Ubuntu 14.04 network interface–Update modification without rebooting

Once a new NIC is added to  /etc/network/interface, we don’t have to reboot to update the configuration.

I’m set up a new installed server with Ubuntu 14.04 this afternoon. Since it has serveral NICs, I had to add them on interface manually. But the ifconfig doesn’t show the update though I tried

sudo /etc/init.d/networking restart

or

sudo service networking restart

After googling, it turned out that one should turn off and on the network devices before restarting the network service.

sudo ifdown eth0 && sudo ifup eth0

sudo service networking restart

Now the new NIC is now in the interface!

Sending raw Ethernet packets from a specific interface in C on Linux

Austin's blog

Lately I’ve been writing some code to send packets to a specific MAC address from a specific interface. I’m sure this will come in handy again so here is how it goes:

Includes:
(might not need all of these)

#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <net/if.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <netinet/ether.h>
#include <linux/if_packet.h>

Open the raw socket:

int sockfd;
...
/* Open RAW socket to send on */
if ((sockfd = socket(AF_PACKET, SOCK_RAW, IPPROTO_RAW)) == -1) {
    perror("socket");
}

Get the index of the interface to send on:

struct ifreq if_idx;
...
memset(&if_idx, 0, sizeof(struct ifreq));
strncpy(if_idx.ifr_name, "eth0", IFNAMSIZ-1);
if (ioctl(sock, SIOCGIFINDEX, &if_idx) < 0)
    perror("SIOCGIFINDEX");

Get the MAC address of the interface to send on:

struct ifreq if_mac;
...
memset(&if_mac, 0, sizeof(struct ifreq));
strncpy(if_mac.ifr_name, "eth0", IFNAMSIZ-1);
if (ioctl(sock, SIOCGIFHWADDR, &if_mac) < 0)
    perror("SIOCGIFHWADDR");

Get the IP address of the interface to send on:

struct ifreq if_ip; …

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