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@node Kernel Interface
@chapter Kernel Interface
There are several different methods for reading kernel routing table
information, updating kernel routing tables, and for looking up
interfaces.
@table @samp
@item ioctl
The @samp{ioctl} method is a very traditional way for reading or writing
kernel information. @samp{ioctl} can be used for looking up interfaces
and for modifying interface addresses, flags, mtu settings and other
types of information. Also, @samp{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.
@item sysctl
@samp{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 @samp{ioctl}.
@item proc filesystem
@samp{proc filesystem} provides an easy way of getting kernel
information.
@item routing socket
@item netlink
On recent Linux kernels (2.0.x and 2.2.x), there is a kernel/user
communication support called @code{netlink}. It makes asynchronous
communication between kernel and Frr 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Today, the /dev/route special device file is obsolete.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 Frr.
You can use netlink as a dynamic routing update channel between Frr
and the kernel.
@end table
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