lecture_10_nomadic

Lecture 10Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs : 

Lecture 10Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs Wireless Networks and Mobile Systems

Lecture Objectives : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 2 Lecture Objectives Describe the role of nomadic services in mobile networking Describe the objectives and operation of IP virtual private networks (VPNs) Describe the objectives and operation of the Dynamic Host Configuration Protocol (DHCP) Describe the objectives and operation of network address translation (NAT) Describe firewall and packet filter functions, especially as related to NAT Provide some high-level background in web services, especially for a wireless “hot spot” service

Agenda : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 3 Agenda Nomadic services Virtual private networks (VPNs) Dynamic Host Configuration Protocol (DHCP) Network address translation (NAT) Firewalls and packet filtering HTML and web programming Brief comments on a wireless “hot spot” service

Nomadic Services : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 4 Nomadic Services Nomadic services support hosts that attach to different networks, but where host reconfiguration is acceptable Compare to mobile services where hosts can move to a different network without reconfiguring Functions Changing the host’s IP address to that of the current network to which it is attached  DHCP Limited number of public Internet addresses available in the current network (or any network)  NAT Lack of trust of the current network (or any network)  VPN A wireless “hot spot” usually combines DHCP, NAT, and firewall functions

Nomadic Services Functions : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 5 Nomadic Services Functions Address via DHCP Secure Data, Private Address Secure Data, Public Address VPN endpoint VPN endpoint DHCP NAT Public Network Private Network Private Network NomadicNode

Agenda : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 6 Agenda Nomadic services Virtual private networks (VPNs) Dynamic Host Configuration Protocol (DHCP) Network address translation (NAT) Firewalls and packet filtering HTML and web programming Brief comments on a wireless “hot spot” service

Virtual Private Networks (1) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 7 Virtual Private Networks (1) Virtual private networks (VPNs) Enable end-to-end security (authentication and, optionally, privacy) for a single (mobile) host connecting to a private network over untrusted (public) intermediate networks Enable security for private network-to-network communication over untrusted intermediate networks Support quality-of-service and other attributes of a service level agreement over a shared network for network-to-network connectivity

Virtual Private Networks (2) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 8 Virtual Private Networks (2) Tunneling protocols Point-to-Point Tunneling Protocol (PPTP) Layer 2 Tuneling Protocol (L2TP) IP Security (IPSec) VPNClient VPNServer GeneralHost PublicNetwork PrivateNetwork Secure Tunnel

Point-to-Point Tunneling Protocol : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 9 Point-to-Point Tunneling Protocol PPTP is an extension of the Point-to-Point Protocol (PPP) to support tunneling Can carry IP and non-IP packets Layer 2 Header IP Header PPP Packet GREHeader

Layer 2 Tunneling Protocol : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 10 Layer 2 Tunneling Protocol Resulted from the IETF’s merger of PPTP and the Layer 2 Forwarding Protocol (L2FP) Can carry IP and non-IP packets over IP and other networks Packet Transport (UDP, FR, ATM, etc.) L2TP Data Channel (unreliable) L2TP Control Channel (unreliable) L2TP Data Messages (unreliable) PPPFrames L2TP ControlMessages

IP Security : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 11 IP Security IPSec has two main components Authentication Header (AH) Encapsulating Security Payload (ESP) Two modes Transport mode Tunnel mode IPHeader AH (or ESP) IPPayload Inner IPHeader Original IP Datagram TunnelMode

VPN References : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 12 VPN References K. Hamzeh, G. Pall, W. Verthein, J. Taarud, W. Little, G. Zorn, “Point-to-Point Tunneling Protocol,” RFC 2637, July 1999. W. Townsley, A. Valencia, A. Rubens, G. Pall, G. Zorn, B. Palter, “Layer Two Tunneling Protocol ‘L2TP’,” RFC 2661, Aug. 1999. S. Kent, R. Atkinson, “Security Architecture for the Internet Protocol,” RFC 2401, Nov. 1998. D. Fowler, Virtual Private Networks, Morgan-Kaufmann Publishers, 1999.

Agenda : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 13 Agenda Nomadic services Virtual private networks (VPNs) Dynamic Host Configuration Protocol (DHCP) Network address translation (NAT) Firewalls and packet filtering HTML and web programming Brief comments on a wireless “hot spot” service

DHCP : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 14 DHCP DHCP provides all necessary configuration information to allow a stationary node to become a viable Internet host Applications To simplify system administration in traditional networks To improve utilization of IP address space To allow mobile hosts to obtain collocatedcare-of addresses on foreign networks R. Droms, “Dynamic Host Configuration Protocol,” RFC 2131, March 1997. C. E. Perkins, Mobile IP: Design Principles and Practices, Addison-Wesley, Reading, MA, 1998 (Chapter 9).

DHCP: Client-Server Model (1) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 15 DHCP: Client-Server Model (1) DHCP adheres to a client-server model Client requests service Server provides response Request and reply must be sent without the benefit of the client being an Internet host DHCPServer DHCPClient 1 DHCPClient 2 request reply

DHCP: Client-Server Model (2) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 16 DHCP: Client-Server Model (2) Client broadcasts request to network Broadcast received by server or relay If a relay is used, it forwards request with other information to the server Server responds with configuration information Client acknowledges receipt Server reserves IP address (for some lease time) and notifies client that address is reserved Client must renew the lease

DHCP Initialization (1) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 17 DHCP Initialization (1) Client broadcasts a discover message (DHCPDISCOVER) Sent via UDP to port 67 Received by one or more DHCP servers (or relays) Responding servers … Determine configuration Send an offer message (DHCPOFFER) to the client Client selects a configuration that it wants Sends a request message (DHCPREQUEST) to the selected server Sends the same request message to servers not selected so they can release reserved IP address

DHCP Initialization (2) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 18 DHCP Initialization (2) Selected server … Commits configuration Replies with an acknowledge message (DHCPACK) to complete initialization

DHCP Initialization (3) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 19 DHCP Initialization (3) Server 1(selected) Client Server 2 (not selected) DHCPDISCOVER DHCPDISCOVER DHCPOFFER DHCPOFFER DHCPREQUEST DHCPREQUEST DHCPACK

Lease and Renewals (1) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 20 Lease and Renewals (1) Server grants use of the IP address for a limited time, the lease time Client should renew the lease about after about two-thirds of the lease time has expired Lease renewal … Client sends DHCPREQUEST message to the original selected server via unicast Server responds with DHCPACK message If no response from the server, client must start again with DHCP initialization

Lease and Renewals (2) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 21 Lease and Renewals (2) Server Client DHCPREQUEST DHCPACK

Graceful Shutdown : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 22 Graceful Shutdown Client can perform a graceful shutdown by sending a DHCP release message (DHCPRELEASE) to the server Allows server to release reserved IP address Often, clients just shutdown and IP address is released after the lease time expires Server Client DHCPRELEASE

DHCP Options : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 23 DHCP Options DHCP servers can provide optional information beyond the assigned IP address Default router Subnet mask Network Time Protocol (NTP) servers Service Location Protocol (SLP) servers Domain Name System (DNS) servers Local domain name Host name Request in discover or request message Response in offer or acknowledge message Type, Length, Value (TLV) option

Agenda : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 24 Agenda Nomadic services Virtual private networks (VPNs) Dynamic Host Configuration Protocol (DHCP) Network address translation (NAT) Firewalls and packet filtering HTML and web programming Brief comments on a wireless “hot spot” service

Network Address Translation : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 25 Network Address Translation NAT “mangles” a packet’s addressing headers as it passes through a router to change either the source or destination address Most common form of NAT: Network and port address translation A.k.a. IP Masquerading – Linux A.k.a. Port Address Translation (PAT) – Cisco

What is Masquerading? : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 26 What is Masquerading? One-to-many translation The process of routing Internet-bound traffic from a private network through a gateway router that modifies the traffic to look like its own On the return, the router, demultiplexes the traffic back to the appropriate hosts by source/destination port/address pairs (remembered from transmission)

Example Configuration : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 27 Example Configuration Trace a packet from Host1 to google.com IP address: 216.239.39.101 Host1 Host2 Host3 Router eth1 – 12.34.56.78 Internal Network – 192.168.1.xxx External Network .4 .3 .2 eth0 – 192.168.1.254

Packet Trace : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 28 Packet Trace Packet sent to HTTP server at google.com *Note: Masquerading changes the source port as well as source address for assured demultiplexing. Value depends on implementation.

Packet Trace (2) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 29 Packet Trace (2) Returning packet

Implementation of Masquerading : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 30 Implementation of Masquerading Linux – built into kernel firewall Resident for years ipfwadm, ipchains, iptables Windows – Internet Connection Sharing Partially with Microsoft Windows 98SE and Windows ME (only share certain interfaces) Full implementation in Microsoft Windows 2000 and Windows XP (share any interface)

Agenda : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 31 Agenda Nomadic services Virtual private networks (VPNs) Dynamic Host Configuration Protocol (DHCP) Network address translation (NAT) Firewalls and packet filtering HTML and web programming Brief comments on a wireless “hot spot” service

Firewalls : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 32 Firewalls Routers with “attitude” Process packets based on rules Rules based on any packet characteristics or attributes Source and destination addresses and ports (e.g., source port 1234 from host 10.0.3.23) Protocol flags (e.g., TCP SYN, TCP ACK) Protocol types (e.g., ICMP, UDP) Connection status (e.g., new or established)

Firewall Services : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 33 Firewall Services Data Link Physical Transport Network Presentation Session Application Application-specific proxy, Application-specific filter Gateway, User Filter Port map, Port filter,Address map, Address filter Address map, Address filter, Protocol filter Address filter, Protocol filter

Types of Firewalls (1) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 34 Types of Firewalls (1) Two types Stateful Stateless Stateless Simple, less secure than stateful Makes decisions based on individual packet information Does not maintain any connection status Example: Allow all traffic inbound with destination port 80 Deny all traffic from 192.168.1.0/24 on the external interface

Types of Firewalls (2) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 35 Types of Firewalls (2) Stateful All the attributes of a stateless firewall plus … Connection status (context for decisions) Watches traffic for SYN, ACK, and FIN packets Knows connection status (established, initiating) More complex, better security Example: Deny all ICMP Echo Reply packets not associated with an Echo Request Deny all TCP sessions not initiated from the inside network

Firewall Implementations : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 36 Firewall Implementations Implementations Hardware and software Hardware (network devices) Cisco PIX, Sonicwall, Watchguard Firebox Software (applications) Windows – ZoneAlarm, Norton Personal Firewall, BlackICE Unix and variants – ipfw, ipchains, iptables, ipf

iptables (1) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 37 iptables (1) Linux firewall (and more) Present with the 2.4 series kernel Part of the netfilter project http://www.netfilter.org/ Consists of two parts Firewall code in the kernel User space “iptables” executable to manipulate kernel code Oskar Andreasson, Iptables Tutorial 1.1.19,http://iptables-tutorial.frozentux.net/.

iptables (2) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 38 iptables (2) Three parts Rules Chains Tables

iptables (3) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 39 iptables (3) Rule Lowest-level (most basic) entity in firewalling A single tuple of what to do (action) and packets to which to apply the action (filter) Filter – identifies packets to which the rule applies Addresses, ports, status Action – what to do with the packet (stream) Accept, reject (drop, but reply with ICMP error message), drop, redirect, masquerade, go to another chain, and more

iptables (4) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 40 iptables (4) Chains An ordered list of rules Traversed in order The first matching rule in the chain is selected Important predefined chains in FILTER table INPUT – all incoming packets go here FORWARD – packets to be routed OUTPUT – all outgoing packets go here

iptables (5) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 41 iptables (5) Tables Separate different types of operations Three built-in tables FILTER – general filtering NAT – dealing with network address translation MANGLE – other packet changes Each contain multiple chains

iptables (6) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 42 iptables (6) Incoming packet traversal Example: Setting DSCP Example: Redirecting Example: Typical Firewall Functions Example: Typical Firewall Functions

iptables (7) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 43 iptables (7) Outgoing packet traversal Example: IP Masquerading Example: Typical Firewall Functions

iptables (8) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 44 iptables (8) Rule placement Rule type specifies table Address translation and IP masquerading map to the NAT table Simple packet filtering maps to the filter table Rule stage specifies chain Prerouting versus postrouting Traffic from local application versus forwarded traffic

Firewall Comments : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 45 Firewall Comments “Good” firewall rules are difficult to write Must consider all possible traffic Only allow what should pass Stateful firewalls are more secure (and more complex) than stateless firewalls Stepping forward Intrusion Detection System (IDS) – “smarter” stateful firewall

Agenda : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 46 Agenda Nomadic services Virtual private networks (VPNs) Dynamic Host Configuration Protocol (DHCP) Network address translation (NAT) Firewalls and packet filtering HTML and web programming Brief comments on a wireless “hot spot” service

Web-Based Authentication : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 47 Web-Based Authentication Consider a wireless LAN “hot spot” service This will require consideration and use of… DHCP Firewalling Authentication IP masquerading (NAT) Authentication is commonly done using a web-based scheme − here is one approach… The first attempt to access any web page is redirected to an authentication page for the service A script or program must perform authentication and updates the configuration to allow access, if appropriate

HTML : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 48 HTML HyperText Markup Language (HTML) Web page “language” (content) Currently in version 4.01 Maintained by the World Wide Web Consortium (W3C) http://www.w3c.org Uses “tags”: <begin_tag>text</end_tag> Formatting language Take data and add formatting, pictures, input, and/or links

HTML (2) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 49 HTML (2) Many extensions and add-ons Responsible for rich web content Tags interpreted by web browser; no server processing involved May be edited by hand or with a WYSWYG editor By hand: notepad, emacs, vi WYSWYG: MS Frontpage, Dreamweaver

Web Programming : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 50 Web Programming Common Gateway Interface (CGI) A way for web servers to interact with standard programs to generate dynamic web content Input typically HTML form data Output dynamic content (web pages) Can be written using C++, Perl, Fortran, or PHP Can do many functions with the appropriate library (1) URL, param (5) HTML, text, … (2) CGI (4) HTML, text, … WebBrowser HTTP Server GatewayProgram (3) Process

Web Programming (2) : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 51 Web Programming (2) Model Client request Server reference Server processing (CGI, SSI, PHP) Request sent to client Browser processing (JavaScript, HTML, CSS)

No Experience? : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 52 No Experience? PHP suggested for those with no experience with web programming PHP code is embedded in HTML code No compilation Quick editing Familiar syntax Borrows syntax “look and feel” from Java, Perl, and C++

Agenda : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 53 Agenda Nomadic services Virtual private networks (VPNs) Dynamic Host Configuration Protocol (DHCP) Network address translation (NAT) Firewalls and packet filtering HTML and web programming Brief comments on a wireless “hot spot” service

A Test Network Configuration : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 54 A Test Network Configuration DHCP server Firewall IP masquerading Web-based authentication Private Network “Public” Internet Private Public

Summary : 

Mobile Networks: Nomadic Services, DHCP, NAT, and VPNs 55 Summary Nomadic services enable Internet access Security, addressing, filtering VPNs provide authentication and privacy for nomadic users and protect private networks DHCP allows nomadic users to obtain an IP address and other configuration information NAT conserves addresses in private networks, allowing support for nomadic hosts Firewalls and packet filtering provide security and enable access control HTML and web programming can be used to authenticate nomadic users for a hot spot service