Router

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Router

  1. 1. Router
  2. 2. Router • A router is an electronic device that interconnects two or more computer networks • Works at Layer 3, Network Layer in an intelligent manner • Can connect different network segments, whether they are in the same building or even on the opposite side of the globe
  3. 3. Router : Network Layer Interface X MEDIUM X MEDIUM PHYSICAL LAYER PHYSICAL LAYER DATA LINK LAYER DATA LINK LAYER NETWORK LAYER ROUTER NETWORK LAYER
  4. 4. Router • Works in LAN, WAN environments • Allows access to resources by selecting the best path • Can interconnect different networks • Changes packet size and format to match the requirements of the destination network
  5. 5. Internetworking with a Router IEEE 802.3 Sub-network IEEE 802.5 Sub-network PC-NFS Sub-network Router
  6. 6. Devices and Layers PHYSICAL LAYER DATA LINK LAYER NETWORK LAYER Switches Routers Repeaters Switches Layer 1 Layer 2 Layer 3
  7. 7. Difference Between Routers, Switches and Hubs • Hubs – Simply provides the mechanical and electrical connections between the nodes • Switches – Examine the data packet for the destination address – Do not alter the data packets • Routers – Examine and alter the data packets – Perform protocol conversion
  8. 8. Delivery, Forwarding & Routing • Delivery – Refers to the way a packet is handled by the underlying networks under the control of the network layer.
  9. 9. Delivery, Forwarding & Routing • Forwarding – Refers to the way a packet is delivered to the next station.
  10. 10. Delivery, Forwarding & Routing • Routing – Refers to the way routing tables are created to help in forwarding.
  11. 11. Functions of a Router • Two primary functions: • Determine the 'best path' • Share details of routes with other routers
  12. 12. Router has • Routing Table - a database which keeps track of the routes to networks and the associated costs • Routing Protocol - uses a special algorithm to route data across a network eg RIP
  13. 13. Format of Routing Table Mask Network Address Next-hop Address Interface Flags Reference Count Use
  14. 14. Format of Routing Table • Mask – This field defines the mask applied for the entry.
  15. 15. Format of Routing Table • Network Address – Defines the network address to which the packet is finally delivered.
  16. 16. Format of Routing Table • Next-hop Address – Defines the address of the next-hop router to which the packet is delivered.
  17. 17. Format of Routing Table • Interface – Shows the name of the interface.
  18. 18. Format of Routing Table • Flags – U(up): If this flag is not present, it means that the router is down. – G(gateway): Destination is in another network. – H(host-specific): Indicates that the entry in the Network Address field is a host- specific address.
  19. 19. Flags Contd. – D(added by redirection): Indicates that the routing information for this destination has been added to the host routing table by a redirection message from ICMP. – M(modified by redirection): Indicates that the routing information for this destination has been modified by a redirection message from ICMP.
  20. 20. Format of Routing Table • Reference Count – Gives the number of users of this route at the moment.
  21. 21. Format of Routing Table • Use – Shows the number of packets transmitted through this router for the corresponding destination.
  22. 22. Types of Routing Tables • Static Routing Table – – Routes are manually configured by a network administrator – Cannot update automatically when there is a change in the internet
  23. 23. Types of Routing Tables • Dynamic Routing Table – Adjusts automatically to changes in network topology – Uses one of the dynamic routing protocols such as RIP
  24. 24. RIP • Stands for Routing Information Protocol • RIP implementation considerations: – We are dealing with routers and networks(links) – Routers have routing tables; networks do not
  25. 25. RIP Implementation Considerations Contd. – The destination in a routing table is a network. •This means the first column defines a network address – Metric used is very simple; distance defined as no. of links to reach destination
  26. 26. RIP Implementation Considerations Contd. – Infinity is defined as 16 •Which means no route can have more than 15 hops – Next-node column defines the address of the router to which the packet is to be sent to reach its destination.
  27. 27. Router Hardware • Similarity with a PC: – A CPU – A memory – Ports & interfaces • Dissimilarity: – Routers are diskless
  28. 28. Router Motherboard
  29. 29. Router CPU • 50 MHz CPUs are generally used for small offices & homes. • For more powerful purposes, processors from Motorola, Silicon Graphics, etc. are used.
  30. 30. Router Memory • RAM/DRAM • NVRAM • Flash Memory • ROM
  31. 31. RAM/DRAM • Stands for random access memory/dynamic random access memory • Used by the router’s central processor to do its work • Cisco’s smallest router ships with a minimum of 16MB of DRAM
  32. 32. NVRAM • Stands for nonvolatile RAM – retains information after losing power • stores a copy of the router’s configuration file – enables the router to restart in its proper configuration in case of accidental shutdown
  33. 33. Flash memory • Originally developed by Intel • also nonvolatile • differs from NVRAM in that it can be erased and reprogrammed as needed • used to store one or more copies of the IOS software – Helps in upgrading IOS on all routers
  34. 34. ROM • Used to hold a so-called bootstrapprogram – which is a file that can be used to boot to a minimum configuration state after a catastrophe
  35. 35. Router Ports • Port means a physical connection through which I/O can pass – a serial port, for example

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