6.2 Verifying Connectivity

Question 1

ICMP

Answer 1

Internet Control Message Protocol

ICMP is mainly used by a router or remote host to communicate why transmission has failed back to the origin of the transmission.

Question 2

ICMP PACKET

Answer 2

It has a header with a few fields and a data section that’s used by a host to figure out which of their transmissions generated the error.

1 TYPE FIELD
2 CODEFIELD
3 CHECKSUM
4 REST OF HEADER
5 DATA PAYLOAD

Question 3

1 TYPE FIELD

Answer 3

Eight bits long, which specifies what type of message is being delivered.

Question 4

2 CODEFIELD

Answer 4

Indicates a more specific reason for the message than just the type.

Question 5

3 CHECKSUM

Answer 5

16-bit checksum that works like every other checksum field.

Question 6

4 REST OF HEADER

Answer 6

32-bit field optionally used by some of the specific types and codes to send more data.

Question 7

5 DATA PAYLOAD

Answer 7

The payload for an ICMP packet exists entirely so that the recipient of the message knows which of their transmissions caused the error being reported.
It contains the entire IP header and the first eight bytes of the data payload section of the offending packet.

Question 8

PING

Answer 8

With Ping, you have a way to determine if you can reach a certain computer from another one.

Is a program that lets you send a special type of ICMP message called an ECHO REQUEST.
An ICMP echo request essentially just as a destination.

If the destination is up and running and able to communicate on the network, it’ll send back an ICMP echo reply message type.

Output of the ping command is very similar across each of the different operating systems.
Every line of output will generally display the address sending the ICMP echo reply and how long it took for the round-trip communications.
It will also have the TTL remaining and how large the ICMP message is in bytes.

Question 9

TRACEROUTE, TRACERT

Answer 9

Traceroute is a utility that lets you discover the paths between two nodes, and gives you information about each hop along the way.

Question 10

MTR, PATHPING

Answer 10

These two tools act as long running trace routes.
So you can better see how things change over a period of time.

Question 11

NETCAT, TEST-NETCONNECTION

Answer 11

This is a way for you to actually send application layer data to the listening service from your own keyboard.