CIS 81 Fundamentals of Networking Chapter 8: IP Addressing Part 2 – ICMP (ICMPv4) CCNA...

CIS 81 Fundamentals of NetworkingChapter 8: IP AddressingPart 2 – ICMP (ICMPv4)

CCNA Introduction to Networking 5.0

Rick Graziani

Cabrillo College

[email protected]

Fall 2013

Chapter 8: Objectives

Part 1Describe the structure of an IPv4 address.Describe the purpose of the subnet mask.Compare the characteristics and uses of the unicast, broadcast and multicast IPv4 addresses.

Part 2Describe ICMP and ICMPv4

Part 3Explain the need for IPv6 addressing.Describe the representation of an IPv6 address.Describe types of IPv6 network addresses.Configure global unicast addresses.Describe ICMPv6

Testing the Network

IP

IP is a best effort delivery system. No mechanism to ensure that the data is delivered

So how do we know if a packet encountered a problem along the way?

Internet Control Message Protocol (ICMP)

Internet Control Message Protocol (ICMP)

ICMP is available for both IPv4 and IPv6. ICMPv4 is the messaging protocol for IPv4. ICMPv6 provides these same services for IPv6 but includes

additional functionality. ICMP messages common to ICMPv4 and ICMPv6 include:

Host confirmation Destination or Service Unreachable Route redirection Time exceeded

ICMPv6 includes additional functionality.

ICMP

ICMP is used for: Informational messages (ping, traceroute) Error messages (network unreachable)

ICMP is a layer 3 protocol directly encapsulated in another layer 3 protocol IP. No transport header

Knowledge of ICMP control messages is an essential part of network troubleshooting.

7

The ICMP packets are identified by type and code fields.

TCP/IP Suite Control Messages

The ICMPv4 packet identifies the type of control message in the “Type” field.

Host Confirmation (PING)

Ping is a utility used to verify connectivity to an IP host. It measures the round-trip time for messages sent from the

originating host to a destination computer. Ping uses an ICMP Echo Message to determine if a host is reachable.

A host initiates a ping (ICMP Echo Request) and the destination replies (ICMP Echo Reply).

ICMP only reports on the status of the delivered packet to the source device.

ICMP Packet

Apples-MacBook-Pro:~ rigrazia$ ping www.google.com

PING www.google.com (74.125.239.115): 56 data bytes

64 bytes from 74.125.239.115: icmp_seq=0 ttl=55 time=27.417 ms


--- www.google.com ping statistics ---

3 packets transmitted, 3 packets received, 0.0% packet loss

round-trip min/avg/max/stddev = 25.898/31.963/42.574/7.529 ms

Apples-MacBook-Pro:~ rigrazia$ ping 74.125.239.115

PING 74.125.239.115 (74.125.239.115): 56 data bytes



--- 74.125.239.115 ping statistics ---




PING 192.168.1.1 (192.168.1.1): 56 data bytes



--- 192.168.1.1 ping statistics ---




PING 192.168.1.119 (192.168.1.119): 56 data bytes



--- 192.168.1.119 ping statistics ---



Apples-MacBook-Pro:~ rigrazia$

15

Use the ping command to help you troubleshoot / verify connectivity.

Steps to verify: Ping the remote

host using the domain name

Ping the remote host using its IP address

Ping your default gateway

Ping your system

Ping a Remote Host

Ping the Default Gateway

Ping Yourself

Destination or Service Unreachable

When a router cannot deliver a packet, it sends an ICMP Destination Unreachable message to the source. Message includes a code indicating why it could not be delivered.

Some of the Destination Unreachable codes for ICMPv4 are: 0 - net unreachable. 1 - host unreachable. 2 - protocol unreachable. 3 - port unreachable.

Note: ICMPv6 has similar but slightly different codes for Destination

Unreachable messages.


ICMP only reports on the status of the delivered packet to the source device.

For example: PC1 pings PC2. The ping crosses R1, then R2, but R3 encounters a link error. Since the packet only contains the source and destination IP

addresses, R3 may notify PC1 of the failure (optional). It’s unaware of the exact path the packet took No ICMP messages are sent to R1 or R2.

PC1PC2R1 R2 R3


The Destination Unreachable message is generated by the router to inform the client that the destination host is unreachable.

Reasons: The physical connection to the host

does not exist (distance is infinite) The indicated protocol or port is not

active

The Destination Unreachable message is generated by the router to inform the client that the destination host is unreachable.

Reasons: The physical connection to the host

does not exist (distance is infinite) The indicated protocol or port is not

active


The Destination Unreachable (Type 3) packet codes are:

0 = net unreachable 1 = host unreachable 2 = protocol unreachable 3 = port unreachable

The Destination Unreachable (Type 3) packet codes are:

0 = net unreachable 1 = host unreachable 2 = protocol unreachable 3 = port unreachable


Codes 0 (net unreachable) is sent when a router does not have the requested network.

Code 1 (host unreachable) is sent when a router receives a packet for which it has an attached route but is unable to deliver the packet to the host on the attached network.

Code 2 (protocol unreachable) and Code 3 (port unreachable) are used by an end host to indicate that the TCP segment or UDP datagram contained in a packet could not be delivered to the upper layer service.



Code 2 (protocol unreachable) and Code 3 (port unreachable) are used by an end host to indicate that the TCP segment or UDP datagram contained in a packet could not be delivered to the upper layer service.


C:\Users\Bob> ping 192.168.1.115

Pinging 192.168.1.115 with 32 bytes of data:Reply from 192.168.1.116: Destination host unreachable.Reply from 192.168.1.116: Destination host unreachable.Reply from 192.168.1.116: Destination host unreachable.Reply from 192.168.1.116: Destination host unreachable.

Ping statistics for 192.168.1.115: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

C:\Users\Bob>

C:\Users\Bob> ping 192.168.2.115

Pinging 192.168.1.115 with 32 bytes of data:Reply from 192.168.1.116: Destination net unreachable.Reply from 192.168.1.116: Destination net unreachable.Reply from 192.168.1.116: Destination net unreachable.Reply from 192.168.1.116: Destination net unreachable.

Ping statistics for 192.168.1.115: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

C:\Users\Bob>





Route Redirection

A router may use the ICMP Redirect Message to notify the hosts on a network that a better route is available for a particular destination. This message may only be used when the source host is on the

same physical network as both gateways.

Both ICMPv4 and ICMPv6 use route redirection messages.

Route Redirection

The Redirect Message (Type 5) informs a host to redirect its routing information (to send packets on an alternate route).

If the host tries to send data through a router (R1) and then another router (R2) to reach the host, and a direct path from the host to R2 is available, the redirect will inform the host of such a route.

The Redirect Message (Type 5) informs a host to redirect its routing information (to send packets on an alternate route).

If the host tries to send data through a router (R1) and then another router (R2) to reach the host, and a direct path from the host to R2 is available, the redirect will inform the host of such a route.

Route Redirection

Host A sends a packet to Host B on network 10.0.0.0/8, but since they are not on the same network, it forwards it to the default gateway, R1.

R1 finds the correct route to network 10.0.0.0/8 is through the same interface and forwards out of its E0 interface to R2.

R1 also forwards an ICMP Redirect message to Host A telling it to use R2 as the gateway to forward all future requests to network 10.0.0.0/8.

B

A

Time Exceeded

An ICMPv4 Time Exceeded message is used by a router to indicate that a packet cannot be forwarded because the Time to Live (TTL) field of the packet was decremented to 0. If a router receives a packet and decrements the TTL field in the

IPv4 packet to zero, it discards the packet and sends a Time Exceeded message to the source host.

ICMPv6 also sends a Time Exceeded message if the router cannot forward an IPv6 packet because the packet has expired. IPv6 does not have a TTL field; it uses the hop limit field to

determine if the packet has expired.

Detecting Excessively Long Routes

Whether the actual path includes too many hops or a circular routing path exists, the packet will eventually reach the end of its life, known as its time-to-live (TTL).

Time Exceeded Message

The Time Exceeded (Type 11) message is an ICMP message which is generated by a gateway to inform the source of a datagram that the datagram has been discarded due to the time to live field reaching zero.

Time exceeded messages are used by the traceroute utility to identify gateways on the path between two hosts.

The Time Exceeded (Type 11) message is an ICMP message which is generated by a gateway to inform the source of a datagram that the datagram has been discarded due to the time to live field reaching zero.

Time exceeded messages are used by the traceroute utility to identify gateways on the path between two hosts.

Traceroute

Ping is used to indicate the connectivity between two hosts. Traceroute (tracert) is used to observe the path between these

hosts. The trace lists hops successfully reached along the way providing us

with important verification and troubleshooting information. If the data fails at some hop along the way, we have the address of the

last router that responded to the trace indicating where the problem or security restrictions are.

Traceroute

TTL 1

ICMP Time Exceeded

TTL 1 – 1 =0

TTL 2

ICMP Time Exceeded

TTL 2 – 1 =1

TTL 1

TTL 1 – 1 =0

TTL 3

ICMP Time Exceeded

TTL 3 – 1 =2

TTL 2

TTL 2 – 1 =1 TTL 2 – 1 =0

TTL 1

Traceroute Example

C:\Users\Bob> tracert www.eurocom.fr

Tracing route to eurocom.fr [92.243.13.96]over a maximum of 30 hops:

1 11 ms 2 ms 6 ms Home-Net [192.168.1.1] 2 19 ms 18 ms 17 ms 24-139-15-1.eastlink.ca [24.139.15.1] 3 22 ms 19 ms 17 ms 10.250.35.1 4 13 ms * 13 ms on-sdbr-dr001.on.eastlink.ca [24.139.7.66] 5 16 ms 19 ms 19 ms 24-139-15-26.eastlink.ca [24.139.15.26] 6 22 ms 27 ms 29 ms 24-139-7-138.eastlink.ca [24.139.7.138] 7 24 ms 27 ms 38 ms xe-1-0-1.mpr2.tor1.ca.above.net [208.185.21.193] 8 43 ms 48 ms 48 ms xe-7-2-0.cr1.lga5.us.above.net [64.125.22.222] 9 55 ms 58 ms 49 ms xe-3-2-0.cr1.dca2.us.above.net [64.125.26.101] 10 49 ms 57 ms 58 ms xe-0-0-0.mpr1.bwi9.us.above.net [64.125.28.137] 11 43 ms 48 ms 49 ms 64.125.192.86.t00709-01.above.net [64.125.192.86] 12 133 ms 129 ms 137 ms xe2-6-core1-d.paris.gandi.net [217.70.176.229] 13 132 ms 128 ms 125 ms xe1-5-5-dist1-d.paris.gandi.net [217.70.176.238] 14 129 ms 129 ms 127 ms 92.243.13.96

Trace complete.

C:\Users\Bob>

Three delay measurements.

Traceroute ExampleC:\Users\Bob> tracert cern.ch

Tracing route to cern.ch [137.138.144.169]over a maximum of 30 hops:

1 6 ms 8 ms 6 ms Home-Net [192.168.1.1] 2 * * * Request timed out. 3 14 ms 17 ms 24 ms 24-139-15-1.eastlink.ca [24.139.15.1] 4 11 ms 17 ms 17 ms 10.250.35.1 5 * 17 ms 11 ms on-sdbr-dr001.on.eastlink.ca [24.139.7.66] 6 19 ms 23 ms 14 ms 24-139-15-26.eastlink.ca [24.139.15.26] 7 37 ms 26 ms 33 ms te-4-3.car1.Montreal2.Level3.net [4.59.176.237] 8 137 ms 197 ms 138 ms ae-5-5.ebr2.NewYork1.Level3.net [4.69.141.6] 9 141 ms 138 ms 139 ms ae-45-45.ebr2.NewYork2.Level3.net [4.69.141.22] 10 133 ms 139 ms 136 ms ae-1-100.ebr1.NewYork2.Level3.net [4.69.135.253] 11 140 ms 139 ms 137 ms 4.69.201.93 12 137 ms 137 ms 139 ms ae-43-43.ebr2.Paris1.Level3.net [4.69.137.57] 13 254 ms 289 ms 267 ms ae-9-9.car1.Lyon1.Level3.net [4.69.134.49] 14 299 ms 210 ms 229 ms ae-5-5.car1.Geneva1.Level3.net [4.69.137.81] 15 135 ms 127 ms 138 ms h4allr1.safe-order.ch [213.242.73.22] 16 129 ms 137 ms 143 ms e513-e-rbrxl-2-ne0.cern.ch [192.65.184.38] 17 * * * Request timed out. 18 * * * Request timed out. 19 * * * Request timed out. 20 134 ms 141 ms 145 ms webr8.cern.ch [137.138.144.169] 21 * * * Request timed out. 22 132 ms 128 ms 129 ms webr8.cern.ch [137.138.144.169]

Trace complete.

C:\Users\Bob>

Traceroute ExampleC:\Users\Bob> tracert ehawaii.gov

Tracing route to ehawaii.gov [66.175.95.42]over a maximum of 30 hops:

1 6 ms 8 ms 9 ms Home-Net [192.168.1.1] 2 * * * Request timed out. 3 13 ms 29 ms 19 ms 24-139-15-1.eastlink.ca [24.139.15.1] 4 18 ms 30 ms 18 ms 10.250.35.1 5 * * * Request timed out. 6 24 ms 16 ms 19 ms 24-139-15-26.eastlink.ca [24.139.15.26] 7 225 ms 186 ms 218 ms te-4-3.car1.Montreal2.Level3.net [4.59.176.237] 8 38 ms 45 ms 41 ms ae-5-5.ebr2.NewYork1.Level3.net [4.69.141.6] 9 35 ms 52 ms 50 ms 4.69.201.38 10 33 ms 49 ms 44 ms ae-2-52.edge3.NewYork2.Level3.net [4.69.138.228] 11 40 ms 49 ms 59 ms jfk-brdr-04.inet.qwest.net [63.146.26.5] 12 171 ms 170 ms 168 ms hnl-edge-04.inet.qwest.net [67.14.17.226] 13 159 ms 158 ms 158 ms 67.129.94.138 14 163 ms 168 ms 166 ms 66.135.224.243 15 * * * Request timed out. 16 * * * Request timed out. 17 * * * Request timed out. 18 * * * Request timed out. 19 * * * Request timed out.

http://www.yougetsignal.com/tools/visual-tracert /

http://www.yougetsignal.com/tools/visual-tracert%20/

tracert -h 160 216.81.59.173traceroute -m 100 -q 1 216.81.59.173

http://www.youtube.com/watch?v=_QevOSlLTFw

CIS 81 Fundamentals of NetworkingChapter 8: IP AddressingPart 2 – ICMP (ICMPv4)

CCNA Introduction to Networking 5.0

Rick Graziani

Cabrillo College

[email protected]

Fall 2013

CIS 81 Fundamentals of Networking Chapter 8: IP Addressing Part 2 – ICMP (ICMPv4) CCNA...

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