Internet Engineering Task Force W. Townsley
Internet-Draft O. Troan
Intended status: Standards Track Cisco
Expires: January 8, 2010 July 7, 2009
IPv6 via IPv4 Service Provider Networks
draft-townsley-ipv6-6rd-00
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Abstract
This document specifies a protocol mechanism tailored to advance
deployment of IPv6 to end users via a Service Provider's IPv4 network
infrastructure. Key aspects include automatic IPv6 prefix delegation
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to sites, stateless operation, simple provisioning, and service which
is equivalent to native IPv6 outside of the SP's IPv4 network
infrastructure.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. 6rd Prefix Delegation . . . . . . . . . . . . . . . . . . . . 5
5. Address selection . . . . . . . . . . . . . . . . . . . . . . 7
6. Provisioning the 6rd CE router . . . . . . . . . . . . . . . . 7
6.1. 6rd DHCP option . . . . . . . . . . . . . . . . . . . . . 8
6.2. 6rd PPP IPCP option . . . . . . . . . . . . . . . . . . . 9
6.3. 6rd Broadband Forum TR-69 Object . . . . . . . . . . . . . 9
7. Provisioning the Service Provider 6rd Border Relay . . . . . . 10
8. Encapsulation considerations . . . . . . . . . . . . . . . . . 10
9. Receiving Rules . . . . . . . . . . . . . . . . . . . . . . . 11
10. Transition Considerations . . . . . . . . . . . . . . . . . . 11
11. Security Considerations . . . . . . . . . . . . . . . . . . . 11
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
14.1. Normative References . . . . . . . . . . . . . . . . . . . 12
14.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
The original idea and the name of the mechanism (6rd) specified in
this document is described in draft-despres-6rd [I-D.despres-6rd],
which details a successful commercial "rapid deployment" of the 6rd
mechanism by a residential Service Provider and is recommended
background reading.
This document describes the 6rd mechanism, extended for use in more
general environments, and intended for advancement on the IETF
Standards Track. Throughout this document, the term 6rd is used to
refer to the new mechanisms described here and 6to4 as that which is
described in RFC 3056.
6rd specifies a protocol mechanism to deploy IPv6 to sites via a
Service Provider's (SP's) IPv4 network. It builds on 6to4 [RFC3056],
with the key differentiator that it utilizes an SP's own IPv6 address
prefix rather than 2002::/16. By using the SP's IPv6 prefix, the
operational domain of 6rd is limited to the SP network and under its
direct control. From the perspective of customer sites and the IPv6
Internet at large connected to the 6rd-enabled SP network, the IPv6
service provided is equivalent to native IPv6.
6rd does not translate IPv4 into IPv6, it encapsulates IPv6 in IPv4
with a destination IPv4 address which is either encoded within the
IPv6 destination address itself, or is the destination address of a
preconfigured 6rd Border Relay router that can decapsulate the IPv4
header and route the IPv6 packet outside the SP's IPv4 network. This
way, IPv6 packets follow the IPv4 routing topology within the SP
network, and Border Relays are traversed only for IPv6 packets which
are destined outside the SP's IPv4 network. The 6rd mechanism is
fully stateless, so the Border Relay routers may be addressed via
anycast within the SP network for added resiliency.
The 6rd Customer Edge router (6rd CE) plays a critical role in a 6rd
deployment. 6rd decouples deployment of IPv6 on the "LAN" side of the
6rd CE router from that on the "WAN" side, allowing IPv6 on either
side to be deployed and evolve independently. On the LAN (e.g.,
"Home") side of the 6rd CE router, 6rd expects that IPv6 is
implemented as it would be for any native dual-stack IP service
delivered by the SP. On the WAN side of the 6rd CE router, the 6rd
CE WAN interface itself, the access network between it and partnering
6rd equipment, and the OSS system including DHCP, AAA, etc. may
remain IPv4-only (e.g., there is no need to deploy DHCPv6 [RFC3315],
IPv6 Neighbor Discovery, IPv6 routing, create IPv6 address plans,
etc. within the SP network to deliver IPv6 to the customer site).
6rd relies on IPv4 and is designed to deliver "production-quality"
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dual-stack IPv6 and IPv4 Internet access to customer sites. IPv6
deployment within the SP network itself may continue for the SP's own
purposes outside of delivering IPv6 service to customers. Once IPv6
is fully available, 6rd may be discontinued and IPv4 eventually
turned off or tunneled over IPv6 as described in
draft-ietf-softwire-dual-stack-lite
[I-D.durand-softwire-dual-stack-lite].
2. 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 RFC 2119 [RFC2119].
3. Terminology
6rd Delegated Prefix The IPv6 prefix determined by the 6rd CE device
for use by hosts within the customer site.
This prefix can be considered logically
equivalent to a DHCPv6 IPv6 Delegated Prefix
[RFC3633], though it is calculated by combining
the 6rd SP Prefix, 6rd Domain ID, and end
user's IPv4 address obtained via IPv4
configuration methods.
6rd SP Prefix An IPv6 prefix selected by the Service Provider
for use by a given 6rd deployment. This may be
the entire IPv6 prefix obtained from an RIR and
announced to the IPv6 Internet, or a more-
specific assigned just to given 6rd deployment.
6rd CE The 6rd "Customer Edge" router that sits
between an IPv6-enabled site and an IPv4-enable
SP network. In a residential broadband
deployment this is sometimes referred to as the
"Residential Gateway (RG)," "Customer Premises
Equipment," (CPE) or "Internet Gateway Device"
(IGD). This router has a one internal 6rd
Virtual Interface acting as an endpoint for the
IPv6 in IPv4 encapsulation and forwarding, at
least one "6rd CE LAN Side" interface and "6rd
CE WAN Side" interface, respectively.
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6rd CE LAN Side The functionality of a 6rd CE router that
serves the "Local Area Network (LAN)" or "Home"
side of a broadband service provider
connection. The 6rd CE LAN Side interface is
fully IPv6 enabled.
6rd CE WAN Side The functionality of a 6rd CE Router that
serves the "Wide Area Network" or "Service
Provider" side of the 6rd CE Router. The 6rd
CE WAN side is IPv4-only, except that it
delivers IPv6 packets encapsulated in IPv4 by
the 6rd Virtual Interface.
6rd BR A 6rd-enabled "Border Relay" router located at
the SP premises. The 6rd BR router has at
least one IPv4 interface, an internal 6rd
Virtual Interface for multi-point tunneling,
and at least one IPv6 interface that is
reachable via the IPv6 Internet or IPv6-enabled
portion of the SP network.
6rd Virtual Interface Internal multi-point tunnel interface where 6rd
encapsulation and decapsulation of IPv6 packets
inside IPv4 occurs. A typical 6rd CE or 6rd BR
implementation requires one 6rd Virtual
Interface.
6rd Domain ID 6rd deployment domains are differentiated by
areas of a network where RFC 1918 Private IPv4
addresses may overlap, or administrative
separation of a 6rd deployment is desired.
4. 6rd Prefix Delegation
In 6rd, a customer site's IPv6 Delegated Prefix is derived from 3
elements:
1. An IPv6 Prefix selected by the SP to be the common 6rd SP Prefix
for the given 6rd deployment.
2. An optional Domain ID field
3. An assigned IPv4 address for the subscriber. This IPv4 address
may be a global IPv4 address, or a Private RFC 1918 [RFC1918]
IPv4 address.
From these three items, the 6rd Delegated Prefix is automatically
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created for the customer site when IPv4 service is obtained. From
the perspective of the 6rd CE LAN-Side functionality, this IPv6
delegated prefix is used in the same manner as a prefix obtained via
DHCPv6 Prefix Delegation [RFC3633].
In 6to4, the location of the stored 32-bit IPv4 prefix is at a fixed
location within the IPv6 address. In 6rd it varies, so the size of
the SP IPv6 prefix and the optional Domain ID is important. Also, in
6rd the SP chooses how many suffix bits of the IPv4 prefix are used
in the algorithm to create the IPv6 prefix for its subscribers. This
allows the SP to adjust the balance between IPv6 addresses used by
the 6rd mechanism, and how many are left to be delegated to end user
sites. To allow for stateless address auto-configuration and sub
delegation a 6rd delegated prefix MUST be shorter than a /64.
The 6rd Delegated Prefix is created by concatenating the 3 items
above in order. The sum of the number of bits used by each
determines the size of the prefix that is delegated to the 6rd CE
router for use by the customer site.
/n + d + (<= 32) + (<= 16) + 64 = 128 bits
+-----------------+----------+-----------+-------------------------+
| SP-prefix | D | V4ADDR | Subnet ID | Interface ID |
+-----------------+----------+-----------+-------------------------+
|<---6rd Delegated Prefix--->|<--- End user's address space ---->|
Figure 1
For example, if a 6rd SP Prefix (SP-prefix) is /28 bits, and we use
24 suffix bits of an IPv4 address (V4ADDR), and choose a 4 bit domain
ID (D), the delegated 6rd prefix for the site is 28 + 24 + 4 = 56
bits. This allows a /56 prefix to be delegated to each end user
site.
Embedding less than the full 32 bits of an IPv4 address is possible
only with an aggregated block of IPv4 addresses for a given 6rd SP
Prefix. This may not be practical for global IPv4 addresses at a
given SP, but is quite likely in a deployment where private addresses
are being assigned to end users (for example 10.0.0.0/8). If private
addresses overlap within a given SP deployment, the Domain ID is
suitable for disambiguating between them. In effect, the common part
of the IPv4 address is being replaced by a shorter Domain ID value
which allows for a shorter IPv6 prefix used by 6rd.
Multiple encodings are possible within a single 6rd deployment, but
each must be used with a different IPv6 SP prefix. For example, if
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global and private IPv4 addresses are used within the same 6rd site,
and the number of IPv4 bits encoded in the IPv6 Delegated Prefix
varies between the two (e.g., 32 bits for global, and 24 bits for
private), then a different 6rd SP Prefix must be used to disambiguate
the two different encoding settings. The 6rd Domain ID is only
applicable among common 6rd IPv4 encoding styles.
Since 6rd IPv6 prefixes are selected algorithmically from an IPv4
address, changing the IPv4 address will cause a change in the IPv6
delegated prefix which would normally ripple through the site's
network and be disruptive. As such, if possible the service provider
should utilize a long-lived IPv4 address assignment for a given end
user.
6rd IPv6 address assignment and hence the IPv6 service itself is tied
to the IPv4 address lease (whether set via DHCP, PPP, or otherwise),
thus the 6rd service is also tied to this in terms of authorization,
accounting, etc. For example, the 6rd Delegated Prefix has the same
DHCP lease time as its associated IPv4 address. The prefix lifetimes
advertised in Router Advertisements or used by DHCP on the 6rd CE LAN
side MUST be equal or shorter than the IPv4 address lease time.
For trouble-shooting and traceability, a 6rd IPv6 address and the
associated IPv4 address for the same site can always be determined
algorithmically. This may be useful for referencing logs and other
data at an SP that may be limited to IPv4 address assignment
activity.
5. Address selection
A 6rd delegated prefix is a native IPv6 prefix in the 6rd site. For
the purpose of source and destination address selection the prefix
should be treated as native IPv6 and no changes to the source address
selection or destination address selection policy table [RFC3484] is
needed.
6. Provisioning the 6rd CE router
The 6rd CE router must be configured with the 6rd SP prefix, the
common IPv4 prefix length and a 6rd BR router IPv4 address. The 6rd
Domain ID is appended to the 6rd SP prefix, making it implicit within
the SP 6rd IPv6 prefix (a given 6rd CE router is expected to exist in
only one 6rd domain, making this possible).
This information can be configured into the device in a variety of
ways. DHCP and IPCP are defined here, other automatic provisioning
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protocols may be used as well.
6.1. 6rd DHCP option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_6RD | len |v4prefix-length|v6prefix-length|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6rd Border Relay IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SP 6rd SP Prefix and 6rd Domain ID |
| (variable, up to 16 octets) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2
option code OPTION_6RD(TBD)
len Total length of option in octets.
v4prefix-length Prefix length of the common part of the
encoded IPv4 address in number of bits.
This number of bits MUST be removed from
the IPv4 address when generating the 6rd
Delegated Prefix. For example, if this
value is 8, 24 bits of the subscriber IPv4
prefix will be used when creating the IPv6
Delegated Prefix, determining the
destination IPv4 encapsulation address,
etc. If the value is 0, then the whole 32
bits of the IPv4 address is used in the
encoding.
v6prefix-length IPv6 Prefix length of the SP IPv6 prefix in
number of bits.
6rd Border Relay IPv4 address The IPv4 address of the 6rd Relay
(likely anycast).
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SP 6rd IPv6 prefix Variable length field containing the
Service Provider's 6rd IPv6 prefix for this
deployment and this 6rd CE router, zero
padded to at least a full octet. Length of
the field is determined by the reported
length of the entire DHCP option (len). An
implementation must handle receipt of this
option with zero padding up to a full 16
octets, for deployments preferring to send
a fixed size option.
The client must validate the values received in the option as
follows:
The 6rd IPv6 prefix includes the domain ID embedded within it, sizing
the v6prefix-length accordingly to cover both the 6rd SP prefix size
and domain ID for this 6rd route entry.
The 6rd router MUST install a default route to the relay. Using the
addresses in the example above with a 6rd IPv4 relay address of
10.0.0.1, the RIB will look like:
::/0 -> 2001:ABC1:0000:0100:: (default route)
2001:ABC1:6464:0100::/56 -> Null0 (6rd prefix sink route)
6.2. 6rd PPP IPCP option
PPP [RFC1661], and PPPoE [RFC2516], remains a common way for a
residential broadband end user to obtain configuration. In such
deployments, the DHCPINFORM message may be used along with the DHCP
option described above after IPCP [RFC1332] completes. However, PPP-
based deployments often have no DHCP infrastructure in place,
obtaining IP configuration solely from RADIUS servers and network
equipment via IPCP.
The PPP IPCP option is identical to the DHCP option, aside of the
OPTION_6RD field, which is assigned by IANA. It's fields and their
function are identical, and not repeated here.
6.3. 6rd Broadband Forum TR-69 Object
A large number of 6rd CE routers are managed directly by service
providers via the Broadband Forum's "TR-69" management interface.
This section will make informational reference to the associated
Broadband Forum document that describes this object.
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7. Provisioning the Service Provider 6rd Border Relay
As the 6rd IPv4 relay address is configurable, there is no need for a
well known anycast address as specified in RFC3068 [RFC3068]. For
increased reliability and load-balancing, the relay address can be an
anycast address shared by all of the provider's relays for that 6rd
domain. As 6rd is stateless, any relay may be used at any time. The
6rd relay MUST use its anycast IPv4 address as the source address in
packets relayed via the SP network to the 6rd CE router.
Since 6rd uses provider address space, no specific routes need to be
advertised externally for 6rd to work, neither in IPv6 or IPv4 BGP.
However, the 6rd IPv4 relay anycast addresses must be advertised in
the providers IGP.
For example:
SP prefix: 2001:ABC0::/28
6rd domain id: 1
Making the SP prefix a /32: 2001:ABC1::/32
6rd IPv4 prefix: 10.0.0.0/8
6rd router IPv4 address: 10.100.100.1
6rd site IPv6 prefix: 2001:ABC1:6464:0100::/56
8. Encapsulation considerations
IPv6 in IPv4 encapsulation is done as specified in 6to4 [RFC3056] and
in Basic Transition Mechanisms for IPv6 Hosts and Routers [RFC4213].
IPv6 packets from a 6rd site are encapsulated in IPv4 packets when
they leave the site via its external IPv4 connection. The V4ADDR
MUST be configured on the IPv4 interface.
MTU and fragmentation issues for IPv6 in IPv4 tunnelling is discussed
in detail in section 3.2 of RFC4213 [RFC4213]. 6rd's scope is limited
to a service provider network. If the MTU is well-managed such that
the IPv4 MTU on the 6rd CE WAN interface is set so that no
fragmentation occurs within the boundary of the SP, then the IPv6 MTU
should be set to the IPv4 MTU minus the size of the encapsulating
IPv4 header. IPv4 Path MTU discovery MAY be used to adjust the MTU
of the tunnel as described in section 3.2.2 of RFC4213 [RFC4213] or
the IPv6 tunnel MTU may be explicitly configured.
The IPv6 tunnel MTU, whether determined automatically or configured
directly, MUST be advertised on the LAN-side by setting the MTU
option in Router Advertisements [RFC4861] messages to the IPv6 tunnel
MTU.
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9. Receiving Rules
The 6rd router and relay on receiving a packet on its 6rd virtual
interface SHOULD validate the packet as follows:
- if IPv4 SA is not covered by the 6rd IPv4 prefix
drop packet
- if the IPv4 SA is the 6rd IPv4 relay address:
goto ipv6_checks;
- if IPv4 SA does not match the IPv4 address in the IPv6 SA
drop packet
ipv6_checks:
- if IPv6 DA does not match the 6rd CE router's 6rd IPv6 prefix
drop packet
- if IPv6 forwarding leads to the packet being sent back out the
same 6rd interface
drop packet
10. Transition Considerations
6rd is intended to deliver a production-level service to customer
sites. Once 6rd IPv6 access is available, the SP network can migrate
to IPv6 at its own pace with no affect on the customer. When native
IPv6 is fully available, the 6rd CE router is provisioned with IPv6
on its WAN-side. 6rd and native IPv6 can coexist for a time while the
customer site is adopts the new IPv6 native prefix, and then 6rd
deprovisioned. Alternatively, the same numbering plan for 6rd may be
used for the native service, though this might require a "flag day"
when the 6rd service is turned off and native service is initialized.
While 6rd bears resemblance to 6to4 and utilizes the same
encapsulation and base mechanisms, it is not intended as a
replacement for 6to4. Unlike 6to4, 6rd is for use only in an
environment where a service provider cooperates closely to deliver
the IPv6 service. 6to4 routes with the 2002::/16 prefix may exist
alongside 6rd in the 6rd CE router, and doing so may offer some
efficiencies when communicating directly with 6to4 routers.
11. Security Considerations
A 6to4 router as specified in RFC 3056 [RFC3056] can be used as an
open relay. It can be used to relay IPv6 traffic and as a traffic
anonymizer. By restricting the 6rd domain to within a provider
network a 6rd router only needs to accept packets from a single or
small set of known 6rd relay routers. As such many of the threats
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against 6to4 as described in RFC3964 [RFC3964] do not apply.
12. IANA Considerations
IANA is requested to assign a new DHCP Option code point for
OPTION_6RD.
IANA is requested to assign a new IPCP Type for 6RD_IPCP_TYPE.
13. Acknowledgements
This draft is based on Remi Despres' original idea described in
[I-D.despres-6rd] and the work done by Rani Assaf, Alexandre Cassen,
and Maxime Bizon at Free Telecom. Brian Carpenter and Keith Moore
documented 6to4, which all of this work is based upon. Many others
have provided review and encouragement.
14. References
14.1. Normative References
[RFC1332] McGregor, G., "The PPP Internet Protocol Control Protocol
(IPCP)", RFC 1332, May 1992.
[RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
RFC 1661, July 1994.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2516] Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D.,
and R. Wheeler, "A Method for Transmitting PPP Over
Ethernet (PPPoE)", RFC 2516, February 1999.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
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[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC3964] Savola, P. and C. Patel, "Security Considerations for
6to4", RFC 3964, December 2004.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
14.2. Informative References
[I-D.despres-6rd]
Despres, R., "IPv6 Rapid Deployment on IPv4
infrastructures (6rd)", draft-despres-6rd-03 (work in
progress), April 2009.
[I-D.durand-softwire-dual-stack-lite]
Durand, A., Droms, R., Haberman, B., and J. Woodyatt,
"Dual-stack lite broadband deployments post IPv4
exhaustion", draft-durand-softwire-dual-stack-lite-01
(work in progress), November 2008.
[RFC3068] Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
RFC 3068, June 2001.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
Authors' Addresses
Mark Townsley
Cisco
Paris,
France
Phone: +33 15 804 3483
Email: townsley@cisco.com
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Ole Troan
Cisco
Bergen,
Norway
Phone: +47 917 38519
Email: ot@cisco.com
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