RTMNEWADDRRTMDELADDR

RTM_NEWADDR and RTM_DELADDR are Netlink routing message types used by the Linux kernel to notify user-space about changes to network interface addresses. They are part of the NETLINK_ROUTE family and are emitted when an IP address is added, changed, or removed on a network interface. Applications such as network managers, DHCP clients, and tools like iproute2 listen for these messages to keep their internal view of the system’s addressing up to date.

These messages carry information about the affected interface and address data. The payload includes an ifaddrmsg structure, which specifies the address family (IPv4 or IPv6), the prefix length, scope, and interface index, followed by one or more attributes (rtattr). Common attributes include IFA_ADDRESS (the address), IFA_LOCAL (the local address used for routing), and IFA_LABEL (the interface label). The interface index allows user-space to map the event to a human-readable interface name. RTM_NEWADDR is used for new addresses and for updates to existing ones, while RTM_DELADDR signals the removal of an address.

Typical use cases include adding or removing IPv4 or IPv6 addresses on interfaces via commands like ip addr add/del. When such an operation occurs, the kernel publishes RTM_NEWADDR or RTM_DELADDR to any listening netlink sockets, enabling tools to update routing tables, firewall rules, or UI displays accordingly.

See also: NETLINK_ROUTE, RTM_NEWLINK, IP addressing, iproute2.