Notes Odom, Chapter 13 Operating Cisco Routers Flashcards Set:

Transcription

1 EDTECH 552 (SP11) Susan Ferdon Notes Odom, Chapter 13 Operating Cisco Routers Flashcards Set: Bandwidth Boot field Clock rate Configuration register IOS image POST ROMMON RxBoot A reference to the speed of a networking link. Its origins come from earlier communications technology in which the range, or width, of the frequency band dictated how fast communications could occur. The low-order 4 bits of the configuration register in a Cisco router. The value in the boot field in part tells the router where to look for a Cisco IOS image to load. The speed at which a serial link encodes bits on the transmission medium. In Cisco routers, a 16-bit, user-configurable value that determines how the router functions during initialization. In software, the bit position is set by specifying a hexadecimal value using configuration commands. A file that contains the IOS (internetwork Operating System). Power-on self-test The process on any computer, including routers and switches, in which the computer hardware first runs diagnostics on the required hardware before even trying to load a bootstrap program. ROM Monitor A shorter name for ROM Monitor, which is a low-level operating system that can be loaded into Cisco routers for several seldom needed maintenance tasks, including password recovery and loading a new IOS when Flash memory has been corrupted. A limited-function version of IOS stored in ROM in some older models of Cisco routers, for the purpose of performing some seldom needed low-level functions, including loading a new IOS into Flash memory when

2 Bootstrap Program Flash has been deleted or corrupted. A simple computer program that activates a more complicated system of programs. In the start up process, a small program initializes and tests that a basic requirement of hardware, peripherals and external memory devices are connected. It then loads a program from one of them and passes control to it, thus allowing the loading of larger programs (such as an operating system). From an old expression "to pull oneself up by one's bootstraps." Routers differ from switches in terms of core purposes. Switches forward Ethernet frames by comparing the frame s destination MAC address to the switch s MAC address table. Routers forward packets by comparing the destination IP address to the router s IP routing table. Cisco routers and switches use the same CLI. (p. 399) Installing Cisco Routers Installing Enterprise Routers To support devices at each site (the computers, IP phones, printers, and other devices), the network includes at least one LAN switch at each site and a router that connects to the LAN switch and to some WAN link. The WAN link provides connectivity from each remote site, back to the central site, and to other sites via the connection to the central site. CSU/DSU hardware resides outside the router or is integrated into the router s serial interface. Telco cable goes directly into router (RJ-48 connector) or goes into CSU/DSU with serial cable to router s serial port.

3 Cisco Integrated Services Routers (p. 406) Rather than require multiple separate devices at one site, as shown in Figure 13-2, Cisco offers single devices that act as both router and switch, and provide other functions (VoIP, VPN) as well. Cisco has several router product series called Integrated Services Routers (ISR), with the name emphasizing the fact that many functions are integrated into a single device. Steps to install a router generally follow the same steps used for installation of LAN switches install the cables for the interfaces, connect the console (as needed), and connect the power. Most switches do not have a power on/off switch once the switch is connected to power, the switch is on. Cisco routers do have on/off switches. For details of physical installation, see page 406. Installing Internet Access Routers Routers play a key role in SOHO networks, connecting the LAN-attached end-user devices to a high-speed Internet access service. A SOHO Installation with a Separate Switch, Router, and Cable Modem The main differences between SOHO connection and enterprise relate to the Internet connection. An Internet connection that uses CATV or DSL needs a device (Cable/DSL modem) that converts between the Layer 1 and 2 standards used on the CATV cable or DSL line, and the Ethernet used by the router. For details of physical installation, see page 408. Cisco Router IOS CLI Cisco routers use the same switch IOS CLI as described in Chapter 8. However, because routers and switches perform different functions, the actual commands differ in some cases. Comparisons between Switch CLI and Router CLI Most configuration commands are the same. Differences: o Configuration of IP addresses (switch configures one IP address for switch, router configures multiple IP address for various ports). o Questions asked in setup mode differ.

4 o Routers have auxiliary (Aux) port which connects to external modem or phone line to allow remote users to dial into router and access CLI. o Beyond these three items, router and switch CLI differ just because the devices do different things. Router Interfaces The CCNA exams refer to two general types of physical interfaces on routers: Ethernet interfaces and serial interfaces. o Ethernet interface - any type of Ethernet interface. The name referenced by the CLI refers to the fastest speed possible on the interface. o Serial interfaces used to support point-to-point leased lines and Frame Relay access links that use the same underlying Layer 1 standards. The network engineer chooses which data link layer protocol to use - HDLC or PPP for leased lines, Frame Relay for Frame Relay connections - and configures the router to use the correct data link layer protocol. o Routers use numbers to distinguish between the different interfaces of the same type. The interface numbers might be a single number, or two numbers separated by a slash, or three numbers separated by slashes. o To view info about interfaces: show ip interface brief brief list of interfaces show protocols type number brief details about a particular interface show interfaces a lot of detail about each interface including stats and flow show interfaces type number to see details for just that interface Interfaces Status Codes Four combinations of settings exist for the status codes when

5 troubleshooting a network. Table 13-3 (p. 413) lists the four combinations, along with an explanation of the typical reasons why an interface would be in that state. Router Interface IP Addresses For proper operation, for every interface a router should use for forwarding IP packets, the router needs an IP address. To configure the address and mask, simply use the ip address address mask interface subcommand. Bandwidth and Clock Rate on Serial Interfaces (p. 415) To deal with the wide range of WAN speeds, routers physically slave themselves to the speed as dictated by the CSU/DSU through a process called clocking. Routers can use serial links without the need for additional configuration or autonegotiation to sense the serial link s speed. The CSU/DSU knows the speed and sends clock pulses over the cable to the router. The router reacts blindly to the CSU/DSU clocking signal. The physical details of how clocking works prevent routers from sensing and measuring the speed used on a link with CSU/DSUs. So, routers use two different interface configuration commands that specify the speed of the WAN link connected to a serial interface, namely the clock rate and bandwidth interface subcommands. o The clock rate command dictates the actual speed used to transmit bits on a serial link, but only when the physical serial link is actually created with cabling in a lab. o The clock rate speed interface subcommand sets the rate in bits per second on the router that has the DCE cable plugged into it. The bandwidth command tells IOS the speed of the link, in kilobits per second, regardless of whether the router is supplying clocking. Used for documentation purposes, does not change the speed at which bits are transmitted. If configuration does not match actual speed, the router changes the bandwidth settings. Router Auxiliary (Aux) Ports (p. 417) Auxiliary Port is connected via a cable to external analog modem which connects to a phone line. Then a PC, terminal emulator, and modem are used to call the remote router. Once connected, the terminal emulator is used to access the router CLI, starting in user mode as usual. Aux ports can be configured beginning with the line aux 0 command to reach aux line configuration mode (login, password, etc.). Initial Configuration Mode (p. 417)

6 Basically the same as setting up a switch (see list on page 417). The main difference between the setup mode on switches and routers relates to the information requested while in setup mode. For example, routers need to know the IP address and mask for each interface on which you want to configure IP, whereas switches have only one IP address. Upgrading Cisco IOS Software and the Cisco IOS Software Boot Process (p. 420) You may need a later release upgrade process might include copying a newer IOS image into Flash memory, configuring the router to tell it which IOS image to use, and deleting the old one. Alternately, you could copy a new image to a TFTP server, with some additional configuration on the router to tell it to get the new IOS from the TFTP server the next time the router is reloaded. Upgrading a Cisco IOS Software Image into Flash Memory (p. 420) Flash memory is rewriteable, permanent storage, which is ideal for storing files that need to be retained when the router loses power. Also, there are no moving parts in Flash memory, so there is a smaller chance of failure as compared with disk drives. Steps to follow are listed on page 421. Use the show flash command to verify the contents of Flash memory, as demonstrated in Example 13-6 (p. 423). Once the new IOS has been copied into Flash, the router must be reloaded to use the new IOS image. The Cisco IOS Software Boot Sequence (p. 423) When a router powers on it follows these four steps: o 1. Perform power-on self test (POST) to discover hardware components and make sure they are working properly. o 2. Copy bootstrap program from ROM into RAM and run it. o 3. Bootstrap determines which IOS image to load into RAM, loads it, then turns over router control to newly loaded OS. o 4. IOS finds the configuration file (typically startup-config in NVRAM) and loads it into RAM as the running-config. There is no real advantage to storing the initial configuration anywhere else except NVRAM. The IOS image is typically a compressed file so that it consumes less space in Flash memory. The router decompresses the IOS image as is it loaded into RAM. The Three Router Operating Systems (p. 425)

7 Cisco routers can use a different OS to perform some troubleshooting, to recover router passwords, and to copy new IOS files into Flash when Flash has been inadvertently erased or corrupted. o ROMMON ROM Monitor, used in old and new routers o RxBoot boot Boot ROM, used only in older routers o boot helper Boot ROM, used only in older routers The Configuration Register (p. 425) A 16-bit number that can be set on any Cisco router which control different settings for some low-level operating characteristics of the router. For example, the console runs at a speed of 9600 bps by default, but that console speed is based on the default settings of a couple of bits in the configuration register. You can set the configuration register value with the config-register global configuration command. Engineers set the configuration register to different values for many reasons, but the most common are to help tell the router what IOS image to load, and in the password recovery process. The value is automatically saved but is not used until the next time the router is reloaded. The show version command shows the configuration register s current value and, if different, the value that will be used once the router is reloaded. On most Cisco routers, the default configuration register setting is hexadecimal How a Router Chooses Which OS to Load (p. 426) A router chooses the OS to load based on the low-order 4 bits in the configuration register and the details configured in any boot system global configuration commands found in the startup-config file. The low-order 4 bits (the 4th hex digit) in the configuration register are called the boot field, with the value of these bits being the first value a router examines when choosing which OS to try and load. o If Boot Field = 0, use ROMMON OS o If Boot Field = 1, use load first OS in Flash memory o If Boot Field = 2, try boot system commands in startup-config until one works. If none works, load first OS in Flash memory. Once the router succeeds in loading one of the referenced IOS images, the process is complete, and the router can ignore the remaining boot system commands. Note: Each new file in Flash gets a higher number, boot looks for lowest number (older) files first. The boot system commands need to refer to the exact file that the router should load.

8 If no OS is found, the router will send broadcasts looking for a TFTP server, guess at a filename for the IOS image, and load an IOS image (assuming that a TFTP server is found). In practice it is highly unlikely to work. The final step is to simply load ROMMON, which is designed in part to provide tools to recover from these unexpected types of problems. The show version Command and Seeing the Configuration Register s Value (p. 429) The show version command supplies a wide variety of information about a router, including both the current value of the configuration register and the expected value at the next reload of the router. Detailed list can be found on page 429.

9 Do I Know This Already Quiz, Chapter 13 - pp TOPIC Q# 1 st Try 2 nd Try Answer 1 B, E Installing Cisco Routers 2 B, C 3 A, C 4 B B, D Cisco Router IOS CLI 5 B, C C 6 B, E C, E 7 B B, C Upgrading Cisco IOS software 8? D, F and the Cisco IOS Software Boot Process 9 A Q4: You just bought two Cisco routers for use in a lab, connecting each router to a different LAN switch with their Fa0/0 interfaces. You also connected the two routers serial interfaces using a back-to-back cable. Which of the following steps is not required to be able to forward IP on both routers interfaces? a. Configuring an IP address on each router s FastEthernet and serial interfaces b. Configuring the bandwidth command on one router s serial interface c. Configuring the clock rate command on one router s serial interface d. Setting the interface description on both the FastEthernet and serial interface of each router Answer: B and D Explanation: A is required because data cannot be sent without a destination IP address and if the router doesn t have an address, it will not be found. C is required because a device must be the master for clocking in order for them to communicate. Typically a CSU/DSU provides clocking, but if it s just routers, one must act as DCE (Data Communications Equipment provides clocking) and other act as DTE (Data Terminal Equipment receive clocking). B is not required because the routers aren t online it s a direct connection. D is not required because there is no ISP to provide bandwidth, speed, etc.

10 Q5: The output of the show ip interface brief command on R1 lists interface status codes of down and down for interface Serial 0/0. Which of the following could be true? a. The shutdown command is currently configured for that interface. b. R1 s serial interface has been configured to use Frame Relay, but the router on the other end of the serial link has been configured to use PPP. c. R1 s serial interface does not have a serial cable installed. d. Both routers have been cabled to a working serial link (CSU/DSUs included), but only one router has been configured with an IP address. Answer: C Explanation: I was considering both downs as being independent from one another. If the first (physical) is down then the next (data link) must also be down so only C would apply to this scenario. Q6: Which of the following commands does not list the IP address and mask of at least one interface? a. show running-config b. show protocols type number c. show ip interface brief d. show interfaces e. show version Answer: C and E Explanation: Commands Does not list IP Address (answer) o Show version (E) Displays IOS version, ROM version, router uptime system image file name, boot method, number and type of interfaces installed, amount of RAM, NVRAM and flash. Config register. Also, see textbook, page 429. Does list IP Address o Show running-config (A) Displays current config running in RAM. Includes host name, passwords, interface IP addresses, routing prtocol activated, DHCP and NAT configuration. Must be issued in EXEC mode. o Show protocols type number (B) routed protocols and net_addresses of interfaces. I disagree with text: I think the answer should be D, not C.

11 o Book says C does not show IP address, but info I found contradicts that: Show ip interface brief (C) Displays all interfaces with IP addess with interface status (up/down/admin down) and line protocol status (up/down). o Book says D does list IP address, but info I found contradicts that: show interfaces (D) Displays one or all interfaces with line (protocol) status, bandwidth, delay, reliability, encapsulation, duplex and I/O statistics. o Either way, my answer was wrong because I had only E (show version). Q7: Which of the following is different on the Cisco switch CLI as compared with the Cisco router CLI? a. The commands used to configure simple password checking for the console b. The number of IP addresses configured c. The types of questions asked in setup mode d. The configuration of the device s host name e. The configuration of an interface description Answer: B and C Explanation: I answered B. I didn t choose C, types of questions asked in setup mode, because I remembered them being very similar. However, there are enough differences to make that answer also correct. Q8: Which of the following could cause a router to change the IOS that is loaded when the router boots? a. reload EXEC command b. boot EXEC command c. reboot EXEC command d. boot system configuration command e. reboot system configuration command f. configuration register Answer: D and F Explanation: I had no clue so I didn t even answer the question. Not A, B, or C because those are execute commands they don t change configuration or IOS, they just load or reload what s there. Not E (reboot) because that will reload what was already running. D and E are correct - A router chooses

12 the OS to load based on the low-order 4 bits in the configuration register and the details configured in any boot system global configuration commands found in the startup-config file (page 426).