Matias Freytes wrote:
> 1) I've been using "Unix Network Programming" by R. Stevens
> (1990). Is there any updated Linux Network Programming? I'd like
> to have an updated ioctl tutorial/handbook.
By the time a Linux book reaches the shelves, it's usually out of
date. Particularly with regard to networking, which is probably the
most intensively developed subsystem in the kernel.
There is a list of ioctl() requests in the ioctl_list(2) manpage. The
only documentation for most of these is the source code.
> 2)I'm working on a network application and need to fill a menu
> with the available network interfaces (up). How can I get this
> info? I think this is quite related to my first question.
To get a list of interfaces, use ioctl(SIOCGIFCONF), e.g.
struct ifconf ifc;
struct ifreq ifrs[100];
int sk;
int i;
sk = socket(PF_INET, SOCK_DGRAM, 0);
ifc.ifc_len = sizeof(ifrs);
ifc.ifc_req = ifrs;
ioctl(sk, SIOCGIFCONF, &ifc);
for (i = 0; i < ifc.ifc_len / sizeof(struct ifreq); i++) {
struct ifreq *ifr = &ifrs[i];
struct sockaddr_in *addr = (struct sockaddr_in *) &ifr->ifr_addr;
printf("%2d %-8s %-15s\n", i, ifr->ifr_name, inet_ntoa(addr->sin_addr));
}
close(sk);
[error handling removed for brevity.]
To find out if a given interface is up, use ioctl(SIOCGIFFLAGS), e.g.
const char *if_name = /* interface name, e.g. ifr->ifr_name */;
int fd;
struct ifreq ifr;
fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);
strcpy(ifr.ifr_name, if_name);
ioctl(fd, SIOCGIFFLAGS, &ifr);
printf("%s is %s\n", if_name, (ifr.ifr_flags & IFF_UP) ? "up" : "down");
> 3) I also need to "capture" full 802.3 encapsulated IP frames
> from my LAN and save them to a file. I' ve read about ether taps
> and packet sockets. What should I use? This is for a group of
> students who want to play a little bit with "frame decoding". I'd
> like to get
You can use "tcpdump -i eth0 -s 1518 -w <filename> ...". If you want
to do it yourself, you can use libpcap (as used by tcpdump), or create
a PF_PACKET socket (as used by libpcap); see the packet(7) manpage.
--
Glynn Clements <glynn.clements@virgin.net>
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