Hi,

I'm working on a userspace application that needs to find if the kernel has a route configured for a particular destination address, and what port it would be routed from. I'm hoping there is a simple kernel call that will do this for me, but haven't been able to find it yet :-)

I don't want to actually send a packet to do this, just query the kernel if where it *would* send the packet if I did.

The only method I've come up with is to get the kernel routing table through rtnetlink then check each entry to see if it matches my destination address. I guess this will work (after one or two tries to get the logic right ;-) ) but I'd rather do a single call if there is one.

Thanks in advance

Yes there is a simple kernel call but that requires a parameter. That parameter values can be enabled/disables in "/etc/sysctl.conf"


File: /etc/sysctl.conf

net.ipv4.ip_forward = 0 // Value Zero denotes disableing

or

net.ipv4.ip_forward = 1 // Value One denotes enabling


sysctl -p /etc/sysctl.conf // Enable the changes made in sysctl.conf

Thanks,

Thanks prodev, but this isn't exactly what I'm looking for. I want to ask the kernel if it has a route to a particular address, not if routing/forwarding is enabled.

One approach that I'm following up is using connect() syscall to connect to a UDP port. This should fail with EHOSTUNREACH if there is no route to the destination IP address.