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Open Shortest Path First (OSPF) Protocol:

It is a Link-State dynamic routing protocol used primarily in large networks. It routes packets within an AS (Autonomous System) – Interior gateway protocol (IGP). OSPF networks as assigned an Area identifier (32 bit length). The area identifier can be same as the IP address. OSPF can handle duplicate ip addresses without any conflict.

OSPF does not use UDP or TCP but rather directly encapsulated into IP datagrams.

OSPF areas include Backbone area (area 0), Stub area, not so stubby area (NSSA).

Border Gateway Protocol (BGP):

It is a path-vector based dynamic protocol that is widely used in ISP. It is an exterior gateway protocol (EGP)

WAN (Wide Area Network) types

There are 5 major WAN technologies available

  1. Point to Point Link
  2. Circuit Switched Network
  3. Packet Switched Network
  4. High Level Data Link control (HDLC)
  5. Synchronous Data Link control (SDLC)

Point to Point Link

Uses a public career for establishing WAN connectivity

Technology Details
SLIP (Serial Line IP)
  1. Enables serial devices such as modems to connect to remote network
  2. Asynchronous
  3. Slow speed
  4. Little or no security
Point to Point Protocol (PPP)
  1. Successor of SLIP
  2. Asynchronous and Synchronous operation
  3. More security features than SLIP
Point to Point tunneling protocol
  1. Relies on PAP,CHAP or EAP to provide encryption
  2. Developed by Microsoft
  3. Used in VPNs
Layer 2 Forwarding protocol
  1. Used in VPN with PPP
  2. Little or no security
  3. Developed by CISCO
Layer 2 Tunneling protocol
  1. Used in VPN
  2. Uses IPSec for encryption
  3. Uses UDP port 1701

Circuit Switched Network

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WAN (Wide Area Network) Circuits




64 Kbits/Sec


1.544 Mbits/Sec or 2.048 Mbits/Sec


44.736 Mbits/Sec


1.544 Mbits/Sec


44.736 Mbits/Sec

E1 (Used in Europe)

2.048 Mbits/Sec

E3 (Used in Europe)

34.368 Mbits/Sec

OC-1 (Synchronous Optical WAN)

51.84 Mbits/Sec

OC-3 (Synchronous Optical WAN)

155.52 Mbits/Sec

OC-12 (Synchronous Optical WAN)

622.08 MbitsSec

OC-48 (Synchronous Optical WAN)

2.488 Gbits/Sec

OC-192 (Synchronous Optical WAN)

9.9 Gbits/Sec

WLAN (Wireless LAN protocols)

IEEE 802.11 defines how data packets are transmitted over air.




54 Mbits/Sec, 5 GHz


11 Mbits/Sec, 2.4 GHz


54 Mbits/Sec, 2.4 GHz


600 Mbits/Sec 5 or 2.4 GHz


WLANs use Access Points to connect nodes to Internet.

WLANs typically use WPA2 (WiFi Procted Access) protocol to secure communication.

Lan Protocols

LAN (Local Area Network) can use several Network Protocols to define the Network. These protocols are defined at the OSI Data Link Layer

Protocol Cable used Topology Media Access Advantages Disadvantages
Ethernet Twisted Pair or Fiber Optic Star CSMA/CD Fast; Easy setup and maintenance Possible Collision issues
Token Ring Twisted Pair Ring Token Passing Low error rate Slow (4 or 16 Mbps)
FDDI Fiber Optic (Dual counter rotating ring) Ring Token Passing Low error rate. Redundancy.  Expensive
ARCNet Coaxial Star Token Passing Predicable Network Performance Slow. (Almost extinct)

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OSI Data Link Layer

The second layer in OSI model is the Data Link, a very important layer in ensuring Network connectivity and data delivery. Main functions of Data Link Layer are:

  1. Define Network Protocol (Ex. Ethernet, Token Ring etc)
  2. Ensure Data is delivered to the correct device across Network

Data Link Layer has two sub layers in them

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Networking Equipment in OSI Physical Layer

In OSI Physical layer the following Network Equipment’s are involved.

  1. Network Interface Card
  2. Medium (Cables and Connectors)
  3. Repeaters
  4. Hubs

Network Interface Cards:

NICs connect a computer to the Network. They can be integrated to the Motherboard or can be a separate Card (PCI,ISA etc).


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It transports 1 petabit/sec with 100,000 servers talking to each other at 10Gbits/sec. Yes it is sick. This is how Google achieved that feat.

It is no brainer. With the amount of data google indexes (last time I checked, it is all the data from a small network called Internet), there is no way traditional Data Centers and Network Infrastructure can deliver. The underpinning technology that makes companies like Google take giant leap in Network design is SDN aka Software Defined Networking.

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