[LARTC] Re: problem in Route add using netlink

[Jarek Poplawski <jarkap@poczta.onet.pl>]

On 25-07-2006 16:59, VijayaLakshmi Seshadri wrote:
> Hi all
>  Iam trying to implement "route add " using netlink. The changes are not 
> reflected in the routing table. I have given my code and screen shots of 
> the routing tables.
>  
> Can anybody tell me is there any mistake iam making in defining the fields .
> or any other mistake iam commiting
>  
> thanxs
>  
> viji

I had some free time at the weekend - it's probably to late and I 
hope you've found this bugs yet, but maybe someone else (like me) 
will be looking here some day with similar problem, so here is 
what I've found.

Jarek P

>  
> //////////////////////////////////// CODE 
> //////////////////////////////////////////////////////
> #include <asm/types.h>
> #include <netinet/ether.h>
> #include <netinet/in.h>
> #include <net/if.h>
> #include <stdio.h>
> #include <sys/socket.h>
> #include <sys/ioctl.h>
> #include <linux/netlink.h>
> #include <linux/rtnetlink.h>
> #include <sys/types.h>
> #define BUFSIZE 192
> struct route_info{
>         u_int   dstAddr;
>         u_int   srcAddr;
>         u_int   gateWay;
>         char    ifName[IF_NAMESIZE];
> };
> void fillRoute (struct route_info *rinfo, const char* dstAddr,
>                 const char* srcAddr, const char* gateway, const char* 
> ifName)
> {
>         /* Convert from the standrad numbers and dots notation
>            to binary data  */
>         inet_aton("192.168.51.0", (struct in_addr *)&rinfo->dstAddr);
>         inet_aton("192.168.51.90", (struct in_addr *)&rinfo->gateWay);
> }

Of corse you always have to be sure to have the valid route to 
192.168.51.90 on the testing box...

> int addAttr (struct nlmsghdr *nlhdr, int maxlen, int type,
>                 void *data, int alen)
> {
>         struct rtattr *rta;
>         int len = RTA_LENGTH(alen);
>         if (NLMSG_ALIGN(nlhdr->nlmsg_len) + len > maxlen)
>                 return -1;
>         rta = (struct rtattr*)((char *)nlhdr + 
> NLMSG_ALIGN(nlhdr->nlmsg_len));
>         rta->rta_type = type;
>         rta->rta_len  = len;
>         memcpy(RTA_DATA(rta), data, alen);
>         nlhdr->nlmsg_len = NLMSG_ALIGN(nlhdr->nlmsg_len) + len;
>         return 0;
> }
> int main()
> {
>         struct nlmsghdr *nlMsg;
>         struct rtmsg *rtMsg;
>         char dstAddr[30] ;
>         char srcAddr[30] ;
>         char gateway[30] ;
>         char ifName[30];
>         char msgBuf[BUFSIZE];
>         struct route_info rinfo;
>         int sock, len, msgSeq = 0;
>         int val, i;
>         /* Create Socket */
>         if((sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE)) < 0)
>                 perror("Socket Creation: ");
>         /* Initialize the buffer */
>         memset(msgBuf, 0, BUFSIZE);
>         /* point the header and the msg structure pointers into the 
> buffer */
>         nlMsg = (struct nlmsghdr *)msgBuf;
>         rtMsg = (struct rtmsg *)NLMSG_DATA(nlMsg);
>         /* Fill in the nlmsg header*/
>         nlMsg->nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg)); // Length 
> ofmessage.
>         nlMsg->nlmsg_type = RTM_NEWROUTE;                      // Get 
> the routes from kernel routing table .
>         nlMsg->nlmsg_flags = NLM_F_CREATE ;       // The message is a 

// the flag is needed here
nlMsg->nlmsg_flags = NLM_F_CREATE | NLM_F_REQUEST;

> request for dump.
>         nlMsg->nlmsg_seq = msgSeq++;                           // 
> Sequence of the message packet.
>         nlMsg->nlmsg_pid = getpid();                           // PID of 
> process sending the request.
>         rtMsg->rtm_family = AF_INET;
>         rtMsg->rtm_table = RT_TABLE_UNSPEC;
>         rtMsg->rtm_dst_len = 16;
>         rtMsg->rtm_src_len = 16;

// this should be address' lenghts in bits so:
          rtMsg->rtm_dst_len = 32;
          rtMsg->rtm_src_len = 32;

>         rtMsg->rtm_scope = RT_SCOPE_UNIVERSE;
>         rtMsg->rtm_type = RTN_UNICAST;
>         rtMsg->rtm_protocol = RTPROT_UNSPEC;
>         rtMsg->rtm_flags   = RTM_F_NOTIFY;
>         fillRoute (&rinfo, dstAddr, srcAddr, gateway, ifName);
>         addAttr (nlMsg, BUFSIZE, RTA_DST,
>                         &rinfo.dstAddr, 4);
>                 addAttr (nlMsg, BUFSIZE, RTA_GATEWAY,
>                         &rinfo.gateWay, 4);
>         /* Send the request */
>         if((val = send(sock, nlMsg, nlMsg->nlmsg_len,0 )) < 0){
>                 printf("Write To Socket Failed...\n");
>                 return -1;
>         }
>         printf (" No of Bytes sent %d \n", val);
>         printf (" Value that is sent \n " );
>         for (i =0 ; i < val ; i ++)
>           printf ("%u", msgBuf[i]);
>         printf ("\n");
>         close(sock);
> return 0;
> }
> 
> //////////////////////////////////////////////////////////////////////////////////////////////////////////
>                               OUTPUT
> [root@vijdom]gcc netlink_addroute.c -o addroute
> [root@vijdom]# ./addroute
>  No of Bytes sent 44
>  Value that is sent
>  4400024004000042949672398800216160000101008010429496723242949672085108050429496723242949672085190
> ////////////////////////////////////////////////////////////////////////////////////////////////////////// 
> 
>                               SCREEN SHOTS
>  
> *Routing table before execution of program*
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use 
> Iface
> 192.168.51.0    *               255.255.255.0   U     0      0        0 eth0
> 169.254.0.0     *               255.255.0.0     U     0      0        0 eth0
> 127.0.0.0       *               255.0.0.0       U     0      0        0 lo
> default         embedded        0.0.0.0         UG    0      0        0 eth0
>  
> *Routing table after the execution of program
> *Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use 
> Iface
> 192.168.51.0    *               255.255.255.0   U     0      0        0 eth0
> 169.254.0.0     *               255.255.0.0     U     0      0        0 eth0
> 127.0.0.0       *               255.0.0.0       U     0      0        0 lo
> default         embedded        0.0.0.0         UG    0      0        0 eth0
> 
>  
>  
>  
>  
> 
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