day12 network os. what is an os? provides resource management and conflict resolution. –this...
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Day12
Network OS
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What is an OS?• Provides resource management
and conflict resolution.– This includes
• Memory• CPU• Network Cards
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Scarce Resources• Memory
– Everyone wants it, there is a limited supply
– Must request memory from OS. • OS may
– Impose limits– Manages swap space as necessary– Manages CPU registers and cache
– When a program exits memory is reclaimed
– A Preemptive multitasking OS allows the OS to force a program to give back memory and exit.
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Different OS’s• Windows NT/2000/XP/2003• Windows 95/98/ME• Unix (solaris, BSD)• Linux (Redhat,Suse,Debian…)• Mac OSX, os9…• Each has its own advantages and
disadvantages.– License– Stability– Support
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Network component• In order for an OS to be a NOS it
must:– Support network interface cards
(NIC), via drivers– Support protocols such as TCP/IP,
Appletalk etc.– Provide client or server software
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Client-Server• The model we are now most
familiar with.– Lots of clients (laptops, desktops)– A few servers
• Web Servers• File Servers• Mail servers
• A single server can talk to many clients.
• Each client can talk to many servers.
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Peer To Peer• There is no concept of a single server,
everyone just talks to whoever they wish. – Each machine may act as a client to some
people and a server to others
• File sharing software– Often you connect to a central server to find
a list of other peers. – You can search for files by asking everyone
if they have it– Multiple servers can return parts of a file to
you.
• Advantage are harder to track, better fault tolerance.
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Clients• Just about all machines act as
clients– You must have client software
• Internet Explorer, WSFTP, Putty/SecureCRT, AIM, Terminal Service Client etc.
– Many things are now available via the web, so specialized software is less important so long as you have a browser with all the plug-ins.
• You’ll want to protect it from unwanted stuff– Viruses, Spyware, Worms, Spam etc.
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Servers• Typically must have static IP
– So people can find them
• Must have some software installed to perform server function– Apache, wu-ftp, IIS, Exchange,
sendmail, Samba, etc.
• Nothing magical about the hardware, any computer can be a server– However, high end servers tend to
have lots of RAM, many CPUs, RAID disks. Some have redundant internals.
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Redundancy/Scalability• If a server performs an important
duty:– You’ll want more than 1 of them
• In case one fails• To help handle requests when a lot of
people want that service
– Often you’ll use a load balancer to achieve this.• Most large networking companies make
load balancers for this task.
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Backups• Few do it right, everyone should• You only realize you need it when
you need it, and then its too late.– Servers should be backed up to
ensure a failure doesn’t mean a loss of data. Often the data is worth more than the machine
– Backups don’t have to be fancy, CDs, DVDs, Tapes, Zip disks, Jump drives all work great.
– Remember to plan for the worst. • Backup often, and keep some at another
location
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UPS• Sometimes the power goes out
– Batteries are your friend– Hard shutdown of computer is bad
• Disk cache, memory cache• If you do it often enough, you’ll eventually
lose data, or the OS.
– UPS/generators can keep you alive when the power goes out.
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Authentication• Username and password can be
used to prove your identity– But you don’t want to have to log in
for EVERY file you transfer off a machine.
– Authentication Tokens.• A single server (Domain Controller, NIS,
Kerberos, Radius) authenticates you and gives you a token which proves you’ve authenticated. Now you can just give that token. Eventually the token expires, or can be revoked.
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Keeping track of users• Most modern server OS’s have
some capability to organize users, computers and resources into a structure.– Windows: Active Directory– Netware: NDS– Unix/MAC: Ldap
• They are effectively the same thing, the allow you to group similar things together into “trees”.
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Intrusion Detection• Finding out someone has been
here.– Logs/event viewer are helpful but can
be faked– Scanning for root kits or
administrator compromises.– Tools available such as:
• ISS• Nessus• Snort