Network Working Group S. Shah
Internet-Draft K. Patel
Intended status: Standards Track Cisco Systems
Expires: October 28, 2015 S. Bajaj
Juniper Networks
L. Tomotaki
Verizon
M. Boucadair
France Telecom
Apr 26, 2015
Inter-domain SLA Exchange
draft-ietf-idr-sla-exchange-05
Abstract
Network administrators typically enforce Quality of Service (QoS)
policies according to Service Level Agreement (SLA) with their
providers. The enforcement of such policies often relies upon
vendor-specific configuration language. Both learning of SLA, either
thru SLA documents or via some other out-of-band method, and
translating them to vendor specific configuration language is a
complex, many times manual, process and prone to errors. This
document proposes an in-band method of SLA signaling which can help
to simplify some of the complexities.
This document defines an optional transitive attribute to signal SLA
details in-band, across administrative boundaries (considered as
Autonomous Systems (AS)), thus simplifying and facilitating some of
the complex provisioning tasks.
Though the use case with the proposed BGP attribute is explicitly
defined in this document, purpose of this attribute is not limited to
this use case only.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 28, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. QoS Attribute Definition . . . . . . . . . . . . . . . . . . . 5
3.1. SLA, QoS attribute sub-type, Definition . . . . . . . . . 6
4. Originating SLA Notification . . . . . . . . . . . . . . . . . 16
4.1. SLA Contexts . . . . . . . . . . . . . . . . . . . . . . . 16
4.1.1. SLA Advertisement for Point-to-Point Connection . . . 16
4.1.2. SLA Advertisement for Destination AS Multiple Hops
Away . . . . . . . . . . . . . . . . . . . . . . . . . 17
5. SLA Attribute Handling at Forwarding Nodes . . . . . . . . . . 17
5.1. BGP Node Capable of Processing QoS Attribute . . . . . . . 17
5.2. BGP Node not Capable of Processing QoS Attribute . . . . . 18
5.3. Aggregator . . . . . . . . . . . . . . . . . . . . . . . . 18
6. SLA Attribute Handling at Receiver . . . . . . . . . . . . . . 18
6.1. Traffic Class Mapping . . . . . . . . . . . . . . . . . . 19
7. Deployment Considerations . . . . . . . . . . . . . . . . . . 20
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
10. Security Considerations . . . . . . . . . . . . . . . . . . . 22
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
11.1. Normative References . . . . . . . . . . . . . . . . . . . 22
11.2. Informative References . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
Typically there is a contractual Service Level Agreement (SLA)
established between Customer and Provider or between providers,
possibly using one or the other form of the template [CPP]. This
contractual agreement usually defines the nature of the various
traffic classes (i.e., traffic match conditions) and services needed
for each traffic class. The contract may exist at different levels
of traffic granularity. The contract could be for the full line-rate
or sub line-rate without granular traffic distinction or it could be
for finer granular traffic classes, with services defined. Finer
granular classes can be based on some standard code-points (like
DSCP) or for a specific set of prefixes or for a set of well-known
application types.
Once the SLA is established, SLA parameters are enforced in some or
all participating devices by deriving SLA parameters into
configuration information on respective devices. SLA parameters may
have to be exchanged through organizational boundaries, thru SLA
documents or via some other off-band method to an administrator
provisioning actual devices. In a subsequent step, administrator
requires to translate SLA to QoS policies using router (vendor)
specific provisioning language. In a multi-vendor network,
translating SLAs into technology-specific and vendor-specific
configuration requires to consider specificities of each vendor.
There does not exist any standard protocol to translate SLA
agreements into technical clauses and configurations and thus both
the steps of out of band learning of negotiated SLA and provisioning
them in a vendor specific language can be complex and error-prone.
As an example for voice service, the Provider may negotiate QoS
parameters (like min/max rates) for such traffic based upon the EF
code-point in Diffserv-enabled [RFC2475] networks. Administrator at
the CE side not only will have to know that Provider's service for
voice traffic is EF-based, so that traffic exiting CE is marked
properly, but will also have to know how to implement DSCP EF
classification rule along with Low Latency Service, and possibly min/
max rate enforcement for the optimal use of bandwidth, as per vendor
specific provisioning language.
An in-band signaling method of propagating SLA parameters from
provider, PE in an example above, to contractual devices, CE in an
example above, can help eliminate manual administrative process
described above. Provider may have SLA negotiated with the Customer
via some defined off-band method (based on the specifics defined by
the Provider or using protocols like [CPNP]. The Inter-domain SLA
exchange proposal described in this document does not pre-requisite
any specific method of establishing SLAs). The Provider provisions
established SLA on the Provider device. This SLA instance then can
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be signaled to the Customer via in-band signaling protocol. In
reaction to this signal, receiver router may translate that to
relevant QoS policy definition on the device.
For an in-band signaling, we propose to use BGP as a transport. The
details of SLA parameters are specific to the granularity of traffic
classes and their respective treatment, which is independent of the
BGP protocol itself. Though we find BGP as a suitable transport for
inter-domain SLA exchange for the following reasons:
- The need to exchange SLA parameters between domains (Automated
Systems (AS)), where in use-cases described in this document,
BGP is a suitable protocol for inter-domain exchange [RFC4271]
[RFC4364]
- There is no specifically defined protocol available today for
SLA exchange
- BGP updates already advertise specific set of prefixes (flow
or flow-group). Other QoS-related attributes, apart from the
the use of SLA advertisement, can be added to these updates
in the future
The proposal is to define a new BGP attribute to advertise/learn SLA
details in-band. The proposed attribute is intended to advertise SLA
from one AS to a list of destined ASes. The advertised QoS
information could be for the incoming traffic to the advertiser, that
is advertising SLA or could be for the outgoing traffic from the
advertiser or could be for both directions. Reception of and
reaction to advertised SLAs are optional for the receiver.
We propose QoS as an optional transitive attribute, keeping SLA
advertisement and discovery (request) as one of the sub-types of QoS
attribute. This is to keep the QoS attribute open for extensions.
For example, SLA Negotiation and Assurance is out of scope of this
document but can be envisioned as another sub-type.
2. Terminology
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 [RFC2119].
3. QoS Attribute Definition
The QoS Attribute proposed here is an optional transitive attribute
(attribute type code to be assigned by IANA). SLA is defined as one
of the sub-types in the QoS attribute.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attr flag | Attr type QoS | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ ~
| QoS Attr length/Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+..........................
Attribute flags
highest order bit (bit 0) -
MUST be set to 1, since this is an optional attribute
2nd higher order bit (bit 1) -
MUST be set to 1, since this is a transitive attribute
3.1. SLA, QoS attribute sub-type, Definition
The value field of the QoS Attribute contains TLVs, followed to QoS
Attribute flags described in the previous section. One of the TLVs
that we define is a tuple of (SLA sub-type, Length, Value)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| QoS Attr flags| subType | sub type Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+..........................
The first octet in the Value field of the QoS attribute is QoS
attribute specific flags
highest order bit (bit 0) -
It defines if update message MUST be dropped (if set to 1)
without updating routing information base, when this is the
last BGP receiver from the list of destination ASes this
attribute is announced to, or MUST announce (if set to 0)
further to BGP peers
The purpose of this bit is discussed further in subsequent
sections.
Remaining bits are currently unused and MUST be set to 0
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subType - 8 bits
0x00 = reserved
0x01 = SLA
0x02 - 0x0f = for future use
SLA sub-type specific value field details. These details contain
information about 1) sender and receiver(s) and 2) SLA parameters.
SLA Parameters include SLA event type (such as Advertise, Request)
and contents associated to that event type.
The format of SLA message is,
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32-bit source AS (Advertiser) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Optional advertiserid total len| Advertiser id TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
| |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32-bit destination AS count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| variable list of destination AS |
~ .... ~
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Event | SLA id | SLA length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Content as per SLA Event |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Source AS
32-bit source AS number. This is the AS that is advertising SLA
0 = ignore Source and Destination AS list from this Value field.
Instead refer to Source and Destination AS as defined by BGP
message.
Optional advertiser id total len
16-bit Source address identifier (optional).
0 = No optional identifier
In general any additional qualifier for an advertiser is not
required. The SLA definition is in the context of prefix
advertised in the NLRI definition. The exception is where a BGP
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speaker, in the middle of an update path to the destination AS,
aggregates prefixes. We will refer this middle BGP speaker, that
aggregates routes, as an Aggregator. Aggregator is then required
to insert original NLRI details in the optional advertiser field
Optional Advertiser id TLV
4-bit type
0x0 = reserved
0x1 = ORIGIN_NLRI, variable length
0x2 to 0xf = for future use,
Destination AS count
32-bit destination AS count to take variable length AS list.
This count has no functional value when Source AS is 0
0 = QoS attribute is relevant to every receiver of the message
Destination AS list
32-bit destination AS number
....
.... [as many as AS count]
SLA Event Type
4-bits
0x0 = reserved
0x1 = ADVERTISE
0x2 = REQUEST
0x3 to 0xf, for future use
SLA Id
16-bit identifier unique within the scope of source AS
The significance of an SLA identifier is in the context of the
source that is advertising SLA parameters. The SLA identifier
is not globally unique but it MUST be unique within the source
AS (advertiser).
The SLA content is optional for an advertised SLA id. If SLA
content does not exist in BGP update messages with advertised
QoS attribute, that contains the SLA sub-type, then receiver
MUST inherit prior advertised SLA content for the same SLA id
from the same Source AS.
If advertised SLA id is different from earlier advertised one,
for the same prefix, previous SLA content MUST be replaced
with the new advertised one.
SLA is aggregate for all the traffic to prefixes that share
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same source AS and SLA id.
SLA Length
12-bits
The format of SLA ADVERTISE event message is,
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|dir| Traffic Class count | Class Desc Len| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~
| |
~ Traffic Class Description ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Traffic Class Elements count/values ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Count| service type/value pair |
+-+-+-+-+-+-+-+-+ ~
| |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Repeat from Traffic Class Description for next Traffic Class ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Repeat from direction for SLA in the other direction ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Direction
02-bit for incoming or outgoing traffic,
0x0 = reserved
0x1 = incoming, from destination AS towards source AS
0x2 = outgoing, from source AS towards destination AS
0x3 = for future use
Traffic Class count (Classifier Groups count)
16-bit, count of number of classifier groups
00 = Advertisement to invalidate previous advertised SLA if any
Traffic Class Descr Length
08-bit, size of the length
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0 = No description
Traffic Class Description
Ascii Description of the Traffic Class
Traffic Class Elements Count in a Traffic Class,
08-bit count of classifier elements in a specific Traffic Class
00 = this has relative definition. It means classify rest all
traffic that is not classified via earlier described
Traffic Classes.
It is RECOMMENDED that Traffic Class, that has 0 elements,
is present last in the advertised list of Traffic Classes.
If Advertised message has it positioned some-where else,
then receiver MUST re-order it, for the forwarding purpose,
to the last position in the advertised list of Traffic
Classes from a given source AS. QoS attribute advertised
from a specific source MUST NOT have more than one such
Traffic Classes (Traffic Class with 0 element count). If
there are more than one such Traffic Classes present then
advertised SLA parameters MUST be ignored. It is okay
though to have none Traffic Class with element count 0.
Classifier Element values in a Traffic Class (optional),
08-bit = IPFIX Element Identifier
variable-length = based on type of the Element
Given IPFIX [RFC5102] has well defined identifier set for a
large number of packet attributes, IPFIX IANA registry is
"https://www.ietf.org/assignments/ipfix" chosen to specify
packet classification attributes. However, since not all
identifiers from IPFIX would be applicable to this proposal,
only a limited set identified here can be supported by BGP
SLA exchange. Any new element identifier, in future, added
to the IPFIX IANA registry does not automatically mean
supported for this proposal.
+----+----------------------------+
| ID | Name |
+----+----------------------------+
|195 | ipDiffServCodePoint |
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|203 | mplsTopLabelExp |
|244 | dot1qPriority |
| 8 | sourceIPv4Address |
| 27 | sourceIPv6Address |
| 9 | sourceIPv4PrefixLength |
| 29 | sourceIPv6PrefixLength |
| 44 | sourceIPv4Prefix |
|170 | sourceIPv6Prefix |
| 12 | destinationIPv4Address |
| 28 | destinationIPv6Address |
| 13 | destinationIPv4PrefixLength|
| 30 | destinationIPv6PrefixLength|
| 45 | destinationIPv4Prefix |
|169 | destinationIPv6Prefix |
| 4 | protocolIdentifier |
| 7 | sourceTransportPort |
| 11 | destinationTransportPort |
+----+----------------------------+
Traffic Class Service count (for a Traffic Class under definition)
08-bit count of service attributes fields to follow with
type/value pair
List of service types and relevant values are discussed below
00 = no bounded service (also means Best Effort)
Traffic Class Service (optional),
16-bit = type of the field
variable-length = based on type of the service
- 0x00 = reserved
- 0x01 = TRAFFIC_CLASS_TSPEC
160-bits TSpec Parameter
The TRAFFIC_CLASS_TSPEC parameter consists of the (r), (b), (p),
(m) and (M) parameters as described in Invocation Information
section of [RFC2212]. Note that inheriting definition of TSpec
here does not enable RFC2212 functionality. It purely is the
Traffic Specification that is inherited here for the purpose of
SLA exchange.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Minimum Rate (r) (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Burst Size (b) (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Rate (p) (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Minimum Policed Unit (m) (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Packet Size (M) (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Parameter (r) indicates min-rate of the traffic class. This rate
indicates the minimum rate, measured in bytes of Layer 2 (L2)
datagrams per second, service advertiser is providing for a given
class of traffic on advertiser's hop. Note that it does not
necessarily translate to a minimum rate service to receiver of an
SLA unless the traffic class definition clearly represents a sole
receiver of an SLA. If there is no SLA for min-rate, the value of
(r) MUST be set to 0.
Parameter (b) indicates maximum burst size, measured in bytes of
L2 datagram size. Since queuing delay can be considered a
function of burst size (b) and min-rate (r), in presence of non-
zero parameter (r), parameter (b) represents bounded delay for
the Traffic Class. This delay is a single hop queuing delay when
SLA is to be implemented at the resource constrained bottleneck.
In other words this burst size can be considered as a buffer
size. Value of 0 for parameter (b) means the advertiser does not
mandate specific bounded delay.
Parameter (p) indicates max-rate of the traffic class. Just like
min-rate, max-rate, measured in bytes of L2 packets per second,
field here also indicates service provided by advertiser. If
advertiser does not have any specific value to set for a given
class of traffic, it MAY be set to physical interface line rate
or any other indirect limit that may affect this class' maximum
rate. In absence of any such known value, it MUST be set to
positive infinity. Value 0 is considered an error.
Parameters (r), (b) and (p) are each set as 32-bit IEEE floating
point numbers. Positive infinity is represented as an IEEE single
precision floating-point number with an exponent of all ones and
a sign mantissa of all zeros. The format of IEEE floating-point
numbers is further summarized in [RFC4506].
The minimum policed unit (m) and maximum packet size (M)
parameters have no relevance for the purpose of SLA exchange.
Thus they MUST be ignored.
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- 0x02, L2_OVERHEAD
08-bit, value
By default specification of rate and other packet size related
parameters, advertised in an SLA, includes L2 overhead. For the
receiver next hop, this overhead is the L2 overhead of the local
link where advertised SLA is received. However, in cases where
advertised SLA is for a receiver multiple hops away, L2 overhead
consideration from the source perspective may be different from
the local L2 overhead at the receiver. Explicit notification of
size of L2 overhead from a sender, in such cases, is useful for
a receiver to distinguish local L2 overhead from the sender
advertised one. When receiver choose to react to an advertised
SLA and if this service type is present in advertised SLA,
receiver MUST use advertised L2 overhead over local L2 overhead.
If SLA is required to consider only IP packet size, sender may
advertise this service with a value of 0.
- 0x03 = MINRATE_IN_PROFILE_MARKING
08-bit = IPFIX Element Identifier
variable-length = based on type of the Element
00 Identifier = drop, variable-length for this id is 0.
+----+----------------------------+
| ID | Name |
+----+----------------------------+
|195 | ipDiffServCodePoint |
|203 | mplsTopLabelExp |
|244 | dot1qPriority |
+----+----------------------------+
- 0x04 = MINRATE_OUT_PROFILE_MARKING
08-bit = IPFIX Element Identifier
variable-length = based on type of the Element
00 Identifier = drop, variable-length for this id is 0.
+----+----------------------------+
| ID | Name |
+----+----------------------------+
|195 | ipDiffServCodePoint |
|203 | mplsTopLabelExp |
|244 | dot1qPriority |
+----+----------------------------+
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- 0x05 = MAXRATE_IN_PROFILE_MARKING
08-bit = IPFIX Element Identifier
variable-length = based on type of the Element
00 Identifier = drop, variable-length for this id is 0.
+----+----------------------------+
| ID | Name |
+----+----------------------------+
|195 | ipDiffServCodePoint |
|203 | mplsTopLabelExp |
|244 | dot1qPriority |
+----+----------------------------+
- 0x06 = MAXRATE_OUT_PROFILE_MARKING
08-bit = IPFIX Element Identifier
variable-length = based on type of the Element
00 Identifier = drop, variable-length for this id is 0.
+----+----------------------------+
| ID | Name |
+----+----------------------------+
|195 | ipDiffServCodePoint |
|203 | mplsTopLabelExp |
|244 | dot1qPriority |
+----+----------------------------+
In the case when MINRATE_IN_PROFILE_MARKING,
MINRATE_OUT_PROFILE_MARKING, MAXRATE_IN_PROFILE_MARKING and
MAXRATE_OUT_PROFILE_MARKING all of them are advertised,
- MINRATE_IN_PROFILE_MARKING takes highest precedence
(that is over MAXRATE_IN_PROFILE_MARKING)
- MAXRATE_IN_PROFILE_MARKING takes precedence over
MINRATE_OUT_PROFILE_MARKING
- and MAXRATE_OUT_PROFILE_MARKING takes precedence over
MINRATE_OUT_PROFILE_MARKING
- 0x07 = DROP_THRESHOLD
03-bit count of drop-priority fields to follow with
(type, type-value, burst size) tuple
04-bit, drop priority type
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08-bit = IPFIX Element Identifier
variable-length = based on type of the Element
32-bit, Burst Size (32-bit IEEE floating point number)
+----+----------------------------+
| ID | Name |
+----+----------------------------+
|195 | ipDiffServCodePoint |
|203 | mplsTopLabelExp |
|244 | dot1qPriority |
+----+----------------------------+
This finer granular drop threshold does not require separate
buffer space from the aggregate buffer space. It is just an
indicator beyond which code-point specific traffic to be
discarded when occupancy of aggregate buffers reached to that
threshold.
- 0x08 = RELATIVE_PRIORITY
04-bit, priority value
lower the value, higher the priority
Relative priority indicates scheduling priority. For example
voice traffic, which requires lowest latency compare to any
other traffic, may have lowest value advertised in relative
priority. For two different traffic classification groups
where one application group may be considered more important
than the other but from a scheduling perspective does not
require to be distinguished with a different priority, relative
priority for those classification groups may be advertised with
the same value.
- 0x09 = SUB_TRAFFIC_CLASSES
variable-length, repeats all content described above from Traffic
Class count onwards.
For SLAs where a specific Traffic Class may further have
different sub-services for sub-group of Classifier Elements,
this service type SHOULD be used to further divide Traffic Class
in multiple sub-classes. Each sub-class then defined with their
own classifier elements and service types.
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4. Originating SLA Notification
The QoS attribute to advertise SLA sub-type MUST be added by the
originator of a BGP UPDATE message.
SLA messages SHOULD NOT be sent periodically just for the purpose of
keep alive. Some sort of SLA policy change may be considered as a
trigger for the advertisement.
For any modified SLA parameters, the originator MUST re-advertise the
entire set of SLA parameters. There is no provision to advertise
partial set of parameters. To invalidate previously advertised SLA
parameters, a message MUST be sent with the same SLA id for the same
source with the Traffic Class count set to 0.
4.1. SLA Contexts
In certain cases, the advertisement may relate to an SLA for
aggregate traffic over a point-to-point connection between a specific
destination and a specific source. A point-to-point connection may
be the physical link, that connects two BGP peers, or may be a
virtual link (e.g. a tunnel). A BGP update message, in such cases,
with source AS number and NLRI prefix of source end-point can
uniquely identify physical/virtual link and so establishes advertised
SLA's context for that point to point link.
In the simplest case where Provider (e.g. PE) and Customer (e.g.
CE) devices are directly connected via a physical link and have only
single link between them, CE can uniquely identify the forwarding
link to PE with AS number of the PE and NLRI prefix being an IP
address of PE, to CE (that is the next hop address from CE to PE).
SLA advertised thru BGP update message from PE to CE, with PE's AS
number and IP address, establishes SLA context for the aggregate
traffic through link CE to PE. SLA advertised thru BGP update
message from PE to CE, with PE's AS number and any other prefix
establishes SLA for that specific prefix, subset of traffic under CE
to PE link.
Even though this example is in the context of IP prefixes, SLA
exchange does not have to be limited to the IP address family only.
SLA advertisement is generic to all forms of NLRI types that are
supported by the BGP protocol specification (like IPv4, IPv6, VPN-
IPv4, VPN-IPv6).
4.1.1. SLA Advertisement for Point-to-Point Connection
When SLA messages are intended to be advertised for the point-to-
point connection (physical or logical), the message is destined for
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the next hop and advertised message is in the context of the prefix
of the source end-point of the point to point connection.
The destination AS number set to, within QoS SLA attribute, typically
is of the neighbor BGP speaker's. Alternatively, the originator MAY
not encode source/destination AS numbers (that is the source AS is
set to 0 and destination AS count is set to 0), in the QoS attribute.
The most significant bit of the QoS attribute flag MAY be set to 1,
specifically it MUST be set to 1 when intention is to not install
route update, at the receiver, for the advertised message.
4.1.2. SLA Advertisement for Destination AS Multiple Hops Away
When SLA messages are to be advertised beyond next hop, value of
source AS, in the QoS attribute, MUST be set by the originator of the
update message. If such update is meant to be for a specific list of
AS(es) as receivers, then the list of destination AS MUST be
explicitly described in the QoS attribute message to avoid flooding
of the QoS attribute data in the network beyond those destinations.
When a new prefix is added in the AS, AS for which SLA parameters
have already been advertised before for other existing prefixes, and
if traffic to this new prefix is subject to the same SLA advertised
earlier then BGP update for this new prefix may include QoS attribute
containing just an SLA id, an id that was advertised earlier. The
corresponding Update message does not require to have the whole SLA
content. SLA id is sufficient to relate SLA parameters to new
advertised prefix.
When BGP update messages are triggered as a result of SLA policy
change and thus only for the purpose of SLA exchange, forwarding BGP
update messages beyond intended receivers are not necessary. Highest
order bit in the QoS Attribute flag MUST be set to suggest receiver
to drop entire BGP update message [Note that it is an indication to
drop entire update message, not only QoS attribute], after all
intended receivers have processed it. If update message contains a
list of destination ASes, then the message MUST be dropped only after
all intended receivers (destinations) have received it.
5. SLA Attribute Handling at Forwarding Nodes
5.1. BGP Node Capable of Processing QoS Attribute
If a BGP node is capable of processing QoS attribute, it optionally
MAY process the message. If advertised SLA has a list of destination
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ASes, it MAY trim list and so count of destination AS to exclude ones
that are not required in further announcement of BGP updates.
BGP node MUST drop SLA related sub-type from the QoS attribute, if
none of the AS from the destination list is in the forwarding path.
The rest of the QoS attribute contents MAY be forwarded if there
exist other sub-types of QoS attribute and forwarding rules meets
other sub-types requirements. If there is no other sub-types in the
QoS attribute content then the node MUST drop the QoS attribute all
together. The other attributes and NLRI information may be announced
further if they meet rules defined by other attributes and BGP
protocol.
If the most significant bit in the QoS attribute flag is set to 1
then the entire BGP update message MUST be dropped if there are no
destinations left in the list to advertise to.
Except extracting the entire SLA sub-type of the QoS attribute and
trimming the list of destination AS list and inserting NLRI at the
Aggregator node, all other content MUST NOT be modified by any
intermediate receivers of the message.
5.2. BGP Node not Capable of Processing QoS Attribute
If the BGP node is not capable of processing QoS attribute, it MUST
forward the QoS attribute message unaltered.
5.3. Aggregator
It is RECOMMENDED to not aggregate prefixes from 2 or more BGP update
messages into one BGP update, when original messages contain the QoS
attribute with SLA sub-type contents. If Aggregator MUST aggregate
them then it MUST copy entire parameter set of an SLA sub-type from
the QoS attribute in the new aggregated BGP update message. At the
same time, it MUST also insert NLRI information, from the original
update message, as an optional advertiser id to go along with source
AS inside the QoS attribute.
To support SLA exchange multiple hops away in the path that has one
of the forwarding node acting as an Aggregator, it is required that
the Aggregator node is capable of processing the QoS attribute.
6. SLA Attribute Handling at Receiver
Reception of and processing of advertised QoS SLA content are
optional for the receiver.
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While reacting to SLA advertisement
- receiver SHOULD invalidate previous advertised SLA parameters if
one exists for the same SLA id and source AS. If new advertised
SLA update is with non-zero Traffic Class count, new advertised
SLA SHOULD be installed. If new advertised SLA update is with
Traffic Class count 0, no action is required.
- If advertised QoS Attribute, inside an update message, is with a
flag set indicating to drop that message, a receiver MUST drop
message if it is the last receiver, in update path, that message
is advertised to.
If the advertised SLA is from the next hop, in the reverse path, the
receiver may implement advertised SLA for the whole link, the link
could be physical or virtual link, associated with the next hop. If
NLRI advertised in update message is not of the next hop, receiver
may establish advertised SLA for that specific prefix list under the
relevant link. It is completely up to the receiver to decide for
which prefixes it should accept advertised SLA and for which ones it
won't.
For cases where if earlier messages have not reached the intended
receiver yet, a re-signaling is required. A receiver may intend to
request an SLA message from the originator in such case. Since BGP
messages are considered reliable, it is assumed that advertised
messages always reach intended receivers. Thus discussion of REQUEST
message, for this purpose or any other purpose, is considered out of
the scope of this document.
To handle error conditions, the approach of "attribute-discard" as
mentioned in [IDR-ERR] MAY be used in the event QOS attribute parsing
results in any attribute errors. Alternatively, an approach of
"treat-as-withdraw" MAY be used as mentioned in [IDR-ERR] if an
implementation also wishes to withdraw the associated prefix.
6.1. Traffic Class Mapping
It is possible that switching/routing methods used in 2 different
ASes could be different. For example, Provider may tunnel Customer's
IP traffic thru MPLS cloud. In such cases traffic class definition
for QoS services may differ in both ASes. For the meaningful use of
advertised SLA in such cases, receiver is required to map traffic
class from one type to the other.
In the example given, traffic classification in Customer AS could be
IP Diffserv-based whereas traffic classification in Provider AS could
be MPLS TC-based. Thus for advertised MPLS TC-based SLA would
require to map traffic class from IP Diffserv-based to MPLS TC type.
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There are well-defined recommendations that exist for traffic class
mapping between two technologies. Receiver MAY use those defined
recommendations for traffic class mapping or MAY define its own as
per its network Traffic Class service definition to map to advertised
Traffic Classes. It is completely up to the receiver how to define
such traffic class mapping.
7. Deployment Considerations
One of the use cases is for a Provider to advertise contracted SLA
parameters to Customer Edge (CE). The SLA parameters are provisioned
by the provider on the PE device (facing CE). This provisioned SLA
parameters are then advertised thru proposed BGP QoS attribute to the
CE device. CE device may read the attribute and SLA sub-type content
to implement the QoS policy on the device.
Contracted SLA from PE to CE may be full line-rate or sub line-rate
or finer granular controlled services. SLA advertise can be useful
when contracted service is sub-rate of a link and/or when for finer
granular traffic classes that are controlled (e.g. voice, video
services may be capped to certain rate)
_______________
__________ / \
/ \ / \
/ \ / \
|CustomerSite|-----| Provider |
\ C/E P\E /
\__________/ \ /
\_______________/
AS 3 AS 2
SLA_ADVERTISE: AS2 to AS3
NLRI = PE ip address
Another use case can be to advertise SLAs among different network
sites within one Enterprise network. In Hub and Spoke deployments,
Administrator, being aware of each Spoke's SLA, may define SLAs for
each of them at the Hub and advertise them thru BGP updates, where at
each Spoke, advertised SLA may translate to a forwarding policy. In
a scale network, managing a large number of Spokes can be complex.
The proposal in such cases would be to provision SLA parameters at
the Hub only and distribute them to each Spoke with SLA exchange
protocol described here.
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Alternatively, in a network that supports SLA parameters signaling
capabilities with the Provider, manual administration can be avoided
or minimized even at the Hub. As shown in the figure below, AS2 may
first learn its SLA with the Provider from the Provider Edge it is
connected to. AS2 can advertise the same or a subset of that SLA to
AS3 in the context of tunnel's ip address.
AS 2
_______________ ________
/ \ / \
__________ / \-----| Spoke2 |
/ \ / \ \________/
| Hub |-----| Provider | ________
\__________/ \ / / \
\ /-----| Spoke1 |
AS 3 \_______________/ \________/
AS 1
SLA_ADVERTISE: AS2 to AS3
NLRI = AS2 tunnel address
SLA_ADVERTISE: AS1 to AS3
NLRI = AS1 tunnel address
Deployment options are not limited to involving CEs, PE-to-CE or CE-
to-CE, only. For any contract between two providers, SLA parameters
may be advertised from one to the other.
8. Acknowledgements
Thanks to Fred Baker, David Black, Sue Hares and Benoit Claise for
their suggestions and to Christian Jacquenet, Ken Briley, Rahul
Patel, Fred Yip, Lou Berger, Brian Carpenter, Bertrand Duvivier for
the review.
9. IANA Considerations
The proposal in this document defines a new BGP attribute. IANA
maintains the list of existing BGP attribute types. A new type to be
added in the list for the QoS attribute.
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The proposal also defines a list for Service types associated to
Traffic Class. IANA will be required to maintain this list for
Traffic Class Service type as a new registry. Where-as Traffic Class
Element types, defined in the proposal, refer to existing IPFIX IANA
types.
Proposed definition of Traffic Class Service Types
0x00 = reserved
0x01 = TRAFFIC_CLASS_TSPEC
0x02 = L2_OVERHEAD
0x03 = MINRATE_IN_PROFILE_MARKING
0x04 = MINRATE_OUT_PROFILE_MARKING
0x05 = MAXRATE_IN_PROFILE_MARKING
0x06 = MAXRATE_OUT_PROFILE_MARKING
0x07 = DROP_THRESHOLD
0x08 = RELATIVE_PRIORITY
0x09 = SUB_TRAFFIC_CLASSES
10. Security Considerations
There is a potential for mis-behaved AS to advertise wrong SLA,
stealing identity of another AS. This resembles to problems already
identified and resolved, in the routing world, thru reverse path
forwarding check. One proposal, inline to RPF, to resolve such
threats is to have each BGP speaker node, in the forwarding path,
perform reverse path check on source AS. Since we expect these
messages to originate and distributed in the managed network, there
should not be any risks for identity theft. Thus reverse path check
is not considered in this proposal nor have we considered any
alternates. Such solutions can be explored later if any such need.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2212] Shenker, S., Partridge, C., and R. Guerin, "Specification
of Guaranteed Quality of Service", RFC 2212,
September 1997.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
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Networks (VPNs)", RFC 4364, February 2006.
[RFC4506] Eisler, M., "XDR: External Data Representation Standard",
STD 67, RFC 4506, May 2006.
[RFC5102] Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
Meyer, "Information Model for IP Flow Information Export",
RFC 5102, January 2008.
11.2. Informative References
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[IDR-ERR] Scudder, J., Chen, E., Mohapatra, P., and K. Patel,
"Revised Error Handling for BGP UPDATE Message,
I-D.draft-ietf-idr-error-handling", June 2012.
[CPP] Boucadair, M., Jacquenet, C., and N. Wang, "IP/MPLS
Connectivity Provisioning Profile, I-D.boucadair-
connectivity-provisioning-profile", Sep 2012.
[CPNP] Boucadair, M. and C. Jacquenet, "Connectivity Provisioning
Negotiation Protocol (CPNP), I-D.boucadair-connectivity-
provisioning-protocol", May 2013.
Authors' Addresses
Shitanshu Shah
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
US
Email: svshah@cisco.com
Keyur Patel
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
US
Email: keyupate@cisco.com
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Sandeep Bajaj
Juniper Networks
1194 N. Mathilda Avenue
Sunnyvale, CA 94089
US
Email: sbajaj@juniper.net
Luis Tomotaki
Verizon
400 International
Richardson, TX 75081
US
Email: luis.tomotaki@verizon.com
Mohamed Boucadair
France Telecom
Rennes 35000
France
Email: mohamed.boucadair@orange.com
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