UDP Sockets

Ø Basic UDP Client and Server

Ø Displaying Destination Address

Ø Connected UDP Clients

Ø Reliability of  UDP

Ø Big Packets

Ø Select UDP and TCP

Ø Basic UDP Client and Server:

· Server: udpserv01  ( it uses dg_echo )

· Client: udpcli01     ( it uses dg_cli )

· udpcli03 displays sender IP and port (it uses dgcliinetaddr.c)

n = Recvfrom(sockfd, recvline, MAXLINE, 0, (SA *) replyaddr, &len);
 
printf("received reply from %s, port %d\n", 

inet_ntoa(replyaddr->sin_addr), htons(replyaddr->sin_port));

To test:

% cd ~/stevens3rd.book/unpv13e/udpcliserv

% udpserv01   &

% udpcli01  127.0.0.1
Hi
Hi
^D

% udpcli03   127.0.0.1
Hi
received reply from 127.0.0.1, port 10111
Hi
^D

Ø Displaying Destination Address:

· Example: udpserverDaddr.c

i = 1;

setsockopt (echo_s, IPPROTO_IP, IP_RECVDSTADDR, (char *)&i, sizeof(i));

recvmsg (echo_s, &mhdr, MSG_DONTWAIT));

for (cmptr = CMSG_FIRSTHDR(&mhdr); cmptr != NULL;

cmptr = CMSG_NXTHDR(&mhdr, cmptr)) {

if (cmptr->cmsg_level == IPPROTO_IP &&

cmptr->cmsg_type ==  IP_RECVDSTADDR) {

memcpy(&ip_addr, CMSG_DATA(cmptr), sizeof(struct in_addr));

printf("udp message sent  to: %s\n",  

inet_ntop (AF_INET, &ip_addr, str, sizeof(str)));

}

}

To test:

· Server:

% cd ~/stevens3rd.book/unpv13e/udpcliserv

% udpServerDaddr 10111 224.0.0.1

udp message sent to: 224.0.0.1

udp message sent from: 128.82.4.19:44617

received:KKKK

· Client:

% cd   ~/stevens3rd.book/unpv13e/udpcliserv
% udpcli03 224.0.0.1

KKKK

received reply from 128.82.4.19, port 10111

KKKK

Ø Connected UDP Clients:

· Client: udpcli04 (it uses dgcliconnect.c)

For a connected udp socket:

You can use read/write instead of sendto/recvfrom

· Server: you can use udpserv01.c

To test:

% cd ~/stevens3rd.book/unpv13e/udpcliserv
% udpserv01   &
% udpcli04  127.0.0.1
Hi
Hi
^D

% udpcli04   128.82.4.120
Hi

read error: Connection refused

Why? Because there is no server is running at 28.82.4.120!

This error is reported only to connected upd sockets

but not for unconnected udp sockets.

% sudo tcpdump -N -t | grep 10111

IP something.40498 > somethingelse.10111: UDP,length 3

IP somethingelse > something: ICMP somethingelse udp port 10111 unreachable, length 39

· Client: udpcli09.c displays the local & peer ip/port information even there is no server running!

Ø Reliability of UDP:

· Client: udpcli06    (it uses dgcliloop1.c)

sends 2000 packets to server.

· Server: udpserv06  (it uses dgecholoop1.c)

which receive some, but may not all, the 2000 packets.

OR

· Server: udpserv07  (it uses dgecholoop2.c)

which receive more,   but may not all, the 2000 packets,   

by increasing   socket RCVBUF:

n = 240 * 1024;
Setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &n, sizeof(n));

To test:

% cd   ~/stevens3rd.book/unpv13e/udpcliserv
% udpserv07  

interrupt me

% udpcli06  127.0.0.1

(run before and after interrupt me)

Ø Big Packets:

· Client: udpcli10     (it uses dgclibig.c)

· Server: udpserv10  (it uses dgservbig.c)

Risk! loosing the packet because of fragmentation.

Ø Select UDP and TCP:

· Server: udpservselect01.c

Used to serve UDP & TCP clients.

· Client:

Use any, e.g., udpcli01 &  tcpcli01