Internet DRAFT - draft-sarikaya-sfc-address-sharing-in-sfc
draft-sarikaya-sfc-address-sharing-in-sfc
Network Working Group B. Sarikaya
Internet-Draft L. Xue
Intended status: Informational Huawei
Expires: November 4, 2014 May 3, 2014
Host Identification Problem in Service Function Chaining Use Cases
draft-sarikaya-sfc-address-sharing-in-sfc-00.txt
Abstract
The purpose of this document is to present host identification
problem due to the address and prefix sharing in service function
chaining. We have identified this problem in the use cases of the
parental control service and offloading service in home networks and
also some use cases in mobile networks.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
3. Service Function Execution . . . . . . . . . . . . . . . . . 3
4. Issue Description . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Parental Control Use Case . . . . . . . . . . . . . . . . 4
4.2. Traffic Offload Use Case . . . . . . . . . . . . . . . . 5
4.3. Mobile Network Use Cases . . . . . . . . . . . . . . . . 5
5. Possible Solution Approaches . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The use cases described in this document belong to service function
chaining (SFC) area [I-D.liu-sfc-use-cases],
[I-D.haeffner-sfc-use-case-mobility]. Service functions like
Parental Control, Traffic Offloader, Web Proxy, Load Balancer, etc.
can be executed in a chained fashion. The order of execution of each
function is controlled by an abstract entity called Service Chaining
Enforcement Points (SCEP) [I-D.beliveau-sfc-architecture]. Each
service function is directly connected to an SCEP.
Traffic policy control, such as Parental Control Function and Traffic
Offloader are commonly used by operators to enable flexible service
to the customers. The architecture we assume is shown in Figure 1.
It is a typical home network architecture.
Address sharing/host identification issue comes up if the residential
gateway (RG) is a NAT box in IPv4 or a single prefix is assigned to
the RG in DHCPv6-Prefix Delegation in IPv6
[I-D.boucadair-intarea-host-identifier-scenarios]. Multiple hosts
are sharing the same public IPv4 address or single IPv6 prefix.
In a related document, [I-D.boucadair-sfc-design-analysis], the issue
of host id or subscriber id being part of Service Function Chaining
header is discussed. This discussion is motivated by the same reason
as we have in this document: address and prefix sharing in service
function chaining.
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Some earlier solution approaches to the host identification problem
are analysed in [RFC6967]. It is not clear if those approaches can
also be used in the service function chaining use cases.
2. Conventions and 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 RFC 2119 [RFC2119].
3. Service Function Execution
We assume a service function chaining architecture similar to
[I-D.beliveau-sfc-architecture]. In its simplified form, possibly
suitable in home networks, the service chain enforcement point is
also the ingress router or edge router, e.g. Broadband Network
Gateway. In this case parental control function and all other
functions are directly connected to SCEP. There is an egress router
that routes traffic to the edge router, see Figure 1.
Parental control service function is needed to filter the traffic
from the Internet for certain content. Home users connect to the
Internet after getting their address from RG. In case of NAT at the
RG, all outgoing traffic carries the same address for all users, i.e.
RG address for its WAN interface. In case RG is assigned a single
prefix, all outgoing IPv6 packets contain the same prefix.
Encrypted web traffic (https) represents a very significant part of
Web traffic and is likely to become the main or even the only method
to carry Web data over the Internet. Service functions MUST be able
to decrypt such encrypted traffic, e.g. using Secure Socket Layer
(SSL) [SD326]. In case of address sharing/host identification, being
able to decrypt encrypted data becomes a requirement in order to be
able to access the URL and user information to filter. However this
issue is out of scope.
With data services rapidly increasing, the traditional cellular
network becomes the bottleneck in providing mobile services mainly
because of the increasing bandwidth demand. Operators are trying to
offload the data traffic from the mobile subscribers to the broadband
network. Traffic offloader service function is needed in the
broadband access network for this purpose.
One common broadband access network for offload is home network.
Traffic offloader service function decides on each flow/service
coming from the hosts at home if they should be routed to the
broadband network, i.e. offloaded or they should be sent to the
packet data network gateway fo the mobile network.
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+----------------+ +-----------------+ +-----------------+
Service Function |Parental Control| |Traffic Offloader| |Other Functions |
Chain +----------------+ +-----------------+ +-----------------+
\ /
---------------------------------------------
--+- +----+ \ / --+-
/ \ |Rout| +-------------+ / \ +-------------+
| Home || ed |----| Edge Router |-----|Network | --- | Router |
| Network|| RG | +-------------+ | | | (Egress) |
\ / +----+ \ / +-------------+
---- ---- |
--+-
/ \
|Internet|
| |
\ /
----
Figure 1: Service Chaining in Home Network
4. Issue Description
It is important to note that host identification due to address and
prefix sharing is not specific to the service function chaining.
This problem occurs in many other use cases as discussed in
[I-D.boucadair-intarea-host-identifier-scenarios].
4.1. Parental Control Use Case
Parental control service function searches each packet for certain
content, e.g. destination addresses corresponding to certain URL like
www.thisbizarresite.com. Parental control function should keep this
information (URL and source IP address) in its cache so that all
subsequent packets can be filtered for certain users from the Web
server. Parental control service should send the packet back to SCEP
to be forwarded to the home network [SD326].
Parental control function receives next packet from the recorded URL.
Now it needs to decide to filter it or not. Filtering for specific
host should depend on the source address, i.e. the address of the
host that is being subject to the parental control in IPv4 or the
prefix of the host that is being subject to the parental control in
IPv6. In case of NAT'ed RG, all incoming packets from one RG contain
the same address, i.e. WAN interface address of RG. In case of IPv6
with prefix sharing, all incoming packets contain the same prefix.
In order to do the parental control on the incoming traffic, parental
control service function needs to identify each host. A typical host
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identity is its IP address in broadband network. In Figure 1, RG
knows identifiers of each host in the home network. Edge router
needs to identify the host so that it can inform the service
functions and set the proper service chain.
Edge router MUST set host identifier state in the service functions
that need it, e.g. parental control. Parental control function MUST
be able to identify incoming traffic to be filtered, e.g. specific
URL information. All other traffic is not subject to filtering.
Parental control function filters all traffic coming from indicated
URL only for the specific hosts identified by the service control
enforcement point.
4.2. Traffic Offload Use Case
Traffic offloader service function works on each flow/service and
decides if it should be offloaded to the broadband network or sent
back to the mobile network. In this scenario, the broadband network
MUST obtain the subscriber subscription from the mobile network and
decide if the traffic coming from this subscriber needs to be
offloaded or not. If offloading is needed, this usually means that
the source address of the subscriber needs to be known on the edge
router. In case of NAT'ed RG, all the host's information is lost,
this introduces a major challenge on how to obtain host
identification to decide to offload the traffic or not.
4.3. Mobile Network Use Cases
Many service functions (SF) can be executed in different combinations
in a mobile network as Figure 2 which is adopted from
[I-D.haeffner-sfc-use-case-mobility] shows. Placement of NAT
function plays an important role if it is used.
If NAT function is collocated with P-GW as in [TR23.975] then all
service functions like SF1 through SF9 can only see P-GW Gi interface
address as the source address from all UEs. Individual host
addresses can not be found.
Note that the same problem occurs in case IPv6 is being used by UEs
but UEs need to communicate with an external legacy server which is
IPv4-only. This can be made possible with NAT64 as described in
[RFC6146]. NAT64 uses IPv4 address on its outgoing interface which
is shared by all UEs. So in the case of NAT64 host identification
also becomes an issue in service chaining.
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| +---(S)Gi-LAN -----------+
| | |
| | +---[SF1]-[SF3]-[SF5]--
| | / |
[UE]---[eNB]===[S-GW]===[P-GW+NAT]------[SF2]-[SF4]-[SF6]--
| \ |
| +---[SF7]-[SF8]-[SF9]--
|
Figure 2: Service Chaining in Mobile Network
5. Possible Solution Approaches
A two step solution approach can be taken. In the first step the
gateway gets to know the host identifiers. In mobile network
Figure 2 this is already the case. The next step is signals the host
identifiers to the service function that needs them like parental
control, load balancer, etc.
A simple UDP application can be developed for the first step. The
client, in this case NAT'ed RG can send the host identifier to the
server, the gateway. The same protocol can be used for the second
step, this time the gateway becomes the client and the service
function is the server.
For the second step, a protocol similar to GI-DS-Lite is recommended
in which a Context Identifier (CID) is used to multiplex flows in the
tunnel between the gateway and the service function and the service
function uses CID as the host identifier
[I-D.boucadair-sfc-design-analysis].
Another solution approach for the second step is to define a host
identifier field in SFC header and this field can be optional.
However in order to accomodate the prefix sharing case, this field
should be 128 bits not 64 bits as stated in
[I-D.boucadair-sfc-design-analysis].
6. IANA Considerations
This document makes no request to IANA.
7. Security Considerations
Any security considerations arising from Service Function Chaining
use cases are TBD.
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8. Acknowledgements
TBD.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations", RFC
2663, August 1999.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[TS29.212]
"3GPP TS29.212, Policy and Charging Control (PCC) over Gx/
Sd reference point", December 2011.
9.2. Informative References
[I-D.beliveau-sfc-architecture]
Beliveau, A., "Service Function Chaining Architecture",
draft-beliveau-sfc-architecture-00 (work in progress),
October 2013.
[I-D.boucadair-intarea-host-identifier-scenarios]
Boucadair, M., Binet, D., Durel, S., Chatras, B., Reddy,
T., Williams, B., Sarikaya, B., and L. Xue, "Host
Identification: Use Cases", draft-boucadair-intarea-host-
identifier-scenarios-05 (work in progress), April 2014.
[I-D.boucadair-sfc-design-analysis]
Boucadair, M., Jacquenet, C., Parker, R., and L. Dunbar,
"Service Function Chaining: Design Considerations,
Analysis & Recommendations", draft-boucadair-sfc-design-
analysis-02 (work in progress), February 2014.
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[I-D.haeffner-sfc-use-case-mobility]
Haeffner, W., Napper, J., Stiemerling, M., and D. Lopez,
"Service Function Chaining Use Cases in Mobile Networks",
draft-haeffner-sfc-use-case-mobility-01 (work in
progress), February 2014.
[I-D.liu-sfc-use-cases]
Will, W., Li, H., Huang, O., Boucadair, M., Leymann, N.,
Cao, Z., Qiong, Q., and C. Pham, "Service Function
Chaining (SFC) Use Cases", draft-liu-sfc-use-cases-05
(work in progress), April 2014.
[RFC6967] Boucadair, M., Touch, J., Levis, P., and R. Penno,
"Analysis of Potential Solutions for Revealing a Host
Identifier (HOST_ID) in Shared Address Deployments", RFC
6967, June 2013.
[SD326] BBF, , "Flexible Service Chaining", January 2014.
[TR23.975]
"3GPP TR23.975, IPv6 Migration Guidelines", June 2011.
Authors' Addresses
Behcet Sarikaya
Huawei
5340 Legacy Dr.
Plano, TX 75024
Email: sarikaya@ieee.org
Li Xue
Huawei
NO.156 Beiqing Rd. Z-park, Shi-Chuang-Ke-Ji-Shi-Fan-Yuan,
Beijing, HaiDian District 100095
China
Email: xueli@huawei.com
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