RTNETLINK
NAME SYNOPSIS DESCRIPTION ROUTING ATTRIBUTES MESSAGES VERSIONS BUGS SEE ALSO
rtnetlink, NETLINK_ROUTE - Linux IPv4 routing socket.
#include
rtnetlink_socket = socket(PF_NETLINK, int socket_type, NETLINK_ROUTE);
Rtnetlink allows the kernel's routing tables to be read and altered. It is used within the kernel to communicate between various subsystems, though this usage is not documented here, and for communication with user-space programs. Network routes, ip addresses, link parameters, neighbour setups, queueing disciplines, traffic classes and packet classifiers may all be controlled through NETLINK_ROUTE sockets. It is based on netlink messages, see netlink(7) for more information.
Some rtnetlink messages have optional attributes after the initial header:
struct rtattr { unsigned short rta_len; /* Length of option / unsigned short rta_type; / Type of option / / Data follows / }; These attributes should be only manipulated using the RTA_ macros or libnetlink, see rtnetlink(3).
Rtnetlink consists of these message types (in addition to standard netlink messages):
RTM_NEWLINK, RTM_DELLINK, RTM_GETLINK
Create, remove or get information about a specific network interface. These messages contain an ifinfomsg structure followed by a series of rtattr structures.
struct ifinfomsg { unsigned char ifi_family; /* AF_UNSPEC / unsigned short ifi_type; / Device type / int ifi_index; / Interface index / unsigned int ifi_flags; / Device flags / unsigned int ifi_change; / change mask */ }; ifi_flags contains the device flags, see __netdevice(7)?; ifi_index is the unique interface index, ifi_change__ is reserved for future use and should be always set to 0xFFFFFFFF.
RTM_NEWADDR, RTM_DELADDR, RTM_GETADDR
Add, remove or receive information about an IP address associated with an interface. In Linux 2.2 an interface can carry multiple IP addresses, this replaces the alias device concept in 2.0. In Linux 2.2 these messages support IPv4 and IPv6 addresses. They contain an ifaddrmsg structure, optionally followed by rtaddr routing attributes.
struct ifaddrmsg { unsigned char ifa_family; /* Address type / unsigned char ifa_prefixlen;/ Prefixlength of the address / unsigned char ifa_flags; / Address flags / unsigned char ifa_scope; / Address scope / int ifa_index; / Interface index */ }; ifa_family is the address family type (currently AF_INET or AF_INET6), ifa_prefixlen is the length of the address mask of the address if defined for the family (like for IPv4), ifa_scope is the address scope, ifa_index is the interface index of the interface the address is associated with. ifa_flags is a flag word of IFA_F_SECONDARY for secondary address (old alias interface), IFA_F_PERMANENT for a permanent address set by the user and other undocumented flags.
RTM_NEWROUTE, RTM_DELROUTE, RTM_GETROUTE
Create, remove or receive information about a network route. These messages contain an rtmsg structure with an optional sequence of rtattr structures following. For RTM_GETROUTE setting rtm_dst_len and rtm_src_len to 0 means you get all entries for the specified routing table. For the other fields except rtm_table and rtm_protocol 0 is the wildcard.
struct rtmsg { unsigned char rtm_family; /* Address family of route / unsigned char rtm_dst_len; / Length of source / unsigned char rtm_src_len; / Length of destination / unsigned char rtm_tos; / TOS filter / unsigned char rtm_table; / Routing table id / unsigned char rtm_protocol;/ Routing protocol; see below / unsigned char rtm_scope; / See below / unsigned char rtm_type; / See below */ unsigned int rtm_flags; };
Values larger than RTPROT_STATIC are not interpreted by the kernel, they are just for user information. They may be used to tag the source of a routing information or to distingush between multiple routing daemons. See for the routing daemon identifiers which are already assigned.
rtm_scope is the distance to the destination:
The values between RT_SCOPE_UNIVERSE and RT_SCOPE_SITE are available to the user.
The rtm_flags have the following meanings:
rtm_table specifies the routing table
The user may assign arbitary values between RT_TABLE_UNSPEC and RT_TABLE_DEFAULT.
Fill these values in!
RTM_NEWNEIGH, RTM_DELNEIGH, RTM_GETNEIGH
Add, remove or receive information about a neighbour table entry (e.g. an ARP entry). The message contains an ndmsg structure.
struct ndmsg { unsigned char ndm_family; int ndm_ifindex; /* Interface index / u16 ndm_state; /* State */ u8 ndm_flags; / Flags */ u8 ndm_type; }; struct nda_cacheinfo { u32 ndm_confirmed; u32 ndm_used; u32 ndm_updated; u32 ndm_refcnt; }; ndm_state__ is a bitmask of the following states:
Valid ndm_flags are:
document the members of the struct better
The rtaddr struct has the following meanings for the rta_type field:
If the rta_type field is NDA_CACHEINFO then a struct nda_cacheinfo header follows
RTM_NEWRULE, RTM_DELRULE, RTM_GETRULE
Add, delete or retrieve a routing rule. Carries a struct rtmsg
RTM_NEWQDISC, RTM_DELQDISC, RTM_GETQDISC
Add, remove or get a queueing discipline. The message contains a struct tcmsg and may be followed by a series of attributes.
struct tcmsg { unsigned char tcm_family; int tcm_ifindex; /* interface index / u32 tcm_handle; /* Qdisc handle */ u32 tcm_parent; / Parent qdisc */ __u32 tcm_info; };
In addition various other qdisc module specific attributes are allowed. For more information see the appropriate include files.
RTM_NEWTCLASS, RTM_DELTCLASS, RTM_GETTCLASS
Add, remove or get a traffic class. These messages contain a struct tcmsg as described above.
RTM_NEWTFILTER, RTM_DELTFILTER, RTM_GETTFILTER
Add, remove or receive information about a traffic filter. These messages contain a struct tcmsg as described above.
rtnetlink is a new feature of Linux 2.2.
This manual page is lacking and incomplete.
netlink(7), cmsg(3), ip(7), rtnetlink(3)
5 pages link to rtnetlink(7):
