Networking Concepts Module A Copyright Pearson Prentice Hall 2013

 This is a module that some teachers will cover while others will not  This module is a refresher on networking concepts, which are important in information security  If your teacher does not cover networking, you might want to cover it yourself, to “get the rust out” of your networking knowledge 2 Copyright Pearson Prentice Hall 2013

Copyright Pearson Prentice-Hall 2010  Octet ◦ A Byte (collection of 8 bits)  8 bits = 1 Character ◦ Bit  Is the basic unit of IT represented as a  0 or 1  Host ◦ Any Device connected to the Internet 3

Copyright Pearson Prentice-Hall NIC = Network Interface Card, provides capability for Network communications

 Router ◦ Connects one network to another  Is a Switch ◦ Sends frames between computers  Is a Wireless Access Point (WAP) ◦ Signals are spread wide increasing danger  Contains a Dynamic Host Configuration Protocol (DHCP) ◦ Provides each host an IP address  Provides Network Address Translation (NAT) ◦ Hides IP address from attack Copyright Pearson Prentice-Hall

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 LAN (Local Area Network) ◦ Operate within building not across geographic locations  WAN (Wide Area Network, internet) ◦ Operate across geographic locations ◦ Because corporations don’t have regulatory rights to lay network lines in public areas they rely on commercial companies  Internet ◦ Network of Network’s Copyright Pearson Prentice-Hall

8 Workgroup Switch: connect computers to the network Core Switch: Connect switches to other switches Any computer can plug into a wall jack and potentially gain access to the network x requires any computer to first authenticate before gaining access to the network

Copyright Pearson Prentice-Hall Two Types of Leased Lines Point to Point Public Switched Data Network (PSDN) – passes frames between multiple sites Connections to these Networks is limited Security by Obscurity – not the best if it is breached there is no security Connections to these Networks is limited Security by Obscurity – not the best if it is breached there is no security

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11 Network Browser Packet Router Packet Router Packet Route Webserver Software Router The global Internet has thousands of networks connected by routers The global Internet has thousands of networks connected by routers Copyright Pearson Prentice Hall 2013

 Messages (data) can move from any computer to any other computer on any other network connected to the Internet  Frames: ◦ Messages (data) between a single network (LAN or WAN)  Packets ◦ Messages (data) between computers across the Internet ◦ Packets are contained within Frames  Different Frame per Network ◦ Internet was designed specifically to NOT ADD SECURITY! Copyright Pearson Prentice-Hall

13 Packet travels in a different frame in each network Packet travels in a different frame in each network Copyright Pearson Prentice Hall 2013

Copyright Pearson Prentice-Hall US Backbone Map

 Networks must “talk” with each other ◦ Interoperability  Requires Standards  Standards Security Issues: 1.Is it inherently secureinherently  an essential constituent or characteristic 2.Explicitly designed into standard 3.If added “after-the-fact” usually to newer versions going forward 4.Vendor implementations can be defective Copyright Pearson Prentice-Hall

Copyright Pearson Prentice-Hall Super LayerDescription ApplicationCommunication between application programs on different hosts attached to different networks on an internet. InternetworkingTransmission of packets across an internet. Packets contain application layer messages. Single NetworkTransmission of frames across a network. Frames contain packets. Core Standards for each sub-system of the network communication process

17 Super LayerTCP/IPOSIHybrid TCP/IP-OSI Application Presentation Session InternetTransport InternetNetworkInternet Single NetworkSubnet AccessData Link Physical Copyright Pearson Prentice Hall 2013

18 In a single network, a physical link connects adjacent devices. A data link is the path that a frame takes across a single network. One data link; three physical links. Copyright Pearson Prentice Hall 2013

 Device Connection Types ◦ UTP  Links between computers and switches  Uses voltage changes (high vs low)  Act like radio antennas, so signal can be intercepted without tapping ◦ Optical Fiber  Uses light changes (on or off)  Require tapping for interception of data ◦ Wireless  Uses radio waves for transmission  Spread widely and easily intercepted Copyright Pearson Prentice-Hall

 Internet ◦ How routers forward packets ◦ Main standard is Internet Protocol (IP)  Transport ◦ Main standard is Transport Control Protocol (TCP)  Fixes transmission errors  Ensures proper order of packets  Slows transmission if necessary ◦ For transmissions that do NOT require these capabilities will use  User Datagram Protocol (UDP) Copyright Pearson Prentice-Hall

 Connection-Oriented ◦ Requires agreement for transmission to commence ◦ Monitors transmission for errors to ensure Reliability of transmission  Connectionless ◦ Does NOT require agreement, transmission occurs when needed ◦ No monitoring of transmission for errors occurs Copyright Pearson Prentice-Hall

 Connectionless  Unreliable  Purpose ◦ How are packets organized ◦ How routers move packets to destination host  Versions ◦ IPv4  32 bit address size 2 32 = 4,294,967,296 ◦ IPv6  128 bit address size = 3.4e+38 Copyright Pearson Prentice-Hall

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Copyright Pearson Prentice-Hall Total Length (16 bits) Identification (16 bits) Header Checksum (16 bits) Time to Live (8 bits) Flags Protocol (8 bits) 1=ICMP, 6=TCP, 17=UDP Bit 0Bit 31 IP Version 4 Packet Source IP Address (32 bits) Fragment Offset (13 bits) Diff-Serv (8 bits) Header Length (4 bits) Version (4 bits) Destination IP Address (32 bits) Options (if any)Padding Data Field 0100

 Represented as 32 bit rows  Consists of: ◦ Header consists of 5 rows  May have optional rows ◦ Data Copyright Pearson Prentice-Hall

 Version ◦ 0100 = 4  Header Length (usually 5 rows) ◦ 0101 = 5 ◦ More than 5 rows usually indicates an attack so examining this part of the header is important to detect attacks  Diff-Serv ◦ Rarely uses intended to provide priority to different packets (Network Neutrality)  Total Length ◦ Length of (entire packet - header) in bytes ◦ Maximum size of a packet is 2 16 = 65,536 Copyright Pearson Prentice-Hall Total Length (16 bits) Diff-Serv (8 bits) Header Length (4 bits) Version (4 bits)

 Used if a packet is too large and is divided into smaller packets  This is rare and can indicate an attack  Most O/S don’t allow fragmentation Copyright Pearson Prentice-Hall Identification (16 bits)FlagsFragment Offset (13 bits)

 Time to Live (TTL) ◦ Set to a value between 0 and 255  Usually set to 64 or 128 by O/D ◦ As packet moves from router to router ◦ TTL decremented by 1 ◦ If TTL reaches 0 the packet is discarded ◦ Attackers can determine how many router hops are between hacker and victim host by examining TTL and guessing 64 or 128 so…  Protocol Message  Header ChecksumChecksum Copyright Pearson Prentice-Hall Header Checksum (16 bits) Time to Live (8 bits) Protocol (8 bits) 1=ICMP, 6=TCP, 17=UDP

 Each Address is 32 bits long   Kind of hard to remember so…  Divided into 4 8 bit segments & converted to decimal (0 to 255)    4 segments divided into a mask ◦ First 2 are for the network ◦ = UCF ◦ 217 = College of Business ◦ 166 = Web Server Copyright Pearson Prentice-Hall

Copyright Pearson Prentice-Hall Payload length = Total Length from IPv4 Hop Limit = TTL from IPv4 Note there is no Checksum Reliability is assumed from higher level security

 Unlike IPv4 IPv6 utilized optional header rows  One such use is for IPSec  Remember that IP was developed without Security  IPSec was added later to provide security ◦ Everything in the data field of the packet is Secure ◦ Application message is also secure ◦ Two Modes:  Transport – host to host protection  Tunnel – protection between hosts  Details in Chapter 4 Copyright Pearson Prentice-Hall

 Transmission Control Protocol (TCP) ◦ Connection-oriented, reliable ◦ TCP message is called a Segment  User Datagram Protocol (UDP) ◦ Connectionless, unreliable Copyright Pearson Prentice-Hall

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Copyright Pearson Prentice-Hall PC Transport Process Webserver Transport Process 1. SYN (Open) 2. SYN, ACK (1) (Acknowledgement of 1) 3. ACK (2) Open (3) 3-Way Open 1.Syn = Synchronize sequence numbers, I want to send a message 2.SYN, ACK (Acknowledge), OK I’ll accept your message 3.ACK = OK I’m acknowledging that I received your acknowledgement

 Hacker floods victim host with SYN messages  The victim host ◦ Sends SYN, ACK & ◦ Sets aside resources for the upcoming message  Hacker never sends ACK back ◦ Half-open SYN attack Copyright Pearson Prentice-Hall

36 PC transport process Webserver transport process 1. SYN (Open) 2. SYN, ACK (1) (Acknowledgement of 1) 3. ACK (2) 4. Data = HTTP Request 5. ACK (4) 6. Data = HTTP Response 7. ACK (6) Open (3) Carry HTTP Req & Resp (4) Copyright Pearson Prentice Hall 2013

37 PC transport process Webserver transport process 8. Data = HTTP Request (Error) Carry HTTP Req & Resp (4) 9. Data = HTTP Request (No ACK so Retransmit) 10. ACK (9) 11. Data = HTTP Response 12. ACK (11) Error Handling Copyright Pearson Prentice Hall 2013

38 PC transport process Webserver transport process Close (4) 13. FIN (Close) 14. ACK (13) 15. FIN 16. ACK (15) Note: An ACK may be combined with the next message if the next message is sent quickly enough Normal Four-Way Close Copyright Pearson Prentice Hall 2013

Copyright Pearson Prentice-Hall PC Transport Process Webserver Transport Process Close (1) RST Abrupt Close Either side can send A Reset (RST) Segment At Any Time Ends the Session Immediately Rejection of a SYN (from an untrusted host) with a RST will provide Hacker with IP address of internal host, something the hacker tries to get

 Sequence Number field ◦ Allows for segments to be put together in order  First segment uses a randomly generated number  If segment contains no data (SYN, ACK, etc)  number is 1 + last segment  If segment contains data  Number of first octet (byte) for the data field is used  Acknowledgement Number field ◦ Enables verification that a segment has arrived  Number of last octet (byte) for the data field + 1 Copyright Pearson Prentice-Hall

41 Copyright Pearson Prentice Hall 2013

 Clients ◦ Random number used when connecting to Host for transmission session (short-lived session)  Servers ◦ Represents a specific application runningapplication running  Socket ◦ Combination of IP Address and Port Number ◦ :80 Copyright Pearson Prentice-Hall

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 There is NO security built into the standard  Security is instead provided by IPSec in the IP standard since it secures the data package where the TCP segment is contained. Copyright Pearson Prentice-Hall

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 Ping ◦ Are you there?  Traceroute ◦ How do packets go from my client to a host  ICMP messages contain error messages back to originator ◦ Hackers can send mal-formed ICMP message hoping to identify IP address of host Copyright Pearson Prentice-Hall

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 Organized Hierarchically ◦ 13 DNS Root Servers ◦ Top-level Domain Servers (.com,.edu, etc.) ◦ Second-level (University of Central Florida)  Need to know the names of host computers within its own network  Cache Poisoning occurs if an attacker replaces an IP address on the DNS with a fake one Copyright Pearson Prentice-Hall

Becky Granger Director, Information Technology and Member Services EDUCAUSE April 29, 2010

Illustration courtesy of Niranjan Kunwar / Nirlog.comNiranjan Kunwar / Nirlog.com

 DNS Servers cache data to improve performance  But…what happens if the cached data is wrong?

More detailed explanation:

 Packet Interception ◦ DNS's usual behavior of sending an entire query or response in a single unsigned, unencrypted UDP packet makes these attacks particularly easy  Attacker intercepts query to DNS or response back  Substituting their own message  ID Guessing & Query Prediction ◦ Attacker guesses UDP ID for DNS Query  DNS port number is well-known  16 bits per ID so 2 ⌃ 16 – susceptible to brute force  Name Chaining or Cache Poisoning (see previous slide)  DOS – no different from any other server

Original illustration courtesy of Niranjan Kunwar / Nirlog.comNiranjan Kunwar / Nirlog.com

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58 Copyright Pearson Prentice Hall 2013

 Application Exploits ◦ By taking over applications, hackers gain the permissions of the exploited program ◦ A multitude of application standards ◦ Consequently, there is a multitude of security issues at the application level 59 Copyright Pearson Prentice Hall 2013

 Many Applications Need Two Types of Standards ◦ One for the transmission of messages, one for the content of application documents ◦ For the World Wide Web, these are HTTP and HTML, respectively ◦ For transmission, uses SMTP, POP, and IMAP ◦ For message content, uses RFC 2822 (all- text), HTML, and MIME 60 Copyright Pearson Prentice Hall 2013

 FTP and Telnet ◦ Have no security ◦ Passwords are transmitted in the clear so can be captured by sniffers ◦ Secure Shell (SSH) can replace both securely 61 Copyright Pearson Prentice Hall 2013

 Many Other Application Standards Have Security Issues ◦ Voice over IP ◦ Service-oriented architecture (SOA); web services ◦ Peer-to-peer applications 62 Copyright Pearson Prentice Hall 2013

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