Term
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Definition
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Term
| A set of IP address is Mapped to? |
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Definition
| A set of identifiers called Internet domain names |
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Term
| Each host has an IP address. How many ports does a host have? Name some reserved ports. |
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Definition
65536; 20,21 -ftp
23-telnet
80- http
RFC 1700 ~2000 |
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Term
| 32-bit IP addresses are stored in an ip address struct. What order are ip address stored in memory in? |
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Definition
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Term
| What is the structure of a ip address struct? |
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Definition
struct in_addr{
unsigned int s_addr;
}; |
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Term
| What is the convention of an IP address? |
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Definition
| A IP address is represented by a string: decimal values for bytes, separated by a period. IP address: 0x8002C2F2 = 128.2.194.242 |
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Term
| What functions are used to convert between binary IP addresses and dotted decimal strings? |
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Definition
inet_aton- decimal dotted to IP address in network byte order
inet_ntoa: - IP address in network byte order to dotted decimal string
NB: n- network representation
a-application representation |
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Term
| What are the five classes of IP address? |
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Definition
8 16 24 31
ClassA- 0 NetID HostID
ClassB- 1 0 NetID Host I.D
ClassC 1 1 0 NetID Host I.D
CalssD- 1 1 1 0- multicast address
ClassE 1 1 1 1- reserved for experiments |
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Term
| What is the form of a Network I.D? |
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Definition
| w.x.y.z/n where n is the number if bits in the NetID. |
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Term
| How many bits are in the Net ID of Unrouted private IP addresses? |
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Definition
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Term
| What are some first level Domain names? |
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Definition
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Term
| What are some second level Domain names? |
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Definition
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Term
| What are some third level Domain names? |
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Definition
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Term
| What is the worldwide distributed DNS database? |
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Definition
| A mapping between IP addresses and domain names maintained by the Internet |
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Term
| The struct hostent is the structure of an entry in the DNS database. What are the variables and what do they represent? |
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Definition
char *h_name - domain name
char **H_aliases - null terminated array of domain names
int h_addrtype - host type (AF_INET)
h_length - the length of an address in bytes
char **h_addr_list - null terminated array of in_addr |
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Term
What are the query keys of the following?
gethostbyname:
gethostbyaddr: |
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Definition
gethostbyname: DNS domain name
gethostbyaddr: an IP address |
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Term
| Each Host has a locally defined domain name localhost that always maps back to? |
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Definition
| The loopback address 127.0.0.1 |
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Term
| What types of mapping are possible in DNS host entries? |
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Definition
one-to-one
multiple to one IP
mutiple domain names to multiple IP addresses
none---some map to nothing |
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Term
| Domain Information Groper (DIG) does what? |
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Definition
| Provides a scriptable command line interface to DNS |
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Term
| How do clients and servers communicate? |
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Definition
| By sending streams of bytes over connections |
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Term
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Definition
The end point of a connection
An interface between application and network |
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Term
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Definition
| a 16- bit integer that identifies a process |
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Term
| Define the two types of ports |
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Definition
Ephemeral port- assigned automatically on client when client makes a connection request
Well-know port: associated with some service provided by a service |
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Term
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Definition
A unique identifier of a connection by endpoint socket addresses.
cliaddr:cliport, servaddr:servport |
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Term
| What are the two common types of sockets and their features? |
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Definition
Sock_stream (TCP): reliable delivery, in-order guarentee, connection oriented, bidirectional
Sock_dgram (UDP): unreliable delivery, no order guarentees, no notions of "connection" , can send or recieve |
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Term
| How are addresses and ports stored? |
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Definition
As integers, u_short sin_port (16-bit)
in_addr sin_addr (32-bit) |
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Term
| What is a Big edian Machine and what is a little-edian macine? |
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Definition
little-endian: lower bytes first
big-endian: higher bytes first |
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Term
| What is Host byte Odering? |
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Definition
| The byte ordering used by a host (big vs little) |
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Term
| What is Network Byte-Ordering? |
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Definition
| The byte ordering used by the network always big-edian |
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Term
| When transmitting what protocol about ordering followed? |
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Definition
| Any words sent through the network should be converted to Network Byte-Order prior to transmission (and back to Host Byte-Order once received) |
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Term
What do the following do on Big-edian machines?
u_long ntohl(u_long x);
u_short ntohs(u_short x);
u_long htonl(u_long x);
u_short htons(u_short x); |
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Definition
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Term
What do the following do on litte-edian machines?
u_long ntohl(u_long x);
u_short ntohs(u_short x);
u_long htonl(u_long x);
u_short htons(u_short x); |
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Definition
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Term
| name the function to create a socket and the define the variables. |
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Definition
int s= socket(domain, type, protocol)
domain- integer, communication domain
type- communication type sock_stream vs sock_dgram
protocol - specifies protocol (usually set to 0) |
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Term
| What are some example client programs? |
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Definition
| web browsers, ftp, telnet, ssh |
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Term
| How does a client find a server? |
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Definition
The IP address identifies the host
the well-know port in the server socket identifies the service and identifies the server process to perform that service |
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Term
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Definition
| Long-running processes(deamons) |
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Term
| When are servers created and how long do they run? |
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Definition
| Servers are created at boot-time and run continuous until the machine is turned off |
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Term
| Classify and define the port number for a webserver. |
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Definition
Port 80
Resources: files/compute cycle
Sevice: retrives files and runs CGI programs on behalf of the client |
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Term
| Classify and define the port number for a FTP Server |
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Definition
Resources: files
Service: Stores and retrieves files |
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Term
| Classify and define the port number for a telnet server |
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Definition
resources: terminal
Services: Proxies a terminal on the server machine |
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Term
| Classify and define the port number for a mail server |
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Definition
resource: email
service: stores mail messages in a spool file |
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Term
| What is socket to a kernel? |
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Definition
| Endpoint of communication |
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Term
| What is a socket to an application? |
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Definition
| a file descriptor that lets the application read/write from/to the network |
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Term
| What is the main distinction between a regular file I/O and socket I/o |
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Definition
| how the application opens the socket descriptors |
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Term
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Definition
The generic:
struct sockaddr {
u_short sa_family;
char sa_data[14];
};
struct sockaddr_in {
short sin_family;
u_short sin_port;
struct in_addr sin_addr;
char sin_zero[8];
}; |
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Term
What does sa_family do in the following?
struct sockaddr {
u_short sa_family;
char sa_data[14];
}; |
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Definition
specifies which address family is being used
determines how the remaining 14 bytes are used |
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Term
| Why is the generic sock address needed? |
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Definition
| NO void* when C created, needed to connect, bind and sccept |
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Term
| What does the internet-specific socket need to do to connect, bind or accept? |
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Definition
| Must cast (sockaddr_in *) to (sockaddr *) for connect, bind, and accept |
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Term
| What does the bind function do? |
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Definition
| associates and (can exclusively) reserves a port for use by the socket |
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Term
| What is the function for bind? |
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Definition
int status = bind(sockid, &addrport, size);
status: error status, = -1 if bind failed
sockid: integer, socket descriptor
addrport: struct sockaddr, the (IP) address and port of the machine (address usually set to INADDR_ANY – chooses a local address)
size: the size (in bytes) of the addrport structure |
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Term
| When can you skip binding for sock_stream and sock_dgram? |
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Definition
Sock_dgram- if only sending
sock_stream- can always destination determined during conn. setup
don't need to know sending port |
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Term
| True or false connection setup needed for sock_dgram |
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Definition
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Term
| Connection occurs between what types of participants? |
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Definition
passive: waits for an active participant to request connection
active: initiates connection request to passive side
after connection both become equal and can send and receive and terminate connection |
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Term
| What are the steps in setting up a connection? |
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Definition
1. listen for request
2. request and establish (active)
3. accept (passive)
step 4. data transfer |
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Term
| Where is the accepted connection? |
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Definition
| new socket. The old socket listens for more participants |
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Term
| What is the function to listen to a call? |
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Definition
int status = listen(sock, queuelen);
status: 0 if listening, -1 if error
sock: integer, socket descriptor
queuelen: integer, # of active participants that can “wait” for a connection |
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Term
| What is the function to accept a connection? |
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Definition
int s = accept(sock, &name, &namelen);
s: integer, the new socket (used for data-transfer)
sock: integer, the orig. socket (being listened on)
name: struct sockaddr, address of the active participant
namelen: sizeof(name): value/result parameter |
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Term
| What is the function to connect? |
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Definition
int status = connect(sock, &name, namelen);
status: 0 if successful connect, -1 otherwise
sock: integer, socket to be used in connection
name: struct sockaddr: address of passive participant
namelen: integer, sizeof(name) |
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Term
| Which of the following are blocking and non-blocking? Listen, accept and connect, send, recv |
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Definition
| listen-nonblocking accept and connect, count, recieve blokcing, |
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Term
| What is the function to send? |
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Definition
int count = send(sock, &buf, len, flags);
count: # bytes transmitted (-1 if error)
buf: char[], buffer to be transmitted
len: integer, length of buffer (in bytes) to transmit
flags: integer, special options, usually just 0 |
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Term
| What is the function to recieve? |
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Definition
int count = recv(sock, &buf, len, flags);
count: # bytes received (-1 if error)
buf: void[], stores received bytes
len: # bytes received
flags: integer, special options, usually just 0 |
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Term
| What calls are used to send and recieve without a connnection? (sock_dgram) |
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Definition
int count = sendto(sock, &buf, len, flags, &addr, addrlen);
count, sock, buf, len, flags: same as send
addr: struct sockaddr, address of the destination
addrlen: sizeof(addr)
int count = recvfrom(sock, &buf, len, flags, &addr,
&addrlen);
count, sock, buf, len, flags: same as recv
name: struct sockaddr, address of the source
namelen: sizeof(name): value/result parameter |
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Term
| How is a socket closed? and what does closing a socket do? |
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Definition
status = close(s);
s: the file descriptor (socket being closed)
frees up the port used by the socket |
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Term
| What code is used to close a port after a rough exit? |
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Definition
| #include
void cleanExit(){exit(0);}
in socket code:
signal(SIGTERM, cleanExit);
signal(SIGINT, cleanExit); |
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Term
What do the following do?
gets(Sentence);
n=write(clientSocket, Sentence, strlen(Sentence)+1);
n=read(clientSocket, modifiedSentence, sizeof(modifiedSentence));
close(clientSocket); |
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Definition
Get input stream
send line to server
read line from server
close connection |
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Term
| What is a listening descriptor? |
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Definition
End point for client connection requests
Created once and exists for lifetime of the server |
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Term
| What is a connected descriptor? |
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Definition
End point of the connection between client and server
A new descriptor is created each time the server accepts a connection request from a client
Exists only as long as it takes to service client |
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Term
| Why are connected and listening descriptors different? |
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Definition
| Allows for concurrent servers that can communicate over many client connections simultaneously |
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Term
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Definition
is invaluable for testing servers that transmit ASCII strings over Internet connections
Our simple echo server
Web servers
Mail servers |
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Term
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Definition
| unix> telnet
Creates a connection with a server running on and listening on port |
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Term
| How do handle problems with blocking calls? |
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Definition
create multi-process or multi-threaded code
turn off the blocking feature (e.g., using the fcntl file-descriptor control function)
use the select function call. |
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Term
| What does select function do in relation t sockets? |
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Definition
can be permanent blocking, time-limited blocking or non-blocking
input: a set of file-descriptors
output: info on the file-descriptors’ status
i.e., can identify sockets that are “ready for use”: calls involving that socket will return immediately |
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Term
| What is the select function? |
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Definition
int status = select(nfds, &readfds, &writefds, &exceptfds, &timeout);
status: # of ready objects, -1 if error
nfds: 1 + largest file descriptor to check
readfds: list of descriptors to check if read-ready
writefds: list of descriptors to check if write-ready
exceptfds: list of descriptors to check if an exception is registered
timeout: time after which select returns, even if nothing ready - can be 0 or infinity |
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Term
| When using select we the structure fd_set is used. What is it? |
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Definition
it is just a bit-vector
if bit i is set in [readfds, writefds, exceptfds], select will check if file descriptor (i.e. socket) i is ready for [reading, writing, exception] |
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Term
| What calls are needed before select? |
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Definition
FD_ZERO(&fdvar): clears the structure
FD_SET(i, &fdvar): to check file desc. i |
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Term
| What calls are needed after select? |
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Definition
| int FD_ISSET(i, &fdvar): boolean returns TRUE iff i is “ready” |
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Term
What do the following do?
bzero(char* c, int n):
gethostname(char *name, int len):
gethostbyaddr(char *addr, int len, int type): |
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Definition
0’s n bytes starting at c
gets the name of the current host
converts IP hostname to structure containing long integer |
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Term
| TCp types of sockets are? |
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Definition
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