Servers (A2.2 Network Architecture)

Server

Computer system that delivers data, resources, services to other clients (computers) over network

Designed for high reliability, fault-tolerance, robust performance

I. TYPES OF SERVERS

Types of servers discussed in class

Domain Host Control Protocol (DHCP) Server

Automatically assign IP addresses (+network configuration parameters) to clients

• = clients can communicate with other IP networks

• DORA (Discovery Offer Request Acknowledgement) process - how assign IP

  • Discovery - client sends broadcast packet (DHCPDISCOVER) to locate available DHCP servers

  • Offer - DHCP respond to client with offer (DHCPOFFER) containing IP address

  • Request - client responds by requesting (DHCPREQUEST) IP address from one of the servers

  • Acknowledgment - server confirms (DHCPACKNOWLEDGEMENT)  IP address assigned to client for specific time

Proxy Server

Intermediary between client and internet (before reaching firewall)

• Functionalities: ^security, ^performance, ^privacy

• Reverse proxy server - for server instead of just clients

  • = better load-distribution, cache common responses given

    • = save calculation and processing load on servers themselves

  • Scalability: ^ability to handle traffic

  • Reliability: ^fault tolerance capacity

  • Security: shields internal client devices from direct exposure to internet

Domain Name Service (DNS) Server

Translate human-readable domain names (www…) into corresponding IP addresses

• Scalability: distributed database and caching = DNS works easily

• Reliability: mission-critical system for internet = any downtime affects millions

  • Built with redundancy (each server usually has ≥3 alternatives to query)

• Security: frequent target of malicious behavior

  • = servers need ^^^security = countermeasures: firewalls, instruction detection systems

File Server

Store and manage data files and directories in network (= multiple clients access and share files)

• Has ^storage capacities, file management software = handle simultaneous requests

• Database server except DOESN’T convert files to BLOB (Binary Large Objects)

• Scalability: add drives, upgrade NIC speed

• Reliability: RAID (redundant array of independent disks) - allows multiple physical disk drives into 1 logical unit

  • = pool storage together to create one larger drive and/or backup redundancy

  • Ex: two 1TB drives pooled together to present as if 2TB drive

• Security: access permissions set at file/folder level, either read-only or read-write permission

  • = protect against unauthorized access/alteration

Mail Server

Email sending

• Stores emails for local users, exchange with other mail servers

• Commonly used protocols: SMTP (Simple Mail Transfer Protocol), POP3 (Post Office Protocol)

• Scalability: need handle many emails and attachments

  • Many companies contract mail systems to third-party providers to manage demand

• Reliability: use queues and redundant systems = maintain reliability as critical system

• Security: essential as emails frequently used as attack vector (spam, phishing, pharming, malware attachments)

  • Sender Policy Framework (SPF) - domain name owners specify which email servers are authorized to send emails on their behalf

  • DomainKeys Identified Mail (DKIM) - domain name owners sign emails digitally with cryptographic signature: checked by recipient to ensure email hasn’t been tampered with en route

Web Server

Hosts and serves web pages to clients

• Either: Static documents (HTML) OR Dynamically produced at runtime from programming code (Requests application (like reverse proxy) then sends reply to original client)

• Server farm - multiple servers under one domain name

• Scalability: load distributed across multiple servers, reverse proxy server as public interface

• Reliability: redundancy = alternatives if one fails (server fails = all hosted websites fails)

• Security: distributed denial of service, and encryption, authentication through SSL (Secure static layer)  to run HTTPS