ccna r&s-19-operating cisco routers

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Routing and Switching 200-120 19 - Operating Cisco Routers

Operating Cisco Routers


Agenda

Installing Cisco Routers Enabling IPv4 Support on Cisco Routers

Installing Cisco Routers



when you buy a Cisco LAN switch, you can just plug in all the Ethernet cables, power on the switch, and by default, the switch works The Cisco routers used by companies require at least some configuration before the router will start routing IPv4 packets In particular, the router needs to be told what interfaces to use and what IP address to use on each of those interfaces Routers collectively provide the main feature of the network layer—the capability to forward packets end to end through a network



Installing Enterprise Routers

A typical enterprise network has a few centralized sites as well as lots of smaller remote sites To support devices at each, the network includes at least one LAN switch at each site. Additionally, each site has a router, which 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 through the connection to the central site




Generic Enterprise Network Diagram




More Detailed Cabling Diagram for the Same Enterprise Network



Cisco Integrated Services Routers

Product vendors, including Cisco, typically provide several different types of router hardware, including some routers that just do routing, with other routers that serve other functions in addition to routing.

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 Router has modular slots that allow you to add small cards called WAN interface cards (WIC) that add other interfaces



Cisco Integrated Services Routers

Photos of a Model 2901 Cisco Integrated Services Router (ISR)



Physical Installation To install a router, follow these steps: Step 1. Connect any LAN cables to the LAN ports Step 2. If using an external CSU/DSU, connect the router’s serial interface to the CSU/DSU and the CSU/DSU to the line from the telco. Step 3. If using an internal CSU/DSU, connect the router’s serial interface to the line from the telco. Step 4. Connect the router’s console port to a PC (using a rollover cable), as needed, to configure the router. Step 5. Connect a power cable from a power outlet to the power port on the router. Step 6. Power on the router.

Note that the steps for router installation match those for a switch, except that Cisco enterprise routers typically have an on/off switch, while switches do not



Installing Internet Access Routers

Routers play a key role in SOHO networks, connecting the LAN-attached end-user devices to a highspeed Internet access service After they are connected to the Internet, SOHO users can send packets to and from their enterprise network at their company or school



A SOHO Installation with a Separate Switch, Router, and Cable Modem

Devices in a SOHO Network with High-Speed CATV Internet



A SOHO Installation with a Separate Switch, Router, and Cable Modem

An Internet connection that uses CATV or digital subscriber line (DSL) needs a device that converts between the Layer 1 and 2 standards used on the CATV cable or DSL line and the Ethernet used by the router These devices, commonly called cable modems and DSL modems, respectively, convert electrical signals between an Ethernet cable and either CATV or DSL The purpose of the cable modem and DSL modem is similar to a CSU/DSU on a serial link A CSU/DSU converts between the Layer 1 standards used on a telco’s WAN circuit and a serial cable’s Layer 1 standards DSL modems convert between the DSL signals over a home telephone line and Ethernet



A SOHO Installation with an Integrated Switch, Router, and DSL Modem A single SOHO device today includes all of these functions:

Router Switch Cable or DSL modem Wireless access point Hardware-enabled encryption



A SOHO Installation with an Integrated Switch, Router, and DSL Modem

SOHO Network, Using Cable Internet and an Integrated Device

Enabling IPv4 Support on Cisco Routers



A quick informal count of a recent IOS version listed around 5000 CLI commands Many Cisco router and Cisco switch administrative features use the exact same commands. For example, the console, vty, and enable passwords all work the same



Comparisons Between the Switch CLI and Router CLI

However, a couple of topics work differently with the router CLI as compared to the switch CLI, namely:

The configuration of IP addresses differs in some ways Routers have an auxiliary (Aux) port, intended to be connected to an external modem and phone line to allow remote users to dial in to the router, and access the CLI, by making a phone call

Cisco Layer 2 switches support the show mac address-table command, but these Layer 2–only devices do not support the show ip route command, which lists IP routes. Some Cisco routers can do IP routing but not Layer 2 switching, so they support the show ip route command but not the show mac address-table command.



Router Interfaces

One minor difference between Cisco switches and routers is that routers support a much wider variety of interfaces Cisco routers use serial interfaces to connect to a serial link. Each point-to-point serial link can then use High-Level Data Link Control (HDLC, the default) or Point-to-Point Protocol (PPP)

The show ip interface brief displays a list with one line per interface, with some basic information, including the interface IP address and interface status The show interfaces command lists the interfaces, but with a large amount of information per interface



Router Interfaces

Listing the Interfaces in a Router



Router Interfaces



Interface Status Codes

Interface Status Codes and Their Meanings



Interface Status Codes

Typical Combinations of Interface Status Codes



Router Interface IP Addresses

Most Cisco router interfaces default to a disabled (shutdown) state and should be enabled with the no shutdown interface subcommand Cisco routers do not route IP packets in or out an interface until an IP address and mask have been configured; by default, no interfaces have an IP address and mask Cisco routers attempt to route IP packets for any interfaces that are in an up/up state and that have an IP address/mask assigned. (Routers enable IPv4 routing by default due to a default ip routing global configuration command.)




Configuring IP Addresses on Cisco Routers




Verifying IP Addresses on Cisco Routers




Key Commands to List Router Interface Status



Bandwidth and Clock Rate on Serial Interfaces

WAN links can run at a wide variety of speeds To deal with the wide range of speeds, routers physically slave themselves to the speed as dictated by the CSU/DSU through a process called clocking As a result, 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, the CSU/DSU sends clock pulses over the cable to the router, and the router reacts to the clocking signal To build a serial link in a home lab, the routers can use serial interface cards that normally use an external CSU/DSU, and make a serial link, without requiring the expense of two CSU/DSUs




Serial Link in Lab




Using the correct cabling works, as long as you add one command: the clock rate interface subcommand This command tells that router the speed at which to transmit bits on a serial link like The clock rate command is not needed on real serial links, because the CSU/DSU provides the clocking Without any real CSU/DSUs on the link, the router with the DCE cable must supply that clocking function, and the clock rate command tells the router to provide it




Some versions of IOS will automatically implement a default clock rate 20000000 command on serial interfaces that have a DCE cable connected to them We can verify that router can use the clock rate command with the show controllers command. This command confirms that Router has a V.35 DCE cable connected The clock rate command does not allow just any speed to be configured. However, the list of speeds does vary from router to router




Router R1 Configuration with the clock rate Command



Router Auxiliary (Aux) Port

While both routers and switches have a console port to allow administrative access, routers have an extra physical port called an auxiliary (Aux) port The Aux port typically serves as a means to make a phone call to connect into the router to issue commands from the CLI The Aux port works like the console line, except that the Aux port is typically connected through a cable to an external analog modem, which in turn connects to a phone line. The engineer uses a PC, terminal emulator, and modem to call the remote router. Aux ports can be configured beginning with the line aux 0 command to reach aux line configuration mode



Operational Status with the show version Command

Command References


Command References

Operating Cisco Routers


References 1) Cisco Systems, Inc, www.cisco.com/ 2) Wendell Odom ,”Cisco CCENT/CCNA ICND1 100-101 Official Cert Guide”, Cisco Press, USA, 2013

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