Adding upstream version 9.1.upstream/9.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 36 insertions, 0 deletions

diff --git a/doc/user/kernel.rst b/doc/user/kernel.rst
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+.. _kernel-interface:
+
+****************
+Kernel Interface
+****************
+
+There are several different methods for reading kernel routing table
+information, updating kernel routing tables, and for looking up interfaces.
+FRR relies heavily on the Netlink (``man 7 netlink``) interface to
+communicate with the Kernel. However, other interfaces are still used
+in some parts of the code.
+
+- ioctl
+     This 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
+     This is a program that 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
+     This is a special filesystem mount that provides an easy way of getting
+     kernel information.
+
+- routing socket / Netlink
+     Netlink first appeard in Linux kernel 2.0. It makes asynchronous
+     communication between the kernel and FRR possible, similar to a routing
+     socket on BSD systems. Netlink communication is done by reading/writing
+     over Netlink socket.