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CIT237 Ch 5 ICMP
| Term | Definition |
|---|---|
| advertising rate | The rate at which a service (typically a routing service) is announced on a network. An example of an advertising rate is the 10-minute advertising rate for ICMP Router Advertisement packets. |
| allowable data size | The amount of data that can be transferred across a link; the MTU. |
| auto-reconfiguration | The process of automatically changing the configuration of a device. |
| auto-recovery | The process of automatically recovering from a fault. |
| available routes | The known functional routes on an internetwork. Available routes are not necessarily the optimal routes. On IP networks, routers periodically advertise available routes. |
| average response time | The median time required to reply to a query. The history of network average response times is used to provide a measurement for comparison of current network responses. |
| backward compatibility | A feature that enables a device, process, or protocol to operate with earlier versions of software or hardware that do not support all the latest, up-to-date, or advanced features. |
| command-line parameter | Options added to a command issued at a prompt (not in a windowed environment). For example, in the command arp -a, the -a is the parameter for the command arp. |
| connectivity tests | Tests to determine the reachability of a device. IP PING and TRACEROUTE are two utilities that can be used for connectivity testing. |
| Destination Unreachable message | An ICMP error message sent from a router to a network host notifying the host that its message could not be delivered to its destination. |
| Destination Unreachable packets | ICMP packets that indicate a failure to reach a destination due to a fragmentation problem, parameter problem, or other problem. |
| end-to-end minimum MTU size | The smallest data size that can be sent from one host to another host on an internetwork. Packets may be fragmented to reach the end-to-end minimum MTU size, or the PMTU process can be used to determine the minimum size. |
| expired route entry | A route entry that is considered “too old” and won’t be used to forward data through an internetwork. |
| firewalking | A two-staged reconnaissance method involving an initial perimeter device discovery phase and subsequent inverse mapping of filtered devices (by eliciting Time Exceeded responses). |
| fragmentable | Able to be fragmented. A packet must have the May Fragment bit set in order to allow an IP packet to be fragmented if necessary. |
| gateway | In the TCP/IP environment, the term “gateway” is used to refer to a Network layer forwarding device typically known as a router. The default gateway is the router a host sends a packet to when the host has no specific route to a destination. |
| hacker | A person who uses computer and communications knowledge to exploit information or functionality of a device. |
| host probe | A reconnaissance process used to determine which hosts are active on an IP network. Typically, the PING process is used to perform a host probe. |
| ICMP Echo communication | An ICMP process whereby a host sends an Echo packet to another host on an internetwork. If the destination host is active and able, it echoes back the data that is contained in the ICMP Echo packet. |
| ICMP Echo Request packets | Packet that are sent to a device to test connectivity. If the receiving device is functional and can reply, it should echo back the data that is contained in the data portion of the Echo Request packet. |
| ICMP error message | Error messages sent using the ICMP protocol. Destination Unreachable, Time Exceeded, and Parameter Problem are examples of ICMP error messages. |
| ICMP query message | ICMP messages that contain requests for configuration or other information. ICMP Echo Request, Router Solicitation, and Address Mask Request are examples of ICMP query messages. |
| ICMP Router Discovery | A process in which hosts send ICMP Router Solicitation messages to the all-router multicast address (224.0.0.2). Local routers that support the ICMP Router Discovery process reply with an ICMP Router Advertisement unicast to the host. |
| ICMP Router Solicitation | The process that a host can perform to learn of local routers. ICMP Router Solicitation messages are sent to the all-routers multicast address of 224.0.0.2. |
| Internet Control Message Protocol (ICMP) | A key protocol in the TCP/IP protocol suite that provides error messages and the ability to query other devices. IP PING and TRACEROUTE utilities use ICMP. |
| Internet Group Management Protocol (IGMP) | A protocol that supports the formation of multicast groups. Hosts use IGMP to join and leave multicast groups. Routers track IGMP memberships and only forward multicasts on a link that has active members of that multicast group. |
| inverse mapping | The process of identifying live network hosts (mapping internal network layout) positioned behind a filtering device by probing for addresses known not to be in use. |
| IP address scanning | The process of sending PING packets (ICMP Echo Request packets) to each host within an IP address range to obtain a list of active hosts in that range. This method is commonly used by hackers |
| metrics | Measurements that may be based on distance (hop count), time (seconds), or other values. |
| millisecond | One-thousandth of a second. |
| network congestion | A condition that occurs when the delivery time for packets (also known as network latency) increases beyond normal limits. Congestion can result from problems with network links, overloaded hosts or routers, or unusually heavy network usage levels. |
| Network Time Protocol (NTP) | A time synchronization protocol defined in RFC 1305. NTP provides the mechanisms to synchronize and coordinate time distribution in a large, diverse Internet operating at varying speeds. |
| optimal route | The best route possible. Typically, routing protocols are used to exchange routing metric information to determine the best route possible. |
| overhead | The non-data bits or bytes required to move data from one location to another. The datalink header is the overhead required to move an IP packet from one device to another across a network. |
| path | The route that a packet can take through an internetwork. |
| path discovery | The process of learning possible routes through a network. |
| Path MTU (PMTU) | The MTU size that is supported through an entire path; the lowest common denominator MTU through a path. The Path MTU is learned through the PMTU Discovery process. |
| PMTU Discovery | The process of learning the MTU that is supported through an entire path. ICMP is used for PMTU Discovery. |
| Pathping | A Windows utility used to test router and path latency, as well as connectivity. |
| reachability | The ability to find at least one transmission path between a pair of hosts so they can exchange datagrams across an internetwork. |
| reconnaissance process | The process of learning various characteristics about a network or host. Typically, reconnaissance probes precede network attacks. |
| redirect | Point out another path. Using ICMP, a router can redirect a host to another more optimal router. |
| restricting link | A link that does not support forwarding based on the current packet format and configuration. PMTU is used to identify restricting links so hosts can re-send packets using an acceptable MTU size. |
| retry counter | A counter that tracks the number of retransmissions on the network. The most common retry counter found in TCP/IP networking is the TCP retry counter. |
| round-trip time | The amount of time required to get from one host to another host and back. |
| route tracing | A technique for documenting which hosts and routers a datagram traverses in its path from the sender to the receiver. (The Traceroute and Tracert commands use ping in a systematic way to provide this information.) |
| silent discard | The process of discarding a packet without notification to any other device that such a discarding process occurred. For example, a black hole router silently discards packets that it cannot forward. |
| throughput difference | The comparative difference in throughput between two paths. Throughput is measured in Kbps or Mbps. |
| time synchronization | The process of obtaining the exact same time on multiple hosts. Network Time Protocol (NTP) is a time synchronization protocol. |
| Traceroute | The name of the Linux command that uses multiple ping commands to establish the identity and round-trip times for all hosts between a sender and a receiver. |
| Tracert | The name of the Windows command that uses multiple ping commands to establish the identity and round-trip times for all hosts between a sender and a receiver. |
| Universal Time (UT) | Sometimes called Universal Coordinate Time (UCT), Greenwich Mean Time (GMT), or Zulu Time. A time scale based on the Earth’s rotation. |
| unsolicited | Unrequested. Unsolicited replies are advertisements that occur on a periodic basis. For example, ICMP Router Advertisements typically occur on a 7–10 minute basis. |
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Leisac
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