ForCES Working Group Jamal Hadi Salim
Internet Draft Znyx Networks
Hormuzd Khosravi
Intel
Andi Kleen
Suse
Alexey Kuznetsov
INR/Swsoft
November 2001
Netlink as an IP services protocol
draft-ietf-forces-netlink-01.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as ``work in progress.''
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in [RFC-2119].
1. Abstract
This document describes Linux Netlink, which is used in Linux both
as an inter-kernel messaging system as well as between kernel and
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user-space. The purpose of this document is intended as informa-
tional in the context of prior art for the ForCES IETF working
group. The focus of this document is to describe netlink from a
context of a protocol between a Forwording Engine Component (FEC)
and a Control Plane Component(CPC) that define an IP service.
The document ignores the ability of netlink as a inter-kernel mes-
saging system, as a an inter-process communication scheme (IPC) or
its use in configuring other non-network as well as network but
non-IP services (such as decnet etc).
2. Introduction
The concept of IP Service control-forwarding separation was first
introduced in the early 1980s by the BSD 4.4 routing sock-
ets[stevens]. The focus at that time was a simple IP(v4) forward-
ing service and how the CPC, either via a command line configura-
tion tool or a dynamic route daemon, can control forwarding tables
for that IPV4 forwarding service.
The IP world has evolved considerably since those days. Linux
netlink, when observed from a service provisioning point of view
takes routing sockets one step further by breaking the barrier of
focus around IPV4 forwarding. Since the linux 2.1 kernel, netlink
has been providing the IP service abstraction to a few services
other than the classical IPv4 forwarding.
We first give some concept definitions and then describe how
netlink fits in.
2.1. Some definitions
A Control plane(CP) is an execution environment that may have sev-
eral components which we refer to as CPCs. Each CPC provides con-
trol for a different IP service being executed by a FE component.
This means that there might be several CPCs on a physical CP if it
is controlling several IP services. In essence, the cohesion
between a CP component and a FE component is the service abstrac-
tion.
In the diagram below we show a simple FE<->CP setup to provide an
example of the classical IPv4 service with an extension to do some
basic QoS egress scheduling and how it fits in this described
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model.
Control Plane (CP)
.------------------------------------
| /^^^^^ /^^^^^ |
| | | | COPS |- |
| | ospfd | | PEP | |
| / _____/ | |
/------_____/ | | |
| | | | | |
| |_____________________|___|_________|
| | | |
******************************************
Forwarding ************* Netlink layer ************
Engine (FE) *****************************************
.-------------|-----------|------------|---|-----------
| IPv4 forwading | / |
| FE Service / / |
| Component / / |
| ---------------/---------------/--------- |
| | | / | |
packet | | --------|-- ----|----- | packet
in | | | IPV4 | | Egress | | out
-->--->|------>|---->|Forwading |----->| QoS |--->| ---->|---->
| | | | | Scheduler| | |
| | ----------- ---------- | |
| | | |
| --------------------------------------- |
| |
-------------------------------------------------------
2.1.1. Control Plane Components (CPCs)
Control plane components would encompass signalling protocols with
diversity ranging from dynamic routing protocols such as OSPF
[RFC2328] to tag distribution protocols such as CR-LDP [RFC3036].
Classical Management protocols and activities also fall under this
category. These include SNMP [RFC1157], COPS [RFC2748] or propri-
etary CLI/GUI configuration mechanisms.
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The purpose of the control plane is to provide an execution envi-
ronment for the above mentioned activities with the ultimate goal
being to configure and manage the second NE component: the FE. The
result of the configuration would define the way packets travesing
the FE are treated.
In the above diagram, ospfd and COPS are distinct CPCs.
2.1.2. Forwarding Engine Components
The FE is the entity of the NE that incoming packets (from the net-
work into the NE) first encounter.
The FE's service specific component massages the packet to provide
it with a treatment to achieve a IP service as defined by the con-
trol plane components for that IP service. Different services will
utilize different FEC. Service modules maybe chained to achieve a
more complex service (as shown in the diagram). When built for
providing a specific service, the FE service component will adhere
to a Forwading Model.
In the above diagram, the IPV4 FE component includes both the IPV4
Forwarding service module as well as the Egress Scheduling service
module. Another service might may add a policy forwarder between
the IPV4 forwader and the QoS egress Scheduler. A simpler classi-
cal service would have constituted only the IPV4 forwarder.
2.1.3. IP Services
An IP Service is the treatment of an IP packet within the NE. This
treatment is provided by a combination of both the CPC and FEC
The time span of the service is from the moment when the packet
arrives at the NE to the moment it departs. In essence an IP ser-
vice in this context is a Per-Hop Behavior. A service control/sig-
naling protocol/management-application (CP components running on
NEs defining the end to end path) unifies the end to end view of
the IP service. As noted above, these CP components then define the
behavior of the FE (and therefore the NE) to a described packet.
A simple example of an IP service is the classical IPv4 Forwarding.
In this case, control components such as routing protocols(OSPF,
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RIP etc) and proprietary CLI/GUI configurations modify the FE's
forwarding tables in order to offer the simple service of forward-
ing packets to the next hop. Traditionally, NEs offering this sim-
ple service are known as routers.
Over the years it has become important to add aditional services to
the routers to meet emerging requirements. More complex services
extending classical forwarding were added and standardized. These
newer services might go beyond the layer 3 contents of the packet
header. However, the name "router", although a misnomer, is still
used to describe these NEs. Services (which may look beyond the
classical L3 headers) here include firewalling, Qos in Diffserv and
RSVP, NATs, policy based routing etc. Newer control protocols or
management activities are introduced with these new services.
One extreme definition of a IP service is something a service
provider would be able to charge for.
3. Netlink Architecture
IP services components control is defined by using templates.
The FEC and CPC participate to deliver the IP service by communi-
cating using these templates. The FEC might continously get
updates from the control plane component on how to operate the ser-
vice (example for V4 forwarding route additions or deletions).
The interaction between the FEC and the CPC, in the netlink con-
text, would define a protocol. Netlink provides the mechanism for
the CPC(residing in user space) and FEC(residing in kernel space)
to define their own protocol definition. Kernel space and user
space just mean different protection domains direct where direct
memory access is not allowed inbetween. Therefore a wire protocol
is needed to communicate. The wire protocol would be normally be
provided by some privileged service that is able to copy between
multiple protection domains. We will call this service netlink
service. Netlink service could also be mapped to a different
transport layer if the CPC should be running on a different node
than the CPC. The FEC and CPC, using netlink mechanisms, may
choose to define a reliable protocol between each other, for exam-
ple. By default netlink provides an unreliable communication.
Note that the FEC and CPC can both live in the same memory protec-
tion domain and use the connect() system call to create a path to
the peer and talk to each other. We will not discuss this further
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other than to say it is available as a mechanism. Through out this
document we will refer interchangbly to the FEC to mean kernel-
space and the CPC to mean user-space.
Note: Netlink allows participation in IP services by both service
components.
3.1. Netlink Logical model
In the diagram below we show a simple FEC<->CPC logical relation-
ship. We use the example of IPV4 forwarding FEC (NETLINK_ROUTE,
which is discussed further below) as an example.
Control Plane (CP)
.------------------------------------
| /^^^^^ /CPC-2 |
| | CPC-1 | | COPS | |
| | ospfd | | PEP | |
| / _____/ |
| _____/ | |
| | | |
****************************************|
************* BROADCAST WIRE ************
FE---------- *****************************************.
| IPv4 forwading | | / |
| FEC | | | |
| --------------/-----|-----------|-------- |
| | / | | | |
| | .-------. .-------. .------. | |
| | |ingress| | IPV4 | |Egress| | |
| | |police | |Forward| | QoS | | |
| | |_______| |_______| |Sched | | |
| | ------ | |
| --------------------------------------- |
| |
-----------------------------------------------------
Netlink logically models FECs and CPCs in the form of nodes inter-
connected to each other via a broadcast wire.
The wire is specific to a service. The example above shows the
broadcast wire belonging to the extended IPV4 forwarding service.
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Nodes connect to the wire and register to receive specific mes-
sages. CPCs may connect to multiple wires if it helps them to con-
trol the service better. All nodes(CPCs and FECs) dump packets on
the broadcast wire. Packets could be discarded by the wire if mal-
formed or not specifically formated for the wire. Dropped packets
are not seen by any of the nodes. The netlink service MAY signal
an error to the original if it detects an malformatted netlink
packet.
Packets sent on the wire could be broadcast, multicast or unicast.
FECs or CPCs pick specific messages of interest for processing or
just monitoring purposes.
3.2. The message format
There are three levels to a netlink message: The general netlink
message header, the IP service specific template, the IP service
specific data.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Netlink message header |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IP Service Template |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IP Service specific data in TLVs |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.3. Protocol Model
This section expands on how netlink provides the mechanism for ser-
vice oriented FEC and CPC interaction.
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3.3.1. Service Addressing
Access is provided by first connecting to the service on the FE.
This is done by making a socket() system call to the PF_NETLINK
domain. Each FEC is identified by a protocol number. One may open
either SOCK_RAW or SOCK_DGRAM type sockets although netlink doesnt
distinguish the two. The socket connection provides the basis for
the FE<->CP addressing.
Connecting to a service is followed (at any point during the life
of the connection) by issuing either a service specific command
mostly for configuration purposes (from the CPC to the FEC) or sub-
scribing/unsubscribing to service(s') events.
3.3.1.1. Sample Service Hierachy
In the diagram below we show a simple IP service, foo, and the
interaction it has between CP and FE components for the ser-
vice(labels 1-3).
We introduce the diagram below to demonstrate CP<->FE addressing.
In this section we illustrate only the addressing semantics. In
section 4, the diagram is referenced again to define the protocol
interaction between srevice foo's CPC and FEC (labels 4-10).
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CP
[--------------------------------------------------------.
| .-----. |
| | . -------. |
| | CLI | / |
| | | | CP protocol |
| /->> -. | component | <-. |
| __ _/ | | For | | |
| | | IP service | ^ |
| Y | foo | | |
| | ___________/ ^ |
| Y 1,4,6,8,9 / ^ 2,5,10 | 3,7 |
--------------- Y------------/---|----------|-----------
| ^ | ^
**|***********|****|**********|**********
************* Netlink layer ************
**|***********|****|**********|**********
FE | | ^ ^
.-------- Y-----------Y----|--------- |----.
| | / |
| Y / |
| . --------^-------. / |
| |FE component/module|/ |
| | for IP Service | |
--->---|------>---| foo |----->-----|------>--
| ------------------- |
| |
| |
------------------------------------------
The control plane protocol for IP service foo does the following to
connect to its FE counterpart. The steps below are also numbered
above in the diagram.
1) Connect to IP service foo through a socket connect. A typical con-
nection would be via a call to: socket(AF_NETLINK, SOCK_RAW,
NETLINK_FOO)
2) Bind to listen to specific async events for service foo
3) Bind to listen to specific async FE events
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3.3.2. Netlink message header
Netlink messages consist of a byte stream with one or multiple
Netlink headers and associated payload. If the payload is too big
to fit into a single message it can be split over multiple netlink
messages. This is called a multipart message. For multipart mes-
sages the first and all following headers have the NLM_F_MULTI
netlink header
flag set, except for the last header which has the netlink header
type NLMSG_DONE.
The netlink message header is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Process PID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields in the header are:
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Length: 32 bits
The length of the message in bytes including the header.
Type: 16 bits
This field describes the message content.
It can be one of the standard message types:
NLMSG_NOOP message is ignored
NLMSG_ERROR the message signals an error and the payload
contains a nlmsgerr structure. This can be looked
at as a NACK and typically it is from FEC to CPC.
NLMSG_DONE message terminates a multipart message
Individual IP Services specify more message types, for e.g.,
NETLINK_ROUTE Service specifies several types such as RTM_NEWLINK,
RTM_DELLINK, RTM_GETLINK, RTM_NEWADDR, RTM_DELADDR, RTM_NEWROUTE,
RTM_DELROUTE, etc.
Flags: 16 bits
The standard flag bits used in netlink are
NLM_F_REQUEST Must be set on all request messages (typically
from user space to kernel space)
NLM_F_MULTI Indicates the message is part of a multipart
message terminated by NLMSG_DONE
NLM_F_ACK Request for an acknowledgment on success.
Typical direction of request is from user
space to kernel space.
NLM_F_ECHO Echo this request. Typical direction of
request is from user space to kernel space.
Additional flag bits for GET requests on config information in
the FEC.
NLM_F_ROOT Return the complete table instead of a
single entry.
NLM_F_MATCH Return all matching criteria passed in
message content
NLM_F_ATOMIC Return an atomic snapshot of the table being
referenced. This may require special privileges
because it has the potential to interrupt
service in the FE for a longer time.
Convenience macros for flag bits:
NLM_F_DUMP This is NLM_F_ROOT or'ed with NLM_F_MATCH
Additional flag bits for NEW requests
NLM_F_REPLACE Replace existing matching config object with
this request.
NLM_F_EXCL Don't replace the config object if it already
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exists.
NLM_F_CREATE Create config object if it doesn't already
exist.
NLM_F_APPEND Add to the end of the object list.
For those familiar with BSDish use of such operations in route
sockets, the equivalent translations are:
- BSD ADD operation equates to NLM_F_CREATE or-ed
with NLM_F_EXCL
- BSD CHANGE operation equates to NLM_F_REPLACE
- BSD Check operation equates to NLM_F_EXCL
- BSD APPEND equivalent is actually mapped to
NLM_F_CREATE
Sequence Number: 32 bits
The sequence number of the message.
Process PID: 32 bits
The PID of the process sending the message. The PID is used by the
kernel to multiplex to the correct sockets. A PID of zero is used
when sending messages to user space from the kernel. netlink service
fills in an appropiate value when zero.
3.3.2.1. Mechanisms for creating protocols
One could create a reliable protocol between an FEC and a CPC by
using the combination of sequence numbers, ACKs and retransmit
timers. Both sequence numbers and sequence numbers are provided by
netlink. Timers are provided by Linux.
One could create a heartbeat protocol between the FEC and CPC by
using the ECHO flags and the NLMSG_NOOP message.
3.3.2.2. The ACK netlink message
This message is actually used to denote both an ACK and a NACK.
Typically the direction is from kernel to user space (in response
to an ACK request message that is sent). However, user space should
be able to send ACKs back to kernel space when requested. This is
IP service specific.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Netlink message header |
| type = NLMSG_ERROR |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| error code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OLD Netlink message header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Error code: integer (typically 32 bits)
Error code of zero indicates that the message is an ACK response.
An ACK response message contains the original netlink message
header that can be used to compare against (sent sequence numbers
etc).
A non-zero error message is equivalent to a Negative ACK (NACK).
In such a situation, the netlink data that was sent down to the
kernel is returned appended to the original netlink message header.
An error code printable via the perror() is also set (not in the
message header, rather in the executing environment state vari-
able).
3.3.3. FE services' templates
These are services that are offered by the system for general use
by other services. They include ability to configure and listen to
changes in resource management. IP address management, link events
etc fit here. We separate them into this section here for logical
purposes despite the fact that they are accessed via the
NETLINK_ROUTE FEC. The reason that they exist within NETLINK_ROUTE
is due to historical cruft based on the fact that BSD 4.4 rather
narrowly focussed Route Sockets implemented them as part of the
IPV4 forwarding sockets.
3.3.3.1.
Network Interface Service Module
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This service provides the ability to create, remove or get informa-
tion about a specific network interface. The network interface
could be either pohysical or virtual and is network protocol inde-
pendent (example an x.25 interface can be defined via this mes-
sage). The Interface service message template is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Family | Padding | Device Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Device Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Change Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Family: This is always set to AF_UNSPEC
Device Type: This defines the type of the link. The link could be
ethernet, a tunnel etc. Although we are interested only in IPV4,
the link type is protocol independent.
Interface Index: uniquely identifies interface.
Device Flags:
IFF_UP Interface is running.
IFF_BROADCAST Valid broadcast address set.
IFF_DEBUG Internal debugging flag.
IFF_LOOPBACK Interface is a loopback interface.
IFF_POINTOPOINT Interface is a point-to-point link.
IFF_RUNNING Resources allocated.
IFF_NOARP No arp protocol
IFF_PROMISC Interface is in promiscuous mode.
IFF_NOTRAILERS Avoid use of trailers.
IFF_ALLMULTI Receive all multicast packets.
IFF_MASTER Master of a load balancing bundle.
IFF_SLAVE Slave of a load balancing bundle.
IFF_MULTICAST Supports multicast
IFF_PORTSEL Is able to select media type via ifmap.
IFF_AUTOMEDIA Auto media selection active.
IFF_DYNAMIC Interface Address is not permanent.
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Change Mask: Reserved for future use. Must be set to 0xFFFFFFFF.
Applicable attributes:
attribute description
.......................................................
IFLA_UNSPEC - unspecified.
IFLA_ADDRESS hardware address interface L2 address
IFLA_BROADCAST hardware address L2 broadcast
address.
IFLA_IFNAME ascii string Device name.
IFLA_MTU MTU of the device.
IFLA_LINK Link type.
IFLA_QDISC ascii string defining Queueing disci-
pline.
IFLA_STATS Interface Statistics.
Netlink message types specific to this service: RTM_NEWLINK,
RTM_DELLINK, RTM_GETLINK
3.3.3.2. IP Address Service module
This service provides the ability to add, remove or receive information
about an IP address associated with an interface. The Address provi-
sioning service message template is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Family | Length | Flags | Scope |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Family: AF_INET for IPV4 or AF_INET6 for IPV6. Length: the
length of the address mask Flags: IFA_F_SECONDARY for secondary
address (old alias interface),
IFA_F_PERMANENT for a permanent address set by the user as
opposed to dynamic addresses.
other flags include:
IFA_F_DEPRECATED which defines deprecated (IPV6) address
IFA_F_TENTATIVE which defines tentative (IPV6) address
Scope: the address scope
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Applicable attributes:
attribute description
.......................................................
IFA_UNSPEC - unspecified.
IFA_ADDRESS raw protocol address of interface
IFA_LOCAL raw protocol local address
IFA_LABEL ascii string name of the interface
reffered to.
IFA_BROADCAST raw protocol broadcast address.
IFA_ANYCAST raw protocol anycast address
IFA_CACHEINFO cacheinfo address information.
Define cacheinfo here -- JHS
netlink messages specific to this service: RTM_NEWADDR,
RTM_DELADDR, RTM_GETADDR
4. Sample Protocol for The foo IP service
Our proverbial IP service "foo" is used again to demonstrate how
one can deploy a simple IP service control using netlink.
These steps are continued from the "Sample Service Hierachy" sec-
tion.
4) query for current config of FE component
5) receive response to 4) via channel on 3)
6) query for current state of IP service foo
7) receive response to 6) via channel on 2)
9) register the protocol specific packets you would like the FE to
forward to you
10) send specific service foo commands and receive responses for them
if needed
4.1. Interacting with other IP services
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The last diagram shows another control component configuring the
same service. In this case, it is a proprietary Command Line Inter-
face. The CLI (may or ) may not be using the netlink protocol to
communicate to the foo component. If the CLI should issue commands
that will affect the policy of the FEC for service "foo" then, then
the "foo" CPC is notified. It could then make algorithmic decisions
based on this input (example if a policy that foo installed was
deleted, there might be need to propagate this to all the peers of
service "foo").
5. Currently Defined netlink IP services
Although there are many other IP services defined which are using
netlink, we will only mention those integrated into the kernel
today (kernel version 2.4.6). These are:
NETLINK_ROUTE,NETLINK_FIREWALL,NETLINK_ARPD,NETLINK_ROUTE6,NETLINK_IP6_FW
NETLINK_TAPBASE,NETLINK_SKIP,NETLINK_USERSOCK.
5.1. IP Service NETLINK_ROUTE
This service allows CPCs to modify the IPv4 routing table in the
Forwarding Engine. It can also be used by CPCs to receive routing
updates.
5.1.1. Network Route Service Module
This service provides the ability to create, remove or receive informa-
tion about a network route. The service message template is shown
below.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Family | Src length | Dest length | TOS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Table ID | Protocol | Scope | Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Family: Address family of route. AF_INET for IPV4 and AF_INET6 for
IPV6.
Src length: prefix length of source
Dest length: Prefix length of destination IP address
TOS: the 8 bit tos (should be deprecated to make room for DSCP)
Table ID: Table identifier. Upto 255 route tables are supported.
RT_TABLE_UNSPEC an unspecified routing 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.
Protocol: identifies what/who added the route. Described further
below.
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protocol Route origin.
..............................................
RTPROT_UNSPEC unknown
RTPROT_REDIRECT by an ICMP redirect
(currently unused)
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 infor-
mation. They may be used to tag the source of a
routing information or to distingush between multi-
ple routing daemons. See <linux/rtnetlink.h> for
the routing daemon identifiers which are already
assigned.
Scope: Route scope (distance to destination).
RT_SCOPE_UNIVERSE global route
RT_SCOPE_SITE interior route in the
local autonomous system
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.
Type: The type of route.
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Route type description
-------------------------------------------------
RTN_UNSPEC unknown route
RTN_UNICAST a gateway or direct route
RTN_LOCAL a local interface route
RTN_BROADCAST a local broadcast route
(sent as a broadcast)
RTN_ANYCAST a local broadcast route
(sent as a unicast)
RTN_MULTICAST a multicast route
RTN_BLACKHOLE a packet dropping route
RTN_UNREACHABLE an unreachable destination
RTN_PROHIBIT a packet rejection route
RTN_THROW continue routing lookup in another
table
RTN_NAT a network address translation rule
RTN_XRESOLVE refer to an external resolver (not
implemented)
Flags: further qualify the route.
RTM_F_NOTIFY if the route changes, notify the
user via rtnetlink
RTM_F_CLONED route is cloned from another route
RTM_F_EQUALIZE a multicast equalizer (not yet
implemented)
Attributes applicable to this service:
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Attribute description
-----------------------------------------------
RTA_UNSPEC ignored.
RTA_DST protocol address for route
destination address.
RTA_SRC protocol address for route source
address.
RTA_IIF Input interface index.
RTA_OIF Output interface index.
RTA_GATEWAY protocol address for the gateway of
the route
RTA_PRIORITY Priority of route.
RTA_PREFSRC
RTA_METRICS Route metric
RTA_MULTIPATH
RTA_PROTOINFO
RTA_FLOW
RTA_CACHEINFO
additional netlink message types applicable to this service:
RTM_NEWROUTE, RTM_DELROUTE, RTM_GETROUTE
5.1.2. Neighbour Setup Service Module
This service provides the ability to add, remove or receive infor-
mation about a neighbour table entry (e.g. an ARP entry). The ser-
vice message template is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Family | Padding | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| State | Flags | Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Family: Address Family Interface Index: The unique interface index
State: is a bitmask of the following states:
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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
Flags: one of:
NTF_PROXY a proxy arp entry
NTF_ROUTER an IPv6 router
Attributes applicable to this service:
Attribute$ description
------------------------------------
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.
Describe the NDA_CACHEINFO nda_cacheinfo header later --JHS
additional netlink message types applicable to this service:
RTM_NEWNEIGH, RTM_DELNEIGH, RTM_GETNEIGH
5.1.3. Traffic Control Service
This service provides the ability to add, remove or get a queueing dis-
cipline. The service message template is shown below.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Family | Padding | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Qdisc handle |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parent Qdisc |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TCM Info |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.2. IP Service NETLINK_FIREWALL
This service allows CPCs to receive packets sent by the IPv4 fire-
wall service in the FE.
Two types of messages exist that can be sent from CPC to FEC. These
are: Mode messages and Verdict messages. The formats are described
below.
The Verdict message format is as follows
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A ipq_packet_msg packet type is sent from the FEC to the CPC. The
format is described below ==> We need to complete this later
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5.3. IP Service NETLINK_ARPD
This service is used by CPCs for managing the ARP table in FE.
5.4. IP Service NETLINK_ROUTE6
This service allows CPCs to modify the IPv6 routing table in the
FE. It can also be used by CPCs to receive routing updates.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 dst addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 dst addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 dst addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 dst addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 src addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 src addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 src addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 src addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 gw addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 gw addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 gw addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 gw addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| dst length | src length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Info |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.5. IP Service NETLINK_IP6_FW
This service allows CPCs to receive packets that failed the IPv6
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firewall checks by that module in the FE.
5.6. IP Service NETLINK_TAPBASE
This service allows CPCs to simulate an ethernet driver belonging
to the FE.
//are the instances of the ethertap device. Ethertap //is a
pseudo network tunnel device that allows an //ethernet driver to
be simulated from user space.
5.7. IP Service NETLINK_SKIP
This service is reserved for ENskip (?).
5.8. IP Service NETLINK_USERSOCK
This service is reserved for future Control Plane to FE protocols.
6. Security Considerations
Netlink lives in a trusted environment of a single host separated
by kernel and user space. Linux capabilities ensures that only
someone with CAP_NET_ADMIN capability (typically root user) is
allowed to open sockets.
7. References
[RFC1633] R. Braden, D. Clark, and S. Shenker, "Integrated
Services in the Internet Architecture: an Overview", RFC 1633,
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ISI, MIT, and PARC, June 1994.
[RFC1812] F. Baker, "Requirements for IP Version 4
Routers", RFC 1812, June 1995.
[RFC2475] M. Carlson, W. Weiss, S. Blake, Z. Wang, D.
Black, and E. Davies, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[RFC2748] J. Boyle, R. Cohen, D. Durham, S. Herzog, R.
Rajan, A. Sastry, "The COPS (Common Open Policy Service) Pro-
tocol", RFC 2748, January 2000.
[RFC2328] J. Moy, "OSPF Version 2", RFC 2328, April 1998.
[RFC1157] J.D. Case, M. Fedor, M.L. Schoffstall, C. Davin,
"Simple Network Management Protocol (SNMP)", RFC 1157, May
1990.
[RFC3036] L. Andersson, P. Doolan, N. Feldman, A. Fredette,
B. Thomas "LDP Specification", RFC 3036, January 2001.
[stevens] G.R Wright, W. Richard Stevens. "TCP/IP Illus-
trated Volume 2, Chapter 20", June 1995
8. Acknowledgements
1) Andi Kleen for man pages on netlink and rtnetlink.
2) Alexey Kuznetsov is credited for extending netlink to the IP ser-
vice delivery model. The original netlink character device was
written by Alan Cox.
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9. Author's Address:
Jamal Hadi Salim
Znyx Networks
Ottawa, Ontario
Canada
hadi@znyx.com
Hormuzd M Khosravi
Intel
2111 N.E. 25th Avenue JF3-206
Hillsboro OR 97124-5961
USA
1 503 264 0334
hormuzd.m.khosravi@intel.com
Andi Kleen
SuSE
Stahlgruberring 28
81829 Muenchen
Germany
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