Networking Concepts Module A Copyright Pearson Prentice Hall 2013

Definitions and Terms Octet Host internet vs. Internet 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 internet vs. Internet i = computer networks or internet protocol I = The global computer network Copyright Pearson Prentice-Hall 2010

A-1: A Simple Home Network NIC = Network Interface Card, provides capability for Network communications Copyright Pearson Prentice-Hall 2010

Access Router Router Is a Switch Is a Wireless Access Point (WAP) 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 2010

Copyright Pearson Prentice Hall 2013

Network Types 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 2010

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. 802.1x requires any computer to first authenticate before gaining access to the network Copyright Pearson Prentice-Hall 2010

Two Types of Leased Lines Point to Point Connections to these Networks is limited Security by Obscurity – not the best if it is breached there is no security Public Switched Data Network (PSDN) – passes frames between multiple sites Copyright Pearson Prentice-Hall 2010

A-5: The Internet The global Internet has thousands of networks connected by routers Network Browser Webserver Software Packet Packet Router Route Router Router Packet Copyright Pearson Prentice Hall 2013

Messages 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 2010

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

A-7: Internet Service Providers (ISPs) US Backbone Map Copyright Pearson Prentice-Hall 2010

Network Protocols Networks must “talk” with each other Interoperability Requires Standards Standards Security Issues: Is it inherently secure an essential constituent or characteristic of the standard Incidental security results from inherent security Explicitly designed into standard If added “after-the-fact” usually to newer versions going forward Vendor implementations can be defective Copyright Pearson Prentice-Hall 2010

A-8: Three Core Standards Layers Super Layer Description Application Communication between application programs on different hosts attached to different networks on an internet. Internetworking Transmission of packets across an internet. Packets contain application layer messages. Single Network Transmission of frames across a network. Frames contain packets. Core Standards for each sub-system of the network communication process Copyright Pearson Prentice-Hall 2010

Super Layer TCP/IP OSI Hybrid TCP/IP-OSI Application Presentation Session Internet Transport Network Single Network Subnet Access Data Link Physical Copyright Pearson Prentice Hall 2013

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

Physical Layer 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 2010

Internetworking Standards How routers forward packets Best effort protocol No Guarantee packets will arrive or will arrive in order 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 2010

Types of Standards (Protocols) 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 2010

Internet Protocol (IP) Connectionless Unreliable Purpose How are packets organized How routers move packets to destination host Versions IPv4 32 bit address size 232 = 4,294,967,296 IPv6 128 bit address size 2128 = 3.4e+38 Copyright Pearson Prentice-Hall 2010

Copyright Pearson Prentice Hall 2013

A-12: The Internet Protocol (IP) Packet 0100 IP Version 4 Packet Bit 0 Bit 31 Version (4 bits) Header Length (4 bits) Diff-Serv (8 bits) Total Length (16 bits) Identification (16 bits) Flags Fragment Offset (13 bits) Time to Live (8 bits) Protocol (8 bits) 1=ICMP, 6=TCP, 17=UDP Header Checksum (16 bits) Source IP Address (32 bits) Destination IP Address (32 bits) Options (if any) Padding Data Field Copyright Pearson Prentice-Hall 2010

IPv4 Represented as 32 bit rows Consists of: May have optional rows Header consists of 5 rows May have optional rows Data Copyright Pearson Prentice-Hall 2010

IPv4 Row 1 Version Header Length (usually 5 rows) Diff-Serv Total Length (16 bits) Diff-Serv (8 bits) Header Length (4 bits) Version 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 216 = 65,536 Copyright Pearson Prentice-Hall 2010

IPv4 Row 2 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 Flag values: Identification (16 bits) Flags Fragment Offset (13 bits) Copyright Pearson Prentice-Hall 2010

Header Checksum (16 bits) Time to Live (8 bits) Protocol (8 bits) 1=ICMP, 6=TCP, 17=UDP IPv4 Row 3 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 List of IP Protocol Numbers Header Checksum Copyright Pearson Prentice-Hall 2010

IPv4 Source and Destination IP Address Each Address is 32 bits long 111111110000000011 11111100000000 Kind of hard to remember so… Divided into 4 8 bit segments & converted to decimal (0 to 255) 132.170.217.166 www.bus.ucf.edu 4 segments divided into a mask First 2 are for the network 132.170 = UCF 217 = College of Business 166 = Web Server Copyright Pearson Prentice-Hall 2010

A-13: IP Version 6 Packet Payload length = Total Length from IPv4 Hop Limit = TTL from IPv4 Note there is no Checksum Reliability is assumed from higher level security Copyright Pearson Prentice-Hall 2010

IPv6 Optional Header Rows 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 Secure = Encrypted Application message is also secure Two Modes: Transport – host to host protection Tunnel – protection between hosts Details in Chapter 4 Copyright Pearson Prentice-Hall 2010

Transport Layer Protocols Transmission Control Protocol (TCP) Connection-oriented, reliable TCP message is called a Segment User Datagram Protocol (UDP) Connectionless, unreliable Copyright Pearson Prentice-Hall 2010

A-14: Transmission Control Protocol (TCP) Segment Copyright Pearson Prentice-Hall 2010

A-15: Messages in a TCP Session PC Transport Process Webserver Transport Process 1. SYN (Open) Open (3) 2. SYN, ACK (1) (Acknowledgement of 1) 3. ACK (2) 3-Way Open Syn = Synchronize sequence numbers, I want to send a message SYN, ACK (Acknowledge), OK I’ll accept your message ACK = OK I’m acknowledging that I received your acknowledgement Copyright Pearson Prentice-Hall 2010

Using TCP for Denial-of Service Hacks 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 2010

A-15: Messages in a TCP Session (continued) PC transport process Webserver transport process 1. SYN (Open) Open (3) 2. SYN, ACK (1) (Acknowledgement of 1) 3. ACK (2) 4. Data = HTTP Request Carry HTTP Req & Resp (4) 5. ACK (4) 6. Data = HTTP Response 7. ACK (6) Copyright Pearson Prentice Hall 2013

A-15: Messages in a TCP Session (continued) 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

A-15: Messages in a TCP Session (continued) PC transport process Webserver transport process Normal Four-Way Close 13. FIN (Close) Close (4) 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 Copyright Pearson Prentice Hall 2013

A-15: Messages in a TCP Session PC Transport Process Webserver Transport Process Abrupt Close RST Close (1) 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 Copyright Pearson Prentice-Hall 2010

A-14: Transmission Control Protocol (TCP) Segment Copyright Pearson Prentice-Hall 2010

Integrity and Reliability of Message 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 2010

Copyright Pearson Prentice Hall 2013

A-14: Transmission Control Protocol (TCP) Segment Copyright Pearson Prentice-Hall 2010

Port Numbers & Sockets Clients Servers Socket Random number used when connecting to Host for transmission session (short-lived session) Servers Represents a specific application running Socket Combination of IP Address and Port Number 132.170.217.166:80 Copyright Pearson Prentice-Hall 2010

Copyright Pearson Prentice Hall 2013

Copyright Pearson Prentice Hall 2013

TCP Security 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 2010

Copyright Pearson Prentice Hall 2013

A-20: Internet Control Message Protocol (ICMP) Copyright Pearson Prentice Hall 2013

ICMP Ping & Traceroute Ping Traceroute 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 2010

Copyright Pearson Prentice Hall 2013

DNS Server 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 2010

DNSSEC for the .edu Domain Becky Granger Director, Information Technology and Member Services EDUCAUSE April 29, 2010

DNS: A Review Illustration courtesy of Niranjan Kunwar / Nirlog.com

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

DNS is Fundamentally Flawed More detailed explanation: http://www.iana.org/about/presentations/davies-cairo-vulnerability-081103.pdf

DNS Threats Packet Interception ID Guessing & Query Prediction 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

Chain of Trust Can Be Established Original illustration courtesy of Niranjan Kunwar / Nirlog.com

Copyright Pearson Prentice Hall 2013

Copyright Pearson Prentice Hall 2013

A-24: Application Standards 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 Copyright Pearson Prentice Hall 2013

A-24: Application Standards 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, e-mail uses SMTP, POP, and IMAP For message content, e-mail uses RFC 2822 (all- text), HTML, and MIME Copyright Pearson Prentice Hall 2013

A-24: Application Standards 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 Copyright Pearson Prentice Hall 2013

A-24: Application Standards Many Other Application Standards Have Security Issues Voice over IP Service-oriented architecture (SOA); web services Peer-to-peer applications Copyright Pearson Prentice Hall 2013

Copyright © 2013 Pearson Education, Inc. Publishing as Prentice Hall