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Chapter 2. NETWORK AND SERVER SECURITY. Content. Network Protocols Review Securing Servers Border Security. Network Protocols Review. Protocol: is a formal set of rules that describe how computers transmit data and communicate across a network.
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Chapter 2 NETWORK AND SERVER SECURITY
Content • Network Protocols Review • Securing Servers • Border Security
Network Protocols Review • Protocol: is a formal set of rules that describe how computers transmit data and communicate across a network. • Protocols are arranged in a stack of layers in which data is passed from the highest layer to the lowest layer to send a transmission(network stack).
The Functions of Layer • Session Layer: • Establishing the connection. • Transferring data. • Releasing the connection. • Network Layer: • Switching and routing • Forwarding • Addressing • Error detection • Node traffic control • Data Link Layer: • Media Access layer: • Supports the network computer’s access to packet data. • Controls the network computer’s permission to transmit packet data. • Logical Link layer: • Sets up the communication link between entities on a physical channel. • Converts data to be sent into bits for transmission. • Formats the data to be transmitted into frames. • Adds a header to the data that indicates the source and destination IP addresses. • Defines the network access protocol for data transmission and reception. • Controls error checking and frame synchronization. • Supports Ethernet and token-ring operations.
Protocols associated with each layer • Application layer: • File Transfer Protocol (FTP) • Trivial File Transfer Protocol (TFTP) • Domain name system (DNS) • Simple Mail Transfer Protocol (SMTP) • Secure File Transfer Protocol (SFTP) • Shell (SSH) or SSH-2 • Remote login (Rlogin) • Simple Network Management Protocol (SNMP) • BootP • Multipurpose Internet Mail Extensions (MIME) • Presentation Layer • Hypertext Transfer Protocol (HTTP) • Moving Picture Experts Group (MPEG) • Joint Photographic Experts Group (JPEG)
Protocols associated with each layer • Session Layer: • AppleTalk Session Protocol (ASP) • Network File System (NFS) • Remote procedure call (RPC) • Transport Layer: • Transmission Control Protocol (TCP) • Stream Control Transmission Protocol (SCTP) • User Datagram Protocol (UDP) • Sequenced Packet Exchange (SPX) • Network Layer: • Internet Protocol (IP) • Open Shortest Path First (OSPF) • Internet Control Message Protocol (ICMP) • Routing Information Protocol (RIP) • IP security (IPsec) • Address Resolution Protocol (ARP) • Reverse Address Resolution Protocol (RARP) • Data Link Layer: • Serial Line Internet Protocol (SLIP) • Point-to-Point Protocol (PPP)
Best Practices for Network Security • Three basic guidelines for securing the servers on your network: • Designing applications with security in mind(Security by Design) • Maintaining a security mindset • Defense–in-depth
Security by Design • Some of the factors affecting security in the design phase of a development effort are as follows: • The software developers and security professionals (network engineers) historically came from different communities. This is still an issue today, although more software developers are attending security training and security conferences. • The security threat was not well publicized. Security has made the front page more often in recent years. • In many cases, the software developers are building an application that they have never coded before. However, a network engineer who designs a network has probably designed dozens of networks in the past. • Until recently, software developers could not justify time spent on security features, because security features did not seem to affect the bottom line from management’s perspective. • In the highly competitive marketplace for software, there has been a natural rush-to-market approach to beat the competition.
Maintaining a Security Mindset • The following are some approaches to developing a mindset that will help you secure the servers on your network: • Base security decisions on the risk. Security can be like insurance; the risk must be known to determine the coverage needed. • Use defense-in-depth. Many security controls are preferable to a single point of protection. • Keep things simple. Simplicity and clarity will support a more secure environment. • Respect the adversary. Do not underestimate the interest and determination of the threat. • Work on security awareness. Security training is needed at all levels of an organization. • Be paranoid and expect the worst.
Securing Servers • To operate the server securely, an organization must establish a plan with associated procedures. These procedures should include the following key aspects: • Control the server configuration: The server must be configured to minimize exposure to an attack. • Control users and access: A need-to-know and need-to-access environment should be established regarding the server’s data and access. • Monitoring, auditing, and logging: Security does not stop with deployment of the server.
Controlling the Server Configuration • The following are three important considerations when securing the host system: • Physical Security of the System: • Provide an uninterruptible power supply (UPS) unit with surge protection. • Provide fire protection to minimize the loss of data and equipment. • Provide adequate cooling and ventilation. • Provide adequate lighting and work space for maintaining and upgrading the system. • Restrict physical access to the server(server space should be locked, alarmed, and recorded for later evaluation).
Controlling the Server Configuration • Minimizing Services • The following list shows typical services that should be disabled from a host if not needed: • Telnet: The secure alternative, SSH, should be used instead, if needed. • SMTP: Mail server applications are frequent targets of attacks. • FTP: FTP is used to upload files to and download files from a central repository. FTP has a number of vulnerabilities and must be properly configured to be safe. • TFTP: TFTP is used to transfer small files and can be used to upload a malicious file to a computer. • Finger: Finger allows you to determine the name associated with an email address and the last time the user logged on. • Netstat: Netstat is a Windows troubleshooting tool that allows you to see which ports a computer is listening on, as well as other information about the network. • Systat: Systat is a Unix® troubleshooting tool. • Chargen and Echo: These services can be used to launch data-driven attacks and denial-of-service (DoS) attacks. • DNS: This service requires frequent patches and upgrades to be secure. • RPC: Unless the server application explicitly uses RPC to communicate with other systems, this should be disabled.
Managing Windows Services • Windows 2000 (and later) has three built-in accounts that are typically used to run services, but you can also create a special user account and assign it the necessary rights and permissions. • The three built-in accounts are as follows: • Local System: This account has permission to perform any task on the computer and permission to access resources on the network. • Local Service: This account has very limited permissions on the computer and cannot access other computers across the network. • Network Service: This account has the same local permissions as Local Service, but can also access computers across the network. • You change the security context for a service through the Log On tab of the service’s properties.
Blocking Ports and Limiting Input and Output Devices • Blocking Ports: You can block traffic to a specific port by configuring a firewall or IPSec. • Some physical entry points you might consider removing include the following: • Modems • Network adapters • CD-ROM and DVD drives • Floppy drives • Universal Serial Bus (USB) ports • Monitor
Border Security • Segmenting a Network: Network segments can be theoretically classified into the following: • Public networks: allow accessibility to everyone(unsecured Network) • Semi-private networks: sit between public networks and private networks(exclusive subnets of large public networks). • Private networks: are organizational networks that handle confidential and proprietary data and are the most common type of network. • The boundaries of such network segments are established by devices capable of regulating and controlling the flow of packets into and out of the segment, including the following: • Routers • Switches • Bridges • Multi-homed gateways
Firewalls • The reasons for an organization to employ firewalls to secure their networks from other insecure networks: • Poor authentication • Poor authentication • Spoofing • Scanners and crackers • Type of Firewall: • Packet-Filtering Firewalls • Stateful packet-filtering • Application Proxy Firewalls: working at Layer 7 of OSI • Disadvantages of Firewalls • The cost involved in installation.
Network Address Translation • Feature of NAT: • It is used to translate private addresses to public address. • hosts from inside the protected networks (with a private address) are able to communicate with the outside world, but systems that are located outside the protected network have to go through the NAT system to reach internal networks. • The main feature in NAT is the translation table(A single public IP address might be mapped to more than one private IP address). • Translation tables are built using two methods: • Static: In this configuration, the relationships among the public and private IP addresses are fixed. • 2. Dynamic outbound packets: In this mode, the translation tables get updated automatically as outbound packets are processed from the private network.
