Chapter 13: ICMP

What does ICMP stand for?

Internet Control Message Protocol

ICMPv6 includes four new protocols as part of the Neighbor Discovery Protocol (ND or NDP). What are they?

Router Solicitation Router Advertisement Neighbor Solicitation Neighbor Advertisement

After all the request are sent , the ping utility provides a summary of what?

That includes the success rate and average route-trip time to destination.

The types of ICMP messages, and the reasons why they are sent, are extensive. The ICMP messages common to both ICMPv4 and ICMPv6 and discussed in this module include:

Host reachability Destination or Service Unreachable Time Exceeded

Which layer 3 protocol is used to provide error messages and information when communicating with another IP device?

ICMP

Which protocol is used by IPv4 and IPv6 to provide error messaging? NDP ARP DHCP ICMP

ICMP

When a host or gateway receives a packet that it cannot deliver, it can use what type of message to notify the source device that the destination or service is unreachable?

ICMP Destination Unreachable Message

What types of messages does the ping command send to test reachability of a host on an IP network?

ICMP ECHO Request ICMP Echo Reply

What can a ping command be used to measure?

Network performance

Type of connectivity tests performed with ping include the following:

Pinging the local loopback Pinging the default gateway Pinging the remote host

The message will include a code that indicates why the packet could not be delivered. Some of the Destination Unreachable codes for ICMPv4 are as follows:

0 -Net Unreachable 1- Host Unreachable 2- Protocol Unreachable 3- Port Unreachable

Some of the Destination Unreachable codes for ICMPv6 are as follows:

0- No Route to destination 1- Communication with the destination is administratively prohibited (eg Firewall) 2- Beyond the scope of the source address 3- Address unreachable 4- Port Unreachable

An asterisk (*) in a Round Trip Time is used to indicate what?

A lost or unreplied packet

What can an ICMP echo message be used for?

An ICMP Echo Message can be used to test the reachability of a host on an IP network.

A technician is troubleshooting a network where it is suspected that a defective node in the network path is causing packets to be dropped. The technician only has the IP address of the end point device and does not have any details of the intermediate devices. What command can the technician use to identify the faulty node? tracert ping ipconfig /flushdns ipconfig /displaydns

tracert

Ture or False: ICMPv6 ND also includes the redirect message, which has a similar function to the redirect message used in ICMPv4

True

A user calls to report that a PC cannot access the internet. The network technician asks the user to issue the command ping 127.0.0.1 in a command prompt window. The user reports that the result is four positive replies. What conclusion can be drawn based on this connectivity test? The PC can access the network. The problem exists beyond the local network The IP address obtained form the DHCP server is correct The TCP/IP implementation is functional The PC can access the internet. However, the web browser may not work.

The TCP/IP implementation is functional

How does traceroute use the IPv4 TTL and IPv6 Hop Limit

The first sequence of messages sent from traceroute will have a TTL field value of 1. This causes the TTL to time out the IPv4 packet at the first router. This router then responds with an ICMPv4 Time Exceeded message. Traceroute now has the address of the first hop. Traceroute then progressively increments the TTL field (2, 3, 4...) for each sequence of messages. This provides the trace with the address of each hop as the packets time out further down the path. The TTL field continues to be increased until the destination is reached, or it is incremented to a predefined maximum. After the final destination is reached, the host responds with either an ICMP Port Unreachable message or an ICMP Echo Reply message instead of the ICMP Time Exceeded message.

What is the purpose of the ICMP protocol?

The purpose of these messages is to provide feedback about issues related to the processing of IP packets under certain conditions, not to make IP reliable.

How is round trip time calculated?

Using traceroute provides round-trip time for each hop along the path and indicates if a hop fails to respond. The round trip time is the time a packet takes to reach the remote host for the response from the host to return.

What message is sent by a host to check the uniqueness of an IPv6 address before using that address? router solicitation ARP request neighbor solicitation echo request

neighbor solicitation

Which command can be used to test connectivity between two devices using echo request and echo reply messages? ping ICMP netstat ipconfig

ping

Which utility uses the Internet Control Message Protocol (ICMP)? ping RIP DNS NTP

ping

Which two things can be determined by using the ping command? (Choose Two) the average time it takes a packet to reach the destination and for the response to return to the source the number of routers between the source and destination device the destination device is reachable through the network the average time it takes each router in the path between source and destination to respond The IP address of the router nearest the destination device.

the average time it takes a packet to reach the destination and for the response to return to the source the destination device is reachable through the network

A user who is unable to connect to the file server contacts the help desk. The helpdesk technician asks the user to ping the IP address of the default gateway that is configured on the workstation. What is the purpose for this ping command? to request that gateway forward the connection request to the file server to resolve the domain name of the file server to its IP address to test that the host has the capability to reach hosts on other networks to obtain a dynamic IP address form the server

to test that the host has the capability to reach hosts on other networks

A network administrator can successfully ping the server at www.cisco.com, but cannot ping the company web server located at an ISP in another city. Which tool or command would help identify the specific router where the packet was lost or delayed? netstat telnet ipconfig traceroute

traceroute

Which tool uses the time exceeded messages?

traceroute tool

A network administrator is testing network connectivity by issuing the ping command on a router. Which symbol will be displayed to indicate that a time expired during the wait for an ICMP echo reply message? ! . $ U

.

What is the traceroute (tracert) utility used for?

Is a utility that generates a list of hops that were successfully reached along the path.

Which two new ICMPv6 protocols deal with duplicate address detection and address resolutions?

Neighbor Solicitation Neighbor Advertisement

What is ping command used for ?

Ping is an IPv4 and Ipv6 testing utility that uses ICMP echo request and echo reply messages to test connectivity between hosts.

Which type of ICMPv6 message would a host send to acquire an IPV6 configuration when booting up? Neighbor Advertisement (NA) message Neighbor Solicitation (NS) message Router Advertisement (RA) message Router Solicitation (RS) message

RS or Router Solicitation Message

Which two new ICMPv6 protocols deal with dynamic address allocation?

Router Solicitation Router Advertisement

What does a ping timeout message indicate?

That there is a problem, but could also indicate that security features blocking pin messages have been enables on the network.

Which two types of ICMP messages are common to both ICMPv4 and ICMPv6? CHoose two Destination or Service Unreachable Hostname resolution IP configuration Source Unreachable Time Exceeded

Destination or Service Unreachable Time Exeeded

What field content is used by ICMPv6 to determine that a packet has expired? TTL field CRC field Hop limit field Time Exceeded Field

Hop limit field

Which protocol provides feedback form the destination host to the source host about errors in packet delivery? ARP ICMP DNS BOOTP

ICMP

What is the function of the tracert command that differs from the ping command when they are used on a workstation? The tracert command shows the information of routers in the path The tracert command sends one ICMP message to each hop in the path The tracert command teaches the destination faster The tracert command is used to test the connectivity between two devices.

The tracert command shows the information of routers in the path

What can the Round Trip Time information provide?

This information can be used to locate a problematic router in the path or may indicate that the router is configured not to reply. If the display shows high response times or data losses form a particular hop, this is an indication that the resources of the router or its connections may be stressed.

What information can the list generated by the traceroute command providie?

This list can provide important verification and troubleshooting information. If the data reaches the destination, then the trace lists the interface of every router in the path between the hosts. If the data fails at some hop along the way, the address of the last router that responded to the trace can provide an indication of where the problem or security restrictions are found.

Whicn ICMP messaged is used by the traceroute utility during the process of finding the path between two end hosts? redirect time exceeded destination unreachable ping

Time Exceeded

An ICMP Time Exceeded message is used by a router to indicate what ?

To indicate that a packet cannot be forwarded because the Time to Live (TTL) or Hop Limit field of the packet was decremented to 0 and the packet is dropped.