Transcript Network Components and Structure

Network Components and
Structure
IT System Components
Readings
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Burgess, Chapter 2
Mikalsen, Chapter 1
Operating Systems
File Systems
Processes and Job Control
Devices and Controllers
Operating Systems
Software which shares and controls
hardware resources of a computer
Shields user from low-level details
Provides simple access to frequently
needed facilities
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Technical layer (kernel & drivers)
File I/O
User Interface
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Operating Systems
OS
Users
Tasks
CPUs
MS/PC DOS
Windows 3X
Mac System7
Windows 9X
AmigaDOS
Unix-like
VMS
NT/2000/XP
OS390
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NonPre-M
NonPre-M
MMM
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Unix-Like OS
Manufacturer
Type
BSD
Univ.California Berkeley
BSD
SunOS (Solaris 1)
Sun Microsystems
BSD/Sys5
Solaris (2)
Sun Microsystems
Sys5/BSD
Ultrix
DEC/Compaq
BSD
OSF1/Digital Unix
DEC/Compaq
BSD/Sys5
HPUX
Hewlett-Packard
Sys5
AIX
IBM
Sys5/BSD
IRIX
Silicon Graphics
Sys5
GNU/Linux
GPL Free Software
Posix (SysV/BSD)
Unixware
Novell
Sys5
Operating Systems
Multi-programming (Processes/Threads) allows
logical concurrency: multi-user and
EventDriven systems, which yields
Client/Server architecture!
User Interfaces
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Shell, CLI, GUI
Logfiles, Audit trails, Policies:
accounting, security, reliability, performance
Supervisor, Superuser, root user
Comparing UNIX & Windows
Compare Shell Commands
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See Table 2.1 in Burgess
Compare Directory/File structure
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See Table 2.2 in Burgess
Compare software concepts
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See Table 2.3 in Burgess
File Systems
Most OS’s are now multi-user and have
hierarchical file systems (Directories & Links)
Unix File Hierarchy
Directory structure related to function
Link files – Symbolic vs Hard Links
File Access Controls
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Owner,Group,Others method (permission bits)
ACL method
File Permission checking
User OPEN(“filename”,mode) system call
mode = 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 checking
Instead of permBits, directory entries for
files have ACLs
ACLs are of the form:
user1:permBits, user2:permBits, …
Both user and permBits may be wildcards
ACLs may be inherited from parent directory
Checking involves a search of the list to
match the name of the user running the
program with the user in the ACL
Network File Systems
For sharing file systems between hosts.
Methods include:
Drive redirection
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NET USE in DOS/Windows
MAP in Novell
Directory redirection
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Mount in UNIX
Share & Subscribe, Export & Mount
Configured mount or Automount
Distributed Directory systems
Network File Systems
Windows
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LAN Mgr, Workgroups (SMB),
Unix NFS (originally by SUN)
DFS (part of OSI DCE)
Common Internet File System (CIFS) “Samba”
Andrew File System
Netware NDS by Novell
Windows Advanced File System
Multi-Programming
Processes
Each 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 Scheduler
A process may also contain concurrent paths
of execution called Threads
To see process hierarchy
Unix:
Windows:
ps –ef or tops
TaskManager
Processes
Unix 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 Environment
Chains of processes share environment
Environment may be implied or explicit
Environment Variables are text strings
Variables usually set by user or script
Environment 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
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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
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A user with power to configure/maintain
 root, Administrator, SysOp, etc..
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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
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Read the instructions!
Understand interfaces & connectors
Know capabilities and limitations of devices
 Speeds
 Capacities
 Compatibilities
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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
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ATA-IDE
SCSI
Serial ATA
Types of Memory devices
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Fast Page,EDO, SDRAM, ECC, etc…
BIOS and NVRAM settings
Things of Special interest
to SysAdmins
Easy Systems Integration
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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
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Hardware
Data storage &
retrieval
Software
Processing power
Internet Access
Efficient Cooperation
Security
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Centralized
Common backup
Also a Risk!
Costs
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Costly to install
but savings later
Networks contain….
Hosts that run Clients and Services
Media and equipment that connect Hosts
Protocols that govern connections
Users (Vendors or Customers !?!)
Networks allow cooperation….
Cooperation leads to Communities of Users
Clients and Servers
The Hosts and their services need Identity
Identities are usually names
However protocols use numeric addresses
Addresses can be associated with names
using resolver services and directories
This is an Infrastructure service
SysAdmins 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 = Name
Some addresses are fixed (eg HostID, NIC#)
Some must be initialised (eg during startup)
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Internet Addresses must be Globally Unique
therefore can’t use NIC# (IPv6 excepted?)
Static Allocation
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continuous identity (RARP,BOOTP,DNS)
Dynamic Allocation
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transient identity (BOOTP,DHCP)
Naming Services
Used to convert Address to Name
or vice-versa
A Performance and Security nexus
DNS or bind used world-wide
NIS or NIS+ used in Unix
WINS used in Windows
Authentication (Kerberos, Radius)
Directory (X500, ldap, NDS, ActiveServer)
Network Operating Systems
Peer-to-Peer .vs. Server-Workstation
Unix – most general, open and variant
Windows NT/2000/XP
Workgroups or Domains
Novell - NDS
Macintosh – now like Unix (System X)
NOS Functions
I/O optimisation – Various forms of Cache
Fault Tolerance
Directory – Manage server resources
User Sessions
Home Directory, History & Preferences
Multi-Processing Print Spooling
Backup
Concurrency
Network Sharing models
Use synchronous request/reply protocols
Drive mapping
File System Mount
Resource Share & Subscribe
Terminal session – CLI or shell based
GUI interface – X11, Windows
Web-based
(RPC)
Network Hardware
Ethernet, Fast Ethernet, Gigabit Ethernet
Token Ring
Wireless (IEEE 802.11a/b/g)
Fibre Distributed Data interface (FDDI)
ATM
Fibre Channel
High Performance Parallel Interface (HIPPI)
Ethernet Hardware
Network Interface Cards
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(NIC)
Connector, RAM, DMA, I/O port, IRQ
Workstations – PCs or “Thin Clients”
Cables & Connectors
Network Connections
Repeaters, 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
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CSMA/CD
Ethernet Frame format
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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, routers
Repeaters copy incoming bits to all outputs
Bridges filter packets based on MAC address
to isolate local traffic from rest of network
Both extend range (4 repeats max.) or adapt
different media and connectors
Router also, but uses network (IP) address
Switch 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 cable
To reduce the traffic density in large networks, they
need to be divided into separate media areas or
segments
Segments can then be joined using bridges, switches
or routers which forward appropriately
What about Broadcasts? Switches usually forward
them but Routers usually don’t
Network Analysis Checklist
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Topology
Subnets
Network addresses
Default routes
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Netmask
What’s connected
Host Functions
Locate key services