linuxrtnetlinkh

linuxrtnetlinkh is the conventional shorthand for the Linux kernel header file include/linux/rtnetlink.h. This header provides the definitions and structures used by the rtnetlink portion of the Netlink interface, which the kernel and user-space networking tools rely on to manage networking state.

The rtnetlink interface is the kernel’s API for configuring and querying network-related objects such as interfaces, addresses, routes, and neighbour caches. The header defines the message types used in Netlink communications under the NETLINK_ROUTE family. Typical message types include creation, deletion, and retrieval of links (interfaces), addresses, routes, and neighbours. These types form the basis for commands issued by userspace tools and for kernel notifications to userspace.

Key structures and facilities in the header include the rtmsg structure, which encapsulates information about a routing message, including fields such as the family, table, protocol, scope, type, and flags. The header also defines the rtattr structure used for attributes carried with Netlink messages, enabling a flexible, nested encoding of data such as interface names, addresses, and route attributes. Several macros assist in building and parsing these messages, for example, alignment and length helpers (NLMSG_ALIGN, RTA_LENGTH, RTA_SPACE) and a set of RTA_ constants that label attributes like OIF (output interface index), ADDRESS, GATEWAY, DST, and PREFSRC.

linuxrtnetlinkh thus serves as the canonical source for programmers writing kernel code or user-space programs that construct or interpret rtnetlink messages. It underpins tools such as iproute2 and other networking utilities that configure the kernel’s routing tables, interfaces, and related resources. The header is part of the broader Netlink infrastructure and is included by programs that interact with NETLINK_ROUTE to manage networking state.