OSI Model

=Brief OSI Model=
 * OSI Layer Control information and Functions:

= SuperNetting =


 * A network that is formed from the combination of two or more networks (or subnets) with a common Classless Inter-Domain Routing (CIDR) prefix.
 * It must not contain other prefixes of networks that do not lie in the same routing path.
 * Also called Supernetting, Prefix Aggregation, Route Aggregation, or Route Summarization.

192.168.98.0 192.168.99.0 192.168.100.0 192.168.101.0 192.168.102.0 192.168.105.0
 * Steps for calculating a Supernet:


 * Addresses are converted to binary format:


 * Bits at which the common pattern of digits ends are located.
 * The number of common bits is counted.
 * The summary route is found by setting the remaining bits to zero,
 * It is followed by a slash and then the number of common bits.


 * The summarized route is 192.168.96.0/20. The subnet mask is 255.255.240.0.

192.168.96.0 192.168.97.0 192.168.103.0 192.168.104.0 192.168.106.0 192.168.107.0 192.168.108.0 192.168.109.0 192.168.110.0 192.168.111.0
 * This summarized route also contains networks that were not in the summarized group:


 * It must be assured that the missing network prefixes do not exist outside of this route.

Customer A will have the range 172.1.1.0 to 172.1.1.255 Customer B would receive the range 172.1.2.0 to 172.1.2.255 Customer C would receive the range 172.1.3.0 to 172.1.3.255, and so on.
 * Example:
 * An ISP is assigned a block of IP addresses by a regional Internet registry (RIR) of 172.1.0.0 to 172.1.255.255.
 * The ISP might then assign subnetworks to each of their downstream clients, e.g:
 * Instead of an entry for each of the subnets 172.1.1.x and 172.1.2.x, etc., the ISP could aggregate the entire 172.1.x.x address range and advertise the network 172.1.0.0/16 on the Internet community, which would reduce the number of entries in the global routing table.

= Misc =

Encapsulated in an IP Packet(Protocol no 89) Uses Acknowledgement
 * OSPF is a layer 4 protocol


 * RIP is a layer 7 protocol(uses UDP port 512)


 * BGP is a layer 7 protocol (uses Port no 179)


 * A PC can have only 1 Default Gateway configured. Other Interfaces will generally not have any default gateway.


 * References: