Recommendation for Prefix Binding in the Softwire DS-Lite Context
draft-vinapamula-softwire-dslite-prefix-binding-00
Network Working Group S. Vinapamula
Internet-Draft Juniper Networks
Intended status: Standards Track M. Boucadair
Expires: January 30, 2014 France Telecom
July 29, 2013
Recommendation for Prefix Binding in the Softwire DS-Lite Context
draft-vinapamula-softwire-dslite-prefix-binding-00
Abstract
This document describes possible issues induced by the change of the
B4 IPv6 address and sketches a set of recommendations.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. The Problem . . . . . . . . . . . . . . . . . . . . . . . . . 2
4. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
8.1. Normative references . . . . . . . . . . . . . . . . . . 4
8.2. Informative references . . . . . . . . . . . . . . . . . 5
1. Introduction
IPv6 deployment models assumes IPv6 prefixes are delegated by Service
Providers to the connected CPEs (Customer Premise Equipments) or
hosts, which in their turn derive IPv6 addresses out of that prefix.
In the case of DS-Lite [RFC6333], the B4 element derives an address
for the softwire setup purposes.
A B4 element might obtain a new external IPv6 address, for a variety
of reasons including a reboot of the CPE, power outage, DHCP lease
expiry, or other action undertaken by the Service Provider. If this
occurs, traffic forwarded to a B4's previous address might be
delivered to another B4 that now acquired that address. This affects
all mapping types, whether implicit (e.g., by sending a TCP SYN) or
explicit (e.g., using PCP [RFC6887]).
The main goal of this document is to propose a recommendation to
soften the impact of such renumbering issues.
Note that in some deployments, CPE renumbering may be require to
accommodate some privacy-related requirements to avoid the same
prefix be assigned to the same customers. It is out of scope of this
document to discuss such contexts.
This document complements [RFC6908].
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. The Problem
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Since the network behind B4 can be overlapping across multiple CPEs,
B4 address plays a key role in identifying associated resources
assigned for each of the connections. These resources maintain state
of EIM, EIF, APP, and PCP mappings and flows.
However, there can be change in B4 address for any reason, may be
because of change in CPE device or may be because of security
extensions enabled in generating the IPv6 address. When the address
change, the associated mappings created in the AFTR are no more
valid. This may result in creation of new set of mappings.
ISPs may want to limit the usage of these resources on per subscriber
basis for fair usage of resources. To do so, a subscriber is
identified by an IPv6 prefix mask (i.e., the length of the prefixes
assigned to customers, for example /56 or /48). These policies are
used for dimensioning purposes and also to ensure that AFTR resources
are not exhausted. However, this policy doesn't resolve stale
mappings hanging around in the system, consuming not only system
resources, but also reducing the available quota of resources per
subscriber.
When services are hosted behind B4 element, these services has to
advertise about their change, when ever there is a change of the B4
address. Means to discover the change of B4 address are therefore
required.
Clearing those mappings can be envisaged, but that will causes a lot
of churn in the AFTR, and it doesn't address the latency issue where
a service has to advertise its new assigned external IP address and
port and the clients have to consume and re-initiate connections.
PCP-specific failure scenarios are discussed in
[I-D.boucadair-pcp-failure].
4. Recommendations
In order to mitigate the issues discussed in Section 3, the following
recommendations are made:
1. A policy SHOULD enforced at the AFTR level to limit the amount of
active softwires per subscriber. The default value MUST be 1.
2. Resource contexts created at the AFTR level SHOULD be based on
the prefix mask (or the prefix if it is explicitly configured),
and not based on the derived B4 address. Administrators SHOULD
configure per prefix limits of resource usage, instead of per
tunnel limits. These resources include, number of flows,
mappings including PCP, NAT pool resources, etc.
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3. In the event a new IPv6 address is assigned to B4, the AFTR
SHOULD migrate existing state to be bound to the new B4's IP
address. This ensures the traffic destined to the previous IPv6
address will redirected to the new IPv6 address. The destination
address for tunneling return traffic SHOULD be the last seen
address from the CPE. The source address of the tunnel would
remain same as AFTR.
4. In the event of change of the CPE WAN IPv6 prefix, unsolicited
PCP ANNOUNCE messages SHOULD be sent by the B4 element to
internal hosts to update their mappings.
5. When a new prefix is assigned to the CPE, stale mappings may
exist in the AFTR. This will consume both implicit and explicit
resources. In order to avoid such issues, stable IPv6 prefix are
RECOMMENDED.
6. In case for any reason a prefix has to be reassigned, it is
RECOMMENDED to reassign a prefix only when all the resources in
use associated with that prefix are cleared from the AFTR.
5. Security Considerations
Security considerations related to DS-Lite are discussed in
[RFC6333].
6. IANA Considerations
This document does not require any action from IANA.
7. Acknowledgements
G. Krishna reviewed document and provided useful comments
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.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
2013.
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8.2. Informative references
[I-D.boucadair-pcp-failure]
Boucadair, M. and R. Penno, "Analysis of Port Control
Protocol (PCP) Failure Scenarios", draft-boucadair-pcp-
failure-06 (work in progress), May 2013.
[RFC6908] Lee, Y., Maglione, R., Williams, C., Jacquenet, C., and M.
Boucadair, "Deployment Considerations for Dual-Stack
Lite", RFC 6908, March 2013.
Authors' Addresses
Suresh Vinapamula
Juniper Networks
1194 North Mathilda Avenue
Sunnyvale, CA 94089
USA
Phone: +1 408 936 5441
EMail: sureshk@juniper.net
Mohamed Boucadair
France Telecom
Rennes 35000
France
EMail: mohamed.boucadair@orange.com
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