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Chapter 1 Introduction to Routing and Packet Forwarding CIS 82 Routing Protocols and Concepts Rick Graziani Cabrillo College Last.

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Presentation on theme: "Chapter 1 Introduction to Routing and Packet Forwarding CIS 82 Routing Protocols and Concepts Rick Graziani Cabrillo College Last."— Presentation transcript:

1 Chapter 1 Introduction to Routing and Packet Forwarding CIS 82 Routing Protocols and Concepts Rick Graziani Cabrillo College Last Updated: 2/16/2009

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. For a copy of this presentation and access to my web site for other CCNA, CCNP, and Wireless resources please me for a username and password.   Web Site:

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.

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:  ISBN-13:

5 5 Topics 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 Path Determination and Switching Function  Packet Fields and Frame Formats  Best Path and Metrics  Equal Cost Load Balancing  Path Determination  Switching Function CLI Configuration and Addressing  Implementing Basic Addressing Schemes  Basic Router Configuration Building the Routing Table  Introducing the Routing Table  Directly Connected Networks  Static Routing  Dynamic Routing  Routing Table Principles

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 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, Leonard Kleinrock and the first IMP.

8 8 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

9 9 Router interfaces:  LAN  WAN

10 10 Routers Determine the Best Path The router’s primary responsibility:  Determining the best path  Forwarding packets toward their destination

11 11 Routers Determine the Best Path Routing table  Determines best path.  Best match between destination IP address and network address in routing table 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.

12 12 Router CPU and Memory 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  Management interfaces

13 13 Router physical characteristics

14 14 Cisco IOS - Internetwork Operating System Responsible for managing the hardware and software resources:  Allocating memory  Managing processes  Security  Managing file systems Many different IOS images. An IOS image is a file that contains the entire IOS for that router.  Router model  IOS features Example IPv6 or a routing protocol such as Intermediate System– to–Intermediate System (IS-IS).

15 15 Router Bootup Process (more in later course)

16 16 Bootup Process running-config IOS (running) startup-configIOS ios (partial) Bootup program

17 17 running-config IOS (running) startup-configIOS ios (partial) Bootup program Where is the permanent configuration file stored used during boot-up?NVRAM Where is the diagnostics software stored executed by hardware modules?ROM Where is the backup (partial) copy of the IOS stored?ROM Where is IOS permanently stored before it is copied into RAM? FLASH Where are the bootsystem commands stored which are used to locate the IOS? NVRAM

18 18 running-config IOS (running) startup-configIOS ios (partial) Bootup program ? ? ? ? ? ? ?

19 19 running-config IOS (running) startup-config IOS ios (partial) Bootup program startup-config IOS Bootup program ios (partial) running-config IOS (running)

20 20 1. ROM 1. POST 2. Bootstrap code executed 3. Check Configuration Register value (NVRAM) 0 = ROM Monitor mode 1 = ROM IOS = 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) Router Boot Process – Details (later)

21 21 Verify the router boot-up process show version command is used to view information about the router during the bootup process (later).

22 22 Ports and 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. Note: However, these terms are often used interchangeably in the industry and even with IOS output.

23 23 Management Ports 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.

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

25 25 Router Interfaces 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. FastEthernet 0/0 MAC: 0c00-3a44-190a /24 FastEthernet 0/0 MAC: 0c00-41cc-ae /16 Serial 0/ /24 Serial 0/ /24

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

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.

28 28 Routers at the Network Layer 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.

29 29 Routers Operate at Layers 1, 2, and 3

30 Path Determination and Switching Functions Packet Fields and Frame Formats Best Path and Metrics Equal Cost Load Balancing Path Determination Switching Function

31 31 Path Determination and Switching Functions The following sections focus on exactly what happens to data as it moves from source to destination.  Review the packet and frame field specifications  Discuss in detail how the frame fields change from hop to hop, whereas the packet fields remain unchanged

32 32 Ethernet Frame Layer 2 addresses:  Interface-to-Interface on the same network.  Changes as packet is decapsulated and encapsulated 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) IPv4 (Internet Protocol)

33 33 Best Path Router’s best-path to a network:  optimum or “shortest” path Routing protocol dependent Dynamic routing protocols use their own rules and metrics. 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. Example, a router will prefer a path that is one hop away over a path that is two hops away.

34 34 Best Path 1.5 Mbps 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

35 35 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. Equal Cost Load Balancing ? ? To reach the /24 network it is 2 hops via R2 and 2 hops via R /24

36 36 Equal-Cost Paths Versus Unequal- Cost Paths T1 T3 Can a router use multiple paths if the paths (cost, metric) to reach the destination network are not equal? Yes, if the routers are using the EIGRP routing protocol which supports unequal cost load balancing /24

37 37 Path Forwarding Packet forwarding involves two functions:  Path determination function  Switching function

38 38 Path Forwarding 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  Remote network  No route determined Directly connected network Router receives packet. Destination IP address matches a network on one of its directly connected networks. Packet is forwarded out that network.

39 39 Path Forwarding 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  Remote network  No route determined Remote network 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.

40 40 Path Forwarding 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  Remote network  No route determined 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)

41 41 Path Forwarding 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.

42 42 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 Dest. MAC 0B-31 Source MAC Type 800 Trailer Layer 2 Data Link Frame Dest. IP Source IP IP fields Data Layer 3 IP Packet Dest. MAC Source MAC 0A-10 Type 800 Trailer Path Forwarding

43 43 Remember: Encapsulation Now, let’s do an example… Destination IP Address Source IP Address Other IP fields Data Destination Address Source Address Type DataTrailer Layer 3 IP Packet Layer 2 Data Link Frame Current Data Link Address of Host or Router’s exit interface Next hop Data Link Address of Host or Router’s interface These change from host to router, router to router, and router to host. These addresses do not change!

44 44 This is just a summary. The details will be shown next! Now for the details… Dest. MAC Source MAC 0A-10 Type 800 Trailer Layer 2 Data Link Frame Dest. IP Source IP IP fields Data Layer 3 IP Packet Dest. MAC 0B-31 Source MAC Type 800 TrailerDest. IP Source IP IP fields DataDest. Add FF-FF Source AddType 800 Trailer

45 45 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 Dest. MAC Source MAC 0A-10 Type 800 Trailer Layer 2 Data Link Frame Dest. IP Source IP IP fields Data Layer 3 IP Packet

46 46 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 /24 has next-hop-ip address of 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 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 Packet is encapsulated into a new data link (Ethernet) frame. Dest. MAC 0B-31 Source MAC Type 800 Trailer Layer 2 Data Link Frame Dest. IP Source IP IP fields Data Layer 3 IP Packet Dest. MAC Source MAC 0A-10 Type 800 Trailer

47 47 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 /24 has next-hop-ip address of 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. Dest. Add FF-FF Source AddType 800 Trailer Layer 2 Data Link Frame Dest. IP Source IP IP fields Data Layer 3 IP Packet Dest. MAC 0B-31 Source MAC Type 800 Trailer

48 48 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 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 Packet is encapsulated into a new data link (Ethernet) frame and sent out the interface. Dest. MAC 0B-20 Source MAC 0C-22 Type 800 Trailer Layer 2 Data Link Frame Dest. IP Source IP IP fields Data Layer 3 IP Packet Dest. Add FF-FF Source AddType 800 Trailer

49 49 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? Layer 2 Data Link Frame Dest. IP Source IP IP fields Data Layer 3 IP Packet Dest. MAC 0B-20 Source MAC 0C-22 Type 800 Trailer

50 50 The summary once again! Dest. MAC Source MAC 0A-10 Type 800 Trailer Layer 2 Data Link Frame Dest. IP Source IP IP fields Data Layer 3 IP Packet Dest. MAC 0B-31 Source MAC Type 800 TrailerDest. IP Source IP IP fields DataDest. Add FF-FF Source AddType 800 Trailer

51 CLI Configuration and Addressing Implementing Basic Addressing Schemes Basic Router Configuration

52 52 Learning IOS: Lab (Cabrillo College Version) Networking LabNetLabPacket Tracer

53 53 Establishing a HyperTerminal session (next week) 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. Rollover cable Console port Com1 or Com2 serial port Terminal or a PC with terminal emulation software Router

54 54 Establishing a Terminal session Important: A console connection is not the same as a network connection! = Tera Term HyperTerminal (comes with Windows) Putty

55 55 Terminal Connection No network connection needed Console Port When do you need to use a console connection to the router? What software do you need? What cable and ports do you use? When there is not a network connection to the router (can’t use telnet). Tera Term, HyperTerminal, Putty, etc. PC: Serial port & Router: Console Port Rollover or Console Cable Serial

56 56 C:\> telnet C:\> ping Ethernet Connection Network connection needed When can you use a network connection to the router? What software/command do you need? What cable and ports do you use? When should you not use a network connection to configure the router? When there is a network connection to the router (telnet). TCP/IP, Terminal prompt (DOS), Tera Term, etc. PC & Router: Ethernet NIC Ethernet straight-through cable When the change may disconnect the telnet connection. NIC

57 57 Terminal Connection No network connection needed Console Port C:\> telnet C:\> ping Ethernet Connection Network connection needed Serial NIC

58 58 NetLab

59 59 NetLab Basic Router Pod

60 60 Your Interfaces may differ R1# show ip interface brief Interface IP-Address OK? Method Status Protocol FastEthernet0/ YES manual up up FastEthernet0/ YES manual up up Serial0/ YES manual up up Serial0/1 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

61 61 Learning IOS: Lab (Cabrillo College Version)

62 62 Command Overview (partial list from lab) Router>user mode Router> enable Router#privilege mode Router# configure terminal Router(config)# exit Router# config t Router(config)# hostname name Router(config)# enable secret passwordprivilege password Router(config)# line console 0console password Router(config-line)# password password Router(config-line)# login Router(config)# line vty 0 4telnet password Router(config-line)# password password Router(config-line)# login Router(config)# banner motd # message #banner Router(config)# interface type numberconfigure interface Router(config-if)# ip address address mask Router(config-if)# description description Router(config-if)# no shutdown

63 63 Other Commands Router# copy running-config startup-config Router# show running-config Router# show ip route Router# show ip interface brief Router# show interfaces

64 64 Different Modes IOS commands must be entered in the correct mode. Router# hostname R1 ^ % Invalid input detected at '^' marker. Router# configure terminal Router(config)# hostname R1 R1(config)#

65 65 Serial Connectors 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. Smart Serial “Older” Serial

66 66 Serial Connectors Router is typically a DTE device. The DTE cable is connected to the serial interface on the router to a CSU/DSU device (DCE). DTE Cable DCE Cable

67 67 WAN Interface Configuration R1(config)# interface Serial0/0 R1(config-if)# ip address R1(config-if)# description Link to R2 R1(config-if)# clock rate DCE Only R1(config-if)# no shutdown

68 68 Unsolicited Messages from IOS The IOS often sends unsolicited messages  Does not affect the command  Can cause you to lose your place when typing. R1(config)# interface fastethernet0/0 R1(config-if)# ip address R1(config-if)# no shutdown R1(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 Interface FastEthernet0/0, changed state to upption R1(config-if)#

69 69 Unsolicited Messages from IOS To keep the unsolicited output separate from your input, enter line configuration mode for the console port and add the logging synchronous R1(config)# line console 0 R1(config-line)# logging synchronous R1(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 Interface FastEthernet0/0, changed state to up R1(config-if)# description

70 70 LAN Interface Configuration R1(config)# interface FastEthernet0/0 R1(config-if)# ip address R1(config-if)# description R1 LAN R1(config-if)# no shutdown Fa0/1

71 71 Each Interface Belongs to a Different Network R1(config)# interface FastEthernet0/1 R1(config-if)# ip address overlaps with FastEthernet0/0 R1(config-if)# no shutdown overlaps with FastEthernet0/0 FastEthernet0/1: incorrect IP address assignment Fa0/ / /24 Same Network!

72 72 Each Interface Belongs to a Different Network R1# show ip interface brief Interface IP-Address OK? Method Status Protocol FastEthernet0/ YES manual up up Serial0/ YES manual up up FastEthernet0/ YES manual administratively down down Serial0/1 unassigned YES unset administratively down down Fa0/1

73 73 Verifying Interfaces R1# show interfaces FastEthernet0/0 is up, line protocol is up (connected) Hardware is Lance, address is 0007.eca (bia 00e0.f7e4.e47e) Description: R1 LAN Internet address is /24 MTU 1500 bytes, BW 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 Serial0/0 is up, line protocol is up (connected) Hardware is HD64570 Description: Link to R2 Internet address is /24 MTU 1500 bytes, BW 1544 Kbit, DLY usec, rely 255/255, load 1/255 Encapsulation HDLC, loopback not set, keepalive set (10 sec) Last input never, output never, output hang never

74 74 Verify Router Configuration R1# show running-config ! version 12.3 ! hostname R1 ! interface FastEthernet0/0 description R1 LAN ip address ! interface Serial0/0 description Link to R2 ip address clock rate ! banner motd ^C ****************************************** WARNING!! Unauthorized Access Prohibited!! ****************************************** ^C ! line con 0 password cisco login line vty 0 4 password cisco login ! end Note: shutdown is the default. no shutdown does not show in the configuration.

75 75 Save Configuration R1# copy running-config startup-config R1# show startup-config Using 728 bytes ! version 12.3 ! hostname R1 ! interface FastEthernet0/0 description R1 LAN ip address ! interface Serial0/0 description Link to R2 ip address clock rate ! banner motd ^C ****************************************** WARNING!! Unauthorized Access Prohibited!! ****************************************** ^C line con 0 password cisco login line vty 0 4 password cisco login ! end

76 Building the Routing Table Introducing the Routing Table Directly Connected Networks

77 77 Show Routing Table R1# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - 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 - ODR P - periodic downloaded static route Gateway of last resort is not set C /24 is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0

78 78 Introducing the Routing Table Routing table is a data file in RAM that is used to store route information about:  Directly connected networks  Remote networks R1# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - 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 - ODR P - periodic downloaded static route Gateway of last resort is not set C /24 is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0

79 79 Introducing the Routing Table Directly connected interfaces contain the exit interface (more later) R1# show ip route C /24 is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0 Exit Interfaces

80 80 Introducing the Routing Table 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. R1# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP C /24 is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0 Directly Connected Networks

81 81 Introducing 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: (later)  Dynamic routing protocol  Static routes R1# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP C /24 is directly connected, FastEthernet0/0 C /24 is directly connected, Serial0/0 Remote Network

82 Chapter 1 Introduction to Routing and Packet Forwarding CIS 82 Routing Protocols and Concepts Rick Graziani Cabrillo College


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