AT home, I have 2 devices, one device has the IP address of 10.0.0.2 it's the server and another device which has the IP address of 10.0.0.6
so, on the client code I have this pierce of code
sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
/* Construct the server address structure */
ServPort=3200;
servIP="10.0.0.2";
memset(&ServAddr, 0, sizeof(ServAddr)); /* Zero out structure */
ServAddr.sin_family = AF_INET; /* Internet address family */
ServAddr.sin_addr.s_addr = inet_addr(servIP); /* Server IP address */
ServAddr.sin_port = htons(ServPort); /* Server port */
/* Establish the connection to the server */
i= connect(sock, (struct sockaddr *) &ServAddr, sizeof(ServAddr));
I able fully able to connect to the server of 10.0.0.2 from client 10.0.0.6
The code executed successfully.
Then I go to library and now the Server has the IP address 192.168.1.168 and the client device has the IP address 192.168.1.147
so, the code I modified accordingly for the client
sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
/* Construct the server address structure */
ServPort=3200;
servIP="192.168.1.168";
memset(&ServAddr, 0, sizeof(ServAddr)); /* Zero out structure */
ServAddr.sin_family = AF_INET; /* Internet address family */
ServAddr.sin_addr.s_addr = inet_addr(servIP); /* Server IP address */
ServAddr.sin_port = htons(ServPort); /* Server port */
/* Establish the connection to the server */
i= connect(sock, (struct sockaddr *) &ServAddr, sizeof(ServAddr));
Now, I not able to connect to the server.
So, I am confused, all the codes are the same, except the IP address of server device and client device. At home I am able to run the code successfully, but not in the library. this is just TCP, so it should have to do with any firewall.
Related
I have a userspace program which construct its own packet (App, UDP, IP) and write()s it to the TUN device. The packet is intercepted by my own Netfilter module, which it checks if the packet it received is one which we want to process. Then my Netfilter module will skb_clone() the original skb and create a response packet which I fill in with some data to be returned to the user-space program. To send the response, I use dev_queue_xmit(). It randomly returns NET_XMIT_CN even though I just created a fresh TUN device and there is no other traffic passing through. If I keep executing the user-space program (sending new packets to the TUN device), eventually the TUN device will respond, but not consistently. I can't seem to track down why it is behaving so erratically.
Essentially I am using the TUN device as a mechanism to communicate from user-space to kernel-space, and vice versa.
Here's my user-space app:
tun_fd = tun_alloc(dev_name);
packet = ... /* Construct request...*/
nwrite = write(tun_fd, packet, packet_len);
...
unsigned recv_buf[1500];
int received = 0;
while (!received) {
nread = read(tun_fd, recv_buf, 1500);
...
}
...
close(tun_fd);
Here's my Netfilter module:
static struct nf_hook_ops nfho;
static int __init my_hook(void)
{
nfho.hook = hook_func;
nfho.hooknum = 0;
nfho.hook = PF_INET;
nfho.hook = NF_IP_PRI_FIRST;
nf_register_hook(&nfho);
}
unsigned int hook_func(void *priv, struct sk_buff *skb, const struct nf_hook_state *state)
{
struct sk_buff *clone_skb = skb_clone(skb, GFP_KERNEL):
...
/*
* Check if packet is for us.
* Check IP & UDP header, etc
* If so, parse request, put together response clone_skb
*/
...
if ((err = dev_queue_xmit(clone_skb)) != 0) {
printk(....)
/* Either it return 0 (success) or 2, meaning NET_XMIT_CN */
}
return NF_STOLEN;
}
I can't seem to figure out this behavior. Am I misusing the TUN device? Is there an easier way than this?
Please let me know if I should provide any extra details or clarify something.
I am trying to access a PHP file in my server with an Arduino and the Ethernet shield. This file captures the URL parameters "Sensor" and "Value" and stores the read data into a database.
This is my code:
#include <SPI.h>
#include <Ethernet.h>
EthernetClient client;
byte MACaddress[] = {0xDE,0xAD,0xBE,0xEF,0xFE,0xED};
byte IPaddress[] = {10,0,0,178};
byte DNSserverIPaddress[] = {4,4,4,4};
byte gatewayIPaddress[] = { 10, 0, 0, 100 };
byte subnetMask[] = { 255, 255, 255, 0 };
char serverName[] = "log.server.com";
void setup() {
Serial.begin(9600);
Ethernet.begin(MACaddress, IPaddress, DNSserverIPaddress, gatewayIPaddress, subnetMask);
}
void loop()
{
delay (5000);
Serial.println("connecting to server...");
client.connect(serverName, 80);
Serial.println("making HTTP request...");
client.println("GET /logger.php?sensor=temp&value=19 HTTP/1.1");
client.println("HOST: log.server.com");
client.println();
}
After uploading this code to my Arduino Mega + Ethernet shield, nothing changes in my database...
What is wrong?
Well, first you should add a condition check to know if the Arduino think it worked or not:
if (client.connect(...)) {
/* Stuff you do on success */
}
else {
Serial.println("failure! :-(")
}
If it does print failure! you got a network configuration problem on the Arduino side. If it does work, the problem is after the Arduino.
Then try opening a server with nc -kl 42000 and change the port you connect to on 42000 in the Arduino sketch, to be sure whether the network connection works.
If it does work, then you've got a problem on your host side (the webserver), if it does not, you may have a problem on the network between the Arduino and the host.
You should then try to connect to a server's IP address instead of a fully qualified domain name (FQDN). If that works, it may be the DNS server that is unreachable, and you should try to use 8.8.8.8 instead (or your local network's DNS server).
Also check that the IP address you're using is indeed free of use (and not assigned by a DHCP or used by another computer), as well as the MAC address is really unused... (addresses like {0xDE,0xAD,0xBE,0xEF,0xFE,0xED} tend to be used a lot in hacks...).
My opinion, is that your bug is the DNS server that is unreachable, as there's no DNS resolver opened on 4.4.4.4.
I have a project that uses TCP sockets to communicate between a server and one client. As of now I have been doing this on one computer so I have just used local address of "127.0.0.1" for the address to bind and connect to on both sides and its worked fine. Now I have a second computer to act as a client, but I don't know how to change the addresses accordingly. They are connected through a network that is not connected to the Internet. Before the code looked like this -
Server -
struct addrinfo hints;
struct addrinfo *servinfo; //will point to the results
//store the connecting address and size
struct sockaddr_storage their_addr;
socklen_t their_addr_size;
memset(&hints, 0, sizeof hints); //make sure the struct is empty
hints.ai_family = AF_INET; //local address
hints.ai_socktype = SOCK_STREAM; //tcp
hints.ai_flags = AI_PASSIVE; //use local-host address
//get server info, put into servinfo
if ((status = getaddrinfo("127.0.0.1", port, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
return false;
}
//make socket
fd = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol);
if (fd < 0) {
printf("\nserver socket failure %m", errno);
return false;
}
//allow reuse of port
int yes=1;
if (setsockopt(fd,SOL_SOCKET,SO_REUSEADDR,(char*) &yes,sizeof(int)) == -1) {
perror("setsockopt");
return false;
}
//unlink and bind
unlink("127.0.0.1");
if(bind (fd, servinfo->ai_addr, servinfo->ai_addrlen) < 0) {
printf("\nBind error %m", errno);
return false;
}
Client -
struct addrinfo hints;
struct addrinfo *servinfo; //will point to the results
memset(&hints, 0, sizeof hints); //make sure the struct is empty
hints.ai_family = AF_INET; //local address
hints.ai_socktype = SOCK_STREAM; //tcp
hints.ai_flags = AI_PASSIVE; //use local-host address
//get server info, put into servinfo
if ((status = getaddrinfo("127.0.0.1", port, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
return false;
}
//make socket
fd = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol);
if (fd < 0) {
printf("\nserver socket failure %m", errno);
return false;
}
//connect
if(connect(fd, servinfo->ai_addr, servinfo->ai_addrlen) < 0) {
printf("\nclient connection failure %m", errno);
return false;
}
I know it should be simple, but I can't figure out how to change the IPs to get them to work. I tried setting the server computer's IP address in the quotes in these lines -
if ((status = getaddrinfo("127.0.0.1", port, &hints, &servinfo)) != 0)
and
unlink("127.0.0.1");
and then change the address in the client code to the client computer's IP address in this line -
if ((status = getaddrinfo("127.0.0.1", port, &hints, &servinfo)) != 0)
Whenever I do that, it tells me connection refused. I have also tried doing the opposite way of putting the server's address in the client's line and client's address in the server's lines along with a few other attempts. At this point I feel like I am just guessing though. So can someone please help me understand how to change this from using the local address with one computer to connecting two computers? Any help is appreciated.
First, unlink("127.0.0.1"); is totally wrong here, don't do that.
Then, you have two computers connected by some network. Both should have IP addresses. Replace 127.0.0.1 with the server's IP address in both client and the server. The server does not to have to know client's address beforehand - it'll get that information from the accept(2) call. The client needs server's address to know where to connect. The server needs its own address for the bind(2) call.
The main problem is that your putting AI_PASSIVE in your client code. AI_PASSIVE is meant for servers only (that's what it signals).
Also on the server side you should first of all not call unlink. That's for AF_UNIX sockets only, not AF_INET. Secondly you don't need to put "127.0.0.1" in the getaddrinfo line on the server side. It's better to use NULL to bind to all available addresses.
If you change those things, I believe your code should work. However you're actually supposed to loop on the getaddrinfo result using the ai_next pointer and try to connect to each result, using the first that succeeds.
Connection Refused usually means your client received a RST to his SYN. This is most often caused by the lack of a listening socket on the server, on the port you're trying to connect to.
Run your server
On the CLI, type netstat -ant. Do you see an entry that's in LISTEN state on your port?
Something like:
tcp4 0 0 *.3689 *.* LISTEN
I bet you do not, and therefore have a problem with your server listening socket. I also bet the changes you made this this line:
if ((status = getaddrinfo("127.0.0.1", port, &hints, &servinfo)) != 0) {
Weren't quite right. Try changing that IP to 0.0.0.0 on the server to tell it to to bind to any IP on the system. On the client, that line should have the IP address of the server. You should also remove the unlink() call in the server; unnecessary.
If you do have a listening socket, then there's probably a firewall or something in between your boxes that's blocking the SYN. Try typing service iptables stop on the CLI of both systems.
When using TCP under Winsock, is it possible for my client to choose its local port number when connecting?
Thanks,
Dave
Yes. You have to bind the socket before connecting.
sockaddr_in sin;
memset(&sin, 0, sizeof(sin));
sin.sin_family = AF_INET;
sin.sin_port = htons(11234); /* This will be your source port. */
if (SOCKET_ERROR == bind(sock, (SOCKADDR*)&sin, sizeof(sin))) {
/* Handle error. */
}
I am working on Ubuntu 9.04. I am running this on VMware workstation. Here is my C code:
int sockfd,cnt,addrlen;
const int on = 1;
struct sockaddr_in servaddr,cliaddr;
char reply[512];
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd < 0) {
perror("socket");
exit(1);
}
setsockopt(sockfd,SOL_SOCKET,SO_REUSEADDR, &on,sizeof(on));
bzero(&cliaddr, sizeof(cliaddr));
cliaddr.sin_family = AF_INET;
cliaddr.sin_addr.s_addr = htonl(INADDR_ANY);
cliaddr.sin_port = htons(68);
addrlen = sizeof(servaddr);
if (bind(sockfd, (struct sockaddr *) &cliaddr, sizeof(cliaddr)) < 0) {
perror("bind");
exit(1);
}
while(1)
{
cnt = recvfrom(sockfd, reply, sizeof(reply), 0,(struct sockaddr *) &servaddr, &addrlen);
if (cnt < 0) {
perror("recvfrom");
exit(1);
}
printf("\nReply Received\n");
}
I run this program in one terminal and run 'dhclient' on another. I receive no datagrams. What am I doing wrong?
Looks like you're listening on UDP port 68 for a broadcasted message from the client? If I'm reading DHCP correctly, the client will send its broadcase 'discover' request FROM UDP port 68, but TO UDP port 67 on the server, so you would need to be listening on port 67 to receive it.
An easy 'first' test to test you're code before trying it with dhclient would be to try talking to your server with netcat. a command line like
echo "Foo" | netcat -u localhost 68
Should cause a packet to be received by your current code.
Another good debugging tool is wireshark which will let you see exactly what UDP packets are being sent by dhclient and what they contain.
I'm not sure what you're doing wrong but if I were you I'd write my own client which is very simple and see if it can talk to your server code above (who knows what dhclient might do outside of contact your code). I'd also temporarily change the port number to something not well-known. This way I wouldn't be interfering with any other programs and interfaces.
I recommend this tutorial. Also, are you running as root? You can't get that low-numbered port otherwise.