Enabling Secure Internet Access with ISA Server

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Enabling Secure InternetAccess with ISA Server
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Enabling Secure Access to Internet Resources

• What Is Secure Access to Internet Resources?
• Users can access the resources that they need
• The connection to the Internet is secure
• The data that users transfer to and from the
  Internet is secure
• Users cannot download malicious programs from the
  Internet
• Secure access to the Internet also means that the
  users actions comply with the organizations
  security or Internet usage policy.

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What Is Secure Access to Internet Resources

• Secure access
• Only users who have permission to access the
  Internet can access the Internet.
• These users can use only approved protocols and
  applications to access Internet resources.
• These users can gain access only to approved
  Internet resources, or these users cannot gain
  access to denied Internet resources
• These users can gain access to the Internet only
  in accordance with any other restrictions
• the organization may establish, such as when and
  from which computers access is permitted.

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How ISA Server Enables Secure Access to Internet
Resources

• ISA Server provides the following functionality
  to enable secure access
• Implementing ISA Server as a firewall
• Implementing ISA Server as a proxy server.
• Using ISA Server to implement the organizations
  Internet usage policy

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Configuring ISA Server as a Proxy Server

• What Is a Proxy Server?
• A proxy server is a server that is situated
  between a client application and a server to
  which the client connects.
• All client requests are sent to the proxy server.
  The proxy server creates a new request and sends
  the request to the specified server. The server
  response is sent back to the proxy server, which
  then replies to the client application.
• A proxy server can provide enhanced security and
  performance for Internet connections.
• Using a proxy server is to make the users
  connection to the Internet more secure.

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Configuring ISA Server as a Proxy Server

• Proxy servers make the Internet connection more
  secure in the following ways
• User authentication
• Filtering client requests
• Content inspection
• Logging user access
• Hiding the internal network details

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How Proxy Servers Work

• How Does a Forward Proxy Server Work?
• How Does a Reverse Web Proxy Server Work?

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How Does a Forward Proxy Server Work?

• When a proxy server is used to secure outbound
  Internet access, it is configured as a forwarding
  proxy server.
• Forward proxy servers are usually located between
  a Web or Winsock application running on a client
  computer on the internal network and an
  application server located on the Internet

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How Does a Forward Proxy Server Work?
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• 1. A client application, such as a Web browser,
  makes a request for an object located on a Web
  server. The client application checks its Web
  proxy configuration to determine whether the
  request destination is on the local network or on
  an external network.
• 2. If the requested Web server is not on the
  local network, the request is sent to the proxy
  server.
• 3. The proxy server checks the request to confirm
  that there is no policy in place that blocks
  access to the requested content.
• 4. If caching is enabled, the proxy server also
  checks if the requested object exists in its
  local cache. If the object is stored in the local
  cache and it is current, the proxy server sends
  the object to the client from the cache. If the
  page is not in the cache or if the page is out of
  date, the proxy server sends the request to the
  appropriate
• server on the Internet.

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• 5.The Web server response is sent back to the
  proxy server. The proxy server filters the
  response based on the filtering rules configured
  on the server.
• 6. If the content is not blocked and it is
  cacheable, ISA Server saves a copy of the content
  in its cache and the object is then returned to
  the client application that made the original
  request.

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How Does a Reverse Web Proxy Server Work?
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• A user on the Internet makes a request for an
  object located on a Web server that is on an
  internal network protected by a reverse proxy
  server. The client computer performs a DNS lookup
  using the fully qualified domain name (FQDN) of
  the hosting server. The DNS name will resolve to
  the IP address of the external network interface
  on the proxy server.
• 2. The client application sends the request for
  the object to the external address of the proxy
  server

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• 3.The proxy server checks the request to confirm
  that the URL is valid and to ensure that there is
  a policy in place that allows access to the
  requested content.
• 4. The proxy server also checks whether the
  requested object already exists in its local
  cache. If the object is stored in the local cache
  and it is current, the proxy server sends the
  object to the client from the cache. If the
  object is not in the cache, the proxy server
  sends the request to the appropriate server on
  the internal network.
• 5. The Web server response is sent back to the
  proxy server.
• 6. The object is returned to the client
  application that made the original request

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How to Configure ISA Server as a Proxy Server
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How to Configure Web and Firewall Chaining

• ISA Server 2004 Standard Edition supports the
  chaining of multiple servers running ISA Server
  together to provide flexible Web proxy services

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How to Configure Web and Firewall Chaining
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Configuring Access Rule Elements

• By default, ISA Server 2004 denies all network
  traffic between networks connected to the ISA
  Server computer.
• Configuring an access rule is the only way to
  configure ISA Server so that it will allow
  traffic to flow between networks

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What Are Access Rule Elements

• Access rule elements are configuration objects in
  ISA Server that you use to create access rules.
• Exampleyou may want to create an access rule
  that allows only HTTP traffic, ISA Server
  provides an HTTP protocol access rule element
  that you can use when creating the access rule

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Access Rule Element Types
Element Description
Protocols defines protocols that you can use in an access rule.
User Sets defines a group of one or more users to which a rule will be explicitly applied, or which can be excluded from a rule.
Content Types provides common content types to which you may want to apply a rule.
Schedules allows you to designate hours of the week during which the rule applies
Network Objects . allows you to create sets of computers to which a rule will apply, or which will be excluded from a rule.
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How to Configure Access Rule Elements

• ISA Server includes several default access rule
  elements

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How to Configure User Set Elements

• access rule specifies which users will be allowed
  or denied access by the access rule.
• To limit access to Internet resources based on
  users or groups, you must create a user set
  element.
• When you limit an access rule to specific users,
  users must authenticate before they are granted
  access.
• For each group of users, you can define the type
  of authentication required

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How to Configure User Set Elements

• All Authenticated UsersThis set includes all
  users who have authenticated using any type of
  authentication.
• All UsersThis set includes all users, both
  authenticated and unauthenticated.
• System and Network ServiceThis user set includes
  the Local System service and the Network service
  on the computer running ISA Server. This user set
  is used in some system policy rules

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How to Configure User Set Elements

• In ISA Server

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How to Configure Content Type Elements

• Create a new content type element, or use one of
  the existing content type elements when you
  create an access rule.
• Content type elements define Multipurpose
  Internet Mail Extensions (MIME) types and file
  name extensions.
• When a client such asMicrosoft Internet Explorer
  downloads information from the Internet using
  HTTP or File Transfer Protocol (FTP), the content
  is downloaded in either MIME format or as a file
  with a specified file name extension.

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How to Configure Content Type Elements

• Content type elements apply only to HTTP and FTP
  traffic that is tunneled in an HTTP header.
• When a client requests HTTP content, ISA Server
  sends the request to the Web server.
• When the Web server returns the object, ISA
  Server checks the objects MIME type or its file
  name extension, depending on the header
  information returned by the Web server.
• ISA Server determines if a rule applies to a
  content type that includes the requested filename
  extension, and processes the rule accordingly
• ISA Server is preconfigured with the following
  content types Application, Application data
  files, Audio, Compressed files, Documents,
  Hypertext Markup Language (HTML) documents,
  Images, Macro documents, Text, Video, and Virtual
  Reality Modeling Language (VRML).

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• In ISA server

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How to Configure Schedule Elements

• To configure access to the Internet based on the
  time of day.
• ISA Server
• WeekendsDefines a schedule that includes all
  times on Saturday and Sunday
• Work HoursDefines a schedule that includes the
  hours between 0900 (900 A.M.) and 1700 (500
  P.M.) on Monday through Friday

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• In ISA server

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How to Configure Network Objects

• to define which Web sites or servers users can or
  cannot access
• Networks
• A network rule element represents a network,
  which is all the computers connected
• EXInternal, External, Branch Office
• Network Sets
• A network-set rule element represents a grouping
  of one or more networks
• ExAll Protected Networks

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How to Configure Network Objects

• Computer
• A computer rule element represents a single
  computer, identified by its IP address
• ExDC1 (IP Address 192.168.1.10).
• Address Ranges
• An address range is a set of computers
  represented by a continuous range of IP addresses
• ExAll DCs (IP Address Range 192.168.1.10
  192.168.1.20).

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How to Configure Network Objects

• Subnets
• A subnet represents a network subnet, specified
  by a network address and a mask.
• ExBranch Office Network (IP Addresses
  192.168.2.0/24).
• Computer Sets
• A computer set includes a collection of computers
  identified by their IP addresses, a subnet
  object, or an address-range object
• ExAll DCs and Exchange Servers

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How to Configure Network Objects

• URL Sets
• URL sets specify one or more URLs grouped
  together to form a set.
• ExMicrosoft Web Site (http// www.microsoft.com/
  )
• Domain Name Sets
• Domain name sets define one or more domain names
  as a single set, so that you can apply access
  rules to the specified domains

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How to Configure Network Objects

• In ISA server

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Configuring ISA Server Authentication

• to limit access to Internet resources based on
  users or groups
• ISA Server Authentication Options
• Basic authentication
• Basic authentication sends and receives user
  information as plaintext and does not use
  encryption
• Digest authentication
• Digest authentication passes authentication
  credentials through a process called hashing.
• Hashing creates a string of characters based
  onthe password but does not send the actual
  password across the network, ensuring that no one
  can capture a network packet containing the
  password and impersonatethe user.

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• Integrated Windows authentication
• Uses either the Kerberos version 5 authentication
  protocol or NTLM protocol, both of which do not
  send the user name and password across the
  network.
• Digital certificates authentication
• Requests a client certificate from the client
  before allowing the request to be processed.
• Users obtain client certificates from a
  certification authority that can be internal to
  your organization or a trusted external
  organization.
• Remote Authentication Dial-In User Service
• RADIUS is an industry-standard authentication
  protocol.

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ISA Server Clients and Authentication

• SecureNAT Clients
• For SecureNAT clients, there is no user-based
  authentication
• Restrict access to the Internet based only on
  network rules and other access rules
• If an access rule requires authentication,
  SecureNAT clients will be blocked from accessing
  the resources defined by the rule

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• Firewall Clients
• When ISA Server authenticates a Firewall client,
  it uses the credentials of the user making the
  request on the computer running the Firewall
  client

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Configuring Access Rules for Internet Access

• What Are Access Rules

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How to Configure Access Rules
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