What are the five stages for a neighbor cache entry defined in RFC 4861?
What will be an ideal response?
RFC 4861 defines the following five states for a neighbor cache entry:
INCOMPLETE-Address resolution is being performed on the entry. A Neighbor Solicitation message has been sent to the solicited-node multicast address of the target, but the corresponding Neighbor Advertisement message has not yet been received. If a Neighbor Advertisement message is not received after MAX_MULTICAST_SOLICIT (default value of three transmissions), then address resolution has failed and the neighbor entry is removed from the cache.
REACHABLE-The neighbor is considered reachable when either a solicited Neighbor Advertisement message is received or an upper-layer protocol communication indicating forward progress is received within the REACHABLE_TIME variable that is refreshed each time a packet indicating forward progress is received.
STALE-After the REACHABLE_TIME of 30,000 milliseconds has elapsed because of inactivity (no forward progress packets) in communications with the neighbor, the entry is changed to STALE. In addition, if an unsolicited Neighbor Discovery message that also advertises its link-layer is received, the entry is changed to the STALE state to ensure that a proper address resolution process is completed when the node needs to send a packet to the neighbor.
DELAY-After the entry has been changed to STALE and the node sends the first packet to the neighbor, the state changes to DELAY and the DELAY_FIRST_PROBE_TIME variable is set to a default of five seconds. If a reachability message is received within the timer period, the state changes to REACHABLE; otherwise, the state is changed to PROBE. The DELAY state allows upper-layer protocols time to provide reachability confirmation.
PROBE-When the entry changes to the PROBE state, the node sends unicast Neighbor Solicitation messages to the cached link-layer address of the neighbor based on the MAX_UNICAST_SOLICIT variable, which has a default value of three transmissions, and the RETANS_TIMER, which has a default value of 1,000 milliseconds. The neighbor entry is removed from the table if the maximum number of retransmissions and time is exceeded and no response has been received by the neighbor.
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a) expandable events b) tunneling events c) bubbling events d) direct events
In Page layout view, gridlines are shown in _____.
A. light gray B. light blue C. black D. red
Analyze the following code:
``` import javafx.application.Application; import javafx.scene.Scene; import javafx.scene.layout.HBox; import javafx.scene.layout.Pane; import javafx.geometry.Insets; import javafx.stage.Stage; import javafx.scene.image.Image; import javafx.scene.image.ImageView; public class Test extends Application { @Override // Override the start method in the Application class public void start(Stage primaryStage) { // Create a pane to hold the image views Pane pane = new HBox(10); pane.setPadding(new Insets(5, 5, 5, 5)); Image image = new Image("www.cs.armstrong.edu/liang/image/us.gif"); pane.getChildren().addAll(new ImageView(image), new ImageView(image)); // Create a scene and place it in the stage Scene scene = new Scene(pane); primaryStage.setTitle("ShowImage"); // Set the stage title primaryStage.setScene(scene); // Place the scene in the stage primaryStage.show(); // Display the stage } /** * The main method is only needed for the IDE with limited * JavaFX support. Not needed for running from the command line. */ public static void main(String[] args) { launch(args); } }``` a. The program runs fine and displays two images. b. new Image("www.cs.armstrong.edu/liang/image/us.gif") must be replaced by new Image("http://www.cs.armstrong.edu/liang/image/us.gif"). c. The image object cannot be shared by two ImageViews. d. The addAll method needs to be replaced by the add method.
Answer the following statements true (T) or false (F)
1) UDP is a connection-oriented protocol. 2) The IP address 127.0.0.1 refers to the local machine. 3) A server waits at a port for connection requests from clients. 4) Datagram packet transmission over a network is reliable—packets are guaranteed to arrive in sequence. 5) A socket’s send method accepts only a string argument.