ICND1 - 5. Routing
What is a default route?
Also known as the gateway of last resort, a default route is a special type of route with an all-0s network and network mask. The default route directs any packets for which a destination network is not specifically listed in the routing table. By default, if a router receives a packet to a destination network that is not in its routing table, it drops the packet. When a default route is specified, the router does not drop the packet. Instead, it forwards the packet to the IP address specified in the default route.
What is an example of a Layer 2 address?
An example is a MAC address. Ethernet interface manufacturers assign MAC addresses to end devices and are used for communication over the local network. MAC addresses are hard-coded into the network card and Ethernet interfaces.
What is the correct command to add the description "Link to West LA" to an interface on a Cisco router?
C. The command to add a description to an interface is the description interface-description interface configuration command. Note Adding a description to an interface on a Cisco router does not have any performance effects. It just adds a description to help identify the interface.
What are dynamic routes?
Dynamic routes use a routing protocol to dynamically learn routes to remote networks and add them to the routing table. The routing protocol automatically updates route knowledge whenever new topology information is received.
What is fast switching?
Fast switching is a process that uses the cache to speed routing. When a packet is received for a destination, the first packet is process switched and an entry is created in the router's cache. Subsequent packets are switched in the interrupt code using the cache to improve performance.
Upon first boot, a new router does not have a configuration file to load. In the event that a router has no configuration file, what happens?
If a router does not find a configuration file, the router runs setup mode, a question-driven configuration process that allows you to configure basic router parameters. Note The system configuration dialog is run if the router does not find a configuration file in NVRAM or if the setupprivileged mode command is entered at the router's command prompt.
You are configuring an interface on a router and the interface says "Interface is up, line protocol is down." What does this tell you regarding the interface?
If an interface says "Interface is up, line protocol is down," the interface is experiencing Layer 2 problems. This could be caused by not receiving keepalives, no clocking received, or encapsulation mismatch. Note If the interface says, "Interface is down, line protocol is down" and it is not administratively disabled, the interface is having Layer 1 problems.
Define processing switching.
Processing switching is the oldest forwarding mechanism supported on Cisco routers. Every packet processed by the router requires a full lookup in the routing table.
Provide a brief description of routing.
Routing is the process of finding a path to a destination and moving information across an internetwork from the source to the destination.
How do routing protocols maintain their routing tables with each other?
Routing protocols maintain their routing tables through the transmission of messages. These messages are exchanged between routers at periodic intervals or when a change in the network topology occurs. The information contained in the messages varies from routing protocol to routing protocol.
What are static routes?
Static routes are routes to a remote destination that are manually configured on a router. They are administrator-defined routes and allow precise control over routing behavior.
What is the ARP table?
The ARP table stores the reference of each known IP address to its MAC address on the local Layer 3 network. The ARP table is created and maintained dynamically but can also include static ARP entries.
How do you display the status of interface F0 only?
The IOS commands to display the status of interface F0 only are as follows: show interface f0 show ip interface f0 show protocols f0
What are six types of information stored in routing tables?
The following are six types of information stored in routing tables: Destination network address Next-hop address Exiting interface Metric Administrative distance Routing source
What IOS command displays the entries in the routing table?
The following command displays the entries in the routing table: show ip route
What are the four types of routes found in a routing table?
The four types of routes found in a routing table are as follows: Directly connected networks: Route entries that a router is directly connected to. Static routes: Routes entered manually by an administrator. Dynamic routes: Routes learned and populated by a routing protocol. Default route: Used to route packets when the router does not have a specific destination for packets in its routing table. The default route is entered manually or dynamically.
How do you give a Cisco router a name?
The hostname name global configuration command configures a name on a Cisco router. For example, the following command changes the router's host name to RouterA: Router(config)# hostname RouterA RouterA(config)#
When a router is powered on, what three tasks does the router perform?
The router performs the following tasks when powered on: 1. Runs a power-on self-test (POST) to test the hardware 2. Finds and loads the IOS 3. Finds and applies the router configuration file, if one exists
What does the show cdp command display?
The show cdp command displays global CDP information about the device. It tells you how often the device will send CDP packets and the CDP holdtime: RouterB# show cdp Global CDP information: Sending CDP packets every 60 seconds Sending a holdtime value of 180 seconds Sending CDPv2 advertisements is enabled Note For the exam, remember that the default time interval a device sends out CDP information is 60 seconds, and the default holdtime is 180 seconds.
How do you administratively disable an interface on a Cisco router?
You administratively disable an interface on a Cisco router by issuing the shutdown interface configuration command. In this example, the serial interface is issued the shutdown command: RouterA(config)# interface g0 RouterA(config-if)# shutdown 00:27:14: %LINK-5-CHANGED: Interface GigabitEthernet0, changed state to administratively down Note To administratively enable an interface, use the no shutdown interface configuration command
What does the show cdp interface command display?
The show cdp interface command, as follows, displays the status of CDP on all CDP-enabled interfaces on your device: RouterB# show cdp interface Ethernet0 is up, line protocol is down Encapsulation ARPA Sending CDP packets every 60 seconds Holdtime is 180 seconds Serial0 is up, line protocol is up Encapsulation HDLC Sending CDP packets every 60 seconds Holdtime is 180 seconds Serial1 is up, line protocol is up Encapsulation HDLC Sending CDP packets every 60 seconds Holdtime is 180 seconds
What does the show cdp neighbors detail command display?
The show cdp neighbors detail and show cdp entry * commands show the same output. They both display the following: Device ID (host name) of the remote neighbor Layer 3 addresses of the remote device interface that is connected to the local device Device platform and capabilities Local interface and outgoing port ID Local holdtime that is associated to the remote device IOS type and version
What does the show cdp traffic command display?
The show cdp traffic command, as follows, displays information about interface traffic. This includes the number of CDP packets sent and received and CDP errors: RouterB# show cdp traffic CDP counters : Total packets output: 550, Input: 682 Hdr syntax: 0, Chksum error: 0, Encaps failed: 0 No memory: 0, Invalid packet: 0, Fragmented: 0 CDP version 1 advertisements output: 0, Input: 0 CDP version 2 advertisements output: 550, Input: 682
What are some of the things that the show interface interface-type number command displays?
The show interface command displays the following: Whether the interface is administratively down Whether the line protocol is up or down An Internet address (if one is configured) Maximum transmission unit (MTU) and bandwidth Traffic statistics on the interface Interface encapsulation type
What three configuration settings does a host on a TCP/IP network require to communicate with hosts on a remote TCP/IP network?
The three configuration settings needed to communicate with hosts on a remote TCP/IP network are IP address Subnet mask Default gateway address
What are the three packet-forwarding mechanisms supported by Cisco routers?
The three packet-forwarding mechanisms supported by Cisco routers are Process switching Fast switching Cisco Express Forwarding
What are the two key functions that a router performs?
The two key functions that a router performs are path determination (routing) and packet forwarding (switching). Routing protocols used by the routing process are responsible for learning and maintaining awareness of the network topology. The switching function is the process of moving packets from an inbound interface to an outbound interface.
List at least five types of information obtained from CDP.
The types of information obtained from CDP are as follows: Neighbor device ID (host name of remote device) Layer 3 address list of remote devices Device platform Device capabilities (router, switch, and so on) Local interface type and outgoing remote port ID Hold time value IOS version of remote device
How do you disable CDP on Cisco routers?
Two commands disable CDP on a Cisco router. To disable CDP on the entire device, use the no cdp run global command, as follows: RouterB(config)# no cdp run To disable CDP on an interface only, use the no cdp enable interface command, as follows: RouterB(config)# int f0 RouterB(config-if)# no cdp enable This disables CDP on Fast Ethernet interface 0.
List two reasons to disable CDP.
Two reasons to disable CDP are as follows: To save network resources by not exchanging CDP frames. Security. CDP multicasts information about the device every 60 seconds. Sniffers and other devices can view these multicasts to discover information about your network.
What two utilities test IP connectivity?
Two utilities are ping and traceroute (tracert). Ping and traceroute are ICMP utilities. ICMP specifically tests Layer 3 connectivity. Traceroute uses UDP when sending packets and ICMP when responding to the request of connectivity.
How do you configure a default route to point out interface Fast Ethernet 0/0?
Use the following command to configure the default route: RouterB(config)# ip route 0.0.0.0 0.0.0.0 fastethernet0/0
Packets are not being forwarding from one segment to another on your Cisco router. You enter the show interface g0 command and notice that the interface is administratively down. What does this mean, and how do you fix it?
When an interface is administratively down, it has been shut down manually or was never enabled. To remedy this, enter the interface command no shutdown.
What is the difference between a routed and a routing protocol?
A routed protocol is a protocol that provides the information in its network layer to allow a packet to direct traffic and defines the use of fields within a packet. Examples of routed protocols are IPv4 and IPv6. A routing protocol finds routes in an internetwork and maintains route awareness. Routing protocols aid in building and maintaining routing tables that routers will use to determine how routed protocols are routed. Routing Information Protocol v2 (RIPv2), Enhanced IGRP (EIGRP), Intermediate System-to-Intermediate System (IS-IS), Open Shortest Path First (OSPF), and Border Gateway Protocol (BGP) are examples of routing protocols.
How does a router determine the path a packet should take to reach its destination?
A router determines a path a packet should take to reach a destination by picking the best path to the destination. The best path a packet should take is determined by one of the following methods: Static routing Dynamic routing Default routing
What is the Address Resolution Protocol (ARP)?
ARP is used to resolve a known destination IP address to its associated MAC address on the local network. For a host to communicate with another host, it must know the MAC address of the destination host. If the hosts are on the same subnet, the sending host will send an ARP request to the destination asking for its MAC address. The destination host will reply with its MAC address. If the sending host and the destination host are on a different subnets, the ARP request is sent to default gateway. The default gateway will reply to the ARP request with its MAC address on the local subnet of the sending host and the logical address of the destination host. Note ARP takes the destination IP address and resolves it to the MAC address on the local network through a local broadcast. For the exam, remember that ARP is used when a device knows the destination IP of another device and needs to learn the destination MAC address of that device on the local network.
What is the Cisco Discovery Protocol (CDP)?
CDP is a Cisco-proprietary protocol that runs on all Cisco IOS-enabled devices by default. It gathers information about directly connected Cisco devices. CDP operates at Layer 2 of the OSI model and is media independent. With CDP, you can tell the hardware platform and device capability, device identifier, Layer 3 addresses of the connected interface, software version, and interface of the remote device that your Cisco device is attached to. CDP is enabled by default on all Cisco equipment. CDP is a Layer 2 frame that is not routable. Note Frame Relay interface by default will disable CDP.
Define Cisco Express Forwarding.
Cisco Express Forwarding (CEF) is the preferred Cisco IOS packet-forwarding mechanism. CEF consists of two key components: the Forwarding Information Base (FIB) and adjacencies. The FIB is similar to the routing table created by the router but maintains only the next-hop address for a particular route. The adjacency table maintains Layer 2 information linked to a particular FIB entry, avoiding the need to do an ARP request for each table lookup.
List three advantages and disadvantages of static routes when compared with dynamic routing.
Three advantages of static routing are They conserve routing resources that are consumed when using a routing protocol. Simple to configure in a small network. Quick to implement. Three disadvantages are Scalability is limited. Static routes should be used for small networks or stub networks. A lot of manual configuration is required for larger networks. Do not automatically adapt to network changes.
How would you configure a Fast Ethernet interface 0 with an IP address of 192.168.0.1/24 on a Cisco router?
To configure a Fast Ethernet interface 0 with an IP address of 192.168.0.1/24 on a Cisco router, issue the following commands from global configuration mode: Router(config)# interface f0 Router(config-if)# ip address 192.168.0.1 255.255.255.0 Router(config-if)# no shutdown Note By default, every interface on a router is administratively disabled and needs to be enabled using the no shutdowncommand. If you receive any simulators on the exam, you will get the question wrong if you do not manually enable the interface.
How do you configure a static route on a Cisco router?
To configure a static route on a Cisco router, enter the ip route destination-network mask {next-hop-address | outbound-interface} [distance] [permanent] global command. Here's an example: RouterB(config)# ip route 172.17.0.0 255.255.0.0 172.16.0.1 This example instructs the router to route to 172.16.0.1 any packets that have a destination of 172.17.0.0 to 172.17.255.255.
How do you store the active configuration of a Cisco router to NVRAM?
To save the running config to the startup config, use the copy running-config startup-config privileged mode command.
What Cisco IOS router command can you use to see a neighbor router's IP address?
To see a neighbor router's IP address, you must use the show cdp neighbor detail or show cdp entry * user EXEC mode or privileged EXEC command.
When configuring a router interface for the first time, is the interface administratively disabled?
Yes. By default, router interfaces on Cisco routers are administratively disabled. They must be enabled using the no shutdown interface command.
You want to test TCP/IP connectivity between two hosts. What TCP/IP tools can you use to do this?
You can use ping and traceroute. Ping is a tool that that sends Internet Control Message Protocol (ICMP) packets to test network layer connectivity between two hosts. Ping sends an ICMP echo request packet to the target host and listens for an ICMP echo response. Traceroute also uses ICMP, and it maps the path packets use to reach a destination.
On a Cisco router, how do you display the configuration running in RAM?
You display the configuration running in RAM using the show running-config privileged mode command.
On a Cisco router, how do you view the configuration stored in nonvolatile RAM (NVRAM)?
You view the configuration stored in NVRAM using the show startup-config privileged mode command.
