Cis82 e2-1-packet forwarding

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  • A router is a computer : CPU, RAM, ROM, Operating System The first router: used for the Advanced Research Projects Agency Network (ARPANET): IMP (Interface Message Processor) Honeywell 516 minicomputer that brought the ARPANET to life on August 30, 1969.
  • Routers forwarding packets (packet switching) : From the original source to the final destination . Selects best path based on destination IP address A router connects multiple networks: Interfaces on different IP networks Receives a packet on one interface and determines which interface to forward it towards its destination . The interface that the router uses to forward the packet can be: The network of the final destination of the packet The destination IP address of this packet A network connected to another router
  • Router interfaces: LAN WAN
  • The router’s primary responsibility: Determining the best path to send packets Forwarding packets toward their destination
  • The routing table is used to determine the best path. Examines the destination IP address searches for the best match with a network address in the router’s routing table. The routing table includes the exit interface to forward the packet. Router encapsulates the IP packet into the data-link frame of the outgoing or exit interface Packet is the forwarded toward its destination
  • CPU - Executes operating system instructions Random access memory (RAM) (RAM contents lost when power is off) running copy of configuration file. routing table ARP cache Read-only memory (ROM) Diagnostic software used when router is powered up. Router’s bootstrap program Scaled down version of operating system IOS Non-volatile RAM (NVRAM) Stores startup configuration. (including IP addresses, Routing protocol) 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
  • Responsible for managing the hardware and software resources of the router, including: Allocating memory Managing processes Security Managing file systems There are many different IOS images . An IOS image is a file that contains the entire IOS for that router. depending on the model and the features within the IOS. For example, some features can include the ability to run Internet Protocol version 6 ( IPv6 ) or a routing protocol such as Intermediate System–to–Intermediate System ( IS-IS ).
  • Step 1: POST (Power On Self Test) Executes diagnostics from ROM on several hardware components, including the CPU,RAM, NVRAM Step 2: Loading Bootstrap Program Copied from ROM into RAM Executed by CPU Main task is to locate the Cisco IOS and load it into RAM Step 3: Locating the 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: Loading the IOS Some of the older Cisco routers ran the IOS directly from flash Current models copy the IOS into RAM for execution Might see a string of pound signs (#) while the image decompresses. Step 5: Locating the Config File Bootstrap program searches for the startup configuration file (startup-config), in NVRAM. This file has the previously saved configuration commands and parameters, Step 6: Loading the Config File 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, prompt the user to enter setup mode If setup mode not used, a default running-config file is created
  • 1. ROM 1. POST 2. Bootstrap code executed 3. Check Configuration Register value (NVRAM) 0 = ROM Monitor mode 1 = ROM IOS 2 - 15 = startup-config in NVRAM 2. Check for IOS boot system commands in startup-config file (NVRAM) If boot system commands in startup-config a. Run boot system commands in order they appear in startup-config to locate the IOS b If boot system commands fail, use default fallback sequence to locate the IOS (Flash, TFTP, ROM) 3. Locate and load IOS , Default fallback sequence: No IOS boot system commands in startup-config a. Flash (sequential) b. TFTP server (netboot) - The router uses the configuration register value to form a filename from which to boot a default system image stored on a network server. c. ROM (partial IOS) or keep retrying TFTP depending upon router model - If no IOS located, get partial IOS version from ROM 4. Locate and load startup-config configuration a. If startup-config found, copy to running-config b. If startup-config not found, prompt for setup-mode c. If setup-mode bypassed, create a “skeleton” default running-config (no startup-config)
  • 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. Note : However, these terms are often used interchangeably in the industry and even with IOS output.
  • Console port - Most common of the management ports Used to connect a terminal, Or most likely a PC running terminal emulator software, No need for network access to that router. The console port 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 Can also be used to attach a modem. Note : Auxiliary ports will not be used in this curriculum.
  • Interface on Cisco routers refers to a physical connector on the router whose main purpose is to receive and forward packets . Routers have multiple interfaces used to connect to multiple networks which may mean: Various types of networks Different types of media and connectors . Different types of interfaces . Fast Ethernet interfaces for connections to different LANs Serial interfaces are used for WAN connections including T1 , DSL , and ISDN.
  • Every interface on the router: Belongs to a different network Is a host on a different IP network Have an IP address and subnet mask of a different network Cisco IOS will not allow two active interfaces on the same router to belong to the same network. Note: A single interface on a router can be used to connect to multiple networks; however, this is beyond the scope of this course and is discussed in a later course.
  • Examples: Ethernet and Fast Ethernet interfaces. Used to connect the router to the LAN, similar to how a PC’s Ethernet NIC. Layer 2 MAC address Participates in the Ethernet LAN the same way as any other hosts on that LAN. Example: Address Resolution Protocol ( ARP ): Maintains ARP cache for that interface Sends ARP requests when needed Responds with ARP replies when required Typically an RJ-45 jack (UTP). Router to switch: straight-through cable . Router to router via Ethernet interfaces, or PC’s NIC to router’s Ethernet interface: crossover cable .
  • Example: serial, ISDN, and Frame Relay interfaces. Used to connect routers to external networks, usually over a larger geographical distance. The Layer 2 encapsulation can be different types including: PPP Frame Relay HDLC (High-Level Data Link Control). Similar to LAN interfaces, each WAN interface has its own IP address and subnet mask, making it a member of a specific network. Note : MAC addresses are used only on Ethernet interfaces and are not on WAN interfaces. However, WAN interfaces use their own Layer 2 addresses depending on the technology. Layer 2 WAN encapsulation types and addresses are covered in a later course.
  • A router is considered a Layer 3 device because its primary forwarding decision is based on the information in the Layer 3 IP packet, specifically the destination IP address. \\ This is known as routing . When a router receives a packet, it examines the destination IP address. If the destination IP address does not belong to any of the router’s directly connected networks, the router must forward this packet to another router. R1 receives the packet Examines the packet’s destination IP address Searches the routing table Forwards the packet onto R2. R2 receives the packet Examines the packet’s destination IP address Searches its routing table Forwards the packet out its directly connected Ethernet network to PC2
  • A router makes its primary forwarding decision at Layer 3, But also participates in Layer 1 and Layer 2 processes. After a router has examined the destination IP address and consulted its routing table to make its forwarding decision, then forward that packet out the appropriate interface toward its destination. Encapsulate the Layer 3 IP packet into the data portion of a Layer 2 data-link frame appropriate for the exit interface. The Layer 2 frame will then be encoded into the Layer 1 physical signals used to represent these bits over the physical link. R1 receives the stream of bits on its interface. The bits passed up to Layer 2. R1 examines data-link frame’ s destination address to determine whether it matches the receiving interface. If match, the data portion of the frame, the IP packet, is then passed up to Layer 3 R1 makes its routing decision. R1 then reencapsulates the packet into a new Layer 2 data-link frame and forwards it out the outbound interface (bits). The new Layer 2 data-link address is associated with that of the interface of the next-hop router (or final destination IP address).
  • Layer 2 addresses: Interface-to-Interface on the same network. Used to send to the next hop router or final destination. Layer 2 source address: sending interface layer 2 address (if applicable) Layer 3 destination address: destination interface layer 2 address (if applicable). Changes from network to network. Layer 3 addresses: Original source layer 3 address (IP) Final destination layer 3 address (IP) Does not change (except with NAT, but this is not a concern of IP but an internal network process) As a packet travels from one networking device to another The Source and Destination IP addresses NEVER change The Source & Destination Layer 2 (MAC) addresses CHANGE as packet is forwarded from one router to the next. TTL field decrement by one until a value of zero is reached at which point router discards packet (prevents packets from endlessly traversing the network)
  • Router’s best-path determination involves evaluating multiple paths to the same destination network and selecting the optimum or “shortest” path to reach that network. Depends upon routing protocol. RIP uses hop count whereas OSPF uses bandwidth (Cisco’s implementation of OSPF). Dynamic routing protocols use their own rules and metrics to build and update routing tables. A metric is the quantitative value used to measure the distance to a given route. The best path to a network is the path with the lowest metric. For example, a router will prefer a path that is five hops away over a path that is ten hops away. Comparing Dynamic Routing Protocols: RIP and OSPF RIP uses hop count R1 to R3 Fewer links but much slower OSPF uses bandwidth R1 to R2 to R3 More routers but much faster links
  • What happens if a routing table has two or more paths with the same metric to the same destination network? ( equal-cost metric ) Router will perform equal-cost load balancing . The router will forward packets using the multiple exit interfaces as listed in the routing table. Static routes and all dynamic routing protocols perform equal cost load balancing. (More later)
  • Just in case you are wondering, a router can send packets over multiple networks even when the metric is not the same if it is using a routing protocol that has this capability. This is known as unequal-cost load balancing . EIGRP and IGRP are the only routing protocols that can be configured for unequal-cost load balancing. (More in CCNP courses)
  • Packet forwarding involves two functions: Path determination function Switching function Path determination function is the process of how the router determines which path to use when forwarding a packet. To determine the best path, the router searches its routing table for a network address that matches the packet’s destination IP address. One of three path determinations results from this search: Directly connected network : Packet is forwarded directly to the device with the packet’s destination IP address. Remote network : Packet is forwarded to another router. Remote networks can only be reached by forwarding packets to another router. No route determined: If the router does not have a default route, the packet is discarded. The router sends an Internet Control Message Protocol (ICMP) Unreachable message to the source IP address of the packet.
  • Packet forwarding involves two functions: Path determination function Switching function Path determination function is the process of how the router determines which path to use when forwarding a packet. To determine the best path, the router searches its routing table for a network address that matches the packet’s destination IP address. One of three path determinations results from this search: Directly connected network : Packet is forwarded directly to the device with the packet’s destination IP address. Remote network : Packet is forwarded to another router. Remote networks can only be reached by forwarding packets to another router. No route determined: If the router does not have a default route, the packet is discarded. The router sends an Internet Control Message Protocol (ICMP) Unreachable message to the source IP address of the packet.
  • Packet forwarding involves two functions: Path determination function Switching function Path determination function is the process of how the router determines which path to use when forwarding a packet. To determine the best path, the router searches its routing table for a network address that matches the packet’s destination IP address. One of three path determinations results from this search: Directly connected network : Packet is forwarded directly to the device with the packet’s destination IP address. Remote network : Packet is forwarded to another router. Remote networks can only be reached by forwarding packets to another router. No route determined: If the router does not have a default route, the packet is discarded. The router sends an Internet Control Message Protocol (ICMP) Unreachable message to the source IP address of the packet.
  • Packet forwarding involves two functions: Path determination function Switching function Path determination function is the process of how the router determines which path to use when forwarding a packet. To determine the best path, the router searches its routing table for a network address that matches the packet’s destination IP address. One of three path determinations results from this search: Directly connected network : Packet is forwarded directly to the device with the packet’s destination IP address. Remote network : Packet is forwarded to another router. Remote networks can only be reached by forwarding packets to another router. No route determined: If the router does not have a default route, the packet is discarded. The router sends an Internet Control Message Protocol (ICMP) Unreachable message to the source IP address of the packet.
  • Packet forwarding involves two functions: Path determination function Switching function Switching function is the process used by a router to accept a packet on one interface and forward it out another interface. A key responsibility of the switching function is to encapsulate packets in the appropriate data-link frame type for the outgoing data link. What does a router do with a packet received from one network and destined for another network? 1. Decapsulates the Layer 3 packet by removing the Layer 2 frame header and trailer 2. Examines the destination IP address of the IP packet to find the best path in the routing table 3. Encapsulates the Layer 3 packet into a new Layer 2 frame and forwards the frame out the exit interface
  • Packet forwarding involves two functions: Path determination function Switching function Switching function is the process used by a router to accept a packet on one interface and forward it out another interface. A key responsibility of the switching function is to encapsulate packets in the appropriate data-link frame type for the outgoing data link. What does a router do with a packet received from one network and destined for another network? 1. Decapsulates the Layer 3 packet by removing the Layer 2 frame header and trailer 2. Examines the destination IP address of the IP packet to find the best path in the routing table 3. Encapsulates the Layer 3 packet into a new Layer 2 frame and forwards the frame out the exit interface
  • From Host X to Router RTA Host X begins by encapsulating the IP packet into a data link frame (in this case Ethernet) with RTA’s Ethernet 0 interface’s MAC address as the data link destination address. How does Host X know to forward to packet to RTA and not directly to Host Y? IP Source and IP Destination Addresses are on different networks How does Host X know or get RTA’s Ethernet address? Checks ARP Table for Default Gateway IP Address and associated MAC Address. What if it there is not an entry in the ARP Table? Host X sends an ARP Request and RTA sends an ARP Reply
  • RTA 1. RTA examines Destination MAC address, which matches the E0 MAC address, so it copies in the frame. 2. RTA sees the Type field is 0x800, IP packet in the data field, a packet which needs to be routed. 3. RTA strips off the Ethernet frame. RTA looks up the Destination IP Address in its routing table. 192.168.4.0/24 has next-hop-ip address of 192.168.2.2 and an exit-interface of e1. Since the exit interface is on an Ethernet network, RTA must resolve the next-hop-ip address with a destination MAC address. 4. RTA looks up the next-hop-ip address of 192.168.2.2 in its ARP cache. If the entry was not in the ARP cache, the RTA would need to send an ARP request out e1. RTB would send back an ARP reply, so RTA can update its ARP cache with an entry for 192.168.2.2. 5. Packet is encapsulated into a new data link (Ethernet) frame.
  • RTB 1. RTB examines Destination MAC address, which matches the E0 MAC address, and copies in the frame. 2. RTB sees Type field, 0x800, IP packet in the data field, a packet which needs to be routed. 3. RTB strips off the Ethernet frame. RTB looks up the Destination IP Address in its routing table. 192.168.4.0/24 has next-hop-ip address of 192.168.3.2 and an exit-interface of Serial0. Since the exit interface is not an Ethernet network, RTB does not have to resolve the next-hop-ip address with a destination MAC address. When the interface is a point-to-point serial connection , (like a pipe), RTB encapsulates the IP packet into the proper data link frame, using the proper serial encapsulation (HDLC, PPP, etc.). The data link destination address is set to a broadcast (there’s only one other end of the pipe). 5. Packet is encapsulated into a new data link (serial, PPP) frame and sent out the link.
  • RTC 1. RTC copies in the data link (serial, PPP) frame. 2. RTC sees the Type field is 0x800, IP packet in the data field, a packet which needs to be routed. 3. RTC strips off the data link, serial, frame. RTC looks up the Destination IP Address in its routing table. RTC realizes that this Destination IP Address is on the same network as one of its interfaces and it can sent the packet directly to the destination and not another router. Since the exit interface is on an directly connected Ethernet network, RTC must resolve the destination ip address with a destination MAC address. 2. RTC looks up the destination ip address of 192.168.4.10 in its ARP cache. If the entry was not in the ARP cache, the RTC would need to send an ARP request out e0. Host Y would send back an ARP reply, so RTC can update its ARP cache with an entry for 192.168.4.10. 5. Packet is encapsulated into a new data link (Ethernet) frame and sent out the interface.
  • Host Y Layer 2: Data Link Frame 1. Host Y examines Destination MAC address, which matches its Ethernet interface MAC address, and copies in the frame. 2. Host Y sees the Type field is 0x800, IP packet in the data field, which needs to be sent to its IP process. 3. Host Y strips off the data link, Ethernet, frame and sends it to its IP process. Layer 3: IP Packet 4. Host Y’s IP process examines the Destination IP Address to make sure it matches its own IP Address. . If it does not, the packet will be dropped. 5. The packet’s protocol field is examined to see where to send the data portion of this IP packet: TCP, UDP or other? Layer 4: TCP, UDP or other?
  • Take the following steps to connect a terminal to the console port on the router: Connect the terminal using the RJ-45 to RJ-45 rollover cable and an RJ-45 to DB-9 or RJ-45 to DB-25 adapter. Configure the terminal or PC terminal emulation software for 9600 baud, 8 data bits, no parity, 1 stop bit, and no flow control.
  • Important: A console connection is not the same as a network connection!
  • 2500 have the “older,” larger serial interfaces Later Cisco routers use the smart serial interfaces which allows more data to be forwarded across fewer cable pins.
  • Router is typically a DTE device. The DTE cable is connected to the serial interface on the router to a CSU/DSU device (DCE).
  • 2500 have the “older,” larger serial interfaces Later Cisco routers use the smart serial interfaces which allows more data to be forwarded across fewer cable pins.
  • Router is typically a DTE device. The DTE cable is connected to the serial interface on the router to a CSU/DSU device (DCE).
  • The IOS often sends unsolicited messages Does not affect the command Can cause you to lose your place when typing.
  • To keep the unsolicited output separate from your input, enter line configuration mode for the console port and add the logging synchronous
  • Routing table is a data file in RAM that is used to store route information about: Directly connected Remote networks
  • The routing table contains network/next-hop associations The “next hop” is the IP address of a next-hop router. (coming) May also include an outgoing or exit interface (more later)
  • directly connected network is a network that is directly attached to one of the router interfaces. When a router’s interface is configured with an IP address and subnet mask, the interface becomes a host on that attached network. Active directly connected networks are added to the routing table.
  • A remote network is a network that is not directly connected to the router. A remote network is a network that can only be reached by sending the packet to another router. Remote networks are added to the routing table using a dynamic routing protocol or by configuring static routes. Dynamic routes are routes to remote networks that were learned automatically by the router, using a dynamic routing protocol. Static routes are routes to networks that a network administrator manually configured.
  • Cis82 e2-1-packet forwarding

    1. 1. Chapter 1Introduction to Routing andPacket Forwarding CIS 82 Routing Protocols and Concepts Rick Graziani Cabrillo College graziani@cabrillo.edu Spring 2012
    2. 2. This Presentation For detailed information see the notes section within this PowerPoint. This presentation is based on the Exploration course/book, Routing Protocols and Concepts. Notes section may contain additional details For a copy of this presentation and access to my web site for other CCNA, CCNP, and Wireless resources please email me for a username and password.  Email: graziani@cabrillo.edu  Web Site: www.cabrillo.edu/~rgraziani 2
    3. 3. Note This chapter contains mostly introductory material. Most of not all of this information will be explained in more detail in later chapters or later courses.  The bootup process and the IOS are examined in a later course. Do not worry or focus too much on the details for now. This will all be examined and explained in the following chapters. 3
    4. 4. For further information This presentation is an overview of what is covered in the curriculum/book. For further explanation and details, please read the chapter/curriculum. Book:  Routing Protocols and Concepts  By Rick Graziani and Allan Johnson  ISBN: 1-58713-206-0  ISBN-13: 978-58713-206-3 4
    5. 5. Topics Inside the Router  CLI Configuration and Addressing  Routers are computers  Implementing Basic  Router CPU and Memory Addressing Schemes  Internetwork Operating  Basic Router Configuration System  Building the Routing Table  Router Bootup Process  Router Ports and Interfaces  Introducing the Routing  Routers and the Network Table Layer  Directly Connected Path Determination and Networks Switching Function  Static Routing  Packet Fields and Frame  Dynamic Routing Formats  Routing Table Principles  Best Path and Metrics  Equal Cost Load Balancing  Path Determination  Switching Function 5
    6. 6. Inside the Router  Routers are computers  Router CPU and Memory  Internetwork Operating System  Router Bootup Process  Router Ports and Interfaces  Routers and the Network Layer
    7. 7. Routers are Computers Leonard Kleinrock and the first IMP.  A router is a computer:  The first router (ARPANET):  IMP (Interface Message Processor)  Honeywell 516 minicomputer  August 30, 1969. 7
    8. 8. Router physical characteristics 8
    9. 9.  Routers forwarding packets (packet switching):  From the original source to the final destination.  Selects best path A router connects multiple networks:  Interfaces on different IP networks 9
    10. 10.  Router interfaces:  LAN  WAN 10
    11. 11. Routers Determine the Best Path The router’s primary responsibility:  Determining the best path  Forwarding packets toward their destination 11
    12. 12. Routers Determine the Best Path IP Packet enters router’s Ethernet interface. Router examines the packet’s destination IP address. Router searches for a best match between packet’s destination IP address and network address in routing table. Using the exit-interface in the route, the packet is forwarded to the next router or the final destination. Routing table  Determines best path.  Best match between destination IP address and network 12 address in routing table
    13. 13. RouterCPU andMemory CPU - Executes operating system instructions Random access memory (RAM)  running copy of configuration file  routing table  ARP cache Read-only memory (ROM)  Diagnostic software used when router is powered up.  Router’s bootstrap program  Scaled down version of operating system IOS Non-volatile RAM (NVRAM)  Stores startup configuration. (including IP addresses, Routing protocol) 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 13 
    14. 14. Cisco IOS - InternetworkOperating System Many different IOS images.  An IOS image is a file that contains the entire IOS for that router. IOS features  Example IPv6 or a routing protocol such as Intermediate System–to–Intermediate System (IS-IS). 14
    15. 15. Router Bootup Process (more in later course) 15
    16. 16. Bootup Processrunning-config startup-config IOS Bootup programIOS (running) ios (partial) 16
    17. 17. Where is the permanent configuration file stored used during boot-up? NVRAM (B)Where is the diagnostics software stored executed by hardware modules? ROM (D)Where is the backup (partial) copy of the IOS stored? ROM (D)Where is IOS permanently stored before it is copied into RAM? FLASH (C)Where are all changes to the configuration immediately stored? RAM (A) A B C D running-config startup-config IOS Bootup program IOS (running) ios (partial) 17
    18. 18. ? ? ? ? ? ? ?running-config startup-config IOS Bootup programIOS (running) ios (partial) 18
    19. 19. startup-config B running-config A Bootup program D IOS C ios (partial) D IOS (running) A A B C Drunning-config startup-config IOS Bootup programIOS (running) ios (partial) 19
    20. 20. Router Boot Process –Details (later)1. ROM 1. POST 2. Bootstrap code executed 3. Check Configuration Register value (NVRAM) 0 = ROM Monitor mode 1 = ROM IOS 2 - 15 = startup-config in NVRAM2. Check for IOS boot system commands in startup-config file (NVRAM) If boot system commands in startup-config a. Run boot system commands in order they appear in startup-config to locate the IOS b If boot system commands fail, use default fallback sequence to locate the IOS (Flash, TFTP, ROM)3. Locate and load IOS, Default fallback sequence: No IOS boot system commands in startup-config a. Flash (sequential) b. TFTP server (netboot) - The router uses the configuration register value to form a filename from which to boot a default system image stored on a network server. c. ROM (partial IOS) or keep retrying TFTP depending upon router model - If no IOS located, get partial IOS version from ROM4. Locate and load startup-config configuration a. If startup-config found, copy to running-config b. If startup-config not found, prompt for setup-mode c. If setup-mode bypassed, create a “skeleton” default running-config (no startup-config) 20
    21. 21. Verify the router boot-up process show version command is used to view information about the router during the bootup process (later). 21
    22. 22. Ports and Interfaces Port - management ports used for administrative access Interface - capable of sending and receiving user traffic. Note: However, these terms are often used interchangeably. 22
    23. 23. ManagementPorts Console port  Terminal  PC running terminal emulator software  No need for network access  Used for initial configuration Auxiliary (AUX) port  Not all routers have auxiliary ports.  At times, can be used similarly to a console port  Can also be used to attach a modem.  Note: Auxiliary ports will not be used in this curriculum. 23
    24. 24. Router Interfaces Interfaces - Receive and forward packets.  Various types of networks  Different types of media and connectors.  Different types of interfaces. Fast Ethernet interfaces - LANs Serial interfaces - WAN connections including T1, DSL, and ISDN 24
    25. 25. Router Interfaces FastEthernet 0/0 MAC: 0c00-41cc-ae12 10.1.0.1/16 FastEthernet 0/0 MAC: 0c00-3a44-190a 192.168.1.1/24 Serial 0/0 Serial 0/1 172.16.1.1/24 172.16.1.2/24 Router Interface:  Different network  IP address and subnet mask of that network Cisco IOS will not allow two active interfaces on the same router to belong to the same network. 25
    26. 26. LAN Interfaces Ethernet and Fast Ethernet interfaces Connects the router to the LAN  Layer 2 MAC address  Participates in the Ethernet  Address Resolution Protocol (ARP):  Maintains ARP cache for that interface  Sends ARP requests when needed  Responds with ARP replies when required Typically an RJ-45 jack (UTP).  Router to switch: straight-through cable  Router to router: crossover cable 26
    27. 27. WAN Interfaces Point-to-Point, ISDN, and Frame Relay interfaces Connects routers to external networks. The Layer 2 encapsulation can be different types including:  PPP  Frame Relay  HDLC (High-Level Data Link Control). Note: MAC addresses are used only on Ethernet interfaces and are not on WAN interfaces. Layer 2 WAN encapsulation types and addresses are covered in a later course. 27
    28. 28. Routers attheNetworkLayer  Layer 3 device because its primary forwarding decision is based on the information in the Layer 3 IP packet (destination IP address).  This is known as routing. 28
    29. 29. Routers Operate at Layers 1, 2, and 3 29
    30. 30. Path Determination andSwitching Functions
    31. 31. Ethernet Frame IPv4 (Internet Protocol) Layer 2 addresses: Addressing PC/Router-to-PC/Router within a network Layer 3 addresses:  Original source layer 3 address (IP) to final destination layer 3 address (IP)  Does not change (unless NAT is used) 31
    32. 32. Best Path Which is path is my “best path”? RIP’s metric is hop count OSPF’s metric is bandwidth ? Router’s determine best-path to a network:  Depends on the routing protocol  A protocol used to between routers to determine “best path” Routing protocols use their own rules and metrics. A metric:  Quantitative value used to measure the distance to a given route. Best path:  Path with the lowest metric. 32
    33. 33. To reach the 192.168.1.0/24 network it is 2 hops via R2 and 2 hops via R4.Equal Cost ?LoadBalancing ? 192.168.1.0/24 What happens if a routing table has two or more paths with the same metric to the same destination network? (equal-cost metric) Router will perform equal-cost load balancing. 33
    34. 34. ? T1Equal-Cost Paths ?Versus Unequal- T3Cost Paths 192.168.1.0/24 Can a router use multiple paths if the paths (cost, metric) to reach the destination network are not equal? EIGRP routing protocol which supports unequal cost load balancing 34
    35. 35. Packet Forwarding Packet forwarding involves two functions: 1. Path determination function 2. Switching function 35
    36. 36. Path Determination Router receives packet. Destination IP address matches a network on one of its directly connected networks. Packet is forwarded out that network. Directly connected network  Path determination function is the process of how the router determines which path to use when forwarding a packet.  Router searches its routing table for match with packet’s destination IP address.  One of three path determinations results from this search:  Directly connected network  Remote network  No route determined 36
    37. 37. Path Determination Router receives packet. Destination IP address matches a remote network which can only be reached via another router. Packet is forwarded out that network to the next-hop router. Remote network 37
    38. 38. Path Determination Router receives packet. Destination IP address does NOT match any network in the router’s routing table. Packet is dropped. No route determined Does this mean the network does not exist? No, only that the router does not know about that network. (later) 38
    39. 39. Packet Forwarding: Switching Function Switching function is the process used by a router to:  Accept a packet on one interface and  Forward it out another interface Encapsulate the packet in the appropriate data-link frame type for the outgoing data link. 39
    40. 40. 192.168.4.10PathForwarding 192.168.1.10 Layer 2 Data Link Frame Layer 3 IP Packet Dest. MAC Source MAC Type Dest. IP Source IP IP Data Trailer 00-10 0B-31 0A-10 00-20 800 192.168.4.10 192.168.1.10 fields What does a router do with a packet received from one network and destined for another network? 2. Decapsulates the Layer 3 packet by removing the Layer 2 frame header and trailer 3. Examines the destination IP address of the IP packet to find the best path in the routing table 4. Encapsulates the Layer 3 packet into a new Layer 2 frame and forwards the frame out the exit interface 40
    41. 41. Remember: Encapsulation These addresses do not change! These change from Layer 3 IP Packet host to router, router to Destination IP Source IP Other IP Data router, and router to Address Address fields host. Layer 2 Data Link Frame Destination Source Type Data Trailer Address Address Current Data Link Address of Host orNext hop Data Router’s exit interfaceLink Address ofHost or Router’sinterface Now, let’s do an example… 41
    42. 42. Layer 2 Data Link Frame Layer 3 IP Packet Dest. MAC Dest. MAC Add Source MAC Add Type Dest. IP Source IP IP Data Trailer FF-FF 0B-31 00-10 00-20 0A-10 800 192.168.4.10 192.168.1.10 fields This is just a summary. The details will be shown next! Now for the details… 42
    43. 43. Layer 2 Data Link Frame Layer 3 IP PacketDest. MAC Source MAC Type Dest. IP Source IP IP Data Trailer00-10 0A-10 800 192.168.4.10 192.168.1.10 fields 43
    44. 44. Layer 2 Data Link Frame Layer 3 IP PacketDest. MAC Source MAC Source MAC Type Type Dest. IP Source IP IP Data Trailer Trailer00-100B-31 00-20 0A-10 800 800 192.168.4.10 192.168.1.10 fields RTA Routing Table RTA ARP Cache Network Hops Next-hop-ip Exit-interface IP Address MAC Address 192.168.1.0/24 0 Dir.Conn. e0 192.168.2.2 0B-31 192.168.2.0/24 0 Dir.Conn e1 192.168.3.0/24 1 192.168.2.2 e1 192.168.4.0/24 2 192.168.2.2 e1 44
    45. 45. Layer 2 Data Link Frame Layer 3 IP PacketDest. Add MAC Source Add MAC Type Dest. IP Source IP IP Data Trailer0B-31FF-FF 00-20 800 192.168.4.10 192.168.1.10 fields RTB Routing Table Network Hops Next-hop-ip Exit-interface 192.168.1.0/24 1 192.168.2.1 e0 192.168.2.0/24 0 Dir.Conn e0 192.168.3.0/24 0 Dir.Conn s0 192.168.4.0/24 1 192.168.3.2 s0 45
    46. 46. Layer 2 Data Link Frame Layer 3 IP PacketDest. Add Dest. MAC Source Add Source MAC Type Type Dest. IP Source IP IP Data TrailerFF-FF 0B-20 0C-22 800 800 192.168.4.10 192.168.1.10 fields RTC Routing Table RTC ARP Cache Network Hops Next-hop-ip Exit-interface IP Address MAC Address 192.168.1.0/24 2 192.168.3.1 s0 192.168.4.10 0B-20 192.168.2.0/24 1 192.168.3.1 s0 192.168.3.0/24 0 Dir.Conn s0 192.168.4.0/24 0 Dir.Conn e0 46
    47. 47. Layer 2 Data Link Frame Layer 3 IP PacketDest. MAC Source MAC Type Dest. IP Source IP IP Data Trailer0B-20 0C-22 800 192.168.4.10 192.168.1.10 fields 47
    48. 48. Layer 2 Data Link Frame Layer 3 IP Packet Dest. MAC Dest. MAC Add Source MAC Add Type Dest. IP Source IP IP Data Trailer FF-FF 0B-31 00-10 00-20 0A-10 800 192.168.4.10 192.168.1.10 fields The summary once again! 48
    49. 49. CLI Configuration and AddressingBefore we begin: Download: Packet Tracer File:  http://netacad.cabrillo.edu/curriculum/graziani/cis82/labs-e2/e2-1-5-2.p Download and Install Packet Tracer you have not done so already:  http://www.cabrillo.edu/~rgraziani/courses/cis81.html Download Lab:  http://netacad.cabrillo.edu/curriculum/graziani/cis82/labs-e2/en_ERouti 49
    50. 50. Hands-on LabsNetworking Lab: CTC Datacenter NetLab Check-out Pods Packet Tracer (Not for homework) 50
    51. 51. Establishing a HyperTerminal session (next week) Router Console port Terminal or a PC with Rollover cable terminal emulation software Com1 or Com2 serial portTake the following steps to connect a terminal to the console port on the router: Connect the terminal using the RJ-45 to RJ-45 rollover cable and an RJ-45 to DB-9 or RJ-45 to DB-25 adapter. Configure the terminal or PC terminal emulation software for 9600 baud, 8 data bits, no parity, 1 stop bit, and no flow control. 51
    52. 52. Establishing a Terminal session Tera Term HyperTerminal (comes with Windows) Putty = Important: A console connection is not the same as a network connection! 52
    53. 53. When do you need to use a console connection to the router? When there is not a network connection to the router (can’t use telnet). What software do you need? Tera Term, HyperTerminal, Putty, etc. What cable and ports do you use? PC: Serial port & Router: Console Port Rollover or Console Cable Terminal Connection No network connection needed Console PortSerial 53
    54. 54. C:> ping C:> telnet Ethernet Connection Network connection needed NIC When can you use a network connection to the router? When there is a network connection to the router (telnet).What software/command do you need? TCP/IP, Terminal prompt (DOS), Tera Term, etc.What cable and ports do you use? PC & Router: Ethernet NIC Ethernet straight-through cableWhen should you not use a network When the change may 54connection to configure the router? disconnect the telnet connection.
    55. 55. C:> ping C:> telnet Ethernet Connection Network connection needed NIC Terminal Connection No network connection needed Console PortSerial 55
    56. 56. Serial Connectors Smart “Older” Serial Serial 2500 have the “older,” larger serial interfaces Later Cisco routers use the smart serial interfaces which allows more data to be forwarded across fewer cable pins. 56
    57. 57. Serial Cables DCE Cable DTE Cable Router is typically a DTE device. The DTE cable is connected to the serial interface on the router to a CSU/DSU device (DCE). DCE Side DTE Side 57
    58. 58. WAN Interface ConfigurationR1(config)# interface Serial0/0R1(config-if)# ip address 192.168.2.1 255.255.255.0R1(config-if)# description Link to R2R1(config-if)# clock rate 64000 DCE OnlyR1(config-if)# no shutdown 58
    59. 59. Let’s do Lab 1.5.2 using Packet Tracer Download: Packet Tracer File:  http://netacad.cabrillo.edu/curriculum/graziani/cis82/labs-e2/e2-1-5-2.pkt Download Lab:  http://netacad.cabrillo.edu/curriculum/graziani/cis82/labs-e2/E2_Lab_1_5_2_cabrillo.doc 59
    60. 60. Your Interfaces may differR1# show ip interface briefInterface IP-Address OK? Method Status ProtocolFastEthernet0/0 192.168.1.1 YES manual up upFastEthernet0/1 192.168.1.2 YES manual up upSerial0/0 192.168.2.1 YES manual up upSerial0/1 unassigned YES manual up up FastEthernet 0 = FastEthernet 0/0 FastEthernet 1 = FastEthernet 0/1 = FastEthernet 1/0 Serial 0 = Serial 0/0 = Serial 0/0/0 Serial 1 = Serial 0/1 = Serial 0/0/1 60
    61. 61. Command Overview (partial list from lab)Router> user modeRouter> enableRouter# privilege modeRouter# configure terminalRouter(config)# exitRouter# config tRouter(config)# hostname nameRouter(config)# enable secret password privilege passwordRouter(config)# line console 0 console passwordRouter(config-line)# password passwordRouter(config-line)# loginRouter(config)# line vty 0 4 telnet passwordRouter(config-line)# password passwordRouter(config-line)# loginRouter(config)# banner motd # message # bannerRouter(config)# interface type number configure interfaceRouter(config-if)# ip address address maskRouter(config-if)# description descriptionRouter(config-if)# no shutdown 61
    62. 62. Other CommandsRouter# copy running-config startup-configRouter# show running-configRouter# show ip routeRouter# show ip interface briefRouter# show interfaces 62
    63. 63. Different ModesRouter# hostname R1 ^% Invalid input detected at ^ marker.Router# configure terminalRouter(config)# hostname R1R1(config)# IOS commands must be entered in the correct mode. 63
    64. 64. Serial Connectors Smart “Older” Serial Serial 2500 have the “older,” larger serial interfaces Later Cisco routers use the smart serial interfaces which allows more data to be forwarded across fewer cable pins. 64
    65. 65. Serial Connectors DCE Cable DTE Cable Router is typically a DTE device. The DTE cable is connected to the serial interface on the router to a CSU/DSU device (DCE). 65
    66. 66. WAN Interface ConfigurationR1(config)# interface Serial0/0R1(config-if)# ip address 192.168.2.1 255.255.255.0R1(config-if)# description Link to R2R1(config-if)# clock rate 64000 DCE OnlyR1(config-if)# no shutdown 66
    67. 67. Unsolicited Messages from IOSR1(config)# interface fastethernet0/0R1(config-if)# ip address 172.16.3.1 255.255.255.0R1(config-if)# no shutdownR1(config-if)# descri*Mar 1 01:16:08.212: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up*Mar 1 01:16:09.214: %LINEPROTO-5-UPDOWN: Line protocol on InterfaceFastEthernet0/0, changed state to upptionR1(config-if)# The IOS often sends unsolicited messages  Does not affect the command  Can cause you to lose your place when typing. 67
    68. 68. Unsolicited Messages from IOSR1(config)# line console 0R1(config-line)# logging synchronousR1(config-if)# descri*Mar 1 01:28:04.242: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up*Mar 1 01:28:05.243: %LINEPROTO-5-UPDOWN: Line protocol on InterfaceFastEthernet0/0, changed state to upR1(config-if)# description To keep the unsolicited output separate from your input, enter line configuration mode for the console port and add the logging synchronous 68
    69. 69. LAN Interface ConfigurationR1(config)# interface FastEthernet0/0R1(config-if)# ip address 192.168.1.1 255.255.255.0R1(config-if)# description R1 LANR1(config-if)# no shutdown Fa0/1 69
    70. 70. Each Interface Belongs to a Different NetworkR1(config)# interface FastEthernet0/1R1(config-if)# ip address 192.168.1.2 255.255.255.0192.168.1.0 overlaps with FastEthernet0/0R1(config-if)# no shutdown192.168.1.0 overlaps with FastEthernet0/0FastEthernet0/1: incorrect IP address assignment Fa0/1 192.168.1.1/24 192.168.1.2/24 Same Network! 70
    71. 71. Each Interface Belongs to a Different NetworkR1# show ip interface briefInterface IP-Address OK? Method Status ProtocolFastEthernet0/0 192.168.1.1 YES manual up upSerial0/0 192.168.2.1 YES manual up upFastEthernet0/1 192.168.1.2 YES manual administratively down downSerial0/1 unassigned YES unset administratively down down Fa0/1 71
    72. 72. Verifying InterfacesR1# show interfaces<some interfaces not shown>FastEthernet0/0 is up, line protocol is up (connected) Hardware is Lance, address is 0007.eca7.1511 (bia 00e0.f7e4.e47e) Description: R1 LAN Internet address is 192.168.1.1/24 MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, rely 255/255, load 1/255 Encapsulation ARPA, loopback not set ARP type: ARPA, ARP Timeout 04:00:00, Last input 00:00:08, output 00:00:05, output hang never Last clearing of “show interface” counters never Queueing strategy: fifo Output queue :0/40 (size/max) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 0 packets input, 0 bytes, 0 no buffer Received 0 broadcasts, 0 runts, 0 giants, 0 throttles<output omitted>Serial0/0 is up, line protocol is up (connected) Hardware is HD64570 Description: Link to R2 Internet address is 192.168.2.1/24 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input never, output never, output hang never<output omitted> 72
    73. 73. Verify Router ConfigurationR1# show running-config!version 12.3!hostname R1!interface FastEthernet0/0description R1 LAN Note: shutdown is theip address 192.168.1.1 255.255.255.0! default. no shutdown doesinterface Serial0/0 not show in the configuration.description Link to R2ip address 192.168.2.1 255.255.255.0clock rate 64000!banner motd ^C******************************************WARNING!! Unauthorized Access Prohibited!!******************************************^C!line con 0password ciscologinline vty 0 4password ciscologin!end 73
    74. 74. Save ConfigurationR1# copy running-config startup-configR1# show startup-configUsing 728 bytes!version 12.3!hostname R1!interface FastEthernet0/0description R1 LANip address 192.168.1.1 255.255.255.0!interface Serial0/0description Link to R2ip address 192.168.2.1 255.255.255.0clock rate 64000!banner motd ^C******************************************WARNING!! Unauthorized Access Prohibited!!******************************************^Cline con 0password ciscologinline vty 0 4password ciscologin!end 74
    75. 75. Building the Routing Table  Introducing the Routing Table  Directly Connected Networks
    76. 76. Show Routing TableR1# show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGPD - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter areaN1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGPi - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area* - candidate default, U - per-user static route, o - ODRP - periodic downloaded static routeGateway of last resort is not setC 192.168.1.0/24 is directly connected, FastEthernet0/0C 192.168.2.0/24 is directly connected, Serial0/0 76
    77. 77. Introducing the Routing TableR1# show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGPD - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter areaN1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGPi - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area* - candidate default, U - per-user static route, o - ODRP - periodic downloaded static routeGateway of last resort is not setC 192.168.1.0/24 is directly connected, FastEthernet0/0C 192.168.2.0/24 is directly connected, Serial0/0 Routing table is a data file in RAM that is used to store route information about:  Directly connected networks  Remote networks 77
    78. 78. Introducing the Routing TableR1# show ip route<output omitted>C 192.168.1.0/24 is directly connected, FastEthernet0/0C 192.168.2.0/24 is directly connected, Serial0/0 Exit Interfaces Directly connected interfaces contain the exit interface (more later) 78
    79. 79. Introducing the Routing TableR1# show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP<output omitted>C 192.168.1.0/24 is directly connected, FastEthernet0/0C 192.168.2.0/24 is directly connected, Serial0/0Directly ConnectedNetworks directly connected network is a network that is directly attached to one of the router interfaces. When a router’s interface is configured with an IP address and subnet mask, the interface becomes a host on that attached network. Active directly connected networks are added to the routing table. 79
    80. 80. Introducing the Routing TableR1# show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP<output omitted>C 192.168.1.0/24 is directly connected, FastEthernet0/0C 192.168.2.0/24 is directly connected, Serial0/0 Remote Network A remote network is a network that is not directly connected to the router. A remote network is a network that can only be reached by sending the packet to another router. Remote networks are added to the routing table using: (later)  Dynamic routing protocol  Static routes 80
    81. 81. Using NetLab 81
    82. 82. NetLab Basic Router Pod 82
    83. 83. Chapter 1Introduction to Routing andPacket Forwarding CIS 82 Routing Protocols and Concepts Rick Graziani Cabrillo College graziani@cabrillo.edu

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