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Questions and Answers
What is the purpose of ICMP?
What is the purpose of ICMP?
- To make IP connections reliable and error-free.
- To provide feedback for error reporting and diagnostics. (correct)
- To route packets through the network.
- To encrypt data during transmission.
Which of the following ICMP messages indicates that a packet could not reach its destination due to an unresponsive host?
Which of the following ICMP messages indicates that a packet could not reach its destination due to an unresponsive host?
- Router Solicitation
- Destination Unreachable (correct)
- Time Exceeded
- Echo Request
Which ICMPv6 messages are used for address resolution and duplicate address detection?
Which ICMPv6 messages are used for address resolution and duplicate address detection?
- Destination Unreachable and Time Exceeded
- Router Solicitation and Router Advertisement
- Echo Request and Echo Reply
- Neighbor Solicitation and Neighbor Advertisement (correct)
What does the traceroute or tracert command primarily rely on to determine the path taken by packets?
What does the traceroute or tracert command primarily rely on to determine the path taken by packets?
When using ping, what is the significance of pinging the loopback address?
When using ping, what is the significance of pinging the loopback address?
What will a reply of 'Time Exceeded' from a router indicate?
What will a reply of 'Time Exceeded' from a router indicate?
Which ICMPv4 code corresponds to 'host unreachable'?
Which ICMPv4 code corresponds to 'host unreachable'?
Which of the following commands is used in Windows for IPv6 connectivity testing?
Which of the following commands is used in Windows for IPv6 connectivity testing?
Flashcards
What is ICMP?
What is ICMP?
A network protocol used by IPv4 and IPv6 for error reporting, informational messages, and network diagnostics.
What are Echo Request and Echo Reply messages used for?
What are Echo Request and Echo Reply messages used for?
ICMP messages used to test if a host is reachable. They work by sending an Echo Request and waiting for an Echo Reply.
What are Destination Unreachable messages?
What are Destination Unreachable messages?
ICMP messages sent when a host or router cannot deliver a packet. Includes codes for different types of unreachability, like network, host, protocol, or port.
What are Time Exceeded messages?
What are Time Exceeded messages?
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What is Neighbor Discovery (ND)?
What is Neighbor Discovery (ND)?
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What is the 'ping' command used for?
What is the 'ping' command used for?
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What is the 'traceroute' or 'tracert' command used for?
What is the 'traceroute' or 'tracert' command used for?
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What is the role of ICMP in reliable network communication?
What is the role of ICMP in reliable network communication?
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Study Notes
ICMP Overview
- ICMP (Internet Control Message Protocol) is used by IPv4 (ICMPv4) and IPv6 (ICMPv6) to report errors and provide informational messages during network communication.
- It's vital for network diagnostics (e.g., ping, traceroute/tracert).
- ICMP does not ensure reliable delivery; it only provides feedback on issues.
Common ICMP Messages
- Echo Request/Reply: Used by ping to test reachability.
- This test ensures that the host or device is accessible.
- Destination Unreachable: Occurs when a host or router cannot deliver a packet.
- Codes (ICMPv4) for "unreach" error:
0: Net unreachable1: Host unreachable2: Protocol unreachable -3: Port unreachable
- Codes (ICMPv6) for "unreach" error:
0: No route1: Admin prohibited2: Beyond scope3: Address unreachable4: Port unreachable
- Codes (ICMPv4) for "unreach" error:
- Time Exceeded: Sent by a router if the IPv4 TTL or IPv6 Hop Limit reaches zero.
- This is critical for tracing route (e.g., with Traceroute/Tracert), signaling the path a packet follows.
ICMPv6 Enhancements
- ICMPv6 incorporates Neighbor Discovery (ND) messages.
- Router Solicitation (RS) and Router Advertisement (RA): Enable automatic configuration (SLAAC), discover routers, and obtain addressing information.
- Neighbor Solicitation (NS) and Neighbor Advertisement (NA): Handle address resolution (similar to ARP in IPv4) and prevent duplicate addresses.
- Multicast Addresses:
- All nodes:
ff02::1 - All routers:
ff02::2
- All nodes:
Testing Network Connectivity
-
ping: Tests host reachability using ICMP Echo Request/Reply.
- Steps commonly followed:
Ping loopback (127.0.0.1 for IPv4 or ::1 for IPv6)- Verifies the local TCP/IP stack.Ping default gateway- Checks connectivity to the router.Ping remote host- Confirms end-to-end network connectivity.
- No response can suggest multiple possible reasons:
- Host downtime
- ICMP blocking
- Incorrect addressing.
- Steps commonly followed:
-
traceroute/tracert: Displays the path (hops) and round-trip times for packets to a destination. This is possible using the ICMP "Time Exceeded" messages at each hop.
- The path breaks if any router blocks or fails at a particular hop (location).
Summary of Key ICMP Commands
-
Cisco:
pingorping ipv6tracerouteortraceroute ipv6
-
Windows:
pingtracert
-
IPv6 commands are similar (e.g.,
ping -6). Windows often detects IPv6 automatically.
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