On Wed, Apr 25, 2007 at 07:28:42AM +0000, J HU wrote: > Dear experts, > > I'm developing an C++ application with sockets in a debian with a version > of kernel 2.6.x. > > The idea of my application is to send messages using UDP sockets and have > only one receiver socket which receive all the message that are for him, so > to do that I create the socket like follows: > > sock=::socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP)) > > In that way, using the PF_PACKET family allows to the application to > receive packets dealing directly with the network card driver. > > So with that and a filter I create a socket to receive all the packets that > are UDP and starts with... The filter is set like that: > > struct sock_fprog Filter //udp and udp[8:1]==0x7e > .... > setsockopt(sock, SOL_SOCKET, SO_ATTACH_FILTER,&Filter, sizeof(Filter)) > > Therefore my problem is that when I send a UDP message bigger than 16450 > Bytes, the IPv4 layer fragment it, it sends fragments uf 16450 Bytes (I'm > not totally sure about the size) and in my reception I get 2 messages but > one of the is discarted because of my filter. But, even if I change my > filter I will receive two fragments that I will have to ensamble and I > don't like the idea :s... > > So the solution is to disable the fragmentation of the IPv4. I read that > till kernels 2.2.x or pherhaps till kernels 2.4.x there was and option or > the file "/proc/sys/net/ipv4/ip_always_defrag" that it controled the > fragmentation, but in newest kernels this file doesn't exist. > > Therefore, my question is if anyone knows how to disable that fragmentation > or change the size of the fragment to the maximum of 65535. Or if there's > any way of create a socket that receive a IP ensambled messages and could > be set a filter. > > I hope someone could help me. fragmentation is usually set at the link level, most ethernet switches only handle 1500B - there is a standard for jumbo frames. But it might be easier for you program to handle fragmented packets than changed the mtu size. > > Thanks in advance! > > _________________________________________________________________ > Grandes éxitos, superhéroes, imitaciones, cine y TV... > http://es.msn.kiwee.com/ Lo mejor para tu móvil. > > > -- > To UNSUBSCRIBE, email to debian-user-REQUEST@lists.debian.org > with a subject of "unsubscribe". Trouble? Contact > listmaster@lists.debian.org > >
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