Lecture 6 Page 1 Advanced Network Security Review of Networking Basics Advanced Network Security Peter Reiher August, 2014

Lecture 6 Page 2 Advanced Network Security Outline Network basics Packet switching Protocols and layering Internet architecture Routing Naming

Lecture 6 Page 3 Advanced Network Security Introduction Networking is a key technology for modern computer use An inherently complex subject I assume you’ve taken one or more networking classes So we’ll just do a quick review of important points here

Lecture 6 Page 4 Advanced Network Security Networking Basics Modern networks send and receive messages –Explicit operations on each end Depending on specifics, other hardware or media are also involved –Routers, switches, gateways –Media Wireless and wired

Lecture 6 Page 5 Advanced Network Security The Network Link A cable, wire, or perhaps just the aether The medium through which electromagnetic signals travel A piece of equipment on one end of the link creates the signal A piece on the other end receives and interprets it

Lecture 6 Page 6 Advanced Network Security Multihop Networking Most networks consist of more than one physical link Typically connected by routers or switches –We can think of them as special purpose computers Each network link represents a hop on a path from source to destination Modern networks expect most data to travel multiple hops

Lecture 6 Page 7 Advanced Network Security Organizing Multihop Networks Typically, routers and switches connect to a fixed, known set of links –Single hop mobile wireless is an important, but simple, exception –Wireless ad hoc networks are a less important, but complex, exception Part of the network’s job is to figure out which hops to use in each case

Lecture 6 Page 8 Advanced Network Security Circuit Switching Sender Receiver I want to talk to my buddy The network sets up an explicit path The network maintains that path All the information takes that path

Lecture 6 Page 9 Advanced Network Security Packet Switching Sender Receiver I want to talk to my buddy The network finds a new path for each packet The network does not remember paths The information might take many paths

Lecture 6 Page 10 Advanced Network Security Modern Network Characteristics Modern networks are mostly packet switched –More efficient in many ways Mostly using protocols developed for the Internet Mostly traversing networks run by different parties

Lecture 6 Page 11 Advanced Network Security Some Interesting Properties of Networking Physical limitations –Speed of light –Limited spectrum in free space Limited bandwidth for realistic media More hostile environment than single computer

Lecture 6 Page 12 Advanced Network Security More Interesting Properties Inherently shared resource –Not just because of limited availability –Sharing is the point –But shared resource limits all users Usually any participant can address any other

Lecture 6 Page 13 Advanced Network Security Variations in Network Parameters Bandwidth, delay, loss rate can all vary by orders of magnitude –Sometimes geographically –Sometimes temporally Yet networks with extreme parameter values are expected to interoperate

Lecture 6 Page 14 Advanced Network Security The Major Network Parameters Bandwidth Delay Loss rate

Lecture 6 Page 15 Advanced Network Security Bandwidth How much data can be moved across a network in a unit time Limited by physical characteristics of network medium But effective bandwidth delivered can be further limited by implementation

Lecture 6 Page 16 Advanced Network Security Delay Time it takes to deliver a piece of data Again, a fundamental physical limit is at the core –The speed of light But how you do things can make it a lot worse Jitter – the amount of variation observed in network delay

Lecture 6 Page 17 Advanced Network Security Loss Rate How much of the data you submit to the network that does not get delivered –In its correct form Generally due to uncorrected noise in the network But also due to how one handles overload conditions

Lecture 6 Page 18 Advanced Network Security Network Protocols Sets of rules that define how the network is used All communicating parties need to agree on the rules –Or communications don’t work well/at all Modern networks make use of a relatively small set of protocols