sockets -> MTU (Maximum Transfer Unit)

sockets -> MTU (Maximum Transfer Unit)

[ramzez]

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Hi friends...

  In my C app, How do I can know the MTU (Maximum Transfer Unit) of my
net?

thanks

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Re: sockets -> MTU (Maximum Transfer Unit)

[Glynn Clements]

ramzez wrote:

>   In my C app, How do I can know the MTU (Maximum Transfer Unit) of my
> net?

You can obtain the MTU of an interface with ioctl(SIOCGIFMTU), e.g.

	const char if_name[] = "eth0";
	struct ifreq ifr;
	int fd;

	fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);

	strcpy(ifr.ifr_name, if_name);
	ioctl(fd, SIOCGIFMTU, &ifr);

	printf("MTU of %s is %d\n", if_name, ifr.ifr_mtu);

Assuming that path MTU discovery is enabled, you can obtain the path
MTU of an individual connection using getsockopt(SOL_IP, IP_MTU), e.g.

	int mtu;
	int mtulen = sizeof(mtu);

	getsockopt(skt, SOL_IP, IP_MTU, &mtu, &mtulen);

-- 
Glynn Clements <glynn.clements@virgin.net>