Yelena Yesha

1

Networking Technologies

• Yelena Yesha
• Olga Streltchenko
• WAP slides by Anupam Joshi

2
Presentation Overview

• Internet Protocols
• WAP
• Caching and Proxies
• DNS
• Firewalls
• Directory and Discovery Services

3
Internet Protocols

• Originally developed to support simple wide-area
  applications (ftp, e-mail).
• Scaled up very well to support more sophisticated
  distributed applications.
• Standardization of TCP/IP.
• Exceptions
• WAP for wireless applications on portable
  devices
• Special protocols to support MM streaming
  applications.

4
IP Addressing

• Scheme for addressing and routing IP packets.
• 1978-82 TCP/IP standardization provided for 232
  or approximately 4 billion hosts.
• The Internet growth outstripped the predictions.
• The address space allocation has been
  inefficient.
• IP addressnetwork identifierhost identifier
• Written as
• Classes A, B, C, D and E.
• D is reserved for multicast communication, E for
  future uses.

5
IP Addressing (contd)
1
Network ID, 7bits
Class A
Host ID, 24 bits
0
1
Network ID, 14 bits
Host ID, 16 bits
Class B
0
1
1
Network ID, 21 bits
Host ID, 8 bits
Class C
0
1
1
1
Multicast
Class D
Class E
0
1
1
1
1
unused

• A 224 hosts on each subnet, national wide area
  networks
• B more than 255 computers on a subnet, big
  companies.
• C other network operators

6
IP Addressing Drawbacks and Solutions

• Drawbacks
• If a computer is connected to more than one
  network it needs more than one IP address.
• Organizations cannot reliably predict their
  growth and tend to over-budget
• Outcome exhaustion of class B addresses.
• IP address is susceptible to IP spoofing, or
  counterfeiting of the source address in the IP
  header.
• Denial-of-service attacks by placing the
  destination IP address in the target address
  field (remember Feb 2000?).
• Solutions
• Aggressive IPv6 with its 128-bit address fields
• Use of mask fields and CIDR (classless
  inter-domain routing).

7
IP Protocol

• Provides an unreliable or best-effort delivery
  service
• Only checksum is the header checksum.
• IP layer
• Puts IP datagrams into network packets suitable
  for transmission in the underlying network
• E.g., Ethernet.
• When the datagram is longer than MTU of the
  underlying network, it is broken into smaller
  segments and reassembled at the destination.
• Must insert physical network address of the
  message destination if necessary
• Depends on the underlying network technology,
  i.e., Ethernet requires and Ethernet address for
  the host on the local Ethernet.

8
Network Topology Revisited

• The Internet Backbone
• Super-high-bandwidth link between smaller
  networks like intranets
• consists of multiple networks operated by
  multiple companies, like UUnet, ATT, SprintLink,
  Quest, etc.
• These networks come together at various peering
  points.
• Autonomous system (AS) conceptual partition of
  the topological map of the internet.
• Subdivide into areas
• Example intranets of big organizations.

9
Routing protocols

• RIP1 distance-vector algorithm.
• Convergence problems.
• RIP2 amendment of of RIP1 to accommodate CIDR
  and authentication of IP packets, improve
  multicast routing.
• OSPF open-shortest-path-first.
• Better convergence than the one exhibited by RIP.
• Incremental adoption of better routing
  algorithms.
• For routers to cooperate they need to run the
  same routing algorithm.
• For this purpose topological areas have been
  defined the same protocol is used within an area.

10
Overcoming the Problem of the Internet Growth

• Default router
• To prevent routing table size explosion only
  partial information is kept.
• Routers closer to backbones have more complete
  tables.
• The default entry specifies a route to be used
  for all IP packets whose destination is not
  included in the routing table.
• CIDR
• Allocates a batch of contiguous class C IP
  address to a subnet requiring more than 255
  address
• Allows to subdivide class B address space for
  allocation of multiple subnets
• This is achieved by of a mask field by routing
  tables.
• A bit pattern that selects a portion of IP
  address to be compared with the routing table
  entry.

11
IP version 6

• A more permanent solution to the problem of the
  Internet growth.
• Address space 2128
• Factor in inefficiencies of address allocation
  and still get about 1000 IP addresses per m2.
• Routing speed the complexity of the header is
  reduced.
• Real-time and other special services the header
  includes the priority and flow control fields.
• The use of these fields will depend on major
  improvements in the infrastructure (hardware) and
  suitable method of allocating and arbitrating
  resources.

12
IP version 6 (contd)

• Future evolution next header field, which
  defines the type of an extension header that is
  included in the packet.
• Multicast and anycast IPv6 supports anycast, or
  delivery to at least to one of the hosts among
  the relevant addresses.
• Security IPv6 implements authentication and
  encrypted security payload extension header
  types.
• Equivalent to providing a secure channel
• Means that the payload is encrypted and/or
  digitally signed.

13
Mobility and IP

• Dynamic Host Configuration Protocol (DHCP)
• Designed to support the ability of a mobile
  device to maintain simple access to services
• Assigns a temporary IP address to the device.
• To provide permanent access by clients to a
  mobile computer it must maintain a permanent IP
  address.
• Problem IP routing is subnet-based.
• Subnets are at fixed locations.

14
MobileIP

• A transparent solution based on tunnelling.
• When a mobile computer is connected to the
  Internet elsewhere, two agents take
  responsibility for routing.
• Home agent (HA)
• holds up-to-date knowledge of the mobile hosts
  current location
• The IP address at which it can be reached.
• The mobile host informs HA upon leaving home
• HA acts as a proxy to the clients communicating
  to the mobile host during this time.

15
MobileIP (contd)

• Foreign agent (FA)
• Allocates a temporary IP address to a mobile host
  upon its arrival to a new site
• Contact HA and supplies it with the contact
  address for the mobile host (FAs address).
• HA encapsulates original IP packets and sends
  them to FA.
• FA unpacks the packets and delivers them to the
  mobile host.
• HA sends the contact address for the mobile host
  o the original sender
• If the sender is Mobile-enabled it communicates
  to the FA directly from now on
• If not, the HA continues to act as a proxy for it.

16
TCP and UDP

• Provide communication capabilities to the
  application programs.
• IPv6 will support TCP/UDP as well as other
  connection protocols (remember the Internet
  Model).
• Enable interprocess communication through the use
  of ports attached to applications.
• Port number is included in the header.

17
UDP

• Almost transport-level replica of IP.
• Offers no guarantee of delivery.
• The header is short, but includes an optional
  checksum for the payload
• The packets that fail the check are dropped.

18
TCP

• Provides reliable delivery of arbitrary long
  sequences of bytes via stream-based programming
  abstraction.
• Connection-oriented
• The sending and the receiving processes establish
  a communication channel
• Use of ACK (acknowledgement) messages).

19
TCP Reliability Mechanisms

• Sequencing a sequence number is attached to
  every TCP segment
• Used for message re-assembly at the destination.
• Flow control overflow prevention
• The receiver send an ACK with the highest
  sequence number in its input stream (no segments
  before that one have been omitted) and a window
  size.
• Window size specifies the amount of data the
  sender is permitted to send.
• ACK are attached to the backward flow if there is
  any.
• Burstiness of network traffic is smoothed through
  the use of local buffering an a configurable
  time-out on it.
• Naggles algorithm.

20
TCP (contd)

• Due to the unreliability of wireless networks
  these mechanisms are not efficient.
• Solutions WAP and modified TCP.
• Modified TCP for wireless networks.
• Implement a TCP support component at the base
  station (gateway between wired and wireless
  networks).
• The support component snoops on TCP packets to
  and from the wireless network
• re-transmitting segments that are not promptly
  acknowledged.
• Requesting re-transmission of inbound segments
  when gaps in sequence numbers are noticed.

21
WAP

• Wireless Application Protocol
• An open, global specification that empowers
  mobile users with wireless devices to easily
  access and interact with information and services
  instantly. -
  WAP Forum
• The de facto worldwide standard for providing
  Internet communications and advanced telephony
  services on digital mobile phones, pagers,
  personal digital assistants and other wireless
  terminals.
• - WAP Forum (www.wapforum.org)

22
Why is WAP needed?

• Traditional internet protocols (HTML, HTTP, TCP,
  etc.) and their security mechanisms (TLS) are
  inefficient over mobile networks.
• Handheld devices tend to have less powerful CPUs,
  less memory and more restrictions on power
  consumption than desktops, so require special
  considerations.
• Handheld devices tend to use input devices other
  than keyboards (e.g. voice, keypad).

23
Bearer Limitations

• Power consumption
• increased bandwidth requires increased power.
• Cellular network economics
• Fixed bandwidth shared among many users, so
  efficient bandwidth use required.
• Latency
• wide range of network latencies common (lt 1
  second to 10s of seconds).
• Bandwidth
• Less bandwidth than found in wired environments.

24
WAP Forum www.wapforum.org

• WAP Forum founded in December 1997 by Nokia,
  Ericsson, Motorola and Phone.com (formerly
  Unwired Planet)
• Currently contains over 200 members
• Carriers with more than 100 million subscribers
• Infrastructure providers
• Software developers, and others.
• Represent over 95 of the global handset market.
• WAP Protocol development
• Current WAP Version 1.2

25
How does WAP work?

• Uses client-server model.
• Phone incorporates a microbrowser, while the
  intelligence is in the WAP gateways.
• Services and applications reside on servers.
• Similar to Java applications written for WAP,
  which then run on multiple bearers (e.g. GSM,
  SMS, USSD, etc.)

26
What works with WAP?

• Designed for use with
• All mobile phones
• Any service, e.g. SMS (Short Message Service),
  CSD (Circuit Switched Data), USSD (Unstructured
  Supplementary Services Data), GPRS (General
  Packet Radio Service)
• Any network, e.g. CDMA (Code Division Multiple
  Access), GSM (Global System for Mobiles), UMTS
  (Universal Mobile Telephone System)
• Any input device, e.g. keyboard, stylus, touch
  screen, keypad.

27
WAP Protocol Model (Stack)
Wireless Application
Other Services and
Application Layer
Applications
Environment (WAE)
Wireless Session
Session Layer
Protocol (WSP)
Wireless Transaction
Transaction Layer
Protocol (WTP)
Wireless Transport
Security Layer
Layer Security (WTLS)
Transport Layer
Datagrams (UDP/IP)
Datagrams (WDP)
Wireless Bearers
Network Layer
SMS
USSD
CSD
IS-136
CDMA
CDPD
Etc
Source the WAP White Paper, October 1999.
28
WAP Architecture
WAP Gateway
Web Server
WAP Phone
Internet
Gateway
Web Server
Client
Encoded request
Request
Response
Encoded response
29
WDP Layer

• Wireless Datagram Protocol.
• Provides consistent service and common interface
  to upper layers of the protocol.
• Supports SMS, USSD, CSD, CDPD, IS-136 packet
  data, and GPRS.

30
WTLS Layer

• Wireless Transport Layer Security (TLS).
• Implements options for authentication and
  encryption.
• Optimized for mobile environment.
• Based on Transport Layer Security (TLS), which
  was formerly Secure Sockets Layer (SSL).
• Optimized for use over narrow-band communication
  channels.
• Ensures data integrity, privacy, authentication
  and denial-of-service protection.

31
WTP Layer

• Wireless Transaction Protocol
• Runs on top of datagram service.
• Works over both secure and non-secure wireless
  services.
• Features
• Three classes of transaction service
• Class 0 for applications requiring an
  unreliable push service
• Class 1 for applications requiring a reliable
  push service
• Class 2 to provide the basic invoke/response
  transaction service
• Optional user-to-user reliability.
• Asynchronous transactions.
• PDU (protocol data unit) concatenation and
  delayed acknowledgements to reduce number of
  messages sent.

32
WSP Layer

• Wireless Session Protocol
• Provides consistent interface for both
  connection-oriented and connectionless services.
• Provides the following functionality
• HTTP 1.1 compliance
• Long-lived session state
• Session suspend and resume
• Facility for data push.

33
WAE

• Wireless Application Environment
• Interoperable environment for multiple wireless
  platforms.
• Consists of
• Wireless Markup Language (WML)
• WMLScript
• Wireless Telephony Application (WTA)
• Content Formats.

34
WML

• WAP Mark-up Language
• WML is an XML application.
• Also uses WMLScript, which is similar to
  JavaScript.
• Optimized for use with handheld devices.
• Minimal use of CPU and memory.

35
Benefits of WAP

• Reduces amount of data to be transmitted (by
  translating HTTP headers from text into binary).
• Allows sessions to be suspended and resumed.
• Provides reliable datagram service without the
  unnecessary overhead of TCP.
• TCP stack is not required on handheld device.
• WAP protocol stack requires less packets for
  interaction than HTTP/TCP/IP.
• Support for push functionality built into
  protocol.
• WML developers can use standard web tools (e.g.
  CGI, Perl, ASP, etc.).

36
Drawbacks to WAP

• Difficult to configure WAP phones for new WAP
  services.
• Not yet widely supported.
• Current services (e.g. SMS, USSD) not optimized
  for WAP.
• Expected to be expensive.
• WAP does not support cookies.
• Premature encryption endpoint (gateway decrypts
  data, then forwards via https see
  www.gsmworld.com/technology/wap_06.html).

37
Caches and proxy servers

• Cache a store of recently used data objects that
  is closer than the objects themselves.
• When a new object is received it is placed in the
  cache possibly evicting another object.
• When an object is requested, the cache is checked
  first for an up-to-date copy
• If its not available, a fresh copy is fetched.
• A cache can be collocated with each client or
  located on a proxy server.
• Proxy server a machine/process performing tasks
  on behalf of its clients.
• A web proxy server maintains a cache of web
  resources for its clients all the requests go
  though it.
• The actual client is transparent for outside
  servers.

38
DNS

• A name service design whose principal database is
  used across the Internet to perform name
  resolution for web resources.
• A name is resolved when it is translated into
  data about the named resource or object in order
  to invoke an action upon it.

39
The Internet Naming Scheme

• The Internet support a scheme for the use of
  symbolic names for hosts and networks.
• The named entities are organized into a
  hierarchy.
• The named entities are called domains and the
  symbolic names are called domain names.
• Domains are organized into a hierarchy that
  intends to reflect organizational structure.
• Naming is entirely independent from the network
  physical layout.
• Domain names must be translated into IP
• Responsibility of DNS.

40
DNS Operation

• Implemented as a server process that can run on
  host computers anywhere on the Internet.
• There are at least 2 DNS servers in each domain.
• Servers in each domain hold a partial map of the
  domain name tree below their domain.
• Requests for the translation of domain names
  outside their portion of the domain tree are
  handled by issuing requests to DNS servers in the
  relevant domains
• Recursive procedure that follows from right to
  left resolving the name in segments.
• The resulting translation is then cached at the
  server handling the original request.

41
DNS and caching

• Caching is a key to a name service performance
• Assists in maintaining availability and masking
  server crashes.
• Caching is successful because naming data are
  changed relatively rarely.
• The possibility exists of a name service
  returning out-of-date attributes during
  resolution.
• DNS allows naming data to become inconsistent
• Stale data might be provided for periods in order
  of days.

42
Internet and Network Security

• Types of Attacks on Internet
• Break-ins Unauthorized attempts to gain access
  to a secure system
• Denial of service A legitimate user is denied
  access to a service (e.g. Flooding a WWW server
  with requests)
• Bombs Large email messages or other large data
  intended to overwhelm and possibly weaken a
  system.
• Eavesdropping - Listening in on an electronic
  conversation. Perhaps with intent to gather
  information for a future break-in.
• Viruses.

43
Internet and Network Security (contd)

• Who is perpetrating these attacks?
• People with lots of free time
• Former/disgruntled employees
• Current/disgruntled employees
• Current/former/disgruntled customers
• Governments

44
How to Defend?

• Some quick (although not foolproof) suggestions
• Frequent password changes and the use of
  difficult-to-guess passwords.
• Removal of abused services.
• Filters that detect and delete large messages.
• Cryptography.
• Note that many attacks go undetected, even by
  professionals.

45
Example Scenario

• A private company would like the following
• Make some services available within the company
  such as Secure Shell (SSH) and FTP between the
  company's hosts.
• Disallow outside users from gaining access to the
  company's internal hosts via Telnet, FTP, etc.
• Allow users within the company to access other
  services on the Internet such as WWW and FTP.
• Allow users from the Internet to visit the
  company's WWW home pages.
• Allow the exchange of e-mail with others on the
  Internet.

46
But,

• It is difficult to restrict traffic in only one
  direction
• Recall that the TCP/IP protocol sends
  acknowledgements to make sure data arrives whole.
  
• What we need is a more sophisticated gatekeeper
  that can distinguish what services to allow and
  which to block.
• The general term for this is a Firewall.

47
Firewall

• Monitors and controls all the traffic into and
  out of an intranet.
• Firewall security policy
• Service control determine which services are
  available for external access and reject all
  other requests
• Levels of filtering IP, TCP.
• Example reject HTTP request unless they are
  directed to the official website.
• Behavioral control prevent behavior that
  infringes organization policies
• Levels of filtering IP, TCP, application
• Example filtering of spam e-mail.
• User control discriminate between users
  privileges
• Example management of dial-up provided for
  off-site users.

48
Filtering levels

• IP packet filtering
• Decisions made based on the destination and the
  source IP addresses, the service type field in
  the IP header, port numbers in TCP/UDP headers.
• Example prohibition of external access to NFS
  servers.
• Performed by a process within the operating
  system kernel of a router.
• TCP Gateway
• A TCP Gateway process checks TCP connection
  requests and segment transmission for
  correctness.
• Example Denial-of-service attack prevention.

49
Filtering levels (contd)

• Application-level gateway
• An application-level gateway process acts as a
  proxy for an application process.
• Example a Telnet proxy. All telnet requests are
  routed through the proxy process for approval.
• A firewall is a combination of several processes
  working at different protocol levels running on
  more than one machine (for fault-tolerance).
• Two overall (mutually exclusive) policies
• Anything not explicitly denied is allowed.
• Anything not explicitly allowed is denied.

50
Basic Internet Firewalls

• A basic firewall is a router (a host with at
  least 2 network interfaces).
• One interface is connected to the Internet - the
  Host side.
• The other(s) is(are) connected to the company's
  internal network.
• Performs IP packet filtering.

51
Advanced Internet Firewalls

• When TCP and application-level gateway processes
  are required, they usually run on another
  computer Bastion.
• A host located inside the intranet and protected
  by an IP router/filter, to which it is attached
  by a Stub LAN.
• Stub LAN only has 1 or 2 hosts on it. Not
  connected to any other company LANs.
• A bastion host is connected to both the stub LAN
  and to the company network

52
Advanced Internet Firewalls (contd)

• Further protection can be insured by placing
  another router/filter between the bastion and the
  company intranet.
• Note that for performance reasons company web/ftp
  severs are placed on the Stub LAN.

53
Virtual Private Networks

• Suppose a company wants to connect the intranets
  of its 5 offices.
• One option is to lease a private line.
• Another is to connect through the internet.
• But then everything is open.
• The solution is to use encryption schemes to
  establish secure tunnels through the internet.
• Such a set-up is called a virtual private network.

54
Directory and Discovery Services

• Directory service A service that stores
  collections of bindings between names and
  attributes and that looks up entries that match
  attribute-based specifications.
• Example MS Active Directory Service, UNIX X.500,
  etc.
• Discovery service a directory service that
  registers the services in a spontaneous
  networking environment.
• Provides an interface for automatically
  registering and de-registering services (fax
  machines, printers, etc.).
• Provides a lookup interface for mobile devices
• Example Jini

55
Jini

• A system designed for spontaneous networking.
• Java-based assumes that JVMs run on all of the
  computers, allowing them to communicate through
  RMI (remote method invocation, a flavor of
  interprocess communication in an object-oriented
  environment).
• Provides facilities for service discovery,
  transactions and shared data spaces called
  JavaSpaces.

56
Jini Directory-Related Component

• Lookup service, Jini services and Jini clients.
• The lookup service implements what we have termed
  a discovery service
• Jini uses discovery only for discovering the
  lookup service itself.
• Allows Jini services to register the services
  they offer and Jini clients to request services
  that match their requirements.
• A Jini service provides an object that provides
  the service as well as the attributes of the
  service.
• May be registered with several lookup services
  that store the objects.
• Example printing service.

57
Jini Directory-Related Component (contd)

• Jini clients query lookup service to find Jini
  services that match their requirements.
• If a match is found they download an object that
  provides the service from the lookup service.
• Bootstrap connectivity how to find the lookup
  service upon entering a network.
• Solutions
• A priory knowledge of lookup services IP
  addresses.
• Doesnt scale up.
• Use a multicast IP address that is known to all
  instances of Jini software.

58
Jini Directory-Related Component (contd)

• When a Jini client or service starts up it sends
  a request stamped with time-to-live value to a
  well-known multicast address.
• Lookup services listen on a socket bound to this
  address and replies to a unicast address from
  which it received the request.
• The client can then perform RMI to query the
  lookup service.
• Lookup services sometimes broadcast datagrams
  announcing their existence to the same multicast
  address, and client and services listen on it.