Socket error:90:Message Too Long

Question

I have an error from the following scenario with IGMP socket call;

fd = socket(PF_INET,  SOCK_RAW, IPPROTO_IGMP) ;
setsockopt( fd, IPPROTO_IP, IP_HDRINCL, nval, sizeof(nval) );
/** Fill in the IP header and Ethernet header**/
/*** Fill, create the IGMP packet structures***/
if(sendto( fd, &buf, sizeof(buf), 0,(struct sockaddr *) &addr, sizeof(addr)) < 0) {
    printf("Socket Sendto error %d : %s\n", errno, strerror(errno));
    return 0;
}

the sendto call fails saying Message too long. I am using 8192 as the buffer size. So I tried using the following call to fix this error;

if(setsockopt(dlpifd, IPPROTO_IP, SO_SNDBUF, &val, sizeof(int)) < 0) {
   printf("Can't set socket options:%d:%s\n", errno, strerror(errno));
   return 0;`
}

setsockopt( ) call succeeds but the same error for sendto();

So i checked the SO_SNDBUF size with getsockopt( ) call and it shows 1 byte ?!

What is wrong I am doing.

Does the Linux kernel need recompile for IGMP support ? or I am missing something?

Nikolai Fetissov · Answer 1 · 2011-01-25T16:16:35.760

7

Ethernet (the link layer you are most probably working against) frame is usually 1500 bytes long. Give the send() the exact size of the message, not the buffer size.

SO_SNDBUF is the in-kernel per-socket buffer, which tells how much to buffer for TCP, limits the size of datagram for UDP, and does not make any sense for raw sockets.

edited Jan 25 '11 at 16:16

answered Jan 25 '11 at 16:11

Nikolai Fetissov

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Thanks Nik ! for the help. Does that mean for this scenario I should use send( ) and not sendto( ) and the exact message size (even if it is more than 1500 default size?!) and not the buff size. – Sathya Jan 25 '11 at 16:17
HI, I am attempting to send an IGMP packet 'pigmp->igmp_type = IGMP_MEMBERSHIP_QUERY;' and not a TCP or an UDP, I suspect the sequence of calls/things I am doing in the code may be wrong or the arguments/values which I am using for filling the structures should be wrong. I checked and could not find a fault in those aspects. So using send( ) instead of sendto( ) is not hleping to fix this. Anyone worked on IGMP (Multicasting) can throw me some light. -Thanks in advance -Sathya – Sathya Jan 27 '11 at 10:11
Hi Nik, As said, Now it works fine for packet sizes <= 1500. It throws erro:90 for anything more(even for 1501). I tried using setsockopt() to increase the SO_SNDBUF but no effect from that call. Since send( ) call cannot be used for raw socket bcos it is connectionless and the same reason for IGMP packet I am still using sendto( ). I want to know what holds good for setsockopt( ) to SO_SNDBUF change. - Thanks - Sathya – Sathya Jan 28 '11 at 14:29
`sendto()` is fine - I used `send()` as a general name anyway. You won't get anything larger then 1500 bytes through ethernet - that's the hardware limit. `SO_SNDBUF` has no effect here - raw sockets don't do buffering. – Nikolai Fetissov Jan 28 '11 at 15:11

Socket error:90:Message Too Long

1 Answers1