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RTNETLINK(3)			    Linux Programmer's Manual			     RTNETLINK(3)

       rtnetlink - macros to manipulate rtnetlink messages

       #include <asm/types.h>
       #include <linux/netlink.h>
       #include <linux/rtnetlink.h>
       #include <sys/socket.h>

       rtnetlink_socket = socket(AF_NETLINK, int socket_type, NETLINK_ROUTE);

       int RTA_OK(struct rtattr *rta, int rtabuflen);

       void *RTA_DATA(struct rtattr *rta);

       unsigned int RTA_PAYLOAD(struct rtattr *rta);

       struct rtattr *RTA_NEXT(struct rtattr *rta, unsigned int rtabuflen);

       unsigned int RTA_LENGTH(unsigned int length);

       unsigned int RTA_SPACE(unsigned int length);

       All  rtnetlink(7) messages consist of a netlink(7) message header and appended attributes.
       The attributes should be manipulated only using the macros provided here.

       RTA_OK(rta, attrlen) returns true if rta points to a valid routing attribute;  attrlen  is
       the  running length of the attribute buffer.  When not true then you must assume there are
       no more attributes in the message, even if attrlen is nonzero.

       RTA_DATA(rta) returns a pointer to the start of this attribute's data.

       RTA_PAYLOAD(rta) returns the length of this attribute's data.

       RTA_NEXT(rta, attrlen) gets the next attribute after rta.  Calling this macro will  update
       attrlen.  You should use RTA_OK to check the validity of the returned pointer.

       RTA_LENGTH(len)	returns  the  length  which  is  required  for len bytes of data plus the

       RTA_SPACE(len) returns the amount of space which will be needed	in  a  message	with  len
       bytes of data.

       These macros are nonstandard Linux extensions.

       This manual page is incomplete.

       Creating a rtnetlink message to set the MTU of a device:
	   #include <linux/rtnetlink.h>


	   struct {
	       struct nlmsghdr	nh;
	       struct ifinfomsg if;
	       char		attrbuf[512];
	   } req;

	   struct rtattr *rta;
	   unsigned int mtu = 1000;

	   int rtnetlink_sk = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);

	   memset(&req, 0, sizeof(req));
	   req.nh.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg));
	   req.nh.nlmsg_flags = NLM_F_REQUEST;
	   req.nh.nlmsg_type = RTM_NEWLINK;
	   req.if.ifi_family = AF_UNSPEC;
	   req.if.ifi_index = INTERFACE_INDEX;
	   req.if.ifi_change = 0xffffffff; /* ??? */
	   rta = (struct rtattr *)(((char *) &req) +
	   rta->rta_type = IFLA_MTU;
	   rta->rta_len = RTA_LENGTH(sizeof(unsigned int));
	   req.n.nlmsg_len = NLMSG_ALIGN(req.nh.nlmsg_len) +
	   memcpy(RTA_DATA(rta), &mtu, sizeof(mtu));
	   send(rtnetlink_sk, &req, req.nh.nlmsg_len);

       netlink(3), netlink(7), rtnetlink(7)

       This  page  is  part of release 3.55 of the Linux man-pages project.  A description of the
       project,    and	  information	 about	  reporting    bugs,	can    be    found     at

GNU					    2012-03-24				     RTNETLINK(3)
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