bind() call in tcp client

Question

I am trying to change the source ip address for a tcp packet. Code snippet as given bellow

 bzero(&clientaddr,sizeof(clientaddr));
 clientaddr.sin_family = AF_INET;
 clientaddr.sin_addr.s_addr=inet_addr("172.16.2.10");
 clientaddr.sin_port=htons(8080);
 if (bind(sockfd, (struct sockaddr *) &clientaddr, 
   sizeof(clientaddr)) < 0) 
{
    perror("bind");
}

Binding a particular port is working fine, but when i tried to bind with a diffrent ip adress, the bind is failing with error

bind: Cannot assign requested address

I also tried by setting the socket option as follows,]

setsockopt (sockfd, SOL_IP, IP_TRANSPARENT, &n1, sizeof(int));*

then also its failing with same error.

How could i change my source ip address for packet, originated from my PC. Please help me, its for a proxy application.

OS :Linux 2.6.37-tproxy #1 SMP Wed Apr 3 23:34:00 IST 2013 x86_64 x86_64 x86_64 GNU/Linux

Thanks in advance.

Not sure, but you probably have to use raw sockets to do this. — Barmar, Jul 05 '13 at 06:38
@Barmar If am not wrong, I have seen this possible in CentOS/RHEL 6.0 in the same way OP did — VoidPointer, Jul 05 '13 at 06:39
@VoidPointer I am using CentOS 6.3, is it a problem with this? — Justin Jose, Jul 05 '13 at 06:41
No probs I guess, if your kernel supports it. I dont have much experience on this. Thought this system info would help others to help you.. — VoidPointer, Jul 05 '13 at 06:51
Did you run your application as root or with a user having the CAP_NET_ADMIN capability? What was the errno error set by setsockopt, if any? I assume you have read [http://lxr.linux.no/#linux+v3.10/Documentation/networking/tproxy.txt](http://lxr.linux.no/#linux+v3.10/Documentation/networking/tproxy.txt) and are following it. I probably can not help much more, without some more exact error or more code (preferrably [SSCCE](http://www.sscce.org/) — thuovila, Jul 05 '13 at 08:14

score 1 · Answer 1 · answered Sep 27 '13 at 12:48

1

You will need to use a raw socket and create the ip and tcp headers (where you will be able to set the desired IP Address (spoofing).

raw_socket = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);

You can check the linux manual page man 7 raw

answered Sep 27 '13 at 12:48

krouis

129
4

score 0 · Answer 2 · answered Jul 05 '13 at 10:38

0

You can only bind() to an IP address that is local to your computer, i.e. implemented by one of your network interfaces.

answered Jul 05 '13 at 10:38

user207421

305,947
44
307
483

Are you familiar with the Linux transparent proxy functionality? See the tproxy.txt in kernel documenttion and `man 7 ip` at IP_TRANSPARENT option. – thuovila Jul 05 '13 at 14:21

bind() call in tcp client

2 Answers2