Network Working Group C. Xie
Internet-Draft China Telecom
Intended status: Informational W. Liu
Expires: September 5, 2015 Huawei Technologies
March 4, 2015

Host Identification/Address Problem in Service Function Chaining Use Cases
draft-xie-hiaps-hostid-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.

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Table of Contents

1. Introduction

The use cases described in this document belong to service function chaining (SFC) area [I-D.ietf-sfc-long-lived-flow-use-cases], [I-D.liu-sfc-use-cases], [I-D.ietf-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 function Forwarder (SFF) [I-D.merged-sfc-architecture]. Each service function is directly connected to an SFF.

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.

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.merged-sfc-architecture]. In its simplified form, possibly suitable in home networks, the service function forwarder 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 SFF. 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.

         +--------+  +---------+  +---------+                     
 Service |Parental|  | Traffic |  |  Other  |                     
 Function|Control |  |Offloader|  |Functions|          ----       
 Chain   +--------+  +---------+  +---------+        /      \     
              |           |             |           |Internet|    
              |           |             |           |        |    
              +-----------+-------------+            \      /     
                          |                            --+-       
    ----   +----+         |              ----            |        
  /      \ |Rout|   +-------------+    /      \   +-------------+ 
 |  Home  || ed |---| Edge Router |---|Network |--|    Router   | 
 | Network|| RG |   +-------------+   |        |  |   (Egress)  | 
  \      / +----+                      \      /   +-------------+ 
    ----                                 ----                     
        

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 SFF 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 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 function forwarder.

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. Port Quota Enforcer Use Case

Port Control Protocol (PCP) can be used in address sharing systems where PCP Client requests ports to be assigned from a PCP Server [RFC6887]. PCP Server assigns the ports if the user quota is not exceeded.

PCP systems may employ a Port Quota Enforcer to enforce per-subscriber port quotas. Port Quota Enforcers may not be collocated with the address sharing device. It is usually one of the functions in the service chain.

Port Quota Enforcer can not identify uniquely the host by looking at the source address. It needs the source address of the subscriber in order to enforce the port quotas. Such a case applies both home networks Figure 1 and mobile networks Figure 2.

4.4. 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.ietf-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.

      
                            |      +---(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

4.5. Home Network Applications Use Cases

To be finished.

5. IANA Considerations

This document makes no request to IANA.

6. Security Considerations

This document does not define an architecture nor a protocol; as such it does not raise any security concern. SFC-related security considerations are discussed in [I-D.merged-sfc-architecture] and host identifier related security considerations are discussed in [RFC6967].

7. Acknowledgements

TBD.

8. References

8.1. 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, "Policy and Charging Control (PCC); Reference points", 3GPP TS 29.212, September 2013.

8.2. Informative References

[I-D.boucadair-intarea-host-identifier-scenarios] Boucadair, M., Binet, D., Durel, S., Chatras, B., Reddy, T., Williams, B., Sarikaya, B., Xue, L. and R. Wheeldon, "Scenarios with Host Identification Complications", Internet-Draft draft-boucadair-intarea-host-identifier-scenarios-10, February 2015.
[I-D.boucadair-sfc-design-analysis] Boucadair, M., Jacquenet, C., Parker, R. and L. Dunbar, "Service Function Chaining: Design Considerations, Analysis & Recommendations", Internet-Draft draft-boucadair-sfc-design-analysis-03, October 2014.
[I-D.ietf-sfc-long-lived-flow-use-cases] Krishnan, R., Ghanwani, A., Halpern, J., Kini, S. and D. Lopez, "SFC Long-lived Flow Use Cases", Internet-Draft draft-ietf-sfc-long-lived-flow-use-cases-03, February 2015.
[I-D.ietf-sfc-use-case-mobility] Haeffner, W., Napper, J., Stiemerling, M., Lopez, D. and J. Uttaro, "Service Function Chaining Use Cases in Mobile Networks", Internet-Draft draft-ietf-sfc-use-case-mobility-03, January 2015.
[I-D.liu-sfc-use-cases] Will, W., Li, H., Huang, O., Boucadair, M., Leymann, N., Qiao, F., Qiong, Q., Pham, C., Huang, C., Zhu, J. and P. He, "Service Function Chaining (SFC) General Use Cases", Internet-Draft draft-liu-sfc-use-cases-08, September 2014.
[I-D.merged-sfc-architecture] Halpern, J. and C. Pignataro, "Service Function Chaining (SFC) Architecture", Internet-Draft draft-merged-sfc-architecture-02, August 2014.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R. and P. Selkirk, "Port Control Protocol (PCP)", RFC 6887, April 2013.
[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, "IPv6 Migration Guidelines", 3GPP TR 23.975 11.0.0, June 2010.

Authors' Addresses

Chongfeng Xie China Telecom Room 708 No.118, Xizhimenneidajie Beijing, 100035 EMail: xiechf@ctbri.com.cn
Will(Shucheng) Liu Huawei Technologies Bantian, Longgang District Shenzhen, 518129 P.R. China EMail: liushucheng@huawei.com