draft-ietf-v6ops-design-choices-09.txt   draft-ietf-v6ops-design-choices-10.txt 
V6OPS Working Group P. Matthews V6OPS Working Group P. Matthews
Internet-Draft Alcatel-Lucent Internet-Draft Nokia
Intended status: Informational V. Kuarsingh Intended status: Informational V. Kuarsingh
Expires: April 21, 2016 Cisco Expires: April 17, 2017 Cisco
October 19, 2015 October 14, 2016
Some Design Choices for IPv6 Networks Some Design Choices for IPv6 Networks
draft-ietf-v6ops-design-choices-09 draft-ietf-v6ops-design-choices-10
Abstract Abstract
This document presents advice on certain routing-related design This document presents advice on certain routing-related design
choices that arise when designing IPv6 networks (both dual-stack and choices that arise when designing IPv6 networks (both dual-stack and
IPv6-only). The intended audience is someone designing an IPv6 IPv6-only). The intended audience is someone designing an IPv6
network who is knowledgeable about best current practices around IPv4 network who is knowledgeable about best current practices around IPv4
network design, and wishes to learn the corresponding practices for network design, and wishes to learn the corresponding practices for
IPv6. IPv6.
skipping to change at page 1, line 36 skipping to change at page 1, line 36
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 21, 2016. This Internet-Draft will expire on April 17, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Design Choices . . . . . . . . . . . . . . . . . . . . . . . 3 2. Design Choices . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Addresses . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Addresses . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1. Choice of Addresses in the Core . . . . . . . . . . . 3 2.2. Interfaces . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Interfaces . . . . . . . . . . . . . . . . . . . . . . . 7 2.2.1. Mix IPv4 and IPv6 on the Same Layer-3 Interface? . . 3
2.2.1. Mix IPv4 and IPv6 on the Same Layer-3 Interface? . . 7 2.2.2. Interfaces with Only Link-Local Addresses? . . . . . 4
2.2.2. Interfaces with Only Link-Local Addresses? . . . . . 8 2.3. Static Routes . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Static Routes . . . . . . . . . . . . . . . . . . . . . . 9 2.3.1. Link-Local Next-Hop in a Static Route? . . . . . . . 6
2.3.1. Link-Local Next-Hop in a Static Route? . . . . . . . 9 2.4. IGPs . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4. IGPs . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.4.1. IGP Choice . . . . . . . . . . . . . . . . . . . . . 7
2.4.1. IGP Choice . . . . . . . . . . . . . . . . . . . . . 10 2.4.2. IS-IS Topology Mode . . . . . . . . . . . . . . . . . 10
2.4.2. IS-IS Topology Mode . . . . . . . . . . . . . . . . . 12 2.4.3. RIP / RIPng . . . . . . . . . . . . . . . . . . . . . 11
2.4.3. RIP . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.5. BGP . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.5. BGP . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.5.1. Which Transport for Which Routes? . . . . . . . . . . 12
2.5.1. Which Transport for Which Routes? . . . . . . . . . . 13 2.5.1.1. BGP Sessions for Unlabeled Routes . . . . . . . . 13
2.5.1.1. BGP Sessions for Unlabeled Routes . . . . . . . . 15 2.5.1.2. BGP sessions for Labeled or VPN Routes . . . . . 14
2.5.1.2. BGP sessions for Labeled or VPN Routes . . . . . 16 2.5.2. eBGP Endpoints: Global or Link-Local Addresses? . . . 14
2.5.2. eBGP Endpoints: Global or Link-Local Addresses? . . . 16 3. General Observations . . . . . . . . . . . . . . . . . . . . 16
3. General Observations . . . . . . . . . . . . . . . . . . . . 17 3.1. Use of Link-Local Addresses . . . . . . . . . . . . . . . 16
3.1. Use of Link-Local Addresses . . . . . . . . . . . . . . . 17 3.2. Separation of IPv4 and IPv6 . . . . . . . . . . . . . . . 16
3.2. Separation of IPv4 and IPv6 . . . . . . . . . . . . . . . 18 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
5. Security Considerations . . . . . . . . . . . . . . . . . . . 19 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19 7. Informative References . . . . . . . . . . . . . . . . . . . 18
7. Informative References . . . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction 1. Introduction
This document discusses foundational choices that arise when This document discusses routing-related design choices that arise
designing a IPv6-only or dual-stack network. The focus is on routing when designing a Pv6-only or dual-stack network. The focus is on
related design choices that are not normally addressed when designing choices that do not come up when designing an IPv4-only network. The
an IPv4-only network. The document presents each topic area along document presents each choice and the alternatives, and then
with the most common design choices along with the pros and cons of discusses the pros and cons of the alternatives in detail. Where
each choice (or alternative) in detail. Where consensus currently consensus currently exists around the best practice, this is
exists around the best practice, this is documented; otherwise the documented; otherwise the document simply summarizes the current
document simply summarizes the current state of the discussion. Thus state of the discussion. Thus this document serves to both document
this document serves to both document the reasoning behind the best the reasoning behind best current practices for IPv6, and to allow a
current practices for IPv6, and to allow a designer to make an designer to make an informed choice where no such consensus exists.
informed choice where no such consensus exists.
The design choices presented apply to both Service Provider and The design choices presented apply to both Service Provider and
Enterprise network environments. The design areas with the relative Enterprise network environments. Where choices have selection
choices are not specific to Service Provider or Enterprise networks, criteria which differ between the Service Provider and the Enterprise
but the designer should be aware of their network requirements to environment, this is noted. The designer is encouraged to ensure
best utilize the guidance or choice selection which may differ in that they familiarize themselves with any of the discussed
each of these general network environments. Where specific choices technologies to ensure the best selection is made for their
have selection criteria or analysis requirements which may differ environment.
between a Service Provider or Enterprise environment, that will be
noted in the text. The designer is encouraged to ensure that they
familiarize themselves with any of the discussed technologies to
ensure the best selection is made for their environment.
This document does not present advice on strategies for adding IPv6 This document does not present advice on strategies for adding IPv6
to a network, nor does it discuss transition in these areas, see to a network, nor does it discuss transition in these areas, see
[RFC6180] for general advice,[RFC6782] for wireline service [RFC6180] for general advice,[RFC6782] for wireline service
providers, [RFC6342]for mobile network providers, [RFC5963] for providers, [RFC6342]for mobile network providers, [RFC5963] for
exchange point operators, [RFC6883] for content providers, and both exchange point operators, [RFC6883] for content providers, and both
[RFC4852] and [RFC7381] for enterprises. Nor does this document [RFC4852] and [RFC7381] for enterprises. Nor does this document
discuss the particulars of creating an IPv6 addressing plan; for discuss the particulars of creating an IPv6 addressing plan; for
advice in this area, see [RFC5375] or [v6-addressing-plan]. The advice in this area, see [RFC5375] or [v6-addressing-plan]. The
details of ULA usage is also not discussed; for this the reader is details of ULA usage is also not discussed; for this the reader is
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2. Design Choices 2. Design Choices
Each subsection below presents a design choice and discusses the pros Each subsection below presents a design choice and discusses the pros
and cons of the various options. If there is consensus in the and cons of the various options. If there is consensus in the
industry for a particular option, then the consensus position is industry for a particular option, then the consensus position is
noted. noted.
2.1. Addresses 2.1. Addresses
2.1.1. Choice of Addresses in the Core TBD
One of the first choices a network designer needs to make is the type
of IPv6 addresses to be used in the network core. IPv6, unlike IPv4,
introduces new addressing techniques and concepts, as introduced in
[RFC4291] which requires specific attention. The introduction of
concepts such as using multiple-addresses per interface or the
introduction of linked scoped address-types like Link-Local, mean the
designer needs to think beyond the constraints of IPv4. There are
also operational considerations as with the concept of a provider
assign PA (Provider Aggregatable assigned via upstream provider)
versus a Regional Internet Registry assigned PI (Provider Independent
assigned from Registry) address type.
At the time of writing, there are still some known operational issues
with IPv6 deployments which expose near term deployments to
functional or operational gaps that may one day be eliminated. Once
such gap is host address selection challenges as noted in [RFC5220]
and renumbering challenges as described in [RFC6879] and [RFC7010].
Within this document, Unique Local Addresses (ULA) [RFC4193] are
likened to [RFC1918] addresses from an operational perspective.
Although ULAs are not architecturally similar to [RFC1918] private
addresses, the reasons for selecting them, and the challenge that may
arise if they are the only address type available to achieve external
network connectivity are similar. "Private" in this document refers
to the nature that ULAs would be typically used for internal
communications only, or externally with assistance from technologies
like NAT, given the addresses are not routed directly with external
networks.
A related choice is whether to use only link-local addresses on
certain links. That choice is discussed later in the document; this
section is about those addresses that must be visible throughout the
network.
The following table lists the main options available.
+---------+------------+---------------------+----------------------+
| GRT | End-User | ISP | Enterprise |
| Address | Traffic | | |
| Type | | | |
+---------+------------+---------------------+----------------------+
| | | | |
+---------+------------+---------------------+----------------------+
| PI | Hop-by-hop | Works | Works |
+---------+------------+---------------------+----------------------+
| PI | Tunneled | Works. Using | Works. Using private |
| | | private space | space likely a |
| | | likely a better | better option. |
| | | option. | |
+---------+------------+---------------------+----------------------+
| PA | Hop-by-hop | Works | Works |
+---------+------------+---------------------+----------------------+
| PA | Tunneled | Works. Using | Works. Using private |
| | | private addresses | addresses likely |
| | | likely better | better option. |
| | | option. | |
+---------+------------+---------------------+----------------------+
| Private | Hop-by-hop | Will likely cause | Works. Careful |
| | | problems. See | consideration due to |
| | | discussion below. | NAT implications. |
+---------+------------+---------------------+----------------------+
| Private | Tunneled | Works | Works |
+---------+------------+---------------------+----------------------+
As the table indicates, there are three options for the type of
addresses a network designer can use in the network core:
o PI - Globally-unique IPv4 or IPv6 addresses obtained directly from
an address registry. An organization which has such addresses is
considered to have "its own" address space.
o PA - Globally-unique IPv4 or IPv6 addresses obtained from an
upstream provider. Such addresses must be returned if the
relationship with the upstream provider ceases.
o Private - Either IPv4 addresses as per [RFC1918] or unique-local
IPv6 addresses [RFC4193].
In all cases, we are talking about the type of addresses used in the
GRT context (Global Routing Table aka base router). If end-user
traffic is routed hop-by-hop through the network based on the
destination address in the IP header, then this context is visible to
the end-user. However, if all end-user traffic is tunneled through
the core (for example, using MPLS) then this context is not visible
to the end-user.
First, consider the case where at least some end-user traffic is
routed hop-by-hop. In this case, the use of PI space is the best
option, as it gives the most flexibility in the future. However,
some organizations may be unable or unwilling to obtain PI space - in
this case PA space is the next-best choice. For an ISP, the use of
private address space is problematic - see [RFC6752] for a
discussion. For an enterprise, the use of private address space is
an option and may be seen as favourable operationally, but should
only be used after careful consideration of the technological
drawbacks. If ULAs are the only non-Link-Local address available the
hosts, the enterprise will need to use translation technologies such
as NPT[RFC6296] or NAT66 to reach the Internet. If the network has
no connection to the Internet, or the hosts only assigned a ULA do
not need external connectivity, then this limitation is not a
problem.
Now consider the case where all end-user traffic is tunneled through
the core and thus the core is not visible to other networks. In this
case, the use of private addresses in the core is the most reasonable
and re-enforces the desire that these addresses have limited
visibility. The use of PI space is the next-best option - two
reasons for selecting this option is to provide flexibility in case
some traffic needs to be carried hop-by-hop in the future and to be
absolutely sure that there are no address conflicts. Getting IPv4 PI
space at this time will be difficult, but IPv6 PI space is fairly
easy.
The use of PA space is likely a poor option for many organizations
since these networks are connected to more then one upstream provider
and/or may need flexibility on how Internet reachability needs to be
managed. Using PA space subjects the end network to possible
reclamation of address space in the future, which requires a
renumbering activity.
Not shown in the table above are combinations of the basic options.
An example of a combination is using both PA and ULA address space in
the hop-by-hop enterprise case or multiple PA and/or PI addresses.
Combinations can reduce the magnitude of the deficiency with a basic
option, but does not eliminate it completely. For example, using PA
+ ULA for the hop-by-hop enterprise case reduces the amount of
renumbering required when changing providers compared with the pure
PA case, but does not eliminate it completely. Additional work
analyzing the opportunities for using multiple addresses and
overcoming limitations can be found in
[I-D.ietf-v6ops-host-addr-availability].
2.2. Interfaces 2.2. Interfaces
2.2.1. Mix IPv4 and IPv6 on the Same Layer-3 Interface? 2.2.1. Mix IPv4 and IPv6 on the Same Layer-3 Interface?
If a network is going to carry both IPv4 and IPv6 traffic, as many If a network is going to carry both IPv4 and IPv6 traffic, as many
networks do today, then a fundamental question arises: Should an networks do today, then a question arises: Should an operator mix
operator mix IPv4 and IPv6 traffic or keep them separated? More IPv4 and IPv6 traffic or keep them separated? More specifically,
specifically, should the design: should the design:
a. Mix IPv4 and IPv6 traffic on the same layer-3 interface, OR a. Mix IPv4 and IPv6 traffic on the same layer-3 interface, OR
b. Separate IPv4 and IPv6 by using separate interfaces (e.g., two b. Separate IPv4 and IPv6 by using separate interfaces (e.g., two
physical links or two VLANs on the same link)? physical links or two VLANs on the same link)?
Option (a) implies a single layer-3 interface at each end of the Option (a) implies a single layer-3 interface at each end of the
connection with both IPv4 and IPv6 addresses; while option (b) connection with both IPv4 and IPv6 addresses; while option (b)
implies two layer-3 interfaces at each end, one for IPv4 addresses implies two layer-3 interfaces at each end, one for IPv4 addresses
and one with IPv6 addresses. and one with IPv6 addresses.
The advantages of option (a) include: The advantages of option (a) include:
o Requires only half as many layer 3 interfaces as option (b), thus o Requires only half as many layer 3 interfaces as option (b), thus
providing better scaling; providing better scaling;
o May require fewer physical ports, thus saving money; o May require fewer physical ports, thus saving money and
simplifying operations;
o Can make the QoS implementation much easier (for example, rate- o Can make the QoS implementation much easier (for example, rate-
limiting the combined IPv4 and IPv6 traffic to or from a limiting the combined IPv4 and IPv6 traffic to or from a
customer); customer);
o Works well in practice, as any increase in IPv6 traffic is usually o Works well in practice, as any increase in IPv6 traffic is usually
counter-balanced by a corresponding decrease in IPv4 traffic to or counter-balanced by a corresponding decrease in IPv4 traffic to or
from the same host (ignoring the common pattern of an overall from the same host (ignoring the common pattern of an overall
increase in Internet usage); increase in Internet usage);
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support today for individual statistics on IPv4 traffic vs IPv6 support today for individual statistics on IPv4 traffic vs IPv6
traffic when option (a) is used. Other, device-specific, limitations traffic when option (a) is used. Other, device-specific, limitations
exist as well. It is expected that these limitations will go away as exist as well. It is expected that these limitations will go away as
support for IPv6 matures, making option (b) less and less attractive support for IPv6 matures, making option (b) less and less attractive
until the day that IPv4 is finally turned off. until the day that IPv4 is finally turned off.
2.2.2. Interfaces with Only Link-Local Addresses? 2.2.2. Interfaces with Only Link-Local Addresses?
As noted in the introduction, this document does not cover the ins As noted in the introduction, this document does not cover the ins
and outs around creating an IPv6 addressing plan. However, there is and outs around creating an IPv6 addressing plan. However, there is
one fundamental question in this area that often arises: Should an one question in this area that often arises: Should an interface:
interface:
a. Use only a link-local address ("link-local-only"), OR a. Use only a link-local address ("link-local-only"), OR
b. Have global and/or unique-local addresses assigned in addition to b. Have global and/or unique-local addresses assigned in addition to
the link-local? the link-local?
There are two advantages in interfaces with only link-local addresses There are two advantages in interfaces with only link-local addresses
("link-local-only interfaces"). The first advantage is ease of ("link-local-only interfaces"). The first advantage is ease of
configuration. In a network with a large number of link-local-only configuration. In a network with a large number of link-local-only
interfaces, the operator can just enable an IGP on each router, interfaces, the operator can just enable an IGP on each router,
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2.4.1. IGP Choice 2.4.1. IGP Choice
One of the main decisions for a network operator looking to deploy One of the main decisions for a network operator looking to deploy
IPv6 is the choice of IGP (Interior Gateway Protocol) within the IPv6 is the choice of IGP (Interior Gateway Protocol) within the
network. The main options are OSPF, IS-IS and EIGRP. RIPng is network. The main options are OSPF, IS-IS and EIGRP. RIPng is
another option, but very few networks run RIP in the core these days, another option, but very few networks run RIP in the core these days,
so it is covered in a separate section below. so it is covered in a separate section below.
OSPF [RFC2328] [RFC5340] and IS-IS [RFC5120][RFC5120] are both OSPF [RFC2328] [RFC5340] and IS-IS [RFC5120][RFC5120] are both
standardized and link-state protocols. Standardized means they are standardized link-state protocols. Both protocols are widely
widely supported by vendors, while link-state means amongst other supported by vendors, and both are widely deployed. By contrast,
things that they can support RSVP-TE, which is widely used for MPLS EIGRP [ref] is a Cisco proprietary distance-vector protocol. EIGRP
signaling. Both of these protocols are widely deployed. By is rarely deployed in service-provider networks, but is quite common
contrast, EIGRP [ref] is a proprietary distance-vector protocol. in enterprise networks, which is why it is discussed here.
EIGRP is rarely deployed in service-provider networks, but is quite
common in enterprise networks. It is out of scope for this document to describe all the differences
between the three protocols; the interested reader can find books and
websites that go into the differences in quite a bit of detail.
Rather, this document simply highlights a few differences that can be
important to consider when designing IPv6 or dual-stack networks.
Versions: There are two versions of OSPF: OSPFv2 and OSPFv3. The two
versions share many concepts, are configured in a similar manner and
seem very similar to most casual users, but have very different
packet formats and other "under the hood" differences. The most
important difference is that OSPFv2 will only route IPv4, while
OSPFv3 will route both IPv4 and IPv6. OSPFv2 was by far the most
widely deployed version of OSPF when this document was published. By
contrast, both IS-IS and EIGRP have just a single version, which can
route both IPv4 and IPv6.
Transport. IS-IS runs over layer 2 (e.g. Ethernet). This means
that the functioning of IS-IS has no dependencies on the IP layer: if
there is a problem at the IP layer (e.g. bad addresses), two routers
can still exchange IS-IS packets. By contrast, OSPF and EIGRP both
run over the IP layer. This means that the IP layer must be
configured and working OSPF or EIGRP packets to be exchanged between
routers. For EIGRP, the dependency on the IP layer is simple: EIGRP
for IPv4 runs over IPv4, while EIGRP for IPv6 runs over IPv6. For
OSPF, the story is more complex: OSPFv2 runs over IPv4, but OSPFv3
can run over either IPv4 or IPv6. Thus it is possible to route both
IPv4 and IPv6 with OSPFv3 running over IPv6 or with OSPFv3 running
over IPv4. This means that there are number of choices for how to
run OSPF in a dual-stack network:
o Use OSPFv2 for routing IPv4 , and OSPFv3 running over IPv6 for
routing IPv6, OR
o Use OSPFv3 running over IPv6 for routing both IPv4 and IPv6, OR
o Use OSPFv3 running over IPv4 for routing both IPv4 and IPv6.
Summarization and MPLS: For most casual users, the three protocols
are fairly similar in what they can do, with two glaring exceptions:
summarization and MPLS. For summarization, both OSPF and IS-IS have
the concept of summarization between areas, but the two area concepts
are quite different, and an area design that works for one protocol
will usually not work for the other. EIGRP has no area concept, but
has the ability to summarize at any router. Thus a large network
will typically have a very different OSPF, IS-IS and EIGRP designs,
which is important to keep in mind if you are planning on using one
protocol to route IPv4 and a different protocol for IPv6. The other
difference is that OSPF and IS-IS both support RSVP-TE, a widely-used
MPLS signaling protocol, while EIGRP does not: this is due to OSPF
and IS-IS both being link-state protocols while EIGRP is a distance-
vector protocol.
The table below sets out possible combinations of protocols to route The table below sets out possible combinations of protocols to route
both IPv4 and IPv6, and makes some observations on each combination. both IPv4 and IPv6, and makes some observations on each combination.
Here "EIGRP-v4" means "EIGRP for IPv4" and similarly for "EIGRP-v6".
For OSPFv3, it is possible to run it over either IPv4 or IPv6; this
is not indicated in the table.
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
| IGP for | IGP for | Multiple | Protocol | Similar | | IGP for | IGP for | Protocol | Similar | Multiple |
| IPv4 | IPv6 | Known | separation | configuration | | IPv4 | IPv6 | separation | configuration | Known |
| | | Deployments | | possible | | | | | possible | Deployments |
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
| | | | | | | | | | | |
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
| OSPFv2 | OSPFv3 | YES (8) | YES | YES | | OSPFv2 | OSPFv3 | YES | YES | YES (8) |
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
| OSPFv2 | IS-IS | YES (3) | YES | - | | OSPFv2 | IS-IS | YES | - | YES (3) |
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
| OSPFv2 | EIGRP | - | YES | - | | OSPFv2 | EIGRP-v6 | YES | - | - |
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
| OSPFv3 | IS-IS | - | YES | - | | OSPFv3 | IS-IS | YES | - | - |
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
| OSPFv3 | EIGRP | - | YES | - | | OSPFv3 | EIGRP-v6 | YES | - | - |
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
| IS-IS | OSPFv3 | YES (2) | YES | - | | IS-IS | OSPFv3 | YES | - | YES (2) |
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
| IS-IS | IS-IS | YES (12) | - | YES | | IS-IS | IS-IS | - | YES | YES (12) |
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
| IS-IS | EIGRP | - | YES | - | | IS-IS | EIGRP-v6 | YES | - | - |
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
| EIGRP | OSPFv3 | ? (1) | YES | - | | EIGRP-v4 | OSPFv3 | YES | - | ? (1) |
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
| EIGRP | IS-IS | - | YES | - | | EIGRP-v4 | IS-IS | YES | - | - |
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
| EIGRP | EIGRP | ? (2) | - | YES | | EIGRP-v4 | EIGRP-v6 | - | YES | ? (2) |
+---------+---------+---------------+-------------+-----------------+ +----------+----------+-------------+----------------+--------------+
In the column "Multiple Known Deployments", a YES indicates that a In the column "Multiple Known Deployments", a YES indicates that a
significant number of production networks run this combination, with significant number of production networks run this combination, with
the number of such networks indicated in parentheses following, while the number of such networks indicated in parentheses following, while
a "?" indicates that the authors are only aware of one or two small a "?" indicates that the authors are only aware of one or two small
networks that run this combination. Data for this column was networks that run this combination. Data for this column was
gathered from an informal poll of operators on a number of mailing gathered from an informal poll of operators on a number of mailing
lists. This poll was not intended to be a thorough scientific study lists. This poll was not intended to be a thorough scientific study
of IGP choices, but to provide a snapshot of known operator choices of IGP choices, but to provide a snapshot of known operator choices
at the time of writing (Mid-2015) for successful production dual at the time of writing (Mid-2015) for successful production dual
skipping to change at page 12, line 33 skipping to change at page 10, line 29
IGP for quite a few years, but have selected IS-IS as their IPv6 IGP. IGP for quite a few years, but have selected IS-IS as their IPv6 IGP.
However, there are very few (none?) that have made the reverse However, there are very few (none?) that have made the reverse
choice. This is, in part, because routers generally support more choice. This is, in part, because routers generally support more
nodes in an IS-IS area than in the corresponding OSPF area, and nodes in an IS-IS area than in the corresponding OSPF area, and
because IS-IS is seen as more secure because it runs at layer 2. because IS-IS is seen as more secure because it runs at layer 2.
2.4.2. IS-IS Topology Mode 2.4.2. IS-IS Topology Mode
When IS-IS is used to route both IPv4 and IPv6, then there is an When IS-IS is used to route both IPv4 and IPv6, then there is an
additional choice of whether to run IS-IS in single-topology or additional choice of whether to run IS-IS in single-topology or
multi-topology mode. Single-topology mode allows IPv4 and IPv6 to multi-topology mode.
share a single topology and a single set of link costs[RFC5308].
Multi-topology mode allows separate IPv4 and IPv6 topologies with With single-topology mode (also known as Native mode) [RFC5308]:
potentially different link costs.
o IS-IS keeps a single link-state database for both IPv4 and IPv6.
o There is a single set of link costs which apply to both IPv4 and
IPv6.
o All links in the network must support both IPv4 and IPv6, as the
calculation of routes does not take this into account. If some
links do not support IPv6 (or IPv4), then packets may get routed
across links where support is lacking and get dropped. This can
cause problems if some network devices do not support IPv6 (or
IPv4).
o It is also important to keep the previous point in mind when
adding or removing support for either IPv4 or IPv6.
With multi-topology mode [ref]:
o IS-IS keeps two link-state databases, one for IPv4 and one for
IPv6.
o IPv4 and IPv6 can have separate link metrics. Note that most
implementations today require separate link metrics: a number of
operators have rudely discovered that they have forgotten to
configure the IPv6 metric until sometime after deploying IPv6 in
multi-topology mode!
o Some links can be IPv4-only, some IPv6-only, and some dual-stack.
Routes to IPv4 and IPv6 addresses are computed separately and may
take different paths even if the addresses are located on the same
remote device.
o The previous point may help when adding or removing support for
either IPv4 or IPv6.
In the informal poll of operators, out of 12 production networks that In the informal poll of operators, out of 12 production networks that
ran IS-IS for both IPv4 and IPv6, 6 used Single Topology mode, 4 used ran IS-IS for both IPv4 and IPv6, 6 used single topology mode, 4 used
Multi-Topology mode, and 2 did not specify. One motivation often multi-topology mode, and 2 did not specify. One motivation often
cited by then operators for using Single Topology mode was because cited by then operators for using Single Topology mode was because
some device did not support multi-topology mode. some device did not support multi-topology mode.
Traditional thinking has been that multi-topology mode offers the When asked, many people feel multi-topology mode is superior to
most flexibility. Never-the-less, as shown by the poll results, a single-topology mode because it provides greater flexibility at
minimal extra cost. Never-the-less, as shown by the poll results, a
number of operators have used single-topology mode successfully. number of operators have used single-topology mode successfully.
2.4.3. RIP Note that this issue does not come up with OSPF, since there is
nothing that corresponds to IS-IS single-topology mode with OSPF.
A protocol option not described in the table above is RIPng 2.4.3. RIP / RIPng
[RFC2080]. RIPng is a distance vector protocol with limitations in
larger networks. However there is prevalent use case in large A protocol option not described in the table above is RIP for IPv4
operator networks where RIP is used for edge facing core interfaces and RIPng for IPv6 [RFC2080]. These are distance vector protocols
to manage high count aggregation of dynamic routing endpoints. that are almost universally considered to be inferior to OSPF, IS-IS,
Although not a mainline option for the network core as a whole, it is or EIGRP for general use.
commonly used in IPv4, and potentially in IPv6 for a common set of
links/functions. However, there is one specialized use where RIP/RIPng is still
considered to be appropriate: in star topology networks where a
single core device has lots and lots of links to edge devices and
each edge device has only a single path back to the core. In such
networks, the single path means that the limitations of RIP/RIPng are
mostly not relevant and the very light-weight nature of RIP/RIPng
gives it an advantage over the other protocols mentioned above. One
concrete example of this scenario is the use of RIP/RIPng between
cable modems and the CMTS.
2.5. BGP 2.5. BGP
2.5.1. Which Transport for Which Routes? 2.5.1. Which Transport for Which Routes?
BGP these days is multi-protocol. It can carry routes from many BGP these days is multi-protocol. It can carry routes from many
different families, and it can do this when the BGP session, or more different families, and it can do this when the BGP session, or more
accurately the underlying TCP connection, runs over either IPv4 or accurately the underlying TCP connection, runs over either IPv4 or
IPv6 (here referred to as either "IPv4 transport" or "IPv6 IPv6 (here referred to as either "IPv4 transport" or "IPv6
transport"). Given this flexibility, one of the biggest questions transport"). Given this flexibility, one of the biggest questions
skipping to change at page 20, line 18 skipping to change at page 18, line 29
Scudder, J., Appanna, C., and I. Varlashkin, "Multisession Scudder, J., Appanna, C., and I. Varlashkin, "Multisession
BGP", draft-ietf-idr-bgp-multisession-07 (work in BGP", draft-ietf-idr-bgp-multisession-07 (work in
progress), September 2012. progress), September 2012.
[I-D.ietf-idr-dynamic-cap] [I-D.ietf-idr-dynamic-cap]
Ramachandra, S. and E. Chen, "Dynamic Capability for BGP- Ramachandra, S. and E. Chen, "Dynamic Capability for BGP-
4", draft-ietf-idr-dynamic-cap-14 (work in progress), 4", draft-ietf-idr-dynamic-cap-14 (work in progress),
December 2011. December 2011.
[I-D.ietf-v6ops-host-addr-availability] [I-D.ietf-v6ops-host-addr-availability]
Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi, Colitti, L., Cerf, D., Cheshire, S., and d.
"Host address availability recommendations", draft-ietf- dschinazi@apple.com, "Host address availability
v6ops-host-addr-availability-01 (work in progress), recommendations", draft-ietf-v6ops-host-addr-
September 2015. availability-07 (work in progress), May 2016.
[I-D.ietf-v6ops-ula-usage-recommendations] [I-D.ietf-v6ops-ula-usage-recommendations]
Liu, B. and S. Jiang, "Considerations For Using Unique Liu, B. and S. Jiang, "Considerations For Using Unique
Local Addresses", draft-ietf-v6ops-ula-usage- Local Addresses", draft-ietf-v6ops-ula-usage-
recommendations-05 (work in progress), May 2015. recommendations-05 (work in progress), May 2015.
[ISO10589] [ISO10589]
International Standards Organization, "Intermediate system International Standards Organization, "Intermediate system
to Intermediate system intra-domain routeing information to Intermediate system intra-domain routeing information
exchange protocol for use in conjunction with the protocol exchange protocol for use in conjunction with the protocol
skipping to change at page 24, line 14 skipping to change at page 22, line 24
[v6-addressing-plan] [v6-addressing-plan]
SurfNet, "Preparing an IPv6 Address Plan", 2013, SurfNet, "Preparing an IPv6 Address Plan", 2013,
<http://www.ripe.net/lir-services/training/material/ <http://www.ripe.net/lir-services/training/material/
IPv6-for-LIRs-Training-Course/ IPv6-for-LIRs-Training-Course/
Preparing-an-IPv6-Addressing-Plan.pdf>. Preparing-an-IPv6-Addressing-Plan.pdf>.
Authors' Addresses Authors' Addresses
Philip Matthews Philip Matthews
Alcatel-Lucent Nokia
600 March Road 600 March Road
Ottawa, Ontario K2K 2E6 Ottawa, Ontario K2K 2E6
Canada Canada
Phone: +1 613-784-3139 Phone: +1 613-784-3139
Email: philip_matthews@magma.ca Email: philip_matthews@magma.ca
Victor Kuarsingh Victor Kuarsingh
Cisco Cisco
88 Queens Quay 88 Queens Quay
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