draft-ietf-v6ops-design-choices-07.txt   draft-ietf-v6ops-design-choices-08.txt 
V6OPS Working Group P. Matthews V6OPS Working Group P. Matthews
Internet-Draft Alcatel-Lucent Internet-Draft Alcatel-Lucent
Intended status: Informational V. Kuarsingh Intended status: Informational V. Kuarsingh
Expires: October 4, 2015 Dyn Expires: January 7, 2016 Dyn
April 2, 2015 July 6, 2015
Some Design Choices for IPv6 Networks Some Design Choices for IPv6 Networks
draft-ietf-v6ops-design-choices-07 draft-ietf-v6ops-design-choices-08
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
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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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 October 4, 2015. This Internet-Draft will expire on January 7, 2016.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Design Choices . . . . . . . . . . . . . . . . . . . . . . . 3 2. Design Choices . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Interfaces . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Addresses . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1. Mix IPv4 and IPv6 on the Same Layer-3 Interface? . . 3 2.1.1. Choice of Addresses in the Core . . . . . . . . . . . 3
2.1.2. Interfaces with Only Link-Local Addresses? . . . . . 4 2.2. Interfaces . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Static Routes . . . . . . . . . . . . . . . . . . . . . . 6 2.2.1. Mix IPv4 and IPv6 on the Same Layer-3 Interface? . . 5
2.2.1. Link-Local Next-Hop in a Static Route? . . . . . . . 6 2.2.2. Interfaces with Only Link-Local Addresses? . . . . . 6
2.3. IGPs . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.3. Static Routes . . . . . . . . . . . . . . . . . . . . . . 8
2.3.1. IGP Choice . . . . . . . . . . . . . . . . . . . . . 7 2.3.1. Link-Local Next-Hop in a Static Route? . . . . . . . 8
2.4. BGP . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.4. IGPs . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4.1. Which Transport for Which Routes? . . . . . . . . . . 8 2.4.1. IGP Choice . . . . . . . . . . . . . . . . . . . . . 9
2.4.1.1. BGP Sessions for Unlabeled Routes . . . . . . . . 10 2.4.2. IS-IS Topology Mode . . . . . . . . . . . . . . . . . 11
2.4.1.2. BGP sessions for Labeled or VPN Routes . . . . . 11 2.4.3. RIP . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4.2. eBGP Endpoints: Global or Link-Local Addresses? . . . 11 2.5. BGP . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3. General Observations . . . . . . . . . . . . . . . . . . . . 12 2.5.1. Which Transport for Which Routes? . . . . . . . . . . 12
3.1. Use of Link-Local Addresses . . . . . . . . . . . . . . . 12 2.5.1.1. BGP Sessions for Unlabeled Routes . . . . . . . . 13
3.2. Separation of IPv4 and IPv6 . . . . . . . . . . . . . . . 13 2.5.1.2. BGP sessions for Labeled or VPN Routes . . . . . 14
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 2.5.2. eBGP Endpoints: Global or Link-Local Addresses? . . . 14
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14 3. General Observations . . . . . . . . . . . . . . . . . . . . 16
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 3.1. Use of Link-Local Addresses . . . . . . . . . . . . . . . 16
7. Informative References . . . . . . . . . . . . . . . . . . . 15 3.2. Separation of IPv4 and IPv6 . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
7. Informative References . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction 1. Introduction
This document discusses certain choices that arise when designing a This document discusses certain choices that arise when designing a
IPv6-only or dual-stack network. The focus is on routing-related IPv6-only or dual-stack network. The focus is on routing-related
design choices that do not usually come up when designing an design choices that do not usually come up when designing an
IPv4-only network. The document presents each choice and the IPv4-only network. The document presents each choice and the
alternatives, and then discusses the pros and cons of the alternatives, and then discusses the pros and cons of the
alternatives in detail. Where consensus currently exists around the alternatives in detail. Where consensus currently exists around the
best practice, this is documented; otherwise the document simply best practice, this is documented; otherwise the document simply
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does not cover multicast or the issues involved in running MPLS over does not cover multicast or the issues involved in running MPLS over
IPv6 transport. IPv6 transport.
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. Interfaces 2.1. Addresses
2.1.1. Mix IPv4 and IPv6 on the Same Layer-3 Interface? 2.1.1. Choice of Addresses in the Core
One of the first choices a network designer needs to make is the type
of addresses to be used in the network core. Should the network use
provider-independent global addresses, "private" addresses (either
RFC 1918 addresses or unique-local addresses) or something else?
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 better |
| | | likely a 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. Will probably |
| | | problems. See | require some sort of |
| | | discussion below. | NAT on links to the |
| | | | Internet. |
+---------+------------+-------------------+------------------------+
| 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 RFC 1918 IPv4 addresses 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
reasonable, but the enterprise will need to use NAT44 and/or
NPT[RFC6296] on links to the Internet. If the network has no
connection to the Internet, then obviously this 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 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
ensure 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, since there is no short-term
advantage and a high likelihood of having to give back the address
space sometime in the future.
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. 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.
2.2. Interfaces
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 fundamental question arises: Should an
operator mix IPv4 and IPv6 traffic or keep them separated? More operator mix IPv4 and IPv6 traffic or keep them separated? More
specifically, should the design: specifically, 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:
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However, there can be times when option (b) is the pragmatic choice. However, there can be times when option (b) is the pragmatic choice.
Most commonly, option (b) is used to work around limitations in Most commonly, option (b) is used to work around limitations in
network equipment. One big example is the generally poor level of network equipment. One big example is the generally poor level of
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.
2.1.2. 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 fundamental 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,
without going through the tedious process of assigning and tracking without going through the tedious process of assigning and tracking
the addresses for each interface. The second advantage is security. the addresses for each interface. The second advantage is security.
Since packets with Link-Local destination addresses should not be Since packets with Link-Local destination addresses should not be
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links, or because an operator manually assigns the same easy-to-type links, or because an operator manually assigns the same easy-to-type
link-local address to multiple interfaces. All these are allowed in link-local address to multiple interfaces. All these are allowed in
IPv6 as long as the addresses are used on different links. IPv6 as long as the addresses are used on different links.
For more discussion on the pros and cons, see [RFC7404]. See also For more discussion on the pros and cons, see [RFC7404]. See also
[RFC5375] for IPv6 unicast address assignment considerations. [RFC5375] for IPv6 unicast address assignment considerations.
Today, most operators use interfaces with global or unique-local Today, most operators use interfaces with global or unique-local
addresses (option b). addresses (option b).
2.2. Static Routes 2.3. Static Routes
2.2.1. Link-Local Next-Hop in a Static Route? 2.3.1. Link-Local Next-Hop in a Static Route?
For the most part, the use of static routes in IPv6 parallels their For the most part, the use of static routes in IPv6 parallels their
use in IPv4. There is, however, one exception, which revolves around use in IPv4. There is, however, one exception, which revolves around
the choice of next-hop address in the static route. Specifically, the choice of next-hop address in the static route. Specifically,
should an operator: should an operator:
a. Use the far-end's link-local address as the next-hop address, OR a. Use the far-end's link-local address as the next-hop address, OR
b. Use the far-end's GUA/ULA address as the next-hop address? b. Use the far-end's GUA/ULA address as the next-hop address?
skipping to change at page 7, line 5 skipping to change at page 9, line 20
route is redistributed into another routing protocol. In these route is redistributed into another routing protocol. In these
cases, the above text from RFC 4861 notwithstanding, either a GUA or cases, the above text from RFC 4861 notwithstanding, either a GUA or
ULA must be used. ULA must be used.
Furthermore, many network operators are concerned about the Furthermore, many network operators are concerned about the
dependency of the default link-local address on an underlying MAC dependency of the default link-local address on an underlying MAC
address, as described in the previous section. address, as described in the previous section.
Today most operators use GUAs as next-hop addresses. Today most operators use GUAs as next-hop addresses.
2.3. IGPs 2.4. IGPs
2.3.1. IGP Choice 2.4.1. IGP Choice
One of the main decisions for an IPv6 implementer is the choice of One of the main decisions for a network operator looking to deploy
IGP (Interior Gateway Protocol) within the network. The primary IPv6 is the choice of IGP (Interior Gateway Protocol) within the
options are OSPF [RFC2328] [RFC5340] or IS-IS [RFC5120] [RFC5308], network. The main options are OSPF, IS-IS and EIGRP. RIP is another
though some operators may consider RIP [RFC2080] or non-standardized option, but very few networks run RIP in the core these days, so it
protocols. Here we limit our discussion to the pros and cons of OSPF is covered in a separate section below.
vs. IS-IS.
The discussion in this section revolves around the options in the OSPF [RFC2328] [RFC5340] and IS-IS [RFC5120][RFC5120] are both
table below: standardized and link-state protocols. Standardized means they are
widely supported by vendors, while link-state means amongst other
things that they can support RSVP-TE, which is widely used for MPLS
signaling. Both of these protocols are widely deployed. By
contrast, EIGRP [ref] is a proprietary distance-vector protocol.
EIGRP is rarely deployed in service-provider networks, but is quite
common in enterprise networks.
+--------+--------+---------+---------+------------+----------------+ +---------+---------+---------------+-------------+-----------------+
| Option | IGP | IGP for | Known | Hard | Similar | | IGP for | IGP for | Multiple | Protocol | Similar |
| | for | IPv6 | to work | separation | configuration | | IPv4 | IPv6 | Known | separation | configuration |
| | IPv4 | | well | | possible | | | | Deployments | | possible |
+--------+--------+---------+---------+------------+----------------+ +---------+---------+---------------+-------------+-----------------+
| | | | | | | | | | | | |
+--------+--------+---------+---------+------------+----------------+ +---------+---------+---------------+-------------+-----------------+
| a | IS-IS | IS-IS | YES | - | YES | | OSPFv2 | OSPFv3 | YES | YES | YES |
+--------+--------+---------+---------+------------+----------------+ +---------+---------+---------------+-------------+-----------------+
| b | IS-IS | OSPFv3 | - | YES | - | | OSPFv2 | IS-IS | YES | YES | - |
+--------+--------+---------+---------+------------+----------------+ +---------+---------+---------------+-------------+-----------------+
| | | | | | | | OSPFv2 | EIGRP | - | YES | - |
+--------+--------+---------+---------+------------+----------------+ +---------+---------+---------------+-------------+-----------------+
| c | OSPFv2 | IS-IS | YES | YES | - | | OSPFv3 | IS-IS | - | YES | - |
+--------+--------+---------+---------+------------+----------------+ +---------+---------+---------------+-------------+-----------------+
| d | OSPFv2 | OSPFv3 | YES | YES | YES | | OSPFv3 | EIGRP | - | YES | - |
+--------+--------+---------+---------+------------+----------------+ +---------+---------+---------------+-------------+-----------------+
| | | | | | | | IS-IS | OSPFv3 | YES | YES | - |
+--------+--------+---------+---------+------------+----------------+ +---------+---------+---------------+-------------+-----------------+
| e | OSPFv3 | IS-IS | - | YES | - | | IS-IS | IS-IS | YES | - | YES |
+--------+--------+---------+---------+------------+----------------+ +---------+---------+---------------+-------------+-----------------+
| f | OSPFv3 | OSPFv3 | - | - | YES | | IS-IS | EIGRP | - | YES | - |
+--------+--------+---------+---------+------------+----------------+ +---------+---------+---------------+-------------+-----------------+
| EIGRP | OSPFv3 | ? | YES | - |
+---------+---------+---------------+-------------+-----------------+
| EIGRP | IS-IS | - | YES | - |
+---------+---------+---------------+-------------+-----------------+
| EIGRP | EIGRP | ? | - | YES |
+---------+---------+---------------+-------------+-----------------+
Three of the options above are marked as "Known to work well". These Three of the options above are marked as "Mutiple Known
options have seen significant deployments and are generally Deploymentsl". These options have seen significant deployments and
considered to be good choices. The other options represent valid are generally considered to be good choices. The other options
choices, but have not seen widespread use, so it is hard to offer represent valid choices, but have not seen widespread use at time of
comments on how well they work. In particular, options (e) and (f) writing. In particular, two if the options use OSPFv3 to route IPv4
use OSPFv3 to route IPv4 [RFC5838], which is still rather new and [RFC5838], which is still rather new and untested.
untested.
A number of options are marked "Hard separation". These options use A number of options are marked "Protocol separation". These options
a different IGP for IPv4 vs IPv6. With these options, a problem with use a different IGP protocol for IPv4 vs IPv6. With these options, a
routing IPv6 is unlikely to affect IPv4 or visa-versa. problem with routing IPv6 is unlikely to affect IPv4 or visa-versa.
Some operator may consider this as a benefit when first introducing
dual stack capabilities or for ongoing technical reasons.
Three options are marked "Similar configuration possible". This Three options are marked "Similar configuration possible". This
means it is possible (but not required) to use very similar IGP means it is possible (but not required) to use very similar IGP
configuration for IPv4 and IPv6: for example, the same area configuration for IPv4 and IPv6: for example, the same area
boundaries, area numbering, link costing, etc. If you are happy with boundaries, area numbering, link costing, etc. If you are happy with
your IPv4 IGP design, then this will likely be a consideration. By your IPv4 IGP design, then this will likely be a consideration. By
contrast, the options that use IS-IS for one IP version and OSPF for contrast, the options that use, for example, IS-IS for one IP version
the other version will require considerably different configuration, and OSPF for the other version will require considerably different
and will also require the operations staff to become familiar with configuration, and will also require the operations staff to become
the difference between the two protocols. familiar with the difference between the two protocols.
With option (a), there is an additional choice of whether to run IS- With option (a), there is an additional choice of whether to run IS-
IS in single-topology mode (where IPv4 and IPv6 share a single IS in single-topology mode (where IPv4 and IPv6 share a single
topology and a single set of link costs[RFC5308]) or multi-topology topology and a single set of link costs[RFC5308]) or multi-topology
mode (where IPv4 and IPv6 have separate topologies and potentially mode (where IPv4 and IPv6 have separate topologies and potentially
different link costs[RFC5120]). A big problem with single-topology different link costs[RFC5120]). A big problem with single-topology
mode is that it cannot easily accommodate devices that support mode is that it cannot easily accommodate devices that support
IPv4-only or IPv6-only. Thus, today there is general agreement that IPv4-only or IPv6-only. Thus, today there is general agreement that
multi-topology is the right choice as this gives the greatest multi-topology is the right choice as this gives the greatest
flexibility in network design. flexibility in network design.
It should be noted that a number of ISPs have run OSPF as their IPv4 It should be noted that a number of ISPs have run OSPF as their IPv4
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. BGP 2.4.2. IS-IS Topology Mode
2.4.1. Which Transport for Which Routes? 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
multi-topology mode. Single-topology mode allows IPv4 and IPv6 to
share a single topology and a single set of link costs[RFC5308].
Multi-topology mode allows separate IPv4 and IPv6 topologies with
potentially different link costs.
Traditional thinking has been that multi-topology mode offers the
most flexibility. Never-the-less, a number of operators have used
single-topology mode successfully, usually because some device does
not support multi-topology mode.
2.4.3. RIP
A protocol option described in the table in this section is RIP
[RFC2080]. RIP is a distance vector protocol with limitations in
larger networks. However there is prevalent use case in large
operator networks where RIP is used for edge facing core interfaces
to manage high count aggregation of dynamic routing endpoints.
Although not a mainline option for the network core as a whole, it is
commonly used in IPv4, and potentially in IPv6 for a common set of
links/functions.
2.5. BGP
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
when deploying BGP in a dual-stack network is the question of which when deploying BGP in a dual-stack network is the question of which
routes should be carried over sessions using IPv4 transport and which routes should be carried over sessions using IPv4 transport and which
should be carried over sessions using IPv6 transport. should be carried over sessions using IPv6 transport.
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families being carried over a BGP session requires the BGP session to families being carried over a BGP session requires the BGP session to
be reset (unless something like [I-D.ietf-idr-dynamic-cap] or be reset (unless something like [I-D.ietf-idr-dynamic-cap] or
[I-D.ietf-idr-bgp-multisession] is in use). This is generally more [I-D.ietf-idr-bgp-multisession] is in use). This is generally more
of an issue with eBGP sessions than iBGP sessions: for iBGP sessions of an issue with eBGP sessions than iBGP sessions: for iBGP sessions
it is common practice for a router to have two iBGP sessions, one to it is common practice for a router to have two iBGP sessions, one to
each member of a route reflector pair, so one can change the set of each member of a route reflector pair, so one can change the set of
address families on first one of the sessions and then the other. address families on first one of the sessions and then the other.
The following subsections discuss specific scenarios in more detail. The following subsections discuss specific scenarios in more detail.
2.4.1.1. BGP Sessions for Unlabeled Routes 2.5.1.1. BGP Sessions for Unlabeled Routes
Unlabeled routes are commonly carried on eBGP sessions, as well as on Unlabeled routes are commonly carried on eBGP sessions, as well as on
iBGP sessions in networks where Internet traffic is carried unlabeled iBGP sessions in networks where Internet traffic is carried unlabeled
across the network. In these scenarios, operators today most across the network. In these scenarios, operators today most
commonly use two BGP sessions: one session is transported over IPv4 commonly use two BGP sessions: one session is transported over IPv4
and carries the unlabeled IPv4 routes, while the second session is and carries the unlabeled IPv4 routes, while the second session is
transported over IPv6 and carries the unlabeled IPv6 routes. transported over IPv6 and carries the unlabeled IPv6 routes.
There are several reasons for this choice: There are several reasons for this choice:
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will fail and the IPv6 routes will be withdrawn, which will allow will fail and the IPv6 routes will be withdrawn, which will allow
the traffic to be re-routed elsewhere. By contrast, if the IPv6 the traffic to be re-routed elsewhere. By contrast, if the IPv6
routes were transported over IPv4, then the failure of the IPv6 routes were transported over IPv4, then the failure of the IPv6
data path might leave a working IPv4 data path, so the BGP session data path might leave a working IPv4 data path, so the BGP session
would remain up and the IPv6 routes would not be withdrawn, and would remain up and the IPv6 routes would not be withdrawn, and
thus the IPv6 traffic would be sent into a black hole. thus the IPv6 traffic would be sent into a black hole.
o It avoids resetting the BGP session when adding IPv6 to an o It avoids resetting the BGP session when adding IPv6 to an
existing session, or when removing IPv4 from an existing session. existing session, or when removing IPv4 from an existing session.
2.4.1.2. BGP sessions for Labeled or VPN Routes 2.5.1.2. BGP sessions for Labeled or VPN Routes
In these scenarios, it is most common today to carry both the IPv4 In these scenarios, it is most common today to carry both the IPv4
and IPv6 routes over sessions transported over IPv4. This can be and IPv6 routes over sessions transported over IPv4. This can be
done with either: (a) one session carrying both route families, or done with either: (a) one session carrying both route families, or
(b) two sessions, one for each family. (b) two sessions, one for each family.
Using a single session is usually appropriate for an iBGP session Using a single session is usually appropriate for an iBGP session
going to a route reflector handling both route families. Using a going to a route reflector handling both route families. Using a
single session here usually means that the BGP session will reset single session here usually means that the BGP session will reset
when changing the set of address families, but as noted above, this when changing the set of address families, but as noted above, this
is usually not a problem when redundant route reflectors are is usually not a problem when redundant route reflectors are
involved. involved.
In eBGP situations, two sessions are usually more appropriate. In eBGP situations, two sessions are usually more appropriate.
2.4.2. eBGP Endpoints: Global or Link-Local Addresses? 2.5.2. eBGP Endpoints: Global or Link-Local Addresses?
When running eBGP over IPv6, there are two options for the addresses When running eBGP over IPv6, there are two options for the addresses
to use at each end of the eBGP session (or more properly, the to use at each end of the eBGP session (or more properly, the
underlying TCP session): underlying TCP session):
a. Use link-local addresses for the eBGP session, OR a. Use link-local addresses for the eBGP session, OR
b. Use global addresses for the eBGP session. b. Use global addresses for the eBGP session.
Note that the choice here is the addresses to use for the eBGP Note that the choice here is the addresses to use for the eBGP
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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-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-04 (work in progress), October 2014. 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
for providing the connectionless-mode Network Service (ISO for providing the connectionless-mode Network Service (ISO
8473)", International Standard 10589:2002, Nov 2002. 8473)", International Standard 10589:2002, Nov 2002.
[RFC2080] Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080, [RFC2080] Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080,
January 1997. January 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol [RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
Extensions for IPv6 Inter-Domain Routing", RFC 2545, March Extensions for IPv6 Inter-Domain Routing", RFC 2545, March
1999. 1999.
[RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in [RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in
BGP-4", RFC 3107, May 2001. BGP-4", RFC 3107, May 2001.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006. Networks (VPNs)", RFC 4364, February 2006.
[RFC4472] Durand, A., Ihren, J., and P. Savola, "Operational [RFC4472] Durand, A., Ihren, J., and P. Savola, "Operational
Considerations and Issues with IPv6 DNS", RFC 4472, April Considerations and Issues with IPv6 DNS", RFC 4472, April
2006. 2006.
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, June 2006. for OSPFv3", RFC 4552, June 2006.
skipping to change at page 17, line 5 skipping to change at page 20, line 19
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP [RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, June 2010. Authentication Option", RFC 5925, June 2010.
[RFC5963] Gagliano, R., "IPv6 Deployment in Internet Exchange Points [RFC5963] Gagliano, R., "IPv6 Deployment in Internet Exchange Points
(IXPs)", RFC 5963, August 2010. (IXPs)", RFC 5963, August 2010.
[RFC6180] Arkko, J. and F. Baker, "Guidelines for Using IPv6 [RFC6180] Arkko, J. and F. Baker, "Guidelines for Using IPv6
Transition Mechanisms during IPv6 Deployment", RFC 6180, Transition Mechanisms during IPv6 Deployment", RFC 6180,
May 2011. May 2011.
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, June 2011.
[RFC6342] Koodli, R., "Mobile Networks Considerations for IPv6 [RFC6342] Koodli, R., "Mobile Networks Considerations for IPv6
Deployment", RFC 6342, August 2011. Deployment", RFC 6342, August 2011.
[RFC6752] Kirkham, A., "Issues with Private IP Addressing in the
Internet", RFC 6752, September 2012.
[RFC6782] Kuarsingh, V. and L. Howard, "Wireline Incremental IPv6", [RFC6782] Kuarsingh, V. and L. Howard, "Wireline Incremental IPv6",
RFC 6782, November 2012. RFC 6782, November 2012.
[RFC6883] Carpenter, B. and S. Jiang, "IPv6 Guidance for Internet [RFC6883] Carpenter, B. and S. Jiang, "IPv6 Guidance for Internet
Content Providers and Application Service Providers", RFC Content Providers and Application Service Providers", RFC
6883, March 2013. 6883, March 2013.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque [RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217, April 2014. Autoconfiguration (SLAAC)", RFC 7217, April 2014.
 End of changes. 28 change blocks. 
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