Internet DRAFT - draft-ietf-sfc-long-lived-flow-use-cases
draft-ietf-sfc-long-lived-flow-use-cases
SFC Working Group R. Krishnan
Internet Draft Brocade Communications
Category: Informational A. Ghanwani
Dell
J. Halpern
S. Kini
Ericsson
D. R. Lopez
Telefonica I+D
Expires: August 7, 2015 February 6, 2015
SFC Long-lived Flow Use Cases
draft-ietf-sfc-long-lived-flow-use-cases-03
Abstract
Long-lived flows such as file transfers, video streams are common in
today's networks. In the context of service function chaining, this
draft suggests use cases for dynamic bypass of certain service
functions for such flows. The benefit of this approach would be to
avoid expensive Layer 7 service function processing for such flows
based on dynamic decisions and thus improve overall performance.
Status of this Memo
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This Internet-Draft will expire on August, 2015.
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Table of Contents
1. Introduction...................................................3
1.1. Acronyms..................................................4
2. Transparent Firewall Use Case..................................4
2.1. Event Sequence............................................5
3. Long-tail Content CDN Use Case.................................6
3.1. Event Sequence............................................6
4. IPsec Management in Mobile Environments........................7
4.1. Event Sequence............................................8
5. Operational Considerations.....................................8
6. IANA Considerations............................................8
7. Security Considerations........................................9
8. Acknowledgements...............................................9
9. References.....................................................9
9.1. Normative References......................................9
9.2. Informative References....................................9
Authors' Addresses................................................9
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1. Introduction
In the context of service function chaining (SFC), this draft
suggests use cases for dynamic bypass of certain service functions
for long-lived flows such as file transfers and video streams. The
benefit of this approach would be to avoid expensive Layer 4-7
service function processing for such flows and improve overall
performance. The focus would be only on long-lived flows which are
observable and controllable from a control plane perspective;
attempting dynamic bypass for short-lived flows would cause
excessive control plane chattiness without any significant
performance benefit.
For long-lived flows, in order to dynamically bypass certain service
functions in the service function chain, the key is to make sure
that the Layer 7 flow can be identified using Layer 2/3/4 fields in
the packet. Examples of such flows are file transfers (which
typically use FTP/SFTP) and video streams (which typically use
HTTP/HTTPS) which can be mapped to a unique IP 5 tuple (IP source
address, IP destination address, IP protocol, transport protocol
source port, transport protocol destination port). We note that it
may not always be possible to identify a Layer 7 flow based on
L2/L3/L4 fields in the packet header. An example of this could be
file transfers under persistent HTTP sessions where multiple files
may be transferred using the same values for these fields in the
packet headers.
There are cases where the transfer of large content may be
split across multiple transport protocol connections. In such
cases, what may be considered a large flow at the application layer
is dealt with using multiple small flows at the network layer. Such
cases would not fit the ones described in this document.
The definition of long-lived flow in this context can reuse the
definition in [I2RS-large-flow] and [OPSAWG-large-flow], where flows
are categorized into 4 types - short-lived small flows, short-lived
large flows, long-lived small flows and long-lived large flows. In
this draft we are concerned with the last 2 types -- long-lived
small flows and long-lived large flows -- and we refer to these as
long-lived flows. This identification of long-lived flows is based
on L2/L3/L4 fields in the packet header that is consistent with that
the definition of a flow in IPFIX [RFC 7011].
The criteria used by the service function for identifying a long-
lived Layer 4-7 flow can use similar criteria, with appropriate
modification to account for long-lived small flows, as the
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techniques described in [OPSAWG-large-flow] for large flow
identification. The mechanics of dynamic bypass are quite different
for different service functions and are described in the following
sections.
For the mechanisms in this draft, our focus is on the following SFC
components:
. An SFC Control Plane Application which is responsible for
implementing the control plane functionality and programming
the data plane for SFC.
. An SFC edge, which is a switch/router responsible for
adding/removing the service chain header to the packets.
1.1. Acronyms
CDN: Content Delivery Network
DNS: Domain Name Service
DPI: Deep Packet Inspection
eNodeB: Evolved Node B
LTE: Long-Term Evolution
NAPT: Network Address Port Translation
SecGW: Security Gateway
SFC: Service Function Chaining
2. Transparent Firewall Use Case
A transparent firewall may be able to determine that a long-lived
flow (e.g. video stream, file transfer) has no security issues. It
is desirable to have such a long-lived flow dynamically bypass the
firewall service function but continue to execute the other service
functions in the chain (e.g. NAPT). The key benefit is overall
performance improvement. The event sequence for this use case is
detailed below. For this use case, it is assumed that the firewall
is transparent and does not perform any packet modification.
Note that the firewall functionality is applicable only to Layer
2/3/4 headers.
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2.1. Event Sequence
1. The firewall examines packets of a flow and deems that it is
benign. While the criteria for how the firewall determines that
the flow is benign are beyond the scope of this document, some of
the criteria that may be used for this include:
a. The packets which are encrypted at the application layer
using protocols such as HTTPS [RFC 2660] cannot be decrypted
and examined further.
b. The packets are from a trusted source.
c. The packets are from a trusted application.
2. The firewall determines that the flow can be identified using a
Layer 2/3/4 rule in the fast path. The firewall moves the flow
from the internal slow path (which inspects every packet) to the
fast path (which does only switching and skips the detailed
inspection of every packet).
3. Based on the above criteria and also having identified the flow
as a long-lived flow, the firewall determines that the flow is a
benign one and does not need to be processed by the firewall any
more.
4. The firewall signals this information to the SFC Control Plane
Application.
5. The SFC Control Plane Application assigns the flow to a different
service function chain that excludes the firewall.
6. The flow continues to be monitored by the SFC edge switch/router
for activity.
7. Once the flow is detected as having become inactive, the flow is
aged out by the SFC edge switch/router.
8. The SFC edge switch/router signals a flow age event to the SFC
Control Plane Application.
9. The SFC Control Plane Application removes the dynamic service
chain association created for the flow.
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3. Long-tail Content CDN Use Case
Most popular content is of interest to a number of users; typical
examples are newly released movies, latest television episodes, etc.
Such content is very amenable to caching. A single copy of the
content is delivered to the cache; the content is delivered to
multiple users from the cache.
Long-tail personalized content is of interest to only a few users;
typical examples are documentaries, older movies etc. Long-tail
personalized content is typically not shared by many users and is
not amenable to caching [CDNI-long-tail]. Caching of such content
could cause excessive thrashing of the cache.
The idea is to improve performance by identifying such long-tail
content and bypassing the CDN cache in the service chain for such
content. This would be dynamic in nature, since content that is not
popular can later become popular and vice versa. The focus will be
on long-lived content such as movies, catch up episodes which
generate long-lived flows. The key benefit is overall performance
improvement. The event sequence for this use case is detailed below.
For the purpose of this draft, our focus is on the following
components in the CDN:
. CDN Monitoring System: The CDN Monitoring System monitors
various aspects of the content such as
o Dynamic Content Usage: Number of users simultaneously
viewing the same content.
o Content Life: If the content is long-lived or short-lived.
Examples of long-lived content are movies, catch up
episodes, etc., while examples of short-lived content are
video clips, advertisements, etc.
. CDN Cache: This is the node in the network where the content
is cached.
For a general overview of CDNs, see [CDN-overview].
3.1. Event Sequence
1. The CDN Monitoring System monitors the numbers of users and type
of content being accessed. By default, we assume the CDN Cache is
bypassed.
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2. If the number of users viewing the same content exceeds a pre-
programmed up-threshold and the content is long-lived, the CDN
Monitoring System instructs the SFC Control Plane Application to
dynamically switch the any new flows from the existing service
chain A to another service chain B which includes a CDN cache for
caching the content in addition to all of the service functions in
service chain A in the same order. This is done by installing a
rule for the flows corresponding to the content in the SFC edge
switch/router.
3. If the number of users viewing the same content falls below
another pre-programmed down-threshold and the content is long-
lived, the monitoring server instructs the SFC Control Plane
Application to dynamically switch any new flows from the existing
service chain B (the one that was used in the previous event) to
service chain A (again, which includes all of the service
functions in service chain B other than the CDN cache). This is
done by removing the previously installed rule for the flows
corresponding to the content from the SFC edge switch/router.
Note that the CDN use case applies only to new flows; existing flows
follow the service chain that they were originally assigned to.
Additionally, this use case assumes that the caching is transparent
wherein the user does not address the cache explicitly. In other
words, the decision of whether or not to retrieve content from the
cache is not based on DNS, rather it is accomplished using SFC. The
mechanisms described here will apply to encrypted traffic as long
the encryption is at the application layer.
4. IPsec Management in Mobile Environments
Existing security procedures for flow protection in LTE are based on
the use of IPsec tunnels between the radio base stations (eNodeBs)
and some central node in the core, where a security gateway (SecGW)
is deployed. The eNodeB device located on the cell site initiates
the IPSec tunnel through the backhaul network to the SecGW, where
the tunnel is terminated and the traffic is forwarded towards its
final destination. IPsec ESP is the method that LTE standards use
for achieving the required levels of security [TS33.401].
To avoid traffic bottlenecks and in order to guarantee a high level
of service availability, a recommended practice is the concurrent
use of several SecGW devices. The one that is to be used for a
given traffic flow may be determined by several criteria such as the
origin of the traffic (user traffic vs network control), flows with
well-known characteristics, e.g. security properties (HTTPS, secure
VPNs), etc. In this way, more critical traffic can be prioritized,
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and different levels of security can be applied depending of payload
characteristics.
Such an optimization could be applied as well to long-lived flows in
a dynamic way, relaxing security procedures for non-sensitive ones,
e.g. it may not be necessary to secure a well-known video stream
that is openly available, applying differentiated policies to avoid
congestion, or even hardening the security procedures according to
the user's data profile.
4.1. Event Sequence
1. A monitoring element analyzes the new flows arriving at the
default SecGW device used by a given eNodeB device according to
criteria such as:
. Security payload protection;
. Application and transport protocol(s) in use including
encryption schemes;
. Relevant parameters in those protocols (URL, content-transfer
declarations, etc.).
2. If the monitoring element identifies a long-lived flow that
matches its differentiating criteria, it signals the flow to the
SFC Control Plane Application.
3. The SFC Control Plane Application assigns the flow to a different
service function chain that makes the eNodeB device use a
different SecGW device.
4. Once the flow is becomes inactive, it is aged out by the eNodeB
device and signaled as such to the SFC Control Plane Application.
5. The SFC Control Plane Application removes the dynamic service
chain association that was created for the flow.
5. Operational Considerations
Any modification to the SFC path (due to insertion or removal of a
service function) could result in temporary mis-ordering in the
delivery of packets.
6. IANA Considerations
None.
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7. Security Considerations
This draft specifies a use case for SFC and does not introduce any
new security requirements beyond those already under consideration
for SFC.
8. Acknowledgements
The authors would like to thank Qin Wu, Myo Zarny, Reinaldo Penno,
and Tiru Reddy for their comments on the document.
9. References
9.1. Normative References
9.2. Informative References
[OPSAWG-large-flow] Krishnan, R. et al., "Mechanisms for Optimal
LAG/ECMP Component Link Utilization in Networks," February 2014.
[I2RS-large-flow] Krishnan, R. et al., "I2RS Large Flow Use Case,"
November 2013.
[CDNI-long-tail] Krishnan, R. et al., "Best practices and
Requirements for delivering Long Tail personalized content delivery
over CDN Interconnections," work in progress, May 2013.
[CDN-overview] Dilley, J. et al., "Globally distributed content
delivery," IEEE Internet Computing, September-October 2002.
[RFC 7011] Claise, B., "Specification of the IP Flow Information
Export (IPFIX) Protocol for the Exchange of Flow Information,"
September 2013.
[TS33.401] 3GPP Technical Specification 33.401, "Security
Architecture," December 2013.
[RFC 2660] Eric Rescorla et al., "The Secure HyperText Transfer
Protocol," August 1999.
Authors' Addresses
Ram Krishnan
Brocade Communications
ramk@brocade.com
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Anoop Ghanwani
Dell
anoop@alumni.duke.edu
Joel Halpern
Ericsson
joel.halpern@ericsson.com
Sriganesh Kini
Ericsson
Sriganesh.kini@ericsson.com
Diego Lopez
Telefonica I+D
Don Ramon de la Cruz, 82 Street
Madrid, 28006, Spain
+34 913 129 041
diego.r.lopez@telefonica.com
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