calculated.

NET0183 Networks and Communications by Dr Andy Brooks

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Measuring time distance and routes

• The utility traceroute works in a way similar to ping but provides more details.

• The route taken over intermediate nodes is listed with an indication of the round-trip times for each segment of the journey.– Nodes are identified by domain name or IP address.– Nodes with long or unusual domain names may be special

routing computers which normal users are unaware of.• The political and economic structures of the Internet

can be exposed using traceroute.

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NET0183 Networks and Communications by Dr Andy Brooks

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Windows: tracert www.hi.is

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On each line are three measurements of round-trip time.

tracert not traceroute

NET0183 Networks and Communications by Dr Andy Brooks

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Windows: tracert www.bbc.co.uk

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Andy asks: Are the round-trip times, accumulating times?

NET0183 Networks and Communications by Dr Andy Brooks

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Security and confidentiality concerns

• Some networks block the use of ping and traceroute for security reasons.– The ping of death involved sending a malformed ping which crashed

the target computer.– A ping flood involved sending so many ping requests that the target

computer could do nothing else but deal with ping traffic. (A denial-of-service.)

• If country x and y are in conflict. Should network traffic to someone in country x be routed through country y?– Should government traffic to Norway from Iceland be routed

through the UK? Only if it is encrypted.

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