Internet DRAFT - draft-farrer-softwire-br-multiendpoints
draft-farrer-softwire-br-multiendpoints
Softwire Working Group I. Farrer
Internet-Draft Q. Sun
Intended status: Standards Track Deutsche Telekom AG
Expires: January 7, 2016 July 6, 2015
Multiple BR Tunnel Endpoint Addresses
draft-farrer-softwire-br-multiendpoints-01
Abstract
As 'softwire' based approaches for providing IPv4 services to IPv6
networks
Requirements Language
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].
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
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This Internet-Draft will expire on January 7, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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include Simplified BSD License text as described in Section 4.e of
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Analysis of BR Provisioning Approaches . . . . . . . . . . . 3
2.1. Single BR Tunnel Endpoint Approach . . . . . . . . . . . 3
2.2. Per-client Unique BR Tunnel Endpoint Address Approach . . 3
2.3. A Mix of Both . . . . . . . . . . . . . . . . . . . . . . 3
3. Changes to BR's Behavior . . . . . . . . . . . . . . . . . . 4
4. Changes to Initiator's Behavior . . . . . . . . . . . . . . . 5
5. Operational Considerations . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
The Softwire WG has developed a number of IPv4-over-IPv6 transition
mechanisms based on a hub-and-spoke network architecture, with the
Border Router (BR) functioning as the hub. Although the schema for
configuring a BR varies according to the mechanism being implemented
(using either a per-subscriber rule or an algorithmic mapping rule),
vendor's implementations differ in their approach to the provisioning
of tunnel endpoints on the BR. In some implementations, a single
address must be used for terminating all clients traffic, some
implementations require every client to use a different tunnel
endpoint and some employ a 'hybrid' approach, allowing for the
clients to have unique BR addresses, and other clients to be
arbrarily grouped with multiple clients using the same BR tunnel
endpoint address.
From an operator's standpoint, this difference creates a provisioning
problem: The values of the parameters with which softwire initiators
need to be provisioned vary depending on the BR's tunnel endpoint
provisioning approach. In a multi-vendor environment, this becomes
unmanagable and significantly complicates migration of users and geo-
redundancy between BR's from different vendors.
This document proposes that the 'hybrid' approach for BR tunnel
endpoints offers the most flexibility and should be the model
implemented in softwire concentrators.
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2. Analysis of BR Provisioning Approaches
2.1. Single BR Tunnel Endpoint Approach
In this implementation approach, only a single IPv6 address is used
as the BR's IPv6 tunnel address. This address is provisioned to all
softwire initiators to use as the destination for their IPv4-in-IPv6
tunneled traffic, and is used by the BR as the source address for
encapsulated traffic being sent to Softwire initiators.
The obvious advantage is that all clients can be provisioned with the
same address for the BR. In smaller scale deployments, this may be
sufficient for an operator's needs. In larger scale deployments,
this schema makes it difficult to design and plan for the grouping of
users and geographical failover.
Only supporting a single IPv6 BR tunnel endpoint address available
has another limitation: it is not possbile to differentiate client's
tunneled traffic based on BR's address in the encapsulating IPv6
packet.
2.2. Per-client Unique BR Tunnel Endpoint Address Approach
In this implementation approach, each client is provisioned with a
unique /128 address to use as the destination address for their
tunneled traffic. The BR is configured with exactly as many unique
tunnel endpoint addresses as there are softwire initiators.
The main disadvantage with this approach is that it places an
additional provisioning overhead on the operator to ensure that each
client has a unique BR address. When provisioning lw4o6 using DHCPv6
as described in [I-D.ietf-softwire-map-dhcp], maintaining per-client
DHCPv6 entries is a necessary provisioning overhead. But when
dynamic provisionig of lw4o6 clients is used [RFC7341], per-client
entries in the provisioning system are no longer required, as the
IPv4 addresses for clients are taken from an address pool. However,
if each client still needs to be provisioned with a unique tunnel
endpoint address associated with the IPv4 address it has been
allocated, then the provisioning model becomes complex and
potentially unworkable.
2.3. A Mix of Both
This document proposes that a BR SHOULD support per-client IPv6
tunnel endpoints, but not mandate that these addresses are unique.
E.g., the endpoints can be all the same, or unique, or any
combination of unique and shared.
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By implementing multiple IPv6 tunnel endpoint addresses in this
'mixed' mode, the BR can support different classes of users, grouped
through their tunnel endpoint address. Grouping clients based on a
common tunnel endpoint address makes it simple for intermediate IPv6
network elements to identify client's traffic group by examining the
encapsulating IPv6 header, e.g. so that traffic forwarding policies
can be applied.
It also allows for flexible, anycast based geographical resilience
models where each BR supports a primary group of users and a
secondary group, differentiated by the tunnel endpoint address.
Traffic is flexibly routed through auto-routing protocols and Equal-
Cost Multipath (ECMP).
This document describes a method that enables one Border Router to
serve in such a mix mode. The BR's mapping/binding table must hold
an additional "BR source IPv6 address" field for each Softwire
Initiator it is configured to support. The IPv6 addresses of that
field can be all the same or not, based on the operational
requirements.
This mechanism can be applied to lw4over6
[I-D.ietf-softwire-lw4over6], MAP-E [I-D.ietf-softwire-map] and MAP-T
[I-D.ietf-softwire-map-t].
DISCUSSION - Is this necessary for MAP BRs, or can this already be
supported?
3. Changes to BR's Behavior
Existing BRs implementing lw4o6, MAP-E or MAP-T are provisioned with
a set of rules defining packet processing behaviour. The rule/
binding table on the Border Router only contains the mapping between
the IPv6 and IPv4 address and source ports for the Softwire
Initiators. In this mechanism, the rule/binding table is extended to
include the IPv6 tunnel address(es) configured on the BR as another
field. The Softwire Initiators' IPv6-IPv4 mapping rules are then
linked to the related BR's IPv6 tunnel addresses. As such, it is
possible for one BR to serve multiple groups of Softwire Initiators,
independently from each other.
On receiving an IPv6 packet, the BR MUST use both the source and the
destination IPv6 addresses as input parameters to search for a
matching entry in the mapping rule table, instead of only using the
source IPv6 address/prefix information. If a successful match is
made, the encapsulated/translated IPv4 packet is then verified as
documented in related Softwire mechanisms.
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When the BR receives a packet from the IPv4 Internet, it looks up for
the matching entry using the destination IPv4 address and port
number. The BR MUST also retrieve the associated BR's IPv6 address
to use for the encapsulating packet's source IPv6 address. Depending
on the implemented mechanism, the mapping rule for constructing the
destination IPv6 address will need to be retrieved as normal.
The rest of encapsulation/decapsulation/translation process is inline
with the related mechanisms.
4. Changes to Initiator's Behavior
The Softwire Initiator's behavior is identical to that in the related
mechanisms. That is, when it receives an IPv4-in-IPv6 packet it
checks the source and destination addresses against its
configuration. The source address of the packet MUST match the BR's
tunnel endpoint address configured on the client.
5. Operational Considerations
Border Routers need to be provisioned with multiple sets of tunnel
endpoint IPv6 addresses, IPv4-IPv6 mapping rules for Softwire
Initiators and routable IPv4 prefixes. The provisioning mechanisms
could include NETCONF, TR-69 or out-of-band static configuration.
This mechanism is out of scope for this document.
BRs implementing this mechanism can be deployed using IPv6 anycast to
achieve high availability. Since multiple IPv6 anycast addresses can
be configured on the BR as tunnel endpoint addresses, a BR is able to
serve one primary domain while serving other domains as backup. The
BR advertises the IPv6 anycast prefix(es), as well as the routable
IPv4 prefix(es). ECMP can be used to leverage for stateless load-
balancing across multiple BRs.
However, as the reachable IPv4 customer prefixes are being advertised
by all instances serving that domain simultanously, IPv4 traffic
which ingresses the network will, by default, use the cluster which
has the lowest routing metric to the ingress point in the network.
This may results in different paths for egress and ingress traffic.
Whilst stateless and per-subscriber state softwire mechansims
(described in [RFC6269]) don't require the ingress/egress traffic
paths to be symmetrical, it may be desirable for an operator to
engineer this way for effective capacity planning. The exact
mechanism for achieving this will be dependant on the network's
topology and how the operator is utilizes equal-cost multipath based
load balancing.
NOTE: Another possible consideration is that as there is an
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additional lookup action that needs to be carried out for packets at
the BR, there may be a packet processing overhead.
6. Security Considerations
TBD
7. IANA Considerations
This document does not include an IANA request.
8. Acknowledgements
The authors would like to thank Madhusuhdan Vadde for contributions
to this work.
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.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
9.2. Informative References
[I-D.ietf-softwire-lw4over6]
Cui, Y., Qiong, Q., Boucadair, M., Tsou, T., Lee, Y., and
I. Farrer, "Lightweight 4over6: An Extension to the DS-
Lite Architecture", draft-ietf-softwire-lw4over6-13 (work
in progress), November 2014.
[I-D.ietf-softwire-map]
Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S.,
Murakami, T., and T. Taylor, "Mapping of Address and Port
with Encapsulation (MAP)", draft-ietf-softwire-map-13
(work in progress), March 2015.
[I-D.ietf-softwire-map-dhcp]
Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec,
W., Bao, C., Yeh, L., and X. Deng, "DHCPv6 Options for
configuration of Softwire Address and Port Mapped
Clients", draft-ietf-softwire-map-dhcp-12 (work in
progress), March 2015.
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[I-D.ietf-softwire-map-t]
Li, X., Bao, C., Dec, W., Troan, O., Matsushima, S., and
T. Murakami, "Mapping of Address and Port using
Translation (MAP-T)", draft-ietf-softwire-map-t-08 (work
in progress), December 2014.
[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing", RFC 6269, June
2011.
[RFC7341] Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
Farrer, "DHCPv4-over-DHCPv6 (DHCP 4o6) Transport", RFC
7341, August 2014.
Authors' Addresses
Ian Farrer
Deutsche Telekom AG
CTO-ATI,Landgrabenweg 151
Bonn, NRW 53227
Germany
Email: ian.farrer@telekom.de
Qi Sun
Deutsche Telekom AG
CTO-ATI,Landgrabenweg 151
Bonn, NRW 53227
Germany
Email: qui.sun@external.telekom.de
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