The Netlink protocol family has many protocol families. Some of them have been deprecated and some are presently as of the date of this article present in the Linux Kernel. The list (as of Linux 6.13.2) provides the reader in knowing the different protocol families available (I do not claim to know what each of them does individually myself 🙂 )The protocol families are tabulated below.
| Netlink Protocol Family | Description |
| NETLINK_ROUTE | Receives routing and link updates and may be used to modify routing tables |
| NETLINK_UNUSED | Unused netlink family |
| NETLINK_USERSOCK | Reserved for user space IPC between different user space applications using NETLINK socket |
| NETLINK_FIREWALL | (Up to and including Linux 3.4) Transport IPv4 packets from netfilter to user space. Used by ip_queue kernel module. After a long period of being declared obsolete (in favor of the more advanced nfnetlink_queue feature), NETLINK_FIREWALL was removed in Linux 3.5. |
| NETLINK_SOCK_DIAG | (Since Linux 3.3) Query information about sockets of various protocol families from the kernel (see sock_diag(7)). |
| NETLINK_NFLOG | (Up to and including Linux 3.16) Netfilter/iptables ULOG. |
| NETLINK_XFRM | Provides an interface to manage the IPsec security association and security policy databases – mostly used by key-manager daemons using the Internet Key Exchange protocol. (From Wikipedia) |
| NETLINK_SELINUX | SELinux notifications- refer wikipedia page – Wikipedia -SELinux |
| NETLINK_ISCSI | Used for IPC between open-iscsi daemon ) and the Linux kernel’s iSCSI transport module. It facilitates the control plane, such as configuring sessions, logging in/out of targets, and setting parameters, while the actual data path (read/write) remains in the kernel |
| NETLINK_AUDIT | Provides an interface to the audit subsystem found in Linux kernel versions 2.6.6 and later. |
| NETLINK_FIB_LOOKUP | (Since Linux 2.6.13) Access to FIB lookup from user space |
| NETLINK_CONNECTOR | (Since Linux 2.6.14) Kernel connector. See Documentation/driver-api/connector.rst (or /Documentation/connector/connector.* in kernel 5.2 and earlier) in the Linux kernel source tree for further information. |
| NETLINK_NETFILTER | (Since Linux 2.6.14) Netfilter subsystem. |
| NETLINK_IP6_FW | (Up to and including Linux 3.4) Transport IPv6 packets from netfilter to user space. Used by ip6_queue kernel module. |
| NETLINK_DNRT_MSG | DECnet routing messages. |
| NETLINK_KOBJECT_UEVENT | (Since Linux 2.6.10) Kernel messages to user space. |
| NETLINK_GENERIC | (Since Linux 2.6.15) Generic netlink family for simplified netlink usage. |
| NETLINK_SCSITRANSPORT | Linux Netlink family (protocol) used to transmit asynchronous SCSI transport-related events between the Linux kernel (specifically the SCSI mid-layer and low-level drivers) and user-space process |
| NETLINK_ECRYPTFS | Component of the eCryptfs (enterprise cryptographic filesystem) stack in Linux, designed to handle communication between the eCryptfs kernel module and a user-space daemon |
| NETLINK_RDMA | (Introduced in Linux 3.0) Netlink socket family used to facilitate communication between the Linux kernel and user-space applications regarding InfiniBand (IB) and Remote Direct Memory Access (RDMA) subsystems. It is part of the broader Linux RDMA stack that allows high-performance |
| NETLINK_CRYPTO | (Since Linux 3.2) Netlink interface to request information about ciphers registered with the kernel crypto API as well as allow configuration of the kernel crypto API. |
| NETLINK_SMC | Netlink protocol family in the Linux kernel used for communication between user-space applications and the SMC (Shared Memory Communications) subsystem. It facilitates the management, configuration, and monitoring of SMC-R (over RDMA) and SMC-D (over ISM/internal shared memory) sockets. |
| NETLINK_INET_DIAG | Linux kernel Netlink family used to query information about internet sockets (TCP, UDP, etc.) from the kernel. It is essentially a specialized, high-performance interface for obtaining detailed socket diagnostics, often used by tools like ss (socket statistics) to replace the slower, text-based /proc/net/tcp or /proc/net/udp files. |
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