path: root/doc/route.txt

////
	vim.syntax: asciidoc

	Copyright (c) 2011 Thomas Graf <tgraf@suug.ch>
////

Routing Family Netlink Library (libnl-route)
============================================
Thomas Graf <tgraf@suug.ch>
3.1, Aug 11 2011:

== Introduction

This library provides APIs to the kernel interfaces of the routing family.


NOTE: Work in progress.

== Addresses

[[route_link]]
== Links (Network Devices)

The link configuration interface is part of the +NETLINK_ROUTE+ protocol
family and implements the following netlink message types:

- View and modify the configuration of physical and virtual network devices.
- Create and delete virtual network devices (e.g. dummy devices, VLAN devices,
  tun devices, bridging devices, ...)
- View and modify per link network configuration settings (e.g.
  +net.ipv6.conf.eth0.accept_ra+, +net.ipv4.conf.eth1.forwarding+, ...)

.Naming Convention (network device, link, interface)

In networking several terms are commonly used to refer to network devices.
While they have distinct meanings they have been used interchangeably in
the past. Within the Linux kernel, the term _network device_ or _netdev_ is
commonly used In user space the term _network interface_ is very common.
The routing netlink protocol uses the term _link_ and so does the _iproute2_
utility and most routing daemons.

=== Netlink Protocol

This section describes the protocol semantics of the netlink based link
configuration interface. The following messages are defined:

[options="header", cols="1,2,2"]
|==============================================================================
| Message Type   | User -> Kernel                    | Kernel -> User
| +RTM_NEWLINK+  | Create or update virtual network device
| Reply to +RTM_GETLINK+ request or notification of link added or updated
| +RTM_DELLINK+  | Delete virtual network device
| Notification of link deleted or disappeared
| +RTM_GETLINK+  | Retrieve link configuration and statistics | 
| +RTM_SETLINK+  | Modify link configuration | 
|==============================================================================

See link:core.html#core_msg_types[Netlink Library - Message Types] for more
information on common semantics of these message types.

==== Link Message Format

All netlink link messages share a common header (+struct ifinfomsg+) which
is appended after the netlink header (+struct nlmsghdr+).

image:ifinfomsg.png["Link Message Header"]

The meaning of each field may differ depending on the message type. A
+struct ifinfomsg+ is defined in +<linux/rtnetlink.h>+ to represent the
header.

Address Family (8bit)::
The address family is usually set to +AF_UNSPEC+ but may be specified in
+RTM_GETLINK+ requests to limit the returned links to a specific address
family.

Link Layer Type (16bit)::
Currently only used in kernel->user messages to report the link layer type
of a link. The value corresponds to the +ARPHRD_*+ defines found in
+<linux/if_arp.h>+. Translation from/to strings can be done using the
functions nl_llproto2str()/nl_str2llproto().

Link Index (32bit)::
Carries the interface index and is used to identify existing links.

Flags (32bit)::
In kernel->user messages the value of this field represents the current
state of the link flags. In user->kernel messages this field is used to
change flags or set the initial flag state of new links. Note that in order
to change a flag, the flag must also be set in the _Flags Change Mask_ field.

Flags Change Mask (32bit)::
The primary use of this field is to specify a mask of flags that should be
changed based on the value of the _Flags_ field. A special meaning is given
to this field when present in link notifications, see TODO.

Attributes (variable)::
All link message types may carry netlink attributes. They are defined in the
header file <linux/if_link.h> and share the prefix +IFLA_+.

==== Link Message Types

.RTM_GETLINK (user->kernel)

Lookup link by 1. interface index or 2. link name (+IFLA_IFNAME+) and return
a single +RTM_NEWLINK+ message containing the link configuration and statistics
or a netlink error message if no such link was found.

*Parameters:*

* *Address family*
** If the address family is set to +PF_BRIDGE+, only bridging devices will be
   returned.
** If the address family is set to +PF_INET6+, only ipv6 enabled devices will
   be returned.

*Flags:*

* +NLM_F_DUMP+ If set, all links will be returned in form of a multipart
  message.

*Returns:*

* +EINVAL+ if neither interface nor link name are set
* +ENODEV+ if no link was found
* +ENOBUFS+ if allocation failed

.RTM_NEWLINK (user->kernel)

Creates a new or updates an existing link. Only virtual links may be created
but all links may be updated.

*Flags:*

- +NLM_F_CREATE+ Create link if it does not exist
- +NLM_F_EXCL+ Return +EEXIST+ if link already exists

*Returns:*

- +EINVAL+ malformed message or invalid configuration parameters
- +EAFNOSUPPORT+ if a address family specific configuration (+IFLA_AF_SPEC+)
  is not supported.
- +EOPNOTSUPP+ if the link does not support modification of parameters
- +EEXIST+ if +NLM_F_EXCL+ was set and the link exists alraedy
- +ENODEV+ if the link does not exist and +NLM_F_CREATE+ is not set

.RTM_NEWLINK (kernel->user)

This message type is used in reply to a +RTM_GETLINK+ request and carries
the configuration and statistics of a link. If multiple links need to
be sent, the messages will be sent in form of a multipart message.

The message type is also used for notifications sent by the kernel to the
multicast group +RTNLGRP_LINK+ to inform about various link events. It is
therefore recommended to always use a separate link socket for link
notifications in order to separate between the two message types.

TODO: document how to detect different notifications

.RTM_DELLINK (user->kernel)

Lookup link by 1. interface index or 2. link name (+IFLA_IFNAME+) and delete
the virtual link.

*Returns:*

* +EINVAL+ if neither interface nor link name are set
* +ENODEV+ if no link was found
* +ENOTSUPP+ if the operation is not supported (not a virtual link)

.RTM_DELLINK (kernel->user)

Notification sent by the kernel to the multicast group +RTNLGRP_LINK+ when

a. a network device was unregistered (change == ~0)
b. a bridging device was deleted (address family will be +PF_BRIDGE+)

=== Get / List

[[link_list]]
==== Get list of links

To retrieve the list of links in the kernel, allocate a new link cache
using +rtnl_link_alloc_cache()+ to hold the links. It will automatically
construct and send a +RTM_GETLINK+ message requesting a dump of all links
from the kernel and feed the returned +RTM_NEWLINK+ to the internal link
message parser which adds the returned links to the cache.

[source,c]
-----
#include <netlink/route/link.h>

int rtnl_link_alloc_cache(struct nl_sock *sk, int family, struct nl_cache **result)
-----

The cache will contain link objects (+struct rtnl_link+, see <<link_object>>)
and can be accessed using the standard cache functions. By setting the
+family+ parameter to an address familly other than +AF_UNSPEC+, the resulting
cache will only contain links supporting the specified address family.

The following direct search functions are provided to search by interface
index and by link name:

[source,c]
-----
#include <netlink/route/link.h>

struct rtnl_link *rtnl_link_get(struct nl_cache *cache, int ifindex);
struct rtnl_link *rtnl_link_get_by_name(struct nl_cache *cache, const char *name);
-----

.Example: Link Cache

[source,c]
-----
struct nl_cache *cache;
struct rtnl_link *link;

if (rtnl_link_alloc_cache(sock, AF_UNSPEC, &cache)) < 0)
	/* error */

if (!(link = rtnl_link_get_by_name(cache, "eth1")))
	/* link does not exist */

/* do something with link */

rtnl_link_put(link);
nl_cache_put(cache);
-----

[[link_direct_lookup]]
==== Lookup Single Link (Direct Lookup)

If only a single link is of interest, the link can be looked up directly
without the use of a link cache using the function +rtnl_link_get_kernel()+.

[source,c]
-----
#include <netlink/route/link.h>

int rtnl_link_get_kernel(struct nl_sock *sk, int ifindex, const char *name, struct rtnl_link **result);
-----

It will construct and send a +RTM_GETLINK+ request using the parameters
provided and wait for a +RTM_NEWLINK+ or netlink error message sent in
return. If the link exists, the link is returned as link object
(see <<link_object>>).

.Example: Direct link lookup
[source,c]
-----
struct rtnl_link *link;

if (rtnl_link_get_kernel(sock, 0, "eth1", &link) < 0)
	/* error */

/* do something with link */

rtnl_link_put(link);
-----

NOTE: While using this function can save a substantial amount of bandwidth
      on the netlink socket, the result will not be cached, subsequent calls
      to rtnl_link_get_kernel() will always trigger sending a +RTM_GETLINK+
      request.

[[link_translate_ifindex]]
==== Translating interface index to link name

Applications which require to translate interface index to a link name or
vice verase may use the following functions to do so. Both functions require
a filled link cache to work with.

[source,c]
-----
char *rtnl_link_i2name (struct nl_cache *cache, int ifindex, char *dst, size_t len);
int rtnl_link_name2i (struct nl_cache *cache, const char *name);
-----

=== Add / Modify

Several types of virtual link can be added on the fly using the function
+rtnl_link_add()+.

[source,c]
-----
#include <netlink/route/link.h>

int rtnl_link_add(struct nl_sock *sk, struct rtnl_link *link, int flags);
-----

=== Delete

The deletion of virtual links such as VLAN devices or dummy devices is done
using the function +rtnl_link_delete()+. The link passed on to the function
can be a link from a link cache or it can be construct with the minimal
attributes needed to identify the link.

[source,c]
-----
#include <netlink/route/link.h>

int rtnl_link_delete(struct nl_sock *sk, const struct rtnl_link *link);
-----

The function will construct and send a +RTM_DELLINK+ request message and
returns any errors returned by the kernel.

.Example: Delete link by name
[source,c]
-----
struct rtnl_link *link;

if (!(link = rtnl_link_alloc()))
	/* error */

rtnl_link_set_name(link, "my_vlan");

if (rtnl_link_delete(sock, link) < 0)
	/* error */

rtnl_link_put(link);
-----

[[link_object]]
=== Link Object

A link is represented by the structure +struct rtnl_link+. Instances may be
created with the function +rtnl_link_alloc()+ or via a link cache (see
<<link_list>>) and are freed again using the function +rtnl_link_put()+.

[source,c]
-----
#include <netlink/route/link.h>

struct rtnl_link *rtnl_link_alloc(void);
void rtnl_link_put(struct rtnl_link *link);
-----

[[link_attr_name]]
==== Name
The name serves as unique, human readable description of the link. By
default, links are named based on their type and then enumerated, e.g.
eth0, eth1, ethn but they may be renamed at any time.

Kernels >= 2.6.11 support identification by link name.

[source,c]
-----
#include <netlink/route/link.h>

void rtnl_link_set_name(struct rtnl_link *link, const char *name);
char *rtnl_link_get_name(struct rtnl_link *link);
-----

*Accepted link name format:* +[^ /]*+ (maximum length: 15 characters)

[[link_attr_ifindex]]
==== Interface Index (Identifier)
The interface index is an integer uniquely identifying a link. If present
in any link message, it will be used to identify an existing link.

[source,c]
-----
#include <netlink/route/link.h>

void rtnl_link_set_ifindex(struct rtnl_link *link, int ifindex);
int rtnl_link_get_ifindex(struct rtnl_link *link);
-----

[[link_attr_group]]
==== Group
Each link can be assigned a numeric group identifier to group a bunch of links
together and apply a set of changes to a group instead of just a single link.


[source,c]
-----
#include <netlink/route/link.h>

void rtnl_link_set_group(struct rtnl_link *link, uint32_t group);
uint32_t rtnl_link_get_group(struct rtnl_link *link);
-----

[[link_attr_address]]
==== Link Layer Address
The link layer address (e.g. MAC address).

[source,c]
-----
#include <netlink/route/link.h>

void rtnl_link_set_addr(struct rtnl_link *link, struct nl_addr *addr);
struct nl_addr *rtnl_link_get_addr(struct rtnl_link *link);
-----

[[link_attr_broadcast]]
==== Broadcast Address
The link layer broadcast address

[source,c]
-----
#include <netlink/route/link.h>

void rtnl_link_set_broadcast(struct rtnl_link *link, struct nl_addr *addr);
struct nl_addr *rtnl_link_get_broadcast(struct rtnl_link *link);
-----

[[link_attr_mtu]]
==== MTU (Maximum Transmission Unit)
The maximum transmission unit specifies the maximum packet size a network
device can transmit or receive. This value may be lower than the capability
of the physical network device.

[source,c]
-----
#include <netlink/route/link.h>

void rtnl_link_set_mtu(struct rtnl_link *link, unsigned int mtu);
unsigned int rtnl_link_get_mtu(struct rtnl_link *link);
-----

[[link_attr_flags]]
==== Flags
The flags of a link enable or disable various link features or inform about
the state of the link.

[source,c]
-----
#include <netlink/route/link.h>

void rtnl_link_set_flags(struct rtnl_link *link, unsigned int flags);
void rtnl_link_unset_flags(struct rtnl_link *link, unsigned int flags);
unsigned int rtnl_link_get_flags(struct rtnl_link *link);
-----

[options="compact"]
[horizontal]
IFF_UP::           Link is up (administratively)
IFF_RUNNING::      Link is up and carrier is OK (RFC2863 OPER_UP)
IFF_LOWER_UP::     Link layer is operational
IFF_DORMANT::      Driver signals dormant
IFF_BROADCAST::    Link supports broadcasting
IFF_MULTICAST::    Link supports multicasting
IFF_ALLMULTI::     Link supports multicast routing
IFF_DEBUG::        Tell driver to do debugging (currently unused)
IFF_LOOPBACK::     Link loopback network
IFF_POINTOPOINT::  Point-to-point link
IFF_NOARP::        ARP is not supported
IFF_PROMISC::      Status of promiscious mode
IFF_MASTER::       Master of a load balancer (bonding)
IFF_SLAVE::        Slave to a master link
IFF_PORTSEL::      Driver supports setting media type (only used by ARM ethernet)
IFF_AUTOMEDIA::    Link selects port automatically (only used by ARM ethernet)
IFF_ECHO::         Echo sent packets (testing feature, CAN only)
IFF_DYNAMIC::      Unused (BSD compatibility)
IFF_NOTRAILERS::   Unused (BSD compatibility)

To translate a link flag to a link flag name or vice versa:

[source,c]
-----
#include <netlink/route/link.h>

char *rtnl_link_flags2str(int flags, char *buf, size_t size);
int rtnl_link_str2flags(const char *flag_name);
-----

[[link_attr_txqlen]]
==== Transmission Queue Length

The transmission queue holds packets before packets are delivered to
the driver for transmission. It is usually specified in number of
packets but the unit may be specific to the link type.

[source,c]
-----
#include <netlink/route/link.h>

void rtnl_link_set_txqlen(struct rtnl_link *link, unsigned int txqlen);
unsigned int rtnl_link_get_txqlen(struct rtnl_link *link);
-----

[[link_attr_operstate]]
==== Operational Status
The operational status has been introduced to provide extended information
on the link status. Traditionally the link state has been described using
the link flags +IFF_UP, IFF_RUNNING, IFF_LOWER_UP+, and +IFF_DORMANT+ which
was no longer sufficient for some link types.

[source,c]
-----
#include <netlink/route/link.h>

void rtnl_link_set_operstate(struct rtnl_link *link, uint8_t state);
uint8_t rtnl_link_get_operstate(struct rtnl_link *link);
-----

[options="compact"]
[horizontal]
IF_OPER_UNKNOWN::          Unknown state
IF_OPER_NOTPRESENT::       Link not present
IF_OPER_DOWN::             Link down
IF_OPER_LOWERLAYERDOWN::   L1 down
IF_OPER_TESTING::          Testing
IF_OPER_DORMANT::          Dormant
IF_OPER_UP::               Link up

Translation of operational status code to string and vice versa:

[source,c]
-----
#include <netlink/route/link.h>

char *rtnl_link_operstate2str(uint8_t state, char *buf, size_t size);
int rtnl_link_str2operstate(const char *name);
-----

[[link_attr_mode]]
==== Mode
Currently known link modes are:

[options="compact"]
[horizontal]
IF_LINK_MODE_DEFAULT::   Default link mode
IF_LINK_MODE_DORMANT::   Limit upward transition to dormant

[source,c]
-----
#include <netlink/route/link.h>

void rtnl_link_set_linkmode(struct rtnl_link *link, uint8_t mode);
uint8_t rtnl_link_get_linkmode(struct rtnl_link *link);
-----

Translation of link mode to string and vice versa:

[source,c]
-----
char *rtnl_link_mode2str(uint8_t mode, char *buf, size_t len);
uint8_t rtnl_link_str2mode(const char *name);
-----

[[link_attr_alias]]
==== IfAlias
Alternative name for the link, primarly used for SNMP IfAlias.

[source,c]
-----
#include <netlink/route/link.h>

const char *rtnl_link_get_ifalias(struct rtnl_link *link);
void rtnl_link_set_ifalias(struct rtnl_link *link, const char *alias);
-----

*Length limit:* 256

[[link_attr_arptype]]
==== Hardware Type

[source,c]
-----
#include <netlink/route/link.h>
#include <linux/if_arp.h>

void rtnl_link_set_arptype(struct rtnl_link *link, unsigned int arptype);
unsigned int rtnl_link_get_arptype(struct rtnl_link *link);
----

Translation of hardware type to character string and vice versa:

[source,c]
-----
#include <netlink/utils.h>

char *nl_llproto2str(int arptype, char *buf, size_t len);
int nl_str2llproto(const char *name);
-----

[[link_attr_qdisc]]
==== Qdisc
The name of the queueing discipline used by the link is of informational
nature only. It is a read-only attribute provided by the kernel and cannot
be modified. The set function is provided solely for the purpose of creating
link objects to be used for comparison.

For more information on how to modify the qdisc of a link, see section
<<route_tc>>.

[source,c]
-----
#include <netlink/route/link.h>

void rtnl_link_set_qdisc(struct rtnl_link *link, const char *name);
char *rtnl_link_get_qdisc(struct rtnl_link *link);
-----

[[link_attr_promiscuity]]
==== Promiscuity
The number of subsystem currently depending on the link being promiscuous mode.
A value of 0 indicates that the link is not in promiscuous mode. It is a
read-only attribute provided by the kernel and cannot be modified. The set
function is provided solely for the purpose of creating link objects to be
used for comparison.

[source,c]
-----
#include <netlink/route/link.h>

void rtnl_link_set_promiscuity(struct rtnl_link *link, uint32_t count);
uint32_t rtnl_link_get_promiscuity(struct rtnl_link *link);
-----

[[link_num_rxtx_queues]]
==== RX/TX Queues
The number of RX/TX queues the link provides. The attribute is writable but
will only be considered when creating a new network device via netlink.

[source,c]
-----
#include <netlink/route/link.h>

void rtnl_link_set_num_tx_queues(struct rtnl_link *link, uint32_t nqueues);
uint32_t rtnl_link_get_num_tx_queues(struct rtnl_link *link);

void rtnl_link_set_num_rx_queues(struct rtnl_link *link, uint32_t nqueues);
uint32_t rtnl_link_get_num_rx_queues(struct rtnl_link *link);
-----

[[link_attr_weight]]
==== Weight
This attribute is unused and obsoleted in all recent kernels.


[[link_modules]]
=== Modules

[[link_bonding]]
==== Bonding

.Example: Add bonding link
[source,c]
-----
#include <netlink/route/link.h>

struct rtnl_link *link;

link = rtnl_link_alloc();
rtnl_link_set_name(link, "my_bond");
rtnl_link_set_type(link, "bond");

/* requires admin privileges */
if (rtnl_link_add(sk, link, NLM_F_CREATE) < 0)
	/* error */

rtnl_link_put(link);
-----

[[link_vlan]]
==== VLAN

[source,c]
-----
extern char *		rtnl_link_vlan_flags2str(int, char *, size_t);
extern int		rtnl_link_vlan_str2flags(const char *);

extern int		rtnl_link_vlan_set_id(struct rtnl_link *, int);
extern int		rtnl_link_vlan_get_id(struct rtnl_link *);

extern int		rtnl_link_vlan_set_flags(struct rtnl_link *,
						 unsigned int);
extern int		rtnl_link_vlan_unset_flags(struct rtnl_link *,
						   unsigned int);
extern unsigned int	rtnl_link_vlan_get_flags(struct rtnl_link *);

extern int		rtnl_link_vlan_set_ingress_map(struct rtnl_link *,
						       int, uint32_t);
extern uint32_t *	rtnl_link_vlan_get_ingress_map(struct rtnl_link *);

extern int		rtnl_link_vlan_set_egress_map(struct rtnl_link *,
						      uint32_t, int);
extern struct vlan_map *rtnl_link_vlan_get_egress_map(struct rtnl_link *,
						      int *);
-----

.Example: Add a VLAN device
[source,c]
-----
struct rtnl_link *link;
int master_index;

/* lookup interface index of eth0 */
if (!(master_index = rtnl_link_name2i(link_cache, "eth0")))
	/* error */

/* allocate new link object to configure the vlan device */
link = rtnl_link_alloc();

/* set eth0 to be our master device */
rtnl_link_set_link(link, master_index);

if ((err = rtnl_link_set_type(link, "vlan")) < 0)
	/* error */

rtnl_link_vlan_set_id(link, 10);

if ((err = rtnl_link_add(sk, link, NLM_F_CREATE)) < 0)
	/* error */

rtnl_link_put(link);
-----

== Neighbouring

== Routing

[[route_tc]]
== Traffic Control

The traffic control architecture allows the queueing and
prioritization of packets before they are enqueued to the network
driver. To a limited degree it is also possible to take control of
network traffic as it enters the network stack.

The architecture consists of three different types of modules:

- *Queueing disciplines (qdisc)* provide a mechanism to enqueue packets
  in different forms. They may be used to implement fair queueing,
  prioritization of differentiated services, enforce bandwidth
  limitations, or even to simulate network behaviour such as packet
  loss and packet delay. Qdiscs can be classful in which case they
  allow traffic classes described in the next paragraph to be attached
  to them.

- *Traffic classes (class)* are supported by several qdiscs to build
  a tree structure for different types of traffic. Each class may be
  assigned its own set of attributes such as bandwidth limits or
  queueing priorities. Some qdiscs even allow borrowing of bandwidth
  between classes.

- *Classifiers (cls)* are used to decide which qdisc/class the packet
  should be enqueued to. Different types of classifiers exists,
  ranging from classification based on protocol header values to
  classification based on packet priority or firewall marks.
  Additionally most classifiers support *extended matches (ematch)*
  which allow extending classifiers by a set of matcher modules, and
  *actions* which allow classifiers to take actions such as mangling,
  mirroring, or even rerouting of packets.

.Default Qdisc

The default qdisc used on all network devices is `pfifo_fast`.
Network devices which do not require a transmit queue such as the
loopback device do not have a default qdisc attached. The `pfifo_fast`
qdisc provides three bands to prioritize interactive traffic over bulk
traffic. Classification is based on the packet priority (diffserv).

image:qdisc_default.png["Default Qdisc"]

.Multiqueue Default Qdisc

If the network device provides multiple transmit queues the `mq`
qdisc is used by default. It will automatically create a separate
class for each transmit queue available and will also replace
the single per device tx lock with a per queue lock.

image:qdisc_mq.png["Multiqueue default Qdisc"]

.Example of a customized classful qdisc setup

The following figure illustrates a possible combination of different
queueing and classification modules to implement quality of service
needs.

image:tc_overview.png["Classful Qdisc diagram"]

=== Traffic Control Object

Each type traffic control module (qdisc, class, classifier) is
represented by its own structure. All of them are based on the traffic
control object represented by `struct rtnl_tc` which itself is based
on the generic object `struct nl_object` to make it cacheable. The
traffic control object contains all attributes, implementation details
and statistics that are shared by all of the traffic control object
types.

image:tc_obj.png["struct rtnl_tc hierarchy"]

It is not possible to allocate a `struct rtnl_tc` object, instead the
actual tc object types must be allocated directly using
`rtnl_qdisc_alloc()`, `rtnl_class_alloc()`, `rtnl_cls_alloc()` and
then casted to `struct rtnl_tc` using the `TC_CAST()` macro.

.Usage Example: Allocation, Casting, Freeing
[source,c]
-----
#include <netlink/route/tc.h>
#include <netlink/route/qdisc.h>

struct rtnl_qdisc *qdisc;

/* Allocation of a qdisc object */
qdisc = rtnl_qdisc_alloc();

/* Cast the qdisc to a tc object using TC_CAST() to use rtnl_tc_ functions. */
rtnl_tc_set_mpu(TC_CAST(qdisc), 64);

/* Free the qdisc object */
rtnl_qdisc_put(qdisc);
-----

[[tc_attr]]
==== Attributes

Handle::
The handle uniquely identifies a tc object and is used to refer
to other tc objects when constructing tc trees.
+
[source,c]
-----
void rtnl_tc_set_handle(struct rtnl_tc *tc, uint32_t handle);
uint32_t rtnl_tc_get_handle(struct rtnl_tc *tc);
-----

Interface Index::
The interface index specifies the network device the traffic object
is attached to. The function `rtnl_tc_set_link()` should be preferred
when setting the interface index. It stores the reference to the link
object in the tc object and allows retrieving the `mtu` and `linktype`
automatically.
+
[source,c]
-----
void rtnl_tc_set_ifindex(struct rtnl_tc *tc, int ifindex);
void rtnl_tc_set_link(struct rtnl_tc *tc, struct rtnl_link *link);
int rtnl_tc_get_ifindex(struct rtnl_tc *tc);
-----

Link Type::
The link type specifies the kind of link that is used by the network
device (e.g. ethernet, ATM, ...). It is derived automatically when
the network device is specified with `rtnl_tc_set_link()`.
The default fallback is `ARPHRD_ETHER` (ethernet).
+
[source,c]
-----
void rtnl_tc_set_linktype(struct rtnl_tc *tc, uint32_t type);
uint32_t rtnl_tc_get_linktype(struct rtnl_tc *tc);
-----

Kind::
The kind character string specifies the type of qdisc, class,
classifier. Setting the kind results in the module specific
structure being allocated. Therefore it is imperative to call 
`rtnl_tc_set_kind()` before using any type specific API functions
such as `rtnl_htb_set_rate()`.
+
[source,c]
-----
int rtnl_tc_set_kind(struct rtnl_tc *tc, const char *kind);
char *rtnl_tc_get_kind(struct rtnl_tc *tc);
-----

MPU::
The Minimum Packet Unit specifies the minimum packet size which will
be transmitted
ever be seen by this traffic control object. This value is used for
rate calculations. Not all object implementations will make use of
this value. The default value is 0.
+
[source,c]
-----
void rtnl_tc_set_mpu(struct rtnl_tc *tc, uint32_t mpu);
uint32_t rtnl_tc_get_mpu(struct rtnl_tc *tc);
-----

MTU::
The Maximum Transmission Unit specifies the maximum packet size which
will be transmitted. The value is derived from the link specified
with `rtnl_tc_set_link()` if not overwritten with `rtnl_tc_set_mtu()`.
If no link and MTU is specified, the value defaults to 1500
(ethernet).
+
[source,c]
-----
void rtnl_tc_set_mtu(struct rtnl_tc *tc, uint32_t mtu);
uint32_t rtnl_tc_get_mtu(struct rtnl_tc *tc);
-----

Overhead::
The overhead specifies the additional overhead per packet caused by
the network layer. This value can be used to correct packet size
calculations if the packet size on the wire does not match the packet
size seen by the kernel. The default value is 0.
+
[source,c]
-----
void rtnl_tc_set_overhead(struct rtnl_tc *tc, uint32_t overhead);
uint32_t rtnl_tc_get_overhead(struct rtnl_tc *tc);
-----

Parent::
Specifies the parent traffic control object. The parent is identifier
by its handle. Special values are:
- `TC_H_ROOT`: attach tc object directly to network device (root
  qdisc, root classifier)
- `TC_H_INGRESS`: same as `TC_H_ROOT` but on the ingress side of the
  network stack.
+
[source,c]
-----
void rtnl_tc_set_parent(struct rtnl_tc *tc, uint32_t parent);
uint32_t rtnl_tc_get_parent(struct rtnl_tc *tc);
-----

Statistics::
Generic statistics, see <<tc_stats>> for additional information.
+
[source,c]
-----
uint64_t rtnl_tc_get_stat(struct rtnl_tc *tc, enum rtnl_tc_stat id);
-----

[[tc_stats]]
==== Accessing Statistics

The traffic control object holds a set of generic statistics. Not all
traffic control modules will make use of all of these statistics. Some
modules may provide additional statistics via their own APIs.

.Statistic identifiers `(enum rtnl_tc_stat)`
[cols="m,,", options="header", frame="topbot"]
|====================================================================
| ID                 | Type    | Description
| RTNL_TC_PACKETS    | Counter | Total # of packets transmitted
| RTNL_TC_BYTES      | Counter | Total # of bytes transmitted
| RTNL_TC_RATE_BPS   | Rate    | Current bytes/s rate
| RTNL_TC_RATE_PPS   | Rate    | Current packets/s rate
| RTNL_TC_QLEN       | Rate    | Current length of the queue
| RTNL_TC_BACKLOG    | Rate    | # of packets currently backloged
| RTNL_TC_DROPS      | Counter | # of packets dropped
| RTNL_TC_REQUEUES   | Counter | # of packets requeued
| RTNL_TC_OVERLIMITS | Counter | # of packets that exceeded the limit
|====================================================================

NOTE: `RTNL_TC_RATE_BPS` and `RTNL_TC_RATE_PPS` only return meaningful
      values if a rate estimator has been configured.

.Usage Example: Retrieving tc statistics
[source,c]
-------
#include <netlink/route/tc.h>

uint64_t drops, qlen;

drops = rtnl_tc_get_stat(TC_CAST(qdisc), RTNL_TC_DROPS);
qlen  = rtnl_tc_get_stat(TC_CAST(qdisc), RTNL_TC_QLEN);
-------

==== Rate Table Calculations

[[tc_qdisc]]
=== Queueing Discipline (qdisc)

.Classless Qdisc

The queueing discipline (qdisc) is used to implement fair queueing,
priorization or rate control. It provides a _enqueue()_ and
_dequeue()_ operation. Whenever a network packet leaves the networking
stack over a network device, be it a physical or virtual device, it
will be enqueued to a qdisc unless the device is queueless. The
_enqueue()_ operation is followed by an immediate call to _dequeue()_
for the same qdisc to eventually retrieve a packet which can be
scheduled for transmission by the driver. Additionally, the networking
stack runs a watchdog which polls the qdisc regularly to dequeue and
send packets even if no new packets are being enqueued.

This additional watchdog is required due to the fact that qdiscs may
hold on to packets and not return any packets upon _dequeue()_ in
order to enforce bandwidth restrictions.

image:classless_qdisc_nbands.png[alt="Multiband Qdisc", float="right"]

The figure illustrates a trivial example of a classless qdisc
consisting of three bands (queues). Use of multiple bands is a common
technique in qdiscs to implement fair queueing between flows or
prioritize differentiated services.

Classless qdiscs can be regarded as a blackbox, their inner workings
can only be steered using the configuration parameters provided by the
qdisc. There is no way of taking influence on the structure of its
internal queues itself.

.Classful Qdisc

Classful qdiscs allow for the queueing structure and classification
process to be created by the user. 

image:classful_qdisc.png["Classful Qdisc"]

The figure above shows a classful qdisc with a classifier attached to
it which will make the decision whether to enqueue a packet to traffic
class +1:1+ or +1:2+. Unlike with classless qdiscs, classful qdiscs
allow the classification process and the structure of the queues to be
defined by the user. This allows for complex traffic class rules to
be applied.

.List of Qdisc Implementations
[options="header", frame="topbot", cols="2,1^,8"]
|======================================================================
| Qdisc     | Classful | Description
| ATM       | Yes      | FIXME
| Blackhole | No       | This qdisc will drop all packets passed to it.
| CBQ       | Yes      |
The CBQ (Class Based Queueing) is a classful qdisc which allows
creating traffic classes and enforce bandwidth limitations for each
class.
| DRR       | Yes      |
The DRR (Deficit Round Robin) scheduler is a classful qdisc
impelemting fair queueing. Each class is assigned a quantum specyfing
the maximum number of bytes that can be served per round.  Unused
quantum at the end of the round is carried over to the next round.
| DSMARK   | Yes       | FIXME
| FIFO     | No        | FIXME
| GRED     | No        | FIXME
| HFSC     | Yes       | FIXME
| HTB      | Yes       | FIXME
| mq       | Yes       | FIXME
| multiq   | Yes       | FIXME
| netem    | No        | FIXME
| Prio     | Yes       | FIXME
| RED      | Yes       | FIXME
| SFQ      | Yes       | FIXME
| TBF      | Yes       | FIXME
| teql     | No        | FIXME
|======================================================================


.QDisc API Overview
[cols="a,a", options="header", frame="topbot"]
|====================================================================
| Attribute | C Interface
|
Allocation / Freeing::
|
[source,c]
-----
struct rtnl_qdisc *rtnl_qdisc_alloc(void);
void rtnl_qdisc_put(struct rtnl_qdisc *qdisc);
-----
|
Addition::
|
[source,c]
-----
int rtnl_qdisc_build_add_request(struct rtnl_qdisc *qdisc, int flags,
				 struct nl_msg **result);
int rtnl_qdisc_add(struct nl_sock *sock, struct rtnl_qdisc *qdisc,
                   int flags);
-----
|
Modification::
|
[source,c]
-----
int rtnl_qdisc_build_change_request(struct rtnl_qdisc *old,
				    struct rtnl_qdisc *new,
				    struct nl_msg **result);
int rtnl_qdisc_change(struct nl_sock *sock, struct rtnl_qdisc *old,
		      struct rtnl_qdisc *new);
-----
|
Deletion::
|
[source,c]
-----
int rtnl_qdisc_build_delete_request(struct rtnl_qdisc *qdisc,
				    struct nl_msg **result);
int rtnl_qdisc_delete(struct nl_sock *sock, struct rtnl_qdisc *qdisc);
-----
|
Cache::
|
[source,c]
-----
int rtnl_qdisc_alloc_cache(struct nl_sock *sock,
			   struct nl_cache **cache);
struct rtnl_qdisc *rtnl_qdisc_get(struct nl_cache *cache, int, uint32_t);

struct rtnl_qdisc *rtnl_qdisc_get_by_parent(struct nl_cache *, int, uint32_t);
-----
|====================================================================

[[qdisc_get]]
==== Retrieving Qdisc Configuration

The function rtnl_qdisc_alloc_cache() is used to retrieve the current
qdisc configuration in the kernel. It will construct a +RTM_GETQDISC+
netlink message, requesting the complete list of qdiscs configured in
the kernel.

[source,c]
-------
#include <netlink/route/qdisc.h>

struct nl_cache *all_qdiscs;

if (rtnl_link_alloc_cache(sock, &all_qdiscs) < 0)
	/* error while retrieving qdisc cfg */
-------

The cache can be accessed using the following functions:

- Search qdisc with matching ifindex and handle:
+
[source,c]
--------
struct rtnl_qdisc *rtnl_qdisc_get(struct nl_cache *cache, int ifindex, uint32_t handle);
--------
- Search qdisc with matching ifindex and parent:
+
[source,c]
--------
struct rtnl_qdisc *rtnl_qdisc_get_by_parent(struct nl_cache *cache, int ifindex , uint32_t parent);
--------
- Or any of the generic cache functions (e.g. nl_cache_search(), nl_cache_dump(), etc.)

.Example: Search and print qdisc
[source,c]
-------
struct rtnl_qdisc *qdisc;
int ifindex;

ifindex = rtnl_link_get_ifindex(eth0_obj);

/* search for qdisc on eth0 with handle 1:0 */
if (!(qdisc = rtnl_qdisc_get(all_qdiscs, ifindex, TC_HANDLE(1, 0))))
	/* no such qdisc found */

nl_object_dump(OBJ_CAST(qdisc), NULL);

rtnl_qdisc_put(qdisc);
-------

[[qdisc_add]]
==== Adding a Qdisc

In order to add a new qdisc to the kernel, a qdisc object needs to be
allocated. It will hold all attributes of the new qdisc.

[source,c]
-----
#include <netlink/route/qdisc.h>

struct rtnl_qdisc *qdisc;

if (!(qdisc = rtnl_qdisc_alloc()))
	/* OOM error */
-----

The next step is to specify all generic qdisc attributes using the tc
object interface described in the section <<tc_attr>>.

The following attributes must be specified:
- IfIndex
- Parent
- Kind

[source,c]
-----
/* Attach qdisc to device eth0 */
rtnl_tc_set_link(TC_CAST(qdisc), eth0_obj);

/* Make this the root qdisc */
rtnl_tc_set_parent(TC_CAST(qdisc), TC_H_ROOT);

/* Set qdisc identifier to 1:0, if left unspecified, a handle will be generated by the kernel. */
rtnl_tc_set_handle(TC_CAST(qdisc), TC_HANDLE(1, 0));

/* Make this a HTB qdisc */
rtnl_tc_set_kind(TC_CAST(qdisc), "htb");
-----

After specyfing the qdisc kind (rtnl_tc_set_kind()) the qdisc type
specific interface can be used to set attributes which are specific
to the respective qdisc implementations:

[source,c]
------
/* HTB feature: Make unclassified packets go to traffic class 1:5 */
rtnl_htb_set_defcls(qdisc, TC_HANDLE(1, 5));
------

Finally, the qdisc is ready to be added and can be passed on to the
function rntl_qdisc_add() which takes care of constructing a netlink
message requesting the addition of the new qdisc, sends the message to
the kernel and waits for the response by the kernel. The function
returns 0 if the qdisc has been added or updated successfully or a
negative error code if an error occured.

CAUTION: The kernel operation for updating and adding a qdisc is the
         same. Therefore when calling rtnl_qdisc_add() any existing
         qdisc with matching handle will be updated unless the flag
         NLM_F_EXCL is specified.

The following flags may be specified:
[horizontal]
NLM_F_CREATE::  Create qdisc if it does not exist, otherwise
                -NLE_OBJ_NOTFOUND is returned.
NLM_F_REPLACE:: If another qdisc is already attached to the same
                parent and their handles mismatch, replace the qdisc
                instead of returning -EEXIST.
NLM_F_EXCL::    Return -NLE_EXISTS if a qdisc with matching handles
                exists already.

WARNING: The function rtnl_qdisc_add() requires administrator
         privileges.

[source,c]
------
/* Submit request to kernel and wait for response */
err = rtnl_qdisc_add(sock, qdisc, NLM_F_CREATE);

/* Return the qdisc object to free memory resources */
rtnl_qdisc_put(qdisc);

if (err < 0) {
	fprintf(stderr, "Unable to add qdisc: %s\n", nl_geterror(err));
	return err;
}
------

==== Deleting a qdisc

[source,c]
------
#include <netlink/route/qdisc.h>

struct rtnl_qdisc *qdisc;

qdisc = rtnl_qdisc_alloc();

rtnl_tc_set_link(TC_CAST(qdisc), eth0_obj);
rtnl_tc_set_parent(TC_CAST(qdisc), TC_H_ROOT);

rtnl_qdisc_delete(sock, qdisc)

rtnl_qdisc_put(qdisc);
------

WARNING: The function rtnl_qdisc_delete() requires administrator
         privileges.


[[qdisc_htb]]
==== HTB - Hierarchical Token Bucket

.HTB Qdisc Attributes

Default Class::
The default class is the fallback class to which all traffic which
remained unclassified is directed to. If no default class or an
invalid default class is specified, packets are transmitted directly
to the next layer (direct transmissions).
+
[source,c]
-----
uint32_t rtnl_htb_get_defcls(struct rtnl_qdisc *qdisc);
int rtnl_htb_set_defcls(struct rtnl_qdisc *qdisc, uint32_t defcls);
-----

Rate to Quantum (r2q)::
TODO
+
[source,c]
-----
uint32_t rtnl_htb_get_rate2quantum(struct rtnl_qdisc *qdisc);
int rtnl_htb_set_rate2quantum(struct rtnl_qdisc *qdisc, uint32_t rate2quantum);
-----


.HTB Class Attributes

Priority::
+
[source,c]
-----
uint32_t rtnl_htb_get_prio(struct rtnl_class *class);
int rtnl_htb_set_prio(struct rtnl_class *class, uint32_t prio);
-----

Rate::
The rate (bytes/s) specifies the maximum bandwidth an invidivual class
can use without borrowing. The rate of a class should always be greater
or erqual than the rate of its children.
+
[source,c]
-----
uint32_t rtnl_htb_get_rate(struct rtnl_class *class);
int rtnl_htb_set_rate(struct rtnl_class *class, uint32_t ceil);
-----

Ceil Rate::
The ceil rate specifies the maximum bandwidth an invidivual class
can use. This includes bandwidth that is being borrowed from other
classes. Ceil defaults to the class rate implying that by default
the class will not borrow. The ceil rate of a class should always
be greater or erqual than the ceil rate of its children.
+
[source,c]
-----
uint32_t rtnl_htb_get_ceil(struct rtnl_class *class);
int rtnl_htb_set_ceil(struct rtnl_class *class, uint32_t ceil);
-----

Burst::
TODO
+
[source,c]
-----
uint32_t rtnl_htb_get_rbuffer(struct rtnl_class *class);
int rtnl_htb_set_rbuffer(struct rtnl_class *class, uint32_t burst);
-----

Ceil Burst::
TODO
+
[source,c]
-----
uint32_t rtnl_htb_get_bbuffer(struct rtnl_class *class);
int rtnl_htb_set_bbuffer(struct rtnl_class *class, uint32_t burst);
-----

Quantum::
TODO
+
[source,c]
-----
int rtnl_htb_set_quantum(struct rtnl_class *class, uint32_t quantum);
-----

extern int	rtnl_htb_set_cbuffer(struct rtnl_class *, uint32_t);




[[tc_class]]
=== Class

[options="header", cols="s,a,a,a,a"]
|=======================================================================
|        | UNSPEC             | TC_H_ROOT          | 0:pY  | pX:pY
| UNSPEC 3+^|
[horizontal]
qdisc =:: root-qdisc
class =:: root-qdisc:0
|
[horizontal]
qdisc =:: pX:0
class =:: pX:0
| 0:hY 3+^|
[horizontal]
qdisc =:: root-qdisc
class =:: root-qdisc:hY
|
[horizontal]
qdisc =:: pX:0
class =:: pX:hY
| hX:hY 3+^|
[horizontal]
qdisc =:: hX:
class =:: hX:hY
|
if pX != hX
    return -EINVAL
[horizontal]
qdisc =:: hX:
class =:: hX:hY
|=======================================================================

[[tc_cls]]
=== Classifier (cls)

TODO

[[tc_classid_mngt]]
=== ClassID Management

TODO

[[tc_pktloc]]
=== Packet Location Aliasing (pktloc)

TODO

[[tc_api]]
=== Traffic Control Module API

TODO