Networking exercises

NET-1. Networking

QUESTION NET-1A. Which of the following system calls should a programmer expect to sometimes block (i.e., to return after significant delay)? Circle all that apply.

1. socket
2. read
3. accept
4. listen
5. connect
6. write
7. usleep
8. None of these

#2 read, #3 accept, #5 connect, #6 write, #7 usleep.

QUESTION NET-1B. ⚠️ Below are seven message sequence diagrams demonstrating the operation of a client–server RPC protocol. A request such as “get(X)” means “fetch the value of the object named X”; the response contains that value. Match each network property or programming strategy below with the diagram with which it best corresponds. You will use every diagram once.

1. Loss
2. Delay
3. Reordering
4. Duplication
5. Batching
6. Prefetching
7. Exponential backoff

A	B	C	D

E	F	G

#1—B, #2—C, #3—F, #4—D, #5—G, #6—A, #7—E
(A—#6, B—#1, C—#2, D—#4, E—#7, F—#3, G—#5)

While G could also represent prefetching, A definitely does not represent batching at the RPC level—each RPC contains one request—so under the rule that each diagram is used once, we must say G is batching and A is prefetching.

QUESTION NET-1C. List some resources that a DoS attack on a network server might exhaust.

At least: file descriptors, memory (stack), processes/threads. There’re a lot of correct answers, though! You can run out of virtual memory or even physical memory.

QUESTION NET-1D. A server sets up a socket to listen on a connection. When a client wants to establish a connection, how does the server manage the multiple clients? In your answer indicate what system call or calls are used and what they do.

The server calls accept on a listening file descriptor. This creates a new file descriptor that is particular to the connection with a particular client, giving the server uses a different fd for each client.