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Old 04-09-2005, 02:20 AM   #1
sidra
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Registered: Oct 2004
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Distribution: Fedora Core 3, Red Hat 9, CentOS 4.2, Mandriva, Ret Hat Enterprise Linux 4.0
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Packet Transmission in the Kernel


Dear All,

I'm doing linux kernel programming for my senior year project at college. I've studied the tcp/ip implementation in kernel 2.4 to some extent, since i'm working on 2.4. So i was trying to transmit a test IP packet from scratch. This is being done as an extension to the kernel, in a file of my own. My implementation follows the way a packet is being transmitted in the kernel, specifically in the ip_output.c file. The problem i'm having is that when i try to find out the route for my destination using the ip_route_output() function i always get a null and hence the packet transmission doesn't occur. Here's where the problem occurs:

/* Get dst_entry if not present */
ip_route_output(&rt, dest, src, 0, dev-ifindex);

if(rt == NULL)
{
// some error and exit code
}

It turns out that rt is null. src and dest are the source and destination ip addresses in network byte order in hex. rt is defined as struct rtable* and dev is the transmitting device..that is eth0 in this case.

Does anyone have any clue about why rt is turning out to be null?
 
Old 04-09-2005, 07:39 AM   #2
david_ross
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