Monday, May 14, 2012

OSI Layers

Open Systems Interconnection.
Links
http://en.wikipedia.org/wiki/OSI_model

Please Do Not Throw Sausage Pizza Away.
  1. Physical
  2. Data
  3. Network
  4. Transport
  5. Session
  6. Presentation
  7. Application
  1. Physical - Bits
  2. Data Link - Frames
  3. Network - Packets
  4. Transport - Segments

Physical

Physical Topology. Moves Bits between devices. NIC Card. Hub. Repeaters. Wires.

Data Link

Logical Topology. Framing. Error Detection, Notification (NOT Correction). Flow Control. Delivery on LAN using MAC, Physical Addresses. Switches and Bridges. Switches Break up Collision Domains. Data Frames have source and destination MAC Address in header. LLC (Logical Link Control) Header. MAC (Media Access Control) Header.

Network

Routed Protocols IP (Header) and IPV6 transport Data Packets through an internetwork (devices that aren't locally attached). Logical Addressing. Routing Protocols update neighboring routers with Route Update Packets. Examples are RIP Routing Information Protocol, EIGRP Enhanced Interior Gateway Routing Protocol, and OSPF Open Shortest Path First. Routers break up Broadcast Domains, will not forward broadcast or Multicast packets. Routing Table Holds Network Address, Interface, Metric

Transport

TCP, UDP (header). Reliable or Unreliable Delivery. Error Correction before re-transmit. Connection Oriented Communication. Virtual Circuit. SYN, SYN/ACK, ACK. Three way handshake. Flow Control. Receiver governs amt of data sent by sender by sending ack for each segment. Segments are ordered - delivered in the order they are transmitted. Window is the # of segments that can be sent without waiting for a Flow Control ack. Positive acknowledgement with retransmission.

Session

simplex, half duplex,full duplex.

Presentation

Translation. Compression. Encryption. EBCDIC to ASCII

Application

FTP, HTTP, SMTP, SNMP, Telnet, DNS, DHCP.
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Wednesday, April 11, 2012

IP Addresses

The Host ID of 0 is always reserved to represent the network itself. The Host ID of 255 is reserved for broadcasts to all hosts on network. The iana Has a list of all Class A Blocks by company. 127.0.0.0-127.255.255.255 is reserved for Loopback (localhost).

Classful network

Class 1st 4
Bits 		Network ID Range
xyz for Host Octets 		Network
Bit
Length 		# of
Networks 		# of
Hosts 		Host ID Range
wxy for Network Octets
A 0------- 001-126.x.y.z 8 126 16,777,214 w.1-254.1-254.1-254
B 10------ 128-191.1-254.y.z 16 16,384 65,534 w.x.1-254.1-254
C 110----- 192-223.1-254.1-254.z 24 2,097,152 254 w.x.y.1-254
D 1110---- 224-239.x.y.z wiki
E 1111---- 240-254.x.y.z

Subnetting

Supply the Subnet Mask OR CIDR (Classless InterDomain Routing) # and IP Address.
Network ID
Host ID
Hosts Allowed
IP Block Range Min
IP Block Range Max
Class
Default Subnet

Private Address Ranges

Use the following Private Address Ranges for use behined a Firewall, not on the public internet. They cannot be used on the public internet.
CIDR Subnet Mask Network ID Range
xyz for Host Octets 		Host ID Range
y for Network Octets 		IP Range
10.0.0.0/8 255.0.0.0 10.x.y.z 10.1-254.1-254.1-254 10.1.1.1
10.255.255.255
172.16.0.0/12 255.255.240.0 172.16.y.z 172.16.1-254.1-254 172.16.1.1
172.31.255.255
192.168.0.0/16 255.255.0.0 192.168.1-254.z 192.168.y.1-254 192.168.1.1
192.168.255.255
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