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COMP 189: Homework #4 Assigned Jan 31, 2024 Due Feb 7, 2024 Technical Exercises 1. Shortest Routing Paths Diagram an IXP-POP network (as drawn in class) with the following properties. - IXPs are represented as squares, within-network routers are represented as circles, direct wired connections are represented as lines. - Three IXPs (Vancouver, Toronto, and Montreal) - A Rogers network with three routers around each city and a connection into each IXP - A Videotron network with three servers around each city and a connection into all three IXPs. - A McGill network, two routers – with a connection into the Montreal IXP. - Your laptop in Vancouver on the Rogers network - The McGill webserver (at McGill) - Your laptop is accessing the McGill website and it is using a path that goes through the Videotron network because that’s the fastest path. - Add time labels to each edge in your network that produce this fastest path. - Indicate the shortest path and show how it is preferable to staying in the Rogers network.

3. Domestic Routes You are the Chief Technical Officer (CTO) of Canada (this position actually exists) and are tasked with implementing a new “Domestic Routing” initiative – which aims to keep Canadian internet traffic more safe from the snooping view of other countries. The idea is that, if a packet originates in Canada and is bound for a machine in Canada, it can only transit Canadian networks. 1. Using real cities, diagram an IXP-scale network (using conventions from the previous question) in which (a) there is a package originating and ending in Canada, (b) there is a viable path using only Canadian networks, and (c) the fastest path uses a United States (government or corporate) network. Show the path and justify why this path would be taken. 2. In words, describe the new packet routing policy you’ll need to implement in IXPs across Canada to achieve the domestic routing initiative. 1. 2. Canadian-run IXPs could look at the source and destination IP addresses on a packet. If both are Canadian IP addresses, then the IXP should only hand the packet off to a network owned by a Canadian organization.

4. Internet Distance On the internet, distance is measured by how long it takes for your information to get to servers. In this problem, you'll use the command-line command ping to determine your relative distance from various places on the internet. In this problem, the time refers to the minimum time reported by ping. 1. Find three university websites, X, Y, and Z - Measure your distance from them in physical distance. - Measured your distance from them in ping time. Give the host names (e.g., www.mcgill.ca ) and distances (both physical and ping). In a scatter plot, plot physical distance (x-axis) against ping distance (y-axis). Include the output of your ping command to show your work. 2. Explain the relationship (or lack there of) you see between physical distance and ping time in your plot. 1. Answers to this will vary widely. 2. A lack of correlation between physical distance has to do with routing distance being different than physical distance. For example, the routing time from Montreal to Boston is much faster than the time from Montreal to most parts of Vermont because there’s a very fast connection between Montreal and Boston, compared to the much slower links to Vermont.

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Discussion 1. Rerouting internet traffic Here is one article covering a case of curious rerouting of massive internet traffic. How China swallowed 15% of ‘Net traffic for 18 minutes | Ars Technica Find two more events like there where the culprits were different countries (so you’ll find one for country X and one for country Y). Give the culprit, the timeframe of the disruption, a link to the article, and a 1-2 sentence summary. https://arstechnica.com/uncategorized/2008/02/insecure-routing-redirects-youtube-to-pakistan/ Pakistan was attempting to implement a filter that would cause Pakistani requests to YouTube to be routed to “nowhere”. They accidentally published this routing adjustment, however, and temporarily *all* packets destined for YouTube were routed into this “nowhere” space. https://www.technewsworld.com/story/whether-intended-or-accidental-internet-traffic-rerouting-can- be-costly-85679.html Erroneous updates to routing tables in Nigeria propagated to servers globally, causing all traffic destined for Google to actually be routed to Nigerian servers.

2. Rerouting punishment Should organizations be punished when erroneous configurations reroute substantial portions of internet traffic? Why or why not? Incorporate routing concepts from class in your justification. Either position is valid. Some answers might include. Yes. Rerouting internet traffic induces packets to follow longer paths to reach their destination. This creates inconvenience (slower internet, possibly loss of internet) on large user bases. It is hard, often impossible to determine the motivation of the routing error. But, regardless, an organization large enough to play a role in the routing infrastructure has a responsibility to ensure that their routing configurations are accurate. To ensure such responsibilities are not taken lightly, regulations should penalize organizations that fail to maintain practically correct routing tables. No. There are many reasons why a routing configuration might need to be changed. Organizations do not answer to any higher authority on the administration of their networks. As such, should they decide to change routing configurations – and induce packets to follow longer paths – that is within their right as organizations that contribute to the infrastructure of the internet.

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