14. Kernel Interface

There are several different methods for reading kernel routing table information, updating kernel routing tables, and for looking up interfaces.

`ioctl'

The `ioctl' method is a very traditional way for reading or writing kernel information. `ioctl' can be used for looking up interfaces and for modifying interface addresses, flags, mtu settings and other types of information. Also, `ioctl' can insert and delete kernel routing table entries. It will soon be available on almost any platform which zebra supports, but it is a little bit ugly thus far, so if a better method is supported by the kernel, zebra will use that.

`sysctl'

`sysctl' can lookup kernel information using MIB (Management Information Base) syntax. Normally, it only provides a way of getting information from the kernel. So one would usually want to change kernel information using another method such as `ioctl'.

`proc filesystem'

`proc filesystem' provides an easy way of getting kernel information.

`routing socket'

`netlink'

On recent Linux kernels (2.0.x and 2.2.x), there is a kernel/user communication support called netlink. It makes asynchronous communication between kernel and Zebra possible, similar to a routing socket on BSD systems.

Before you use this feature, be sure to select (in kernel configuration) the kernel/netlink support option 'Kernel/User network link driver' and 'Routing messages'.

Today, the /dev/route special device file is obsolete. Netlink communication is done by reading/writing over netlink socket.

After the kernel configuration, please reconfigure and rebuild Zebra. You can use netlink as a dynamic routing update channel between Zebra and the kernel.