Network Components and Structure

IT System Components

Readings Burgess, Chapter 2 Mikalsen, Chapter 1

Operating SystemsFile SystemsProcesses and Job ControlDevices and Controllers

Operating Systems

Software which shares and controls hardware resources of a computerShields user from low-level detailsProvides simple access to frequently needed facilities Technical layer (kernel & drivers) File I/O User Interface

4

Operating SystemsOS Users Tasks CPUs

MS/PC DOS S S 1Windows 3X S NonPre-M 1Mac System7 S NonPre-M 1Windows 9X S M- 1AmigaDOS S M- 1Unix-like M M n

VMS M M nNT/2000/XP M M n

OS390 M M n

Unix-Like OS Manufacturer TypeBSD Univ.California Berkeley BSD

SunOS (Solaris 1) Sun Microsystems BSD/Sys5Solaris (2) Sun Microsystems Sys5/BSD

Ultrix DEC/Compaq BSDOSF1/Digital Unix DEC/Compaq BSD/Sys5

HPUX Hewlett-Packard Sys5AIX IBM Sys5/BSDIRIX Silicon Graphics Sys5

GNU/Linux GPL Free Software Posix (SysV/BSD)Unixware Novell Sys5

Operating SystemsMulti-programming (Processes/Threads) allows logical concurrency: multi-user and EventDriven systems, which yields Client/Server architecture!User Interfaces Shell, CLI, GUI

Logfiles, Audit trails, Policies: accounting, security, reliability, performance

Supervisor, Superuser, root user

Comparing UNIX & Windows

Compare Shell Commands See Table 2.1 in Burgess

Compare Directory/File structure See Table 2.2 in Burgess

Compare software concepts See Table 2.3 in Burgess

File SystemsMost OS’s are now multi-user and havehierarchical file systems (Directories & Links)

Unix File HierarchyDirectory structure related to functionLink files – Symbolic vs Hard LinksFile Access Controls Owner,Group,Others method (permission

bits) ACL method

File Permission checkingUser OPEN(“filename”,mode) system callmode = Create, Read, Write, Append, etc..

System searches directory: locates “filename”

Compares users name (UID) of program with Owner of file. If not same, repeat for Group (GID). Else use Other.Compares “mode” with files permBits: Error if “mode” exceeds files allowed permissions.eg. When mode=Read and permBits=rwx,-,- (700) and UID not = Owner

Access Control List checkingInstead of permBits, directory entries for files have ACLsACLs are of the form:

user1:permBits, user2:permBits, …Both user and permBits may be wildcardsACLs may be inherited from parent directoryChecking involves a search of the list to match the name of the user running the program with the user in the ACL

Network File SystemsFor sharing file systems between hosts. Methods include:Drive redirection NET USE in DOS/Windows MAP in Novell

Directory redirection Mount in UNIX

Share & Subscribe, Export & MountConfigured mount or AutomountDistributed Directory systems

Network File SystemsWindows LAN Mgr, Workgroups (SMB),

Unix NFS (originally by SUN)DFS (part of OSI DCE)Common Internet File System (CIFS) “Samba”

Andrew File SystemNetware NDS by NovellWindows Advanced File System

Multi-Programming

ProcessesEach process is a collection of resources:

instance of a running program in RAM, current directory, open files with current position, User and Group ID, limits, etc…

Processes are “time-sliced” by OS SchedulerA process may also contain concurrent paths of execution called ThreadsTo see process hierarchy

Unix: ps –ef or topsWindows: TaskManager

ProcessesUnix Process Hierarchy

New processes are copy of existing ones“Parent” process may wait for “child” processes to exit before proceeding (synchronous model)

When “parent” does not wait, “child” is said to be “running in the background” (asynchronous model)

Processes send termination status message

Process EnvironmentChains of processes share environmentEnvironment may be implied or explicitEnvironment Variables are text stringsVariables usually set by user or scriptEnvironment is inherited by new processes. This is how command parameters are passed from parent to child.But changes to local environment are not passed back to parent process

Things of Special interest to SysAdmins

Logs and Audit Trails A detailed list of actions recorded by

OS File system Logs used to reinstate data Usage Logs used for billing Auditing used for security

Trace source of activity Provide non-repudiation

Things of Special interest to SysAdmins

Privileged Accounts A user with power to configure/maintain

root, Administrator, SysOp, etc.. Can access or do anything !! Is actually very dangerous Should not be used as everyday login. . . .

use only when required Trusted host concept in TCP/IP can now be

easily circumvented because everyone has superuser access on their own PC !!

Things of Special interest to SysAdmins

Knowing how to care for your hardware Read the instructions! Understand interfaces & connectors Know capabilities and limitations of devices

Speeds Capacities Compatibilities

Know how to handle components Avoid damage due to Static Discharge Packaging and transport Assembly

Things of Special interest to SysAdmins

Types of disk drives ATA-IDE SCSI Serial ATA

Types of Memory devices Fast Page,EDO, SDRAM, ECC, etc…

BIOS and NVRAM settings

Things of Special interest to SysAdmins

Easy Systems Integration System built from identical parts Applies to hardware and software

Network Structures

Refer: Burgess Ch 3

Why Network ??Why do networks appear in Enterprises?

Resource Sharing Hardware Data storage &

retrieval Software Processing power Internet Access

Efficient CooperationSecurity Centralized Common backup Also a Risk!

Costs Costly to install but savings later

Networks contain….Hosts that run Clients and ServicesMedia and equipment that connect HostsProtocols that govern connectionsUsers (Vendors or Customers !?!)Networks allow cooperation….Cooperation leads to Communities of Users

Clients and ServersThe Hosts and their services need IdentityIdentities are usually namesHowever protocols use numeric addressesAddresses can be associated with names using resolver services and directoriesThis is an Infrastructure serviceSysAdmins maintain these too….

Host Identities & Name Services

A host has many different names used in various contexts:

HostID – NIC or CPU serial#

Install Name - /etc/hostname.*

Application Names – eg Oracle database name

Local name list - /etc/hosts

Network Information Service – “yellow pages”

Transport level addresses – TCP/UDP port# + IP#

Physical level addresses – NIC address

DNS names – IP names & info

WINS names – IP, NetBIOS & WfW names

Establishing Network Identity

Identity = Address = NameSome addresses are fixed (eg HostID, NIC#)

Some must be initialised (eg during startup) Internet Addresses must be Globally Unique

therefore can’t use NIC# (IPv6 excepted?)

Static Allocation continuous identity (RARP,BOOTP,DNS)

Dynamic Allocation transient identity (BOOTP,DHCP)

Naming Services

Used to convert Address to Name or vice-versa

A Performance and Security nexusDNS or bind used world-wideNIS or NIS+ used in UnixWINS used in WindowsAuthentication (Kerberos, Radius)Directory (X500, ldap, NDS, ActiveServer)

Network Operating Systems

Peer-to-Peer .vs. Server-WorkstationUnix – most general, open and variant

Windows NT/2000/XPWorkgroups or Domains

Novell - NDSMacintosh – now like Unix (System X)

NOS Functions

I/O optimisation – Various forms of Cache

Fault ToleranceDirectory – Manage server resources

User SessionsHome Directory, History & Preferences

Multi-Processing - Concurrency

Print SpoolingBackup

Network Sharing modelsUse synchronous request/reply protocols

(RPC)

Drive mappingFile System MountResource Share & SubscribeTerminal session – CLI or shell basedGUI interface – X11, WindowsWeb-based

Network Hardware

Ethernet, Fast Ethernet, Gigabit EthernetToken RingWireless (IEEE 802.11a/b/g)Fibre Distributed Data interface (FDDI)ATMFibre ChannelHigh Performance Parallel Interface (HIPPI)

Ethernet Hardware

Network Interface Cards (NIC) Connector, RAM, DMA, I/O port, IRQ

Workstations – PCs or “Thin Clients”

Cables & Connectors

Network ConnectionsRepeaters, Bridges and Routers

An Ethernet is a single collision domain ie a single shared medium (segment)Bus topology (physical or logical)Media Access Control (MAC) “contest” based CSMA/CD

Ethernet Frame format Ethernet, Ethernet II and SNAP

Ethernet cable characteristics: Min.Frame size, Signal propagation speed, Max.Segment length = Collision window size

Network Design with Ethernet

Repeaters/hubs, bridges/switches, routersRepeaters copy incoming bits to all outputsBridges filter packets based on MAC address to isolate local traffic from rest of networkBoth extend range (4 repeats max.) or adapt different media and connectorsRouter also, but uses network (IP) addressSwitch forwards packet only to target address

Network Segments

In a single network devices share a media access protocol (eg CSMA/CD in ethernet)A packet being transmitted usually occupies the medium exclusively over the entire cableTo reduce the traffic density in large networks, they need to be divided into separate media areas or segmentsSegments can then be joined using bridges, switches or routers which forward appropriatelyWhat about Broadcasts? Switches usually forward them but Routers usually don’t

Network Analysis Checklist

1. Topology2. Subnets3. Network

addresses4. Default routes

5. Netmask6. What’s

connected7. Host Functions8. Locate key

services