Transcript Notes as Powerpoint Presentation

Networking 101
An Introduction to Networking
Roger Connell
Innova Solutions
Overview
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IP
TCP
Private Address Ranges
Small Office Network
TCP/IP Tools
Symbolic Name Translation
Windows Resource Sharing
Routers and Firewalls
Analysers
IP
• Datagram
– Send it let it rattle around to its destination
– If it takes too long throw it away
– Address Format (V4)
• 192.168.0.188
4 Octets
• Sits on top of a Data Link Protocol
– Ethernet
• MAC Address Allocated by Card Manufacturer
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https://wwwcoms.murdoch.edu.au/macaddress.html
– But could be
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IEEE 802-2, Token Ring, FDDI, SMDS,SDLC, LAPB, etc.
IP V4 Packet Format
Version
Header
Length
Type of
Service
Total Length
Identification
Time to Live
Fragment Info
Header Checksum
Protocol
Source Address
Destination Address
Multiple 32 bit words of “Options”
Data
IP Address Aspects
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The IP Address applies to a connection not a host
“Networks” and Subnets
– Conceptual Class A,B,C
– Actual implementation is Subnets
• Defined by Subnet Mask 255.255.255.0
– 255.255.255.128 or 255.255.255.192?
• Works with IP Address
??
– 192.168.26.34
– Broadcast all 1’s in subnet 192.168.26.63?
– The Network Address is all 0’s used in routing tables (192.168.26.192)
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Network Address Translation
– Original concept every connection owns an IP address
• Not enough addresses in IP4
– IP6 was solution but
– NAT has solved the problem
– Local Network uses a range of Private IP Addresses
• ISP allocates one Global IP Address for each WAN connection
• NAT used to Translate Address from Local to Global
• http://en.wikipedia.org/wiki/Private_network
Private IP Address
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Private IP Address Ranges
– 10.0.0.0 to 10.255.255.255
– 172.16.0.0 to 172.31.255.255
– 192.168.0.0 to 192.168.255.255
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Gateway provides Address Translation (and other fire wall services)
– Typically the ADSL modem or router or Gateway Computer (for dial up)
– Typical gateway uses .1 or .254 of subnet
– ISP provides global (WAN) IP address
• either dynamically or fixed
• From the WAN all calls are to and from the WAN IP address
– For outgoing calls NAT maintains a cross reference table
• Special rules for some protocols supported by “good” firewalls
– Eg. FTP Data Channel
– Incoming calls must have handling rules (Port forwarding)
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Private IP address ranges not supported in the WAN
– Protects your computers from outside attacks
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Loopback Address
– Localhost, lo or lo0 >> 127.0.0.1
Small Office Network
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Choose a Private Network Range
Allocation Method
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Auto Requires a DCHP server
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Generally supplied with router
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Address may change so servers and shares need to use Windows Host names
Manual Allocation
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You need to have a plan and configure details otherwise supplied by DHCP
Servers and Shares can be referred to by IP address and avoid Windows drop outs
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Provides an IP address, Mask, Gateway and DNS details
You need to set auto allocate range to not conflict with manual Allocations
Or distributed using Hosts and LMHosts
Suggestion
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Auto for Laptops and Manual for servers and shares.
192.168.3.100
IntraNet
192.168.3.0
192.168.3.254
215.56.89.234
Internet
NAT
DHCP
192.168.3.101
Changing IP Properties
• Control Panel>>Network Connections
– Select the connection to change
• Select Properties and on the General Tag
– Select Internet Protocol and press Properties
NB.
The Link Layer Configuration is at the
top of the Connection Properties Dialog
TCP and UDP
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UDP and TCP Add a Port Number
– Destination Port No is the “application” or “service” address on the host
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Applications/services register to listen for incoming data on the defined port
IANA port numbers: http://www.iana.org/assignments/port-numbers
0 to 1023 Well Known ports managed by IANA
1024 to 49151 Registered by IANA as a convenience
49152 to 65535 Dynamic (used for source address)
C:\WINDOWS\system32\drivers\etc\services
– Source Port number used with IP addresses and destination port number to
create a unique identifier for the connection.
– Source port number incremented at each use
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UDP – User Datagram Protocol
– really only IP with port number and optional checksum
– source port optional
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TCP Transport Connection Protocol
– Provides a reliable stream connection
– Requests retransmission of lost or corrupted data and reassembles the original
order.
TCP/IP
TCP
IP
TCP PDU Format
IP Header
Source Port
Destination Port
Sequence Number
Acknowledgement Number
Header
Length
Reserved
Code Bits
Window
Checksum (Hdr + Data)
Urgent Pointer
Multiple 32 bit words of “Options”
Protocol
Data
Header Checksum
TCP IP Tools
• Ping
– ping [-t] [-a] [-n Count] [-l Size] [-f] [-i TTL] [-v TOS] [-r Count] [-s Count]
[{-j HostList | -k HostList}] [-w Timeout] [TargetName]
• IPConfig
– ipconfig [/all] [/renew [Adapter]] [/release [Adapter]] [/flushdns]
[/displaydns] [/registerdns] [/showclassid Adapter]
[/setclassid Adapter [ClassID]]
– http://www.microsoft.com/resources/documentation/windows/xp/all/prod
docs/en-us/ipconfig.mspx?mfr=true
• TraceRt
– tracert [-d] [-h MaximumHops] [-j HostList] [-w Timeout] [TargetName]
• NsLookup
– nslookup [-SubCommand ...] [{ComputerToFind| [-Server]}
• Others
– NetStat,
Meaningful Names
• All packets are directed by IP address but that
has no “meaning”
– Symbolic Name
– Directory Services
• Name Servers translate a symbolic name to an
IP address
• Two main participants
– Domain Name Server (DNS)
– Netbios name service (NBNS)
• Windows Internet Name Service (WINS)
Domain Name Server
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DNS uses a distributed database protocol to delegate control of domain
name hierarchies among zones, each managed by a group of name
servers.
– Manual Configuration but distributed
– Resolution starts from global root nameservers
• Logically only 13 root nameservers
• Physically more using anycast
• Each holds delegations for all Top Level Domains
– .com, .edu, .org, .au, .uk, .at, .nz ………
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Locally configured by ISPs etc.
– Records delegating sub domains
– Records give IP address for servers part of this domain
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Local DNS resolve any unknown name on request
– Having resolved an address a DNS server caches it for a time to live parameter
– There are now services which will allow handling of dynamic IP addresses
• Presumably via very short time to live values
• www.dyndns.org
WINS and Netbios
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Windows Name Resolution
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Is Dynamic
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Mode Determines order of look up
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\%SystemRoot%\System32\drivers\etc\LMHost - For Lookups?
\%SystemRoot%\System32\drivers\etc\Host
- For IP Tools Ping, NetStat, …. Why???
Group (Work Group) just for presentation (I think?)
Broadcast may be blocked by IP Routers
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Name Cache
Additional functions resolve services available
Flat – Name must be unique
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b (broadcast), p (peer), m (mixed), h (hybrid)
Host Files
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Local broadcast
Windows Internet Name Server
LMHosts file
Who has TheDomainIWant
Register name by broadcast
Disappearing Hosts
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Attempting to use a host when it is not available sometimes flushes the cache?
Firewalls can block broadcasts
Radio connections seem to drop the stack while changing log in
Using the Network wizard will reconfigure a host name
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It does not default to existing
Limited number of connections available in XP
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Hosts in excess cannot see services
Wins Setup
WINS and DNS
• WINS
– Resolves NetBios IP Addresses
– Flat and Dynamic Structure
– Supports DHCP
• DNS
– Resolves hostnames to IP Address
– Hierarchical and static structure
– Supports TCP/IP applications that require more
information than hostnames and IP addresses.
– DHCP Dynamic update is possible with Windows NT
Server 5 and higher
Finding Workgroup Computers
• My Computer >
– My Network Places
• Should show all shares on network
– View Work Group Computers
• Should show all computers in the workgroup
– View Entire Network
• Seems a little convoluted and hit and miss to me.
Mapping a Drive
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By Mapping a drive you get a drive indicator in “My computer”
Can map to IP address and browse
– Browse shows all “Shares” which are network enabled.
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My Computer>> Tools >> Map Network Drive
Network Enable a Directory
• My Computer
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Directory
Properties
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Sharing
• Share Folder on the Network
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Share Name
Set writeable
• Share Limit
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XPHome 5 Resources
XPPro 10 Resources
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http://support.microsoft.com/kb/328459
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Notes•For Windows XP Professional-based
computers, the maximum number of concurrent
network connections that are allowed is 10. This
limit includes all transfer and all resource share
protocols. For Windows XP Home Edition-based
computers, the maximum number of concurrent
network connections that are allowed is 5. This limit
is the number of sessions that can be hosted at the
same time from other computers. Therefore, we
cannot use the administrative tool usage to connect
to the system from a remote computer.
Router Configuration
• Router establishes your trusted boundary
– ADSL Modem/Router
– Router connecting to WAN
• Functions
– NAT
• Router determines private network used
– Firewall
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Port forwarding
Response to WAN Ping, Echo, etc
WAN Configuration (NO NO NO)
Virtual Private Network Support
– DHCP
• For dynamic IP addresses
Router Firewall
• The trusted boundary
– Preferably running no other stuff that can
expose it
Allow calls
based on
Permissions
For me
unrestricted
IntraNet
Corporates
often restrict
to only
authenticated
proxies
Block all
Requests
That are not
“Expected”
Internet
DMZ
Host
Basic Setup
• ADSL Password
• WAN IP Address
– Dynamic IP Address from WAN or Fixed IP address
• LAN IP Address and Mask
Router DHCP Setup
• Starting IP Address
• Lease Time
Wireless Setup
• Security Mode – Must have
• MAC Address Filtering
Port Forwarding
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Enable some applications on the LAN servers to accept WAN traffic
– Zebedee Tunnel
– Secure Database
– Traffic is addressed to the IP address of the router WAN Connection
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Demilitarized Zone Host implies all (other?) ports
– Should be seen as being outside the firewall
• If it is compromised it should not be able to attack LAN computers
– Seems not the case with this router
Remote Admin
• NO Way
• If you need to support remotely use a VPN or a Tunnel
(Zebedee) via a LAN server to the LAN address.
– You may turn on remote support via this means before editing the
box configuration
Virtual Private Network
• Enables operation of a distributed private
network using encrypted tunnels
– May need to use same model router
– Different Address Spaces
192.168.4.1
IntraNet
192.168.3.100
124.65.93.178
IntraNet
2
192.168.4.0
192.168.3.1
Internet
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192.168.3.0
192.168.4.100
215.56.89.234
192.168.3.101
Network Analyser
• Gives a view of data on the
wire
– Ethereal
• The latest version of Ethereal can
be found at
• http://www.ethereal.com.
Analyser Filters
• Follow A Stream
– 4033 to 80
Tools >> Follow TCP Stream
References
• An Internet Encyclopedia
http://www.freesoft.org/CIE/index.htm
• Port Numbers http://www.iana.org/assignments/portnumbers
• Private Networks
http://en.wikipedia.org/wiki/Private_network
• Linux Implementation
http://us3.samba.org/samba/docs/using_samba/ch01.html
• Windows Netbios parameters in Registry
http://asksomeone.net/tcpxp.html
• Windows NT TCP/IP by Karanjit s Siyan
• Data Communications, Computer Networks and Open
Systems by Fred Halsall