RTNETLINK(7) Linux Programmer's Manual RTNETLINK(7)
NAME
rtnetlink, NETLINK_ROUTE - Linux IPv4 routing socket.
SYNOPSIS
#include <asm/types.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <sys/socket.h>
rtnetlink_socket = socket(PF_NETLINK, int socket_type,
NETLINK_ROUTE);
DESCRIPTION
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 docu-
mented here, and for communication with user-space pro-
grams. 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.
ROUTING ATTRIBUTES
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).
MESSAGES
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 ifin-
fomsg structure followed by a series of rtattr
structures.
struct ifinfomsg
{
unsigned char ifi_family; /* AF_UNSPEC */
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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 netde-
vice(7); ifi_index is the unique interface index,
ifi_change is reserved for future use and should be
always set to 0xFFFFFFFF.
tab(:); c l l l. Routing attributes rta_type:value
type:description _ IFLA_UNSPEC:-:unspecified.
IFLA_ADDRESS:hardware address:interface L2 address
IFLA_BROADCAST:hardware address:L2 broadcast
address. IFLA_IFNAME:asciiz string:Device name.
IFLA_MTU:unsigned int:MTU of the device.
IFLA_LINK:int:Link type. IFLA_QDISC:asciiz
string:Queueing discipline. IFLA_STATS:T{ struct
net_device_stats T}:Interface Statistics.
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_PER-
MANENT for a permanent address set by the user and
other undocumented flags.
tab(:); c l l l. Attributes rta_type:value
type:description _ IFA_UNSPEC:-:unspecified.
IFA_ADDRESS:raw protocol address:interface address
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IFA_LOCAL:raw protocol address:local address
IFA_LABEL:asciiz string:name of the interface
IFA_BROADCAST:raw protocol address:broadcast
address. IFA_ANYCAST:raw protocol address:anycast
address IFA_CACHEINFO:struct ifa_cacheinfo:Address
information.
RTM_NEWROUTE, RTM_DELROUTE, RTM_GETROUTE
Create, remove or receive information about a net-
work route. These messages contain an rtmsg struc-
ture 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 wild-
card.
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;
};
tab(:); l l l l. rtm_type:Route type _
RTN_UNSPEC:unknown route RTN_UNICAST:a gateway or
direct route RTN_LOCAL:a local interface route
RTN_BROADCAST:T{ a local broadcast route (sent as a
broadcast) T} RTN_ANYCAST:T{ a local broadcast
route (sent as a unicast) T} RTN_MULTICAST:a multi-
cast route RTN_BLACKHOLE:a packet dropping route
RTN_UNREACHABLE:an unreachable destination RTN_PRO-
HIBIT:a packet rejection route RTN_THROW:continue
routing lookup in another table RTN_NAT:a network
address translation rule RTN_XRESOLVE:T{ refer to
an external resolver (not implemented) T}
tab(:); l l. rtm_protocol:Route origin. _
RTPROT_UNSPEC:unknown RTPROT_REDIRECT:T{ by an ICMP
redirect (currently unused) T} RTPROT_KERNEL:by the
kernel RTPROT_BOOT:during boot RTPROT_STATIC:by the
administrator
Values larger than RTPROT_STATIC are not inter-
preted by the kernel, they are just for user
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information. They may be used to tag the source of
a routing information or to distingush between mul-
tiple routing daemons. See <linux/rtnetlink.h> for
the routing daemon identifiers which are already
assigned.
rtm_scope is the distance to the destination:
tab(:); l l. RT_SCOPE_UNIVERSE:global route
RT_SCOPE_SITE:T{ interior route in the local
autonomous system T} RT_SCOPE_LINK:route on this
link RT_SCOPE_HOST:route on the local host
RT_SCOPE_NOWHERE:destination doesn't exist
The values between RT_SCOPE_UNIVERSE and
RT_SCOPE_SITE are available to the user.
The rtm_flags have the following meanings:
tab(:); l l. RTM_F_NOTIFY:T{ if the route changes,
notify the user via rtnetlink T} RTM_F_CLONED:route
is cloned from another route RTM_F_EQUALIZE:a mul-
ticast equalizer (not yet implemented)
rtm_table specifies the routing table
tab(:); l l. RT_TABLE_UNSPEC:an unspecified rout-
ing table RT_TABLE_DEFAULT:the default table
RT_TABLE_MAIN:the main table RT_TABLE_LOCAL:the
local table
The user may assign arbitary values between
RT_TABLE_UNSPEC and RT_TABLE_DEFAULT.
tab(:); c l l l. Attributes rta_type:value
type:description _ RTA_UNSPEC:-:ignored.
RTA_DST:protocol address:Route destination address.
RTA_SRC:protocol address:Route source address.
RTA_IIF:int:Input interface index.
RTA_OIF:int:Output interface index. RTA_GATE-
WAY:protocol address:The gateway of the route
RTA_PRIORITY:int:Priority of route. RTA_PREFSRC::
RTA_METRICS:int:Route metric RTA_MULTIPATH::
RTA_PROTOINFO:: RTA_FLOW:: RTA_CACHEINFO::
Fill these values in!
RTM_NEWNEIGH, RTM_DELNEIGH, RTM_GETNEIGH
Add, remove or receive information about a neigh-
bour table entry (e.g. an ARP entry). The message
contains an ndmsg structure.
struct ndmsg
{
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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:
tab(:); l l. NUD_INCOMPLETE:a currently resolving
cache entry NUD_REACHABLE:a confirmed working cache
entry NUD_STALE:an expired cache entry NUD_DELAY:an
entry waiting for a timer NUD_PROBE:a cache entry
that is currently reprobed NUD_FAILED:an invalid
cache entry NUD_NOARP:a device with no destination
cache NUD_PERMANENT:a static entry
Valid ndm_flags are:
tab(:); l l. NTF_PROXY:a proxy arp entry
NTF_ROUTER:an IPv6 router
document the members of the struct better
The rtaddr struct has the following meanings for
the rta_type field:
tab(:); l l. NDA_UNSPEC:unknown type NDA_DST:a
neighbour cache network layer destination address
NDA_LLADDR:a neighbour cache link layer address
NDA_CACHEINFO:cache statistics.
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 mes-
sage contains a struct tcmsg and may be followed by
a series of attributes.
struct tcmsg
{
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unsigned char tcm_family;
int tcm_ifindex; /* interface index */
__u32 tcm_handle; /* Qdisc handle */
__u32 tcm_parent; /* Parent qdisc */
__u32 tcm_info;
};
tab(:); c l l l. Attributes rta_type:value
type:Description _ TCA_UNSPEC:-:unspecified
TCA_KIND:asciiz string:Name of queueing discipline
TCA_OPTIONS:byte sequence:Qdisc specific options
follow TCA_STATS:struct tc_stats:Qdisc statistics.
TCA_XSTATS:qdisc specific:Module specific statis-
tics. TCA_RATE:struct tc_estimator:Rate limit.
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.
VERSIONS
rtnetlink is a new feature of Linux 2.2.
BUGS
This manual page is lacking and incomplete.
SEE ALSO
netlink(7), cmsg(3), ip(7), rtnetlink(3)
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