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Internet Engineering Task Force (IETF) B. Liu
Request for Comments: 7010 S. Jiang
Category: Informational Huawei Technologies Co., Ltd.
ISSN: 2070-1721 B. Carpenter
University of Auckland
S. Venaas
Cisco Systems
W. George
Time Warner Cable
September 2013
IPv6 Site Renumbering Gap Analysis
Abstract
This document briefly introduces the existing mechanisms that could
be utilized for IPv6 site renumbering and tries to cover most of the
explicit issues and requirements associated with IPv6 renumbering.
The content is mainly a gap analysis that provides a basis for future
works to identify and develop solutions or to stimulate such
development as appropriate. The gap analysis is organized by the
main steps of a renumbering process.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7010.
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Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction ....................................................4
2. Overall Requirements for Renumbering ............................4
3. Existing Components for IPv6 Renumbering ........................5
3.1. Relevant Protocols and Mechanisms ..........................5
3.2. Management Tools ...........................................6
3.3. Procedures and Policies ....................................7
4. Managing Prefixes ...............................................7
4.1. Prefix Delegation ..........................................7
4.2. Prefix Assignment ..........................................8
5. Address Configuration ...........................................8
5.1. Host Address Configuration .................................8
5.2. Router Address Configuration ...............................9
6. Updating Address-Relevant Entries ..............................10
6.1. DNS Records Update ........................................10
6.2. In-Host Server Address Update .............................11
6.3. Address Update in Scattered Configurations ................11
7. Renumbering Event Management ...................................13
7.1. Renumbering Notification ..................................13
7.2. Synchronization Management ................................14
7.3. Renumbering Monitoring ....................................15
8. Miscellaneous ..................................................15
8.1. Multicast .................................................15
8.2. Mobility ..................................................17
9. Gap Summary ....................................................17
9.1. Managing Prefixes .........................................17
9.2. Address Configuration .....................................17
9.3. Address-Relevant Entries Update ...........................18
9.4. Renumbering Event Management ..............................19
9.5. Miscellaneous .............................................19
10. Gaps Considered Unsolvable ....................................20
10.1. Address Configuration ....................................20
10.2. Address-Relevant Entries Update ..........................20
10.3. Miscellaneous ............................................21
11. Security Considerations .......................................21
12. Acknowledgments ...............................................22
13. References ....................................................23
13.1. Normative References .....................................23
13.2. Informative References ...................................23
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1. Introduction
As introduced in [RFC5887], renumbering, especially for medium to
large sites and networks, is currently viewed as expensive and
painful. This error-prone process is avoided by network managers as
much as possible. If IPv6 site renumbering continues to be
considered difficult, network managers will turn to Provider
Independent (PI) addressing for IPv6 as an attempt to minimize the
need for future renumbering. However, widespread use of PI
addressing may create very serious BGP4 scaling problems [RFC4984].
It is thus desirable to develop tools and practices that make
renumbering a simpler process and reduces demand for IPv6 PI space.
Building upon the IPv6 enterprise renumbering scenarios described in
[RFC6879], this document performs a gap analysis to provide a basis
for future work to identify and develop solutions or to stimulate
such development as appropriate. The gap analysis is organized
according to the main steps of a renumbering process, which includes
prefix management, node address (re)configuration, and updates to
address-relevant entries in various devices such as firewalls,
routers and servers, etc. Renumbering event management is presented
independently from the steps of a renumbering process in order to
identify some operational and administrative gaps in renumbering.
This document starts from existing work in [RFC5887] and [RFC4192].
It further analyzes and identifies the valuable and solvable issues,
digs out of some undiscovered gaps, and gives some solution
suggestions. This document considers the make-before-break approach
as a premise for the gap analysis, so readers should be familiar with
[RFC4192].
Renumbering nodes with static addresses has a particular set of
problems, thus discussion of that space has been covered in a related
document [RFC6866].
This document does not cover the unplanned emergency renumbering
cases.
2. Overall Requirements for Renumbering
This section introduces the overall goals of a renumbering event. In
general, we need to leverage renumbering automation to avoid human
intervention as much as possible at a reasonable cost. Some existing
mechanisms already provide useful capabilities.
The automation can be divided into four aspects as follows.
(Detailed analysis of the four aspects is presented respectively in
Sections 4 through 7.)
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o Prefix delegation and delivery should be automatic and accurate in
aggregation and coordination.
o Address reconfiguration should be automatically achieved through
standard protocols with minimum human intervention.
o Address-relevant entry updates should be performed together and
without error.
o Renumbering event management is needed to provide the functions of
renumbering notification, synchronization, and monitoring.
Besides automation, session survivability is another important issue
during renumbering since application outage is one of the most
obvious impacts that make renumbering painful and expensive. Session
survivability is a fundamental issue that cannot be solved within a
renumbering context only. However, the [RFC4192] make-before-break
approach, which uses the address lifetime mechanisms in IPv6
Stateless Address Autoconfiguration (SLAAC) and Dynamic Host
Configuration Protocol for IPv6 (DHCPv6), allows for a smooth
transition mechanism from old to new prefixes. In most cases, since
we can set the transition period to be long enough to cover the
ongoing sessions, we consider this mechanism sufficient to avoid
broken sessions in IPv6 site renumbering. (Please note that if
multiple addresses are running on hosts simultaneously, the address
selection [RFC6724] needs to be carefully handled.)
3. Existing Components for IPv6 Renumbering
Since renumbering is not a new issue, some protocols and mechanisms
have already been utilized for this purpose. There are also some
dedicated protocols and mechanisms that have been developed for
renumbering. This section briefly reviews these existing protocols
and mechanisms to provide a basis for the gap analysis.
3.1. Relevant Protocols and Mechanisms
o Router Advertisement (RA) messages, defined in [RFC4861], are used
to deprecate prefixes that are old or announce prefixes that are
new, and to advertise the availability of an upstream router. In
renumbering, RA is one of the basic mechanisms for host
configuration.
o When renumbering a host, SLAAC [RFC4862] may be used for address
configuration with the new prefix(es). Hosts receive RA messages
that contain a routable prefix(es) and the address(es) of the
default router(s); then hosts can generate an IPv6 address(es) by
themselves.
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o Hosts that are configured through DHCPv6 [RFC3315] obtain new
addresses through the renewal process or when they receive the
reconfiguration messages initiated by the DHCPv6 servers.
o DHCPv6-PD (Prefix Delegation) [RFC3633] enables automated
delegation of IPv6 prefixes using the DHCPv6.
o [RFC2894] defines standard ICMPv6 messages for router renumbering.
This is a dedicated protocol for renumbering, but we are not aware
of real network deployment.
3.2. Management Tools
Some renumbering operations could be automatically processed by
management tools in order to make the renumbering process more
efficient and accurate. The tools may be designed specifically for
renumbering, or common tools could be utilized for some of the
renumbering operations.
Following are examples of such tools:
o IP address management (IPAM) tools. There are both commercial and
open-source solutions. IPAM tools are used to manage IP address
plans and usually integrate the DHCPv6 and DNS services together
as a whole solution. Many mature commercial tools can support
management operations, but normally they do not have dedicated
renumbering functions. However, the integrated DNS/DHCPv6
services and address management function can obviously facilitate
the renumbering process.
o Third-party tools. Some organizations use third-party tools to
push configuration to devices. This is sometimes used as a
supplement to vendor-specific solutions. A representative of such
a third-party tool is [CFENGINE].
o Macros. [LEROY] proposed a mechanism of macros to automatically
update the address-relevant entries/configurations inside the DNS,
firewall, etc. The macros can be delivered through the SOAP
protocol from a network management server to the managed devices.
o Asset management tools/systems. These tools may provide the
ability to manage configuration files in devices so that it is
convenient to update the address-relevant configuration in these
devices.
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3.3. Procedures and Policies
o [RFC4192] proposed a procedure for renumbering an IPv6 network
without a flag day. The document includes a set of operational
suggestions that can be followed step by step by network
administrators. It should be noted that the administrators need
to carefully deal with the address selection issue, while the old
and new prefixes are both available during the overlapping period
as described in the procedures in [RFC4192]. The address
selection policies might need to be updated after renumbering, so
the administrator could leverage the address-selection-policy
distribution mechanism as described in [6MAN-ADDR-OPT].
o [RFC6879] analyzes the enterprise renumbering events and makes
recommendations based on the existing renumbering mechanisms.
According to the different stages, renumbering considerations are
described in three categories: considerations and recommendations
during network design, for the preparation of enterprise network
renumbering, and during the renumbering operation.
4. Managing Prefixes
When renumbering an IPv6 enterprise site, the key procedural issue is
switching the old prefix(es) to a new one(s). A new short prefix may
be divided into longer ones for subnets, so we need to carefully
manage the prefixes to ensure they are synchronized and coordinated
within the whole network.
4.1. Prefix Delegation
For big enterprises, the new short prefix(es) usually comes down
through offline human communication. But, for the SOHO-style (Small
Office, Home Office) SMEs (Small & Medium Enterprises), the prefixes
might be dynamically received by DHCPv6 servers or routers inside the
enterprise networks. The short prefix(es) could be automatically
delegated through DHCPv6-PD. Then the downlink DHCPv6 servers or
routers could begin advertising the longer prefixes to the subnets.
The delegation routers might need to renumber themselves with the new
delegated prefixes. So, there should be a mechanism to inform the
routers to renumber themselves by delegated prefixes; there should
also be a mechanism for the routers to derive addresses automatically
based on the delegated prefixes.
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4.2. Prefix Assignment
When subnet routers receive the longer prefixes, they can advertise a
prefix on a link to which hosts are connected. Host address
configuration, rather than routers, is the primary concern for prefix
assignment, which is described in Section 5.1.
5. Address Configuration
5.1. Host Address Configuration
o SLAAC and DHCPv6 Interaction Problems
Both DHCPv6 and Neighbor Discovery (ND) protocols have an IP
address configuration function, which are suitable for different
scenarios. During renumbering, the SLAAC-configured hosts can
reconfigure IP addresses by receiving ND Router Advertisement (RA)
messages containing new prefix information. (It should be noted
that the prefix delivery could be achieved through DHCPv6
according to [PREFIX-DHCPv6]). The DHCPv6-configured hosts can
reconfigure addresses by initiating RENEW sessions [RFC3315] when
the current addresses' lease times are expired or when they
receive reconfiguration messages initiated by the DHCPv6 servers.
Sometimes the two address configuration modes may be available in
the same network. This would add additional complexity for both
the hosts and network management.
With the flags defined in RA (ManagedFlag (M) indicating the
DHCPv6 service available in the network; OtherConfigFlag (O)
indicating other configurations such as DNS/routing), the two
separated address configuration modes are correlated. However,
the ND protocol does not define the flags as prescriptive but only
as advisory. This has led to variation in the behavior of hosts
when interpreting the flags; different operating systems have
followed different approaches. (For more details, please refer to
[DHCPv6-SLAAC] and [6RENUM-SLAAC].)
The impact of ambiguous M/O flags includes the following aspects:
- DHCPv6-configured hosts might not be able to be renumbered by
RA
It is unclear whether a DHCPv6-configured host will accept
address configuration though RA messages, especially when the M
flag transitions from 1 to 0; this depends on the
implementation of the operating system. It might not be
possible for administrators to only use RA messages for
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renumbering, since renumbering might fail on some already
DHCPv6-configured hosts. This means administrators have to use
DHCPv6 reconfiguration for some DHCPv6-configured hosts. It is
not convenient, and DHCPv6 reconfiguration is not suitable for
bulk usage as analyzed below.
- DHCPv6-configured hosts might not be able to learn new RA
prefixes
[RFC5887] mentions that DHCPv6-configured hosts may want to
learn about the upstream availability of new prefixes or loss
of prior prefixes dynamically by deducing this from periodic RA
messages. Relevant standards [RFC4862] [RFC3315] are ambiguous
about what approach should be taken by a DHCPv6-configured host
when it receives RA messages containing a new prefix. Current
behavior depends on the operating system of the host and cannot
be predicted or controlled by the network.
- SLAAC-configured hosts might not be able to add a DHCPv6
address(es)
The behavior when the host receives RA messages with the M flag
set is unspecified.
The host may start a DHCPv6 session and receive the DHCPv6
address configuration, or it may just ignore the messages.
Whether the hosts start DHCPv6 configuration is outside the
control of the network side.
5.2. Router Address Configuration
o Learning New Prefixes
As described in [RFC5887], "if a site wanted to be multihomed
using multiple provider-aggregated (PA) routing prefixes with one
prefix per upstream provider, then the interior routers would need
a mechanism to learn which upstream providers and prefixes were
currently reachable (and valid). In this case, their Router
Advertisement messages could be updated dynamically to only
advertise currently valid routing prefixes to hosts. This would
be significantly more complicated if the various provider prefixes
were of different lengths or if the site had non-uniform subnet
prefix lengths."
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o Restarting After Renumbering
As [RFC2072] mentions, some routers cache IP addresses in some
situations, so routers might need to be restarted as a result of
site renumbering. While most modern systems support a cache-clear
function that eliminates the need for restarts, there are always
exceptions that must be taken into account.
o Router Naming
[RFC4192] states that "To better support renumbering, switches and
routers should use domain names for configuration wherever
appropriate, and they should resolve those names using the DNS
when the lifetime on the name expires". As [RFC5887] described,
this capability is not new, and currently it is present in most
IPsec VPN implementations. However, many administrators may need
to be alerted to the fact that it can be utilized to avoid manual
modification during renumbering.
6. Updating Address-Relevant Entries
In conjunction with renumbering the nodes, any configuration or data
store containing previous addresses must be updated as well. Some
examples include DNS records and filters in various entities such as
Access Control Lists (ACLs) in firewalls/gateways.
6.1. DNS Records Update
o Secure Dynamic DNS (DDNS) Update
In real network operations, a DNS update is normally achieved by
maintaining a DNS zone file and loading this file into the site's
DNS server(s). Synchronization between host renumbering and the
updating of its AAAA record is hard. [RFC5887] discusses an
alternative that uses the Secure Dynamic DNS Update [RFC3007], in
which a host informs its own DNS server when it receives a new
address.
The Secure Dynamic DNS Update has been widely supported by the
major DNS implementations, but it hasn't been widely deployed.
Normal hosts are not suitable to do the update, mainly because of
the complex key-management issues inherited from secure DNS
mechanisms, so current practices usually assign DHCP servers to
act as DNS clients to request that the DNS server update relevant
records [RFC4704]. The key-management problem is tractable in the
case of updates for a limited number of servers, so Dynamic DNS
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updates could serve as a suitable solution for keeping server DNS
records up to date on a typical enterprise network. However, this
solution is not easily applicable to hosts in general.
To address the larger use case of arbitrary non-server hosts being
renumbered, DHCP servers have to learn that the relevant hosts
have changed their addresses and thus trigger the DDNS update. If
the hosts were numbered and also renumbered by DHCP, it would be
easy for the DHCP servers to learn the address changes; however,
if the hosts were numbered by SLAAC, then there could be trouble.
6.2. In-Host Server Address Update
While DNS stores the addresses of hosts in servers, hosts are also
configured with the addresses of servers, such as DNS and RADIUS
servers [RFC2865]. While renumbering, the hosts must update these
addresses if the server addresses change.
In principle, the addresses of DHCPv6 servers do not need to be
updated since they could be dynamically discovered through
DHCPv6-relevant multicast messages. But in practice, most relay
agents have the option of being configured with a DHCPv6 server
address rather than sending to a multicast address. Therefore, the
DHCP server addresses update might be an issue in practice.
6.3. Address Update in Scattered Configurations
Besides the DNS records and the in-host server address entries, there
are also many places in which IP addresses are configured, for
example, filters such as ACL and routing policies. There are even
more sophisticated cases where the IP addresses are used for deriving
values, for example, using the unique portion of the loopback address
to generate an ISIS net ID.
In renumbering, updating the IP addresses in all the above mentioned
places is burdensome and error-prone. We lack a "one-stop" mechanism
to trigger the updates for all the subsystems on a host/server and
all the external databases that refer to the IP address update. We
break the general "one-stop" gap into the following two aspects.
o Self-Contained Configuration in Individual Devices
Ideally, IP addresses can be defined as a value once, and then the
administrators can use either keywords or variables to call the
value in other places such as a sort of internal inheritance in
CLI (command line interface) or other local configurations. This
makes it easier to manage a renumbering event by reducing the
number of places where a device's configuration must be updated.
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However, it still means that every device needs to be individually
updated, but only once instead of having to inspect the whole
configuration to ensure that none of the separate places that a
given IP address occurs is missed.
Among current devices, some routers support defining multiple
loopback interfaces that can be called in other configurations.
For example, when defining a tunnel, it can call the defined
loopback interface to use its address as the local address of the
tunnel. This can be considered as a kind of parameterized self-
contained configuration. However, this only applies to certain
use cases; it is impossible to use the loopback interfaces to
represent external devices, and it is not always possible to call
loopback interfaces in other configurations. Parameterized self-
contained configuration is still a gap that needs to be filled.
o Unified Configuration Management among Devices
This refers to a more formalized central configuration management
system, where all changes are made in one place, and the system
manages how changes are pushed to the individual devices. This
issue contains two aspects, as follows:
- Configuration Aggregation
Configuration data based on addresses or prefixes are usually
spread out in various devices. As [RFC5887] describes, some
address configuration data might be widely dispersed and much
harder to find. Some will inevitably be found only after the
renumbering event. Because there's a big gap in configuration
aggregation, it is hard to get all the relevant configuration
data together in one place.
- Configuration Update Automation
As mentioned in Section 3.2, [LEROY] proposes a mechanism that
can automatically update the configurations. The mechanism
utilizes macros suitable for various devices such as routers
and firewalls to update configurations based on the new prefix.
Such an automation tool is valuable for renumbering because it
can reduce manual operation, which is error-prone and
inefficient.
Besides the macros, [LEROY] also proposes the use of SOAP to
deliver the macros to the devices. Along with SOAP, we may
consider whether it is possible and suitable to use other
standardized protocols, such as the Network Configuration
Protocol (NETCONF) [RFC6241].
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In current real networks, most devices use vendor-private
protocols to update configurations, so it is not necessarily
valid to assume that there is going to be a formalized
configuration management system to leverage. Although there
are some vendor-independent tools as mentioned in Section 3.2,
a standard and comprehensive way to uniformly update
configurations in multi-vendor devices is still missing.
7. Renumbering Event Management
From the perspective of network management, renumbering is an event
that may need additional processes to make it easier and more
manageable.
7.1. Renumbering Notification
The process of renumbering could benefit from hosts or servers being
made aware of an occurrence of a renumbering event. Following are
several examples of additional processes that may ease renumbering.
o A notification mechanism may be needed to indicate to hosts that a
renumbering event has changed some DNS records in DNS servers
(normally, in an enterprise, it is a local recursive DNS
server(s)), and then the hosts might want to refresh the DNS
cache. That mechanism may also need to indicate that such a
change will happen at a specific time in the future.
o As suggested in [RFC4192], if the DNS service can be given prior
notice about a renumbering event, then delay in the transition to
new IPv6 addresses could be reduced and thus improve the
efficiency of renumbering.
o Router awareness: In a site with multiple domains that are
connected by border routers, all border routers should be aware of
renumbering in one domain or multiple domains and update the
internal forwarding tables and the address-/prefix-based filters
accordingly to correctly handle inbound packets.
o Ingress filtering: ISPs normally enable an ingress filter to drop
packets with source addresses from other ISPs at the end-site
routers to prevent IP spoofing [RFC2827]. In a multihomed site
with multiple PA prefixes, the ingress router of ISP A should be
notified if ISP B initiates a renumbering event in order to
properly update its filters to permit the new legitimate
prefix(es). For large enterprises, it might be practical to
manage this new legitimate prefix information through human
communication. However, for the millions of small enterprises, an
automated notification mechanism is needed.
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o Log collectors: In the NMS (network management system), log
collectors that collect logs through syslog, SNMP notification,
IPFIX, etc. usually treat the UDP message source IP addresses as
the host or router IDs. When one source IP address is changed,
the log collectors will consider that a new device appeared in the
network. Therefore, a mechanism is needed for the NMS
applications to learn the renumbering event including the mappings
of old and new IP addresses for each host/router, so that they
could update the address-relevant mappings as described in Section
7.2.
7.2. Synchronization Management
o DNS Update Synchronization
The DNS changes must be coordinated with node address
configuration changes. DNS has a latency issue of propagating
information from the server to the resolver. The latency is
mainly caused by the Time to Live (TTL) assigned to individual DNS
records and the timing of updates from primary to secondary
servers [RFC4192].
Ideally, during a renumbering operation, the DNS TTLs should
always be shorter than any other lifetimes associated with an
address. If the TTLs were set correctly, then the DNS latency
could be well controlled. However, there might be some
exceptional situations in which the DNS TTLs were already set too
long for the time available to plan and execute a renumbering
event. In these situations, there are currently no mechanisms to
deal with the already configured long DNS TTLs.
o NMS Address-Relevant Mapping Synchronization
As described in Section 7.1, the NMS needs to learn the
renumbering event and thus correlate the old and new address in
the logs. If the NMS applies unique IDs for the hosts or routers,
then the mappings between the unique IDs and IP addresses also
need to be updated after renumbering.
7.3. Renumbering Monitoring
While treating renumbering as a network event, mechanisms to monitor
the renumbering process might be needed to inform the administrators
whether the renumbering has been successful. Considering that the
address configuration operation might be stateless (if ND is used for
renumbering), it is difficult to monitor.
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8. Miscellaneous
Since multicast and mobility are special use cases that might not be
included in routine or common renumbering operations, they are
discussed separately in this miscellaneous section.
8.1. Multicast
From the perspective of interface renumbering operations, renumbering
a multicast address is the same as renumbering a unicast address. So
this section mainly discusses the issues from the perspective of the
impact to the multicast application systems caused by renumbering.
Renumbering also has an impact on multicast. Renumbering of unicast
addresses affects multicast even if the multicast addresses are not
changed. There may also be cases where the multicast addresses need
to be renumbered.
o Renumbering of Multicast Sources
If a host that is a multicast source is renumbered, the
application on the host may need to be restarted for it to
successfully send packets with the new source address.
For ASM (Any-Source Multicast), the impact on a receiver is that a
new source appears to start sending and it no longer receives from
the previous source. Whether this is an issue depends on the
application, but we believe it is likely not to be a major issue.
For SSM (Source-Specific Multicast) however, there is one
significant problem. The receiver needs to learn which source
addresses it must join. Some applications may provide their own
method for learning sources, where the source application may
somehow signal the receiver.
Otherwise, the receiver may, for example, need to get new SDP
(Session Description Protocol) information with the new source
address. This is similar to the process for learning a new group
address; see the "Renumbering of Multicast Addresses" topic below.
o Renumbering of Rendezvous-Point
If the unicast addresses of routers in a network are renumbered,
then the RP (Rendezvous-Point) address is also likely to change
for at least some groups. An RP address is needed by PIM-SM
(Protocol Independent Multicast - Sparse Mode) to provide ASM and
for Bidir PIM. Changing the RP address is not a major issue,
except that the multicast service may be impacted while the new RP
addresses are configured. If dynamic protocols are used to
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distribute group-to-RP mappings, the change can be fairly quick
and any impact time should be very brief. However, if routers are
statically configured, the time impacted depends on how long it
takes to update all the configurations.
For PIM-SM, one typically switches to SPT (Shortest-Path-Tree)
when the first packet is received by the last-hop routers.
Forwarding on the SPT should not be impacted by the change of IP
address. A network operator should be careful not to deprecate
the previous mapping before configuring a new one, because
implementations may revert to Dense Mode if no RP is configured.
o Renumbering of Multicast Addresses
In general, multicast addresses can be chosen independently of the
unicast addresses, and the multicast addresses can remain fixed
even if the unicast addresses are renumbered. However, for IPv6,
there are useful ways of deriving multicast addresses from unicast
addresses, such as described in "Unicast-Prefix-based IPv6
Multicast Addresses" [RFC3306] and "Embedded-RP IPv6 Multicast
Addresses" [RFC3956]. In those cases, the multicast addresses
used may have to be renumbered.
Renumbering group addresses may be complicated. For multicast, it
is common to use literal addresses and not DNS. When multicast
addresses are changed, source applications need to be reconfigured
and restarted.
Multicast receivers need to learn the new group addresses to join.
Note that for SSM, receivers need to learn which multicast
channels to join. A channel is a source and group pair. This
means that for an SSM application, a change of source address is
likely to have the same effect as a change of group address.
Some applications may have dynamic methods of learning which
groups (and possibly sources) to join. If not, the application
may have to be reconfigured and restarted.
One common way for receivers to learn the necessary parameters is
by use of SDP. SDP information may be distributed via various
application protocols or from a file. An SDP file may be
distributed via HTTP, email, etc. If a user is using a web
browser and clicking on a link to launch the application with the
necessary data, it may be a matter of closing the current
application and re-clicking the link.
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In summary, currently, multicast renumbering issues are basically
handled by application-specific methods. There is no standard way
to guarantee that multicast service could live across a
renumbering event.
8.2. Mobility
As described in [RFC5887], if a mobile node's home address changes
unexpectedly, the node can be informed of the new global routing
prefix used at the home site through the Mobile Prefix Solicitation
and Mobile Prefix Advertisement ICMPv6 messages [RFC6275]. However,
if the mobile node is disconnected at the time of home address
renumbering, it will no longer know a valid subnet anycast address
for its home agent, leaving it to deduce a valid address on the basis
of DNS information.
So, for Mobile IP, we need a better mechanism to handle the change of
home agent address while the mobile address is disconnected.
9. Gap Summary
The following is a summary of the gaps identified previously in this
document that are considered solvable, but may require process or
protocol changes to resolve.
9.1. Managing Prefixes
o A mechanism informing the routers to renumber themselves by
delegated prefixes.
o A mechanism for the routers to derive addresses automatically
based on the delegated prefixes.
9.2. Address Configuration
o Host Address Configuration
- DHCPv6-configured hosts might not be able to be renumbered by
RA on some current implementations.
- DHCPv6-configured hosts might not be able to learn new RA
prefixes on some current implementations.
- SLAAC-configured hosts might not be able to add DHCPv6
address(es) on some current implementations.
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o Router Address Configuration
- A mechanism for interior routers in a multihomed site to learn
which upstream providers and prefixes are currently reachable.
- Cache-clear might need to restart (rarely in modern routers).
- Use of router domain names is not widely learned or deployed by
administrators.
9.3. Address-Relevant Entries Update
o DNS Records Update
- For key-management scalability issues, secure dynamic DNS
update is usually done by DHCP servers on behalf of the hosts,
so it might not be practical for SLAAC-configured hosts to do
secure DDNS.
o In-Host Server Address Update
- DHCP relays might be configured with DHCP server addresses
rather than by sending multicast messages to discover the DHCP
server dynamically, so updating the DHCP server addresses might
be an issue in practice.
o Address Update in Scattered Configurations
- For devices that don't support parameterized configuration,
administrators need to individually update all devices in which
IP addresses were previously configured.
- It is hard to get all the address-relevant configurations
spread in various devices through one place.
- Uniformly updating configurations in multi-vendor devices is
currently a big gap that needs to be filled.
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9.4. Renumbering Event Management
o Renumbering Notification
- A mechanism to indicate a host's local recursive DNS is going
to be renumbered.
- A prior notice about a renumbering event for DNS.
- A mechanism for border routers to know internal partial
renumbering.
- For multihomed sites, a mechanism is needed to notify the
egress router connecting to ISP A that the egress router
connecting to ISP B has initiated renumbering.
- A mechanism is needed for the NMS applications to learn the
renumbering event, so that they could correlate the old and new
addresses in the logs, and update the unique ID of the device
and address mappings.
o Synchronization Management
- DNS information propagation latency issue.
- Mechanisms are needed for the NMS applications to correlate the
old and new addresses in logs and to update the unique ID of
the device and address mappings.
o Renumbering Monitoring
- Mechanisms to monitor the process and feedback of renumbering
might be needed.
9.5. Miscellaneous
o Multicast
- A mechanism for SSM receivers to learn the source addresses
when multicast sources are renumbered.
o Mobility
- A better mechanism to handle a change of home agent address
while the mobile address is disconnected.
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10. Gaps Considered Unsolvable
This section lists gaps that have been identified by other documents
but are considered unsolvable.
10.1. Address Configuration
o RA Prefix Lifetime Limitation
Section 5.5.3 of [RFC4862] states "If the received Valid Lifetime
is greater than 2 hours or greater than RemainingLifetime, set the
valid lifetime of the corresponding address to the advertised
Valid Lifetime." So when renumbering, if the previous
RemainingLifetime is longer than two hours, it is impossible to
reduce a prefix's lifetime to less than two hours. This
limitation is to prevent denial-of-service attacks.
10.2. Address-Relevant Entries Update
o DNS Authority
In an enterprise that hosts servers on behalf of collaborators and
customers, it is often the case that DNS zones outside the
administrative control of the hosting enterprise maintain resource
records concerning addresses for hosted nodes within its address
space. When the hosting enterprise renumbers, it does not have
sufficient authority to change those records.
This is an operational and policy issue. It is out of scope for
this document to consider a technical solution or to propose an
additional protocol or mechanism to standardize the interaction
between DNS systems for authority negotiations.
o DNS Entries
DNS entries commonly have matching reverse DNS entries that will
also need to be updated during renumbering. It might not be
possible to combine forward and reverse DNS entry updates in one
procedure where addresses are not being managed using DHCP.
o DNS Data Structure Optimization
[RFC2874] proposed an A6 record type for DNS recording of the IPv6
address and prefix. Several extensions to DNS query and
processing were also proposed. A6 was designed to be a
replacement for the AAAA record. The changes were designed to
facilitate network renumbering and multihoming. With the A6
record and the extensions, an IPv6 address could be defined by
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using multiple DNS records. This feature would increase the
complexity of resolvers but reduce the cost of zone file
maintenance, so renumbering could be easier than with the AAAA
record.
[RFC2874] has been deprecated and moved to Historic status by
[RFC6563]. The A6 record has not been widely used and has been
shown to have various problems and disadvantages (see Section 2 in
[RFC6563]). The idea of a structured record to separate prefix
and suffix is still potentially valuable for renumbering, but
avoiding the problems of the A6 record would require a major
development effort.
10.3. Miscellaneous
o For the transport layer, [RFC5887] said that TCP connections and
UDP flows are rigidly bound to a given pair of IP addresses.
o For the application layer, in general, we can assert that any
implementation is at risk from renumbering if it does not check
whether an address is valid each time it starts session resumption
(e.g., a laptop wakes from sleep state). It is also more or less
risky when it opens a new communications session by using cached
addresses.
We considered the above two points (ID/Locator overloading in
transport layer and address caching in application layer) fundamental
issues that might not be proper to deal with just in terms of
renumbering.
11. Security Considerations
o Prefix Validation
Prefixes from the ISP may need authentication to prevent prefix
fraud. Announcing changes of site prefix to other sites (for
example, those that configure routers or VPNs to point to the site
in question) also needs validation.
In the LAN, Secure DHCPv6 [SECURE-DHCPv6] or Secure Neighbor
Discovery (SEND) [RFC3971] deployment may be needed to validate
prefixes.
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o Influence on Security Controls
During renumbering, security controls (e.g., ACLs) protecting
legitimate resources should not be interrupted. For example, if
some addresses are in a blacklist, they should not escape from the
blacklist due to renumbering.
Addresses in SEND certificates will need to get updated when
renumbering. During the overlap between old and new addresses,
both certificates must remain valid.
o Security Protection for Renumbering Notification
Section 7.1 mentions possible notification mechanisms to signal a
change in the DNS system or in the border routers related to a
renumbering event. Since the DNS system and border routers are
key elements in any network, and they might take action according
to the notification, a security authentication for the renumbering
notification is needed.
o Security Protection for Configuration Update
Automated configuration update approaches like [LEROY] would
increase the risk since a bad actor with the right permission
could cause havoc to the networks.
12. Acknowledgments
This work adopts significant amounts of content from [RFC5887]. In
addition, it draws largely from the "DNS Authority" topic in Section
10.2 from [IPv6-RENUM-THINK]. Both documents offer such important
input for this work that some principles and considerations applied
in this work are implicitly inherited from them. So thanks go to
Randall Atkinson, Hannu Flinck, Tim Chown, Mark Thompson, and Alan
Ford. Some useful materials were provided by Oliver Bonaventure and
his student, Damien Leroy.
Many useful comments and contributions were made by Ted Lemon, Lee
Howard, Robert Sparks, S. Moonesamy, Fred Baker, Sean Turner, Benoit
Claise, Stephen Farrell, Brian Haberman, Joel Jaeggli, Eric Vyncke,
Phillips Matthew, Benedikt Stockebrand, Gustav Reinsberger, Teco
Boot, and other members of the 6renum WG.
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13. References
13.1. Normative References
[RFC3007] Wellington, B., "Secure Domain Name System (DNS) Dynamic
Update", RFC 3007, November 2000.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
13.2. Informative References
[RFC2072] Berkowitz, H., "Router Renumbering Guide", RFC 2072,
January 1997.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP
Source Address Spoofing", BCP 38, RFC 2827, May 2000.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC2874] Crawford, M. and C. Huitema, "DNS Extensions to Support
IPv6 Address Aggregation and Renumbering", RFC 2874, July
2000.
[RFC2894] Crawford, M., "Router Renumbering for IPv6", RFC 2894,
August 2000.
[RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
Multicast Addresses", RFC 3306, August 2002.
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[RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous
Point (RP) Address in an IPv6 Multicast Address", RFC
3956, November 2004.
[RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for
Renumbering an IPv6 Network without a Flag Day", RFC
4192, September 2005.
[RFC4704] Volz, B., "The Dynamic Host Configuration Protocol for
IPv6 (DHCPv6) Client Fully Qualified Domain Name (FQDN)
Option", RFC 4704, October 2006.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J.,
Ed., and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, June 2011.
[RFC4984] Meyer, D., Ed., Zhang, L., Ed., and K. Fall, Ed., "Report
from the IAB Workshop on Routing and Addressing", RFC
4984, September 2007.
[RFC5887] Carpenter, B., Atkinson, R., and H. Flinck, "Renumbering
Still Needs Work", RFC 5887, May 2010.
[RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
Support in IPv6", RFC 6275, July 2011.
[RFC6563] Jiang, S., Conrad, D., and B. Carpenter, "Moving A6 to
Historic Status", RFC 6563, March 2012.
[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version
6 (IPv6)", RFC 6724, September 2012.
[RFC6866] Carpenter, B. and S. Jiang, "Problem Statement for
Renumbering IPv6 Hosts with Static Addresses in
Enterprise Networks", RFC 6866, February 2013.
[RFC6879] Jiang, S., Liu, B., and B. Carpenter, "IPv6 Enterprise
Network Renumbering Scenarios, Considerations, and
Methods", RFC 6879, February 2013.
[6MAN-ADDR-OPT]
Matsumoto, A., Fujisaki T., and T. Chown, "Distributing
Address Selection Policy using DHCPv6", Work in Progress,
August 2013.
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RFC 7010 IPv6 Site Renumbering Gap Analysis September 2013
[6RENUM-SLAAC]
Liu, B., "DHCPv6/SLAAC Address Configuration Switching
for Host Renumbering", Work in Progress, January 2013.
[CFENGINE] CFEngine, <http://cfengine.com/what-is-cfengine>.
[DHCPv6-SLAAC]
Liu, B. and R. Bonica, "DHCPv6/SLAAC Address
Configuration Interaction Problem Statement", Work in
Progress, February 2013.
[IPv6-RENUM-THINK]
Chown, T., Thompson, M., Ford, A., and S. Venaas, "Things
to think about when Renumbering an IPv6 network", Work in
Progress, September 2006.
[LEROY] Leroy, D. and O. Bonaventure, "Preparing network
configurations for IPv6 renumbering", International of
Network Management, 2009, <http://inl.info.ucl.ac.be/
system/files/dleroy-nem-2009.pdf>
[PREFIX-DHCPv6]
Jiang, S., Xia, F., and B. Sarikaya, "Prefix Assignment
in DHCPv6", Work in Progress, February 2013.
[SECURE-DHCPv6]
Jiang, S. and Shen S., "Secure DHCPv6 Using CGAs", Work
in Progress, September 2012.
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Authors' Addresses
Bing Liu
Huawei Technologies Co., Ltd
Q14, Huawei Campus
No. 156 Beiqing Rd.
Hai-Dian District, Beijing 100095
P.R. China
EMail: leo.liubing@huawei.com
Sheng Jiang
Huawei Technologies Co., Ltd
Q14, Huawei Campus
No. 156 Beiqing Rd.
Hai-Dian District, Beijing 100095
P.R. China
EMail: jiangsheng@huawei.com
Brian Carpenter
Department of Computer Science
University of Auckland
PB 92019
Auckland, 1142
New Zealand
EMail: brian.e.carpenter@gmail.com
Stig Venaas
Cisco Systems
Tasman Drive
San Jose, CA 95134
United States
EMail: stig@cisco.com
Wesley George
Time Warner Cable
13820 Sunrise Valley Drive
Herndon, VA 20171
United States
Phone: +1 703-561-2540
EMail: wesley.george@twcable.com
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