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Introduction to Routing and Packet Forwarding

Introduction to Routing and Packet Forwarding. Routing Protocols and Concepts – Chapter 1. Objectives. Identify a router as a computer with an OS and hardware designed for the routing process. Demonstrate the ability to configure devices and apply addresses.

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Introduction to Routing and Packet Forwarding

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  1. Introduction to Routing and Packet Forwarding Routing Protocols and Concepts – Chapter 1

  2. Objectives • Identify a router as a computer with an OS and hardware designed for the routing process. • Demonstrate the ability to configure devices and apply addresses. • Describe the structure of a routing table. • Describe how a router determines a path and switches packets

  3. Router as a Computer • Describe the basic purpose of a router -Computers that specialize in sending packets over the data network. They are responsible for interconnecting networks by selecting the best path for a packet to travel and forwarding packets to their destination • Routers are the network center -Routers generally have 2 connections: -WAN connection (Connection to ISP) -LAN connection

  4. Router as a Computer • Data is sent in form of packets between 2 end devices • Routers are used to direct packet to its destination

  5. Router as a Computer • Routers examine a packet’s destination IP address and determine the best path by enlisting the aid of a routing table

  6. Router as a Computer • Router components and their functions” • CPU - Executes operating system instructions • Random access memory (RAM) - Contains the running copy of configuration file. Stores routing table. RAM contents are lost when power is off • Read-only memory (ROM) - Holds diagnostic software used when router is powered up. Stores the router’s bootstrap program. • Non-volatile RAM (NVRAM) - Stores startup configuration. This may include IP addresses (Routing protocol, Hostname of router) • Flash memory - Contains the operating system (Cisco IOS) • Interfaces - There exist multiple physical interfaces that are used to connect network. Examples of interface types: -Ethernet / fast Ethernet interfaces -Serial interfaces -Management interfaces

  7. Router Bootup Process • Four Basic Tasks: • POST • Bootstrap • Cisco IOS • Configuration

  8. Router Bootup Process • Step 1: Performing the POST (Power On Self Test) • Stored in and run from ROM • Executes diagnostics from ROM on several hardware components (CPU,RAM, NVRAM). • After the POST is successful, the router executes the bootstrap program. POST Perform POST ROM

  9. Router Bootup Process • Step 2: Loading the Bootstrap Program • The program is copied from ROM into RAM. • Executed by CPU. • Its main task is to locate the Cisco IOS and load it into RAM. Bootstrap Load Bootstrap ROM

  10. Router Bootup Process Cisco IOS Locate IOS Flash • Step 3: Locating Cisco IOS • Typically stored in flash memory, but it can be stored in other places such as a TFTP server. • If a full IOS image cannot be located, a scaled-down version of the IOS is copied from ROM. • This version of IOS is used to help diagnose any problems and to try to load a complete version of the IOS into RAM. • Step 4: Load Cisco IOS • Copy the IOS into RAM for execution. TFTP Server

  11. Router Bootup Process Configuration Locate the Configuration File NVRAM • Step 5: Locating the Configuration File • The IOS searches for the previously saved configuration commands (startup configuration file), in NVRAM. • If there is no startup configuration, the program searches for a TFTP server. • If a TFTP server cannot be found, the router will accept input from the Console.(setup-mode configuration) TFTP Server Console

  12. Router Bootup Process Execute the Configuration Fileor enter “Setup” mode. • Step 6: Loading the Startup Configuration or Entering Setup Mode. • If a startup configuration file is found in NVRAM, the IOS loads it into RAM as the running-config file and executes the commands. • If the startup configuration file cannot be located, the IOS prompts the user to enter setup mode.

  13. Router Bootup Process POST Perform POST ROM Bootstrap Load Bootstrap ROM Cisco IOS Locate IOS Flash TFTP Server Load IOS Configuration Locate the Configuration File NVRAM TFTP Server Execute the Configuration Fileor enter “Setup” mode. Console

  14. Router as a Computer • Major phases to the router boot-up process • Test router hardware Power-On Self Test (POST) Execute bootstrap loader • Locate & load Cisco IOS software -Locate IOS -Load IOS • Locate & load startup configuration file or enter setup mode -Bootstrap program looks for configuration file

  15. Router as a Computer • Verify the router boot-up process: -The show version command is used to view information about the router during the bootup process. Information includes: • Platform model number • Image name & IOS version • Bootstrap version stored in ROM • Image file name & where it was loaded from • Number & type of interfaces • Amount of NVRAM • Amount of flash • Configuration register

  16. Verifying the Router Bootup Process • The show versioncommand is used to view information about the router during the bootup process.

  17. Router Interfaces • Port: • Normally means one of the management ports used for administrative access. • Interface: • Normally refers to interfaces that are capable of sending and receiving user traffic. However, these terms are often used interchangeably in the industry

  18. Router Ports Console • Console Port: • Used to connect a terminal or most likely a PC running terminal emulator software, • Must be used during initial configuration of the router. • Auxiliary (AUX) Port: • Not all routers have auxiliary ports. • At times, can be used similarly to a console port and can also be used to attach a modem. Auxiliary

  19. Router Interfaces Ethernet • Router Interface is a physical connector that enables a router to send or receive packets • Each interface connects to a separate network • Consist of socket or jack found on the outside of a router • Routers have multiple interfaces used to connect to multiple networks. • Types of router interfaces: -Ethernet -Fastethernet -Serial . Serial

  20. Every Interface on a router: - Belongs to a different network - Is a host on a different network - Has anIP address on a different network Router Interfaces

  21. Interfaces Belonging to Different Networks • LAN Interfaces: • Ethernet • Fast Ethernet • Used to connect the router to the LAN. • Similar to the connection to a PC’s Ethernet NIC. • Layer 2 MAC address • Participates in the Ethernet LAN like any other host. • Typically an RJ-45 jack . • Router to Switch: straight-through cable. • Router to Router: cross-over cable. • PC to Router: cross-over cable.

  22. Interfaces Belonging to Different Networks • WAN Interfaces: • Serial • Used to connect routers to external networks, usually over a larger geographical distance. • The Layer 2 encapsulation can be different types (PPP, Frame Relay, HDLC). • Similar to LAN interfaces, each WAN interface has its own IP address and subnet mask, making it a member of a specific network.

  23. The clock rate serves to synchronize the receiver on the other side of the link. • Each clock pulse signals the transmission of a bit. • Note that only DCE interfaces are generating/sending a clock

  24. Router as a Computer • Routers and the Network Layer Routers use destination IP address to forward packets • The path a packet takes is determined after a router consults information in the routing table. • After router determines the best path • Packet is encapsulated into a frame • Frame is then placed on network medium in form of Bits

  25. Router as a Computer • Routers Operate at Layers 1, 2 & 3 • Router receives a stream of encoded bits • Bits are decoded and passed to layer 2 • Router de-encapsulates the frame • Remaining packet passed up to layer 3 -Routing decision made at this layer by examining destination IP address • Packet is then re-encapsulated & sent out outbound interface

  26. Configure Devices and Apply Addresses • When designing a new network or mapping an existing network you must provide the following information in the form of a document: -Topologydrawing that Illustrates physical connectivity • Address table that provides the following information: • Device name • Interfaces used • IP addresses • Default gateway

  27. Basic Router Configuration

  28. Configure Devices and Apply Addresses • Basic Router Configuration • A basic router configuration should contain the following: -Router name- Host name should be unique -Banner - At a minimum, banner should warn against unauthorized use: A login banner is displayed whenever someone connects to the router by telnet or console connections. -Passwords - Use strong passwords -Interface configurations- Specify interface type, IP address and subnet mask. Describe purpose of interface. Issue no shutdown command. If DCE serial interface issue clock rate command. • After entering in the basic configuration the following tasks should be completed -Verify basic configuration and router operations. -Save the changes on a router

  29. Configure Devices and Apply Addresses • Verify Basic Router Configuration -Issue the show running-config command -Save the basic router configuration by Issuing the copy running-config startup-config command -Additional commands that will enable you to further verify router configuration are: • Show running-config- Displays configuration currently in RAM • Show startup-config- Displays configuration file NVRAM • Show IP route- Displays routing table • Show interfaces- Displays all interface configurations • Show IP int brief- Displays abbreviated interface configuration information

  30. Basic Router Configuration

  31. Configure Devices and Apply Addresses • Basic Router Configuration • User mode allows you to view the state of the router, but does not allow you to modify its configuration.Router> • The enable command is used to enter the privileged EXEC mode. This mode allows the user to make configuration changes on the router. The router prompt will change from a ">" to a "#" in this mode.Router>enable Router#Router#config t Router(config)#hostname R1

  32. Basic Router Configuration • User and Privileged Modes: • Configure Host Name: Router>user mode Router>enable Router#privilege mode Router#configure terminal Router(config)# exit Router#config t Router(config)# hostname [name]

  33. Basic Router Configuration • Configure Passwords: Privilege password: Router(config)# enable secret [password] Console password: Router(config)# line console 0 Router(config-line)# password [password] Router(config-line)# login Telnet password: Router(config)# line vty 0 4 Router(config-line)# password [password] Router(config-line)# login

  34. Basic Router Configuration • Configure Banner Message of the Day: Router(config)# banner motd [# message #]

  35. Basic Router Configuration • Configure Interfaces: • Each interface MUST belong to a different network. Router(config)# interface [type][number] Router(config-if)# ip address [address] [mask] Router(config-if)# no shutdown

  36. Basic Router Configuration • Verifying the Configuration: • Saving the Configuration: (copy from to) Router# show running-config Router# show ip route Router# show ip interface brief Router# show interfaces Router# copy running-config startup-config

  37. Basic Router Configuration

  38. Basic Router Configuration – R1 • Configure Host Name: Router> Router>enable Router# Router#configure terminal Router(config)#hostname R1 R1(config#)

  39. Basic Router Configuration – R1 • Configure Privilege Password: R1(config#)enable secret class

  40. Basic Router Configuration – R1 • Configure Passwords: R1(config)#line console 0 R1(config-line)#password cisco R1(config-line)#login R1(config)#line vty 0 4 R1(config-line)#password cisco R1(config-line)#login R1(config-line)#exit

  41. Basic Router Configuration – R1 • Configure Banner Message of the Day: • Enter a text message. End with the character‘#’. R1(config)#banner motd # ****************************************** WARNING!! Unauthorized Access Prohibited!! ****************************************** # R1(config)#

  42. Basic Router Configuration – R1 • WAN Interface Configuration: R1(config)#interface Serial0/0/0 R1(config-if)#ip address 192.168.2.1 255.255.255.0 R1(config-if)#clockrate64000(DCE Only) R1(config-if)#no shutdown

  43. Basic Router Configuration – R1 • LAN Interface Configuration: R1(config)#interface FastEthernet0/0 R1(config-if)#ip address 192.168.1.1 255.255.255.0 R1(config-if)#no shutdown

  44. Basic Router Configuration – R1 • Each Interface Belongs to a Separate Network: R1(config)#interface FastEthernet0/1 R1(config-if)#ip address 192.168.1.2 255.255.255.0 192.168.1.0 overlaps with FastEthernet0/0 R1(config-if)#no shutdown 192.168.1.0 overlaps with FastEthernet0/0 FastEthernet0/1: incorrect IP address assignment

  45. Basic Router Configuration – R1 • Verifying Basic Router Configuration: R1#show running-config ! version 12.3 ! hostname R1 ! interface FastEthernet0/0 description R1 LAN ip address 192.168.1.1 255.255.255.0 ! interface Serial0/0

  46. Basic Router Configuration – R1 • Saving the Configuration: R1#copy running-config startup-config R1#show startup-config ! version 12.3 ! hostname R1 ! interface FastEthernet0/0 description R1 LAN ip address 192.168.1.1 255.255.255.0 !

  47. Basic Router Configuration – R1 • Show the Routing Table: R1# show ip route Codes: C - connected, S - static . . (Output Omitted) . Gateway of last resort is not set C 192.168.1.0/24 is directly connected, FastEthernet0/0 C 192.168.2.0/24 is directly connected, Serial0/0/0

  48. Routing Table Structure • Routing Table is data file stored in ram and contains information about: • Directly connected networks- network that is directly attached to one of the router interfaces. • Remotely connected networks- this is a network that is not directly connected to a particular router • Detailed informationabout the networks include source of information, network address & subnet mask, and Ip address of next-hop router • Show ip routecommand is used to view a routing table

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