IRTF D. King
Internet-Draft Lancaster University
Intended status: Informational J. Dang
Expires: August 26, 2021 Huawei Technologies
A. Farrel
Old Dog Consulting
February 22, 2021
Challenges for the Internet Routing Infrastructure Introduced by Changes
in Address Semantics
draft-king-irtf-challenges-in-routing-01
Abstract
Historically, the meaning of an IP address has been to identify an
interface on a network device. Routing protocols have been developed
based on the assumption that a destination address has this semantic.
Many proposals have been made to add semantics to IP addresses.
These proposals may set the meaning of an address within the scope of
a limited domain, or suggest an address semantic that is meaningful
at specific points in the network (such as the source and
destination), and ideally can continue to be used without special
interpretation at transit points.
This document presents a brief survey of technologies related to IP
address semantic proposals and describes the challenges to the
existing routing system that they present. It then summarizes the
opportunities for research into new or modified routing protocols to
make use of new address semantics. It does not pass comment on the
advisability or practicality of any of the solutions.
This document is presented as study to support further research into
clarifying and understanding the issues without directly proposing
technical solutions that are ready for productization, deployment, or
standardization.
Status of This Memo
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working documents as Internet-Drafts. The list of current Internet-
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Current Challenges to Internet Routing . . . . . . . . . . . 5
3. Network Path Selection . . . . . . . . . . . . . . . . . . . 6
3.1. Path Aware Routing . . . . . . . . . . . . . . . . . . . 7
4. What is Semantic Routing? . . . . . . . . . . . . . . . . . . 8
4.1. Architectural Considerations . . . . . . . . . . . . . . 11
4.1.1. Semantic Prefix Domains . . . . . . . . . . . . . . . 11
5. Existing Approaches for Routing Based on Additional Semantics 12
5.1. Non-Address-Based Routing . . . . . . . . . . . . . . . . 12
5.1.1. Deep Packet Inspection . . . . . . . . . . . . . . . 13
5.1.2. Differentiated Services . . . . . . . . . . . . . . . 13
5.1.3. IPv6 Extension Headers . . . . . . . . . . . . . . . 13
5.2. Semantic Overlays . . . . . . . . . . . . . . . . . . . . 14
5.2.1. Application-Layer Traffic Optimization . . . . . . . 14
5.2.2. Multipath TCP . . . . . . . . . . . . . . . . . . . . 14
5.2.3. Service Function Chaining . . . . . . . . . . . . . . 15
5.2.4. Path Computation Element . . . . . . . . . . . . . . 15
5.3. Semantic Addressing . . . . . . . . . . . . . . . . . . . 15
5.3.1. Locator/ID Separation Protocol (LISP) . . . . . . . . 15
5.3.2. Identifier-Locator Network Protocol . . . . . . . . . 16
5.3.3. Segment Routing . . . . . . . . . . . . . . . . . . . 16
5.3.4. Preferred Path Routing . . . . . . . . . . . . . . . 17
5.3.5. Information-Centric Networking . . . . . . . . . . . 17
5.3.6. Connectionless Network Protocol . . . . . . . . . . . 18
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5.4. Group Semantics . . . . . . . . . . . . . . . . . . . . . 19
5.4.1. Anycast . . . . . . . . . . . . . . . . . . . . . . . 19
5.4.2. Prioritycast . . . . . . . . . . . . . . . . . . . . 19
5.4.3. Multicast . . . . . . . . . . . . . . . . . . . . . . 20
5.4.4. Automatic Multicast Tunneling . . . . . . . . . . . . 21
5.4.5. Bit Index Explicit Replication . . . . . . . . . . . 21
6. Overview of Current Routing Research Work . . . . . . . . . . 22
6.1. Path Aware Networking . . . . . . . . . . . . . . . . . . 22
6.2. Clean Slate Approaches . . . . . . . . . . . . . . . . . 22
6.2.1. Scalability, Control, and Isolation on Next-
Generation Networks . . . . . . . . . . . . . . . . . 22
6.2.2. Non IP Approaches . . . . . . . . . . . . . . . . . . 23
6.3. Hybrid Approaches . . . . . . . . . . . . . . . . . . . . 24
6.4. Approaches that Modify Existing Routing Protocols . . . . 24
6.4.1. Dynamic Anycast . . . . . . . . . . . . . . . . . . . 24
6.5. No Changes Needed . . . . . . . . . . . . . . . . . . . . 25
7. Challenges for Internet Routing Research . . . . . . . . . . 25
7.1. Routing Research Questions to be Addressed . . . . . . . 26
8. Security Considerations . . . . . . . . . . . . . . . . . . . 29
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 30
12. Informative References . . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38
1. Introduction
The Internet continues to expand rapidly, and beyond the Internet, IP
has become the global standard in any type of computer network
independent of whether or what connectivity to the Internet it has.
At the same time, there are increasingly varied expectations against
the services and service level objectives required from networks.
Packet delivery expectations beyond best effort is one big area:
throughput, latency, error recovery, and (absence of) packet or
connectivity loss, reordering or jitter. Requirements include
relative or absolute guarantees or predictable elastic changes under
contention on these performance factors. This places significant
pressure on Service Providers to be aware of the type of services
being delivered, and to have access to sufficient information about
how individual packets should be treated to meet the user,
application and application instance requirements.
Internet Protocol (IP) identifies facilitates how a device is
attached to the Internet and is distinguished from every other
device. Addresses are used to direct packets to a destination
(destination address) and indicate to where receiver and network
(error) replies should be sent (source address). An IP address may
be assigned to each network interface of a device connected to a
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network that uses IP. Applications use IP addresses to both identify
a host and to indicate the physical or virtual location of the host.
The meaning of a unicast IPv6 address is defined as "An identifier
for a single interface." [RFC4291]. That document goes on to say,
"A packet sent to a unicast address is delivered to the interface
identified by that address.". The unqualified use of the term IP
address (IPv4/IPv6) always assumes unicast semantic as it is the
original and predominant semantic of IP addresses.
Network routing protocols were developed based on the assumption that
a destination address has this unicast meaning. The protocols are
designed to determine paths through the network toward destination
addresses so that IP packets with a common destination address
converge on that destination. Anycast and multicast addresses were
also defined and these new address semantics necessitated variations
to the routing protocols and the development of new protocols.
This document presents a brief survey of proposals to extend the
semantics of IP addresses by assigning additional meanings to some
parts of the address, or by partitioning the address into a set of
subfields that give scoped addressing instructions. Some of these
proposals are intended to be deployed in limited domains [RFC8799]
(networks) that are IP-based, while other proposals are intended for
use across the Internet. The impact the proposals have on routing
systems may require clean-slate solutions, hybrid solutions,
extensions to existing routing protocols, or potentially no changes
at all.
This document also presents some of the challenges to the existing
routing system that these changes in semantics may present. It then
summarizes the existing research and opportunities for future
research into new or modified routing protocols to make use of new
address semantics.
In this document, the focus is on routing and forwarding at the IP
layer. It is possible that a variety of overlay mechanisms exist to
perform service or path routing at higher layers, and that those
approaches may be based on "semantic addresses", but that is out of
scope for this document.
This document draws on surveys and analysis already performed in "A
Survey of the Research on Future Internet Architectures"
[RESEARCHFIAref], and "ITU-T FG-NET2030 Architecture Framework"
[ITUNET2030ref], and work related to specific Internet technologies,
such as the Internet of Things (IOT) "Overview of Existing Routing
Protocols for Low Power and Lossy Networks" [IOTSURVEYref].
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2. Current Challenges to Internet Routing
Today's Internet faces several significant challenges which are a
consequence of the architectural design decisions and exponential
growth. These challenges include mobility, multihoming, programmable
paths, scalability and security, and were not the focus of the
original design of the Internet. Nevertheless, IP-based networks
have, in general, coped well in an incremental manner as each new
challenge has evolved. This list is presented to give context to the
continuing requirements that routing protocols must meet as new
semantics are applied to IP addresses.
Mobility - Mobility introduces several challenges, including
maintaining a relation between a sender and a receiver in cases
where sender and/or receiver changes their point of network
attachment. The original network must always be informed about
the mobile nodes current location, to allow continuity of
services. Mobility users may also consume resources, while
physical moving. The mobile user service instances and
attachments will also change due to varying load or latency, e.g.,
in Multi-access Edge Computing (MEC) scenarios.
Multihoming - Multihomed stations or multihomed networks are
connected to the Internet via more than one access network and
therefore, may be assigned multiple IP addresses from different
pools of addresses. There are challenges concerning how traffic
is routed back to the source if the source has originated its
traffic using the wrong address for a particular connection, or if
one of the connections to the Internet is degraded.
Multi-path - The Internet was initially designed to find the
single, "best" path to a destination using a distributed routing
algorithm. Current, IP-based networks topologies facilitate
multiple paths each with different characteristics and with
different failure likelihoods. It may be beneficial to send
traffic over multiple paths to achieve reliability and enhance
throughput, and it may be desirable to select one path or another
in order to provide delivery qualities or to avoid transiting
specific areas of an IP-based network. However, the way in which
packets are routed using the best or shortest path means that
distinguishing these alternate paths and directing traffic to them
can be hard. Further, problems concerning scalability, commercial
agreements among Service Providers, and the design of BGP make the
utilization of multi-path techniques difficult for inter-domain
routing. (Note that this discussion is distinct from Equal Cost
Multi-path (ECMP) where packets are directed onto two "parallel"
paths of identical least cost using a hash algorithm operated on
some of the packets' header fields.)
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Multicast - [TBD]
Programmable Paths - The ability to decouple IP-based network
paths from routing protocols and agreements between Service
Providers, would allow users and applications to configure and
select network paths themselves, based on required path (that is,
traffic-delivery) characteristics. Currently, user and
application packets follow the path selected by routing protocols
and the way traffic is routed through a network is under the
exclusive control of the Service Provider that owns the network.
End-Point Selection - [TBD]
Scalability - There are many scaling concerns that pose critical
challenges to the Internet. Not least among these challenges is
the size of the routing tables that routers in an IP-based network
must maintain and exchange with their peers. As the number of
devices attached to the network grows, so the number of addresses
in use also grows, and because of the address allocation schemes,
the mobility of devices, and the various connectivity options
between networks, the routing table sizes also grow and are not
amenable to aggregation. This problem exists even in limited
domains (such as IoT), where the size of the routing table - as
more devices are added to the network - may be a gating factor in
there applicability of certain routing protocols. It may be noted
that scaling issues are exacerbated by multihoming practices if a
host that is multihomed is allocated a different address for each
point of attachment.
Security - [TBD]
Some of the challenges outlined here were previously considered
within the IETF by the IABs "Routing and Addressing Workshop" held in
Amsterdam, The Netherlands on October 18-19, 2006 [RFC4984]. Several
architectures and protocols have since been developed and worked on
within and outside the IETF, and these are briefly examined in
Section 5.
3. Network Path Selection
Two approaches are typically used for network path selection.
Firstly, a priori assessment by having the feasible paths and
constraints computed in advance. Secondly, real-time computation in
response to changing network conditions.
The first scenario may be conducted offline and allows for concurrent
or global optimization based on constraints and policy. As network
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size and complexity increases, the required computing power may
increase exponentially for this type of computation.
The second approach must consider the speed of calculation where
complex constraints are applied to the path selection. The response
processing may delay the service setup or the responsiveness to
changes (such as failures) in the network. Path selection filters
may be applied to reduce the complexity of the network data and the
computation algorithm, however, the path computation accuracy and
optimality may be negatively affected.
In both scenarios, the amount of information that needs to be
imported and processed can become very large (e.g., in large
networks, with many possible paths and route metrics), which might
impede the scalability of either method both in terms of the storage
and the distribution of the information.
In the last decade, significant research has been conducted into the
architecture of the future Internet. During this research, several
techniques emerged, highlighting the benefits of path awareness and
path selection for end-hosts during this research, and multiple path-
aware network architectures have been proposed, including SCION
[SCIONref] and RINA [RINAref], and the work of the Path Aware
Networking Research Group as discussed later in this document.
When choosing the best paths or topology structures, the following
criteria may need to be considered:
o Method by which a path, or set of paths, is to be calculated. For
example, a path may be selected automatically by the routing
protocol or may imposed (perhaps for traffic engineering reasons)
by a central controller or management entity.
o Criteria used for selecting the best path. For example, classic
route preference, or administrative policies such as economic
costs, resilience, security, and if requested, applying
geopolitical considerations.
3.1. Path Aware Routing
The current Internet architecture is built using a best-effort
philosophy. There are techniques discussed in this document that
attempt better-than-best-effort delivery. The start-point and end-
point of a path are identified using IP addresses, but the path might
not run all the way from a packet's source to its destination. The
assumption is that a packet reaching the end of a path is forwarded
to its destination using best-effort techniques.
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Evaluating and building paths that respect requirements that go
beyond the simple best effort model is particularly challenging and
computationally heavy since numerous quality-related parameters need
to be considered.
4. What is Semantic Routing?
Networks are often divided into addressing regions for various
administrative or technological reasons. Different routing paradigms
may be applied in each region, and within a single region specific
"private" semantics may be applied to the IP addresses. This concept
is not new one, a pragmatic solution for achieving network function
in a limited domain is found in (see Section 4.1.1).
These address semantics are established using customer types,
customer connections, topological constraints, performance groups,
and security, etc. Service Provides or network operators will apply
local policies to user and application packets as they enter the
network possibly mapping addresses or possibly encapsulating them
with an additional IP header. In some case, the packet has its
source and destination within a single network and the network
operator can apply address semantics policies across the whole
network. In other cases (such as general IP-based traffic), a packet
will require a path across multiple networks, and each may apply its
own set of traffic forwarding policies. In these cases, there is
often no consistency or guaranteed performance unless a Service Level
Agreement (SLA) is applied to traffic traversing multiple networks.
Many proposals have been made to add semantics to IPv6 addresses
beyond the simple identification of the source and destination
[I-D.jia-scenarios-flexible-address-structure]. These proposals may
set the meaning of an address within the scope of a limited domain,
or suggest an address semantic that is meaningful at specific points
in the network. In this context, a "limited domain" means that the
interpretation of the address is only applicable to a well-defined
set of network nodes, and if a packet bearing an address with a
modified semantic were to escape from the domain, the special meaning
of the address would be lost. Additionally, the meaning of "specific
points in the network" is generally applied to the source and
destination nodes of a packet, while all transit nodes are unaware of
the special semantic, however it could be the case that some key
transit nodes are able to access the meaning of the address and so
apply special routing or other functions to the packet.
Other proposals include providing semantics specific to mobile
networks, multicast traffic, different device types, different
underlying connectivity, hierarchical connectivity, geographic
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location, application or network function usage, or connectivity
requirements.
Some new IP address semantics may have implications for how network
routing is performed. Some proposals might not be supported by
existing routing protocols and so would require changes. Other
proposals might enable advanced routing features or offer benefits in
scaling and management of routing systems. Semantic Routing is the
process of routing packets that contain semantics in their IP
addresses, possibly using that information to perform policy-based
routing or other enhanced routing functions.
Such proposals include the following:
o Providing semantics specific to mobile networks so that a user or
device may move through the network without disruption to their
service [CONTENT-RTG-MOBILEref].
o Enabling optimized multicast traffic distribution by encoding
multicast tree and replication instructions within addresses
[MULTICAST-SRref].
o Using addresses to identify different device types so that their
traffic may be handled differently [SEMANTICRTG].
o Content-based routing (CBR), forwarding of the packet based on
message content rather than the destination addresses
[OPENSRNref].
o Deriving IP addresses from the physical layer identifiers and
using addresses depending on the underlying connectivity.
o Identifying hierarchical connectivity so that routing can be
simplified [EIBPref].
o Providing geographic location information within addresses
[GEO-IPref].
o Indicating the application or network function on a destination
device or at a specific location; or enable Service Function
Chaining (SFC).
o Expressing how a packet should be handled, prioritized, or
allocated network resources as it is forwarded through the network
[TERASTREAMref].
o Using cryptographic algorithms to mask the identity of the source
or destination, masking routing tables within the domain, while
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still enabling packet forwarding across the network
[BLIND-FORWARDINGref].
In many cases, it may be argued that existing mechanisms applied on
top of the common address semantic defined in RFC 4291 can deliver
the correct functionality for these scenarios. That is, packets may
be tunneled over IP using a number of existing encapsulation
techniques. Nevertheless, there is pressure to reduce the amount of
encapsulation (partly to resist reduction in the maximum transmission
unit (MTU) over the network, and partly to achieve a flatter and more
transparent network architecture). This leads to investigations into
whether the current IP addresses can be "overloaded" (without any
negative connotations being attached to that word) by adding
semantics to the addresses.
Bringing new semantics to IP addresses may have implications for how
network routing is performed. Some proposals might not be supported
by existing routing protocols and so would require changes. Other
proposals might enable advanced routing features or offer benefits in
scaling and management of routing systems. The purpose of this
document is to collate and coordinate research into the consequences
for routing of the various semantic addressing proposals, and to
collect references to research work on routing solutions.
The IPv4 protocol suit is widely deployed in the Internet. However,
with the rapid development and expansion of IP-based networking,
weaknesses appeared with IPv4 protocol extensibility. The IPv4
header's restrictions cannot accommodate additional parameters;
address space is also a limiting factor as the number of IP-connected
devices grows exponentially. Therefore, research and development of
IPv4 are comparatively low compared to IPv6 research and clean slate
proposals.
Several technical challenges exist for semantic routing, these
include:
o Address consumption caused by lower address utility rate. The
wastage is mainly comes from aligning.
o Finite allocation for semantic address blocks.
o Encoding too many semantics into prefixes will require evaluation
of which to prioritize.
o Risk of privacy/information leakage.
o Burdening the user, application or prefix assignment node.
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o Source address spoofing preventing mechanism may be required.
o Backwards compatibility with the existing IP-based networking.
4.1. Architectural Considerations
Semantics may be applied in a number of ways to integrate with
existing routing architectures. The most obvious is to build an
overlay such that IP is used only to route packets between network
nodes that utilize the semantics at a higher layer. There are a
number of uses of this approach including Service Function Chaining
(SFC) (see Section 5.2.3) and Information Centric Networking (ICN)
(see Section 5.3.5). An overlay may be achieved in a higher layer,
or may be performed using tunneling techniques (such as IP-in-IP) to
traverse the areas of the IP network that cannot parse additional
semantics and so join together those nodes that use the semantics.
The application of semantics may also be constrained to within a
limited domain (see Section 4.1.1). In some cases, such a domain
will use IP, but be disconnected from Internet. In those cases, the
challenges are limited to enabling the desired function within the
domain. In other cases, traffic from within the domain is exchanged
with other domains that are connected together across an IP-based
network using tunnels or via application gateways. And in another
case traffic from the domain is routed across the Internet to other
nodes and this requires backward-compatible routing approaches,
tunnels, or gateway functions.
4.1.1. Semantic Prefix Domains
A semantic prefix domain [I-D.jiang-semantic-prefix] is a portion of
the Internet over which a consistent set of semantic-based policies
are administered in a coordinated fashion. Examples of semantic
prefix domains include:
o Administrative domains
o Applications
o Autonomous systems
o Hosts
o Network types
o Routers
o Trust regions
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o User groups
A semantic prefix domain has a set of pre-established semantic
definitions which are only meaningful locally. Without an efficient
mechanism for notification, exchange, or configuration of semantics,
the definitions of semantics are only meaningful within the local
semantic prefix domain, and the addresses on a packet from within a
domain risk being misinterpreted by hosts and routers outside the
domain. While, sharing semantic definitions among semantic prefix
domains would enable wider semantic-based network function, such
approaches run the risk of complexity caused by overlapping
semantics, and require a significant trust model between network
operators. More successful approaches to multi-domain semantics
might be to rely either on backwards-compatible techniques or on
standardised semantics.
A semantic prefix domain may also span several physical networks and
traverse multiple service provider networks. However, when an
interim network is traversed (such as when an intermediary network is
used for interconnectivity) the relevance of the semantics is limited
to network domains that share a common semantic policy, and tunneling
may be needed to traverse transit domains.
5. Existing Approaches for Routing Based on Additional Semantics
Several IETF-based approaches are available to allow service
providers to perform policy-based routing, including identifying and
marking IP traffic either by changing the semantic of IP addresses or
by adding such a semantic in other fields/namespaces, enabling
differentiated handling by transit routers (queuing, dropping,
forwarding, etc.). The sections below distinguish between those
schemes that perform routing based on information other than IP
addresses, those that establish an overlay network in which to apply
semantics, and those that add semantics to the addresses. A further
separate group of approaches is presented here to cover the concept
of group semantics where a single address identifies more than one
end point.
5.1. Non-Address-Based Routing
Many routing schemes examine not just the destination address field,
but other field in the packet header to make routing decisions.
These approaches (sometimes referred to as "policy-based routing")
allow packets to follow different paths through the network depending
on semantics assigned to these other fields or simply based on
hashing algorithms operating on the values of those fields.
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5.1.1. Deep Packet Inspection
Deep Packet Inspection (DPI) may be used by a router to learn the
characteristics of packets in order to forward them differently.
This involves looking into the packet beyond the top-level network-
layer header to identify the payload. Once identified, the traffic
type can be used as an input for marking the packets for network
handling, or for performing specific policies on the packets.
However, DPI may be expensive both in processing costs and latency.
The processing costs means that dedicated infrastructure is necessary
to carry out the function and this may have an associated financial
cost. The latency incurred may be too much for use with any delay/
jitter sensitive applications. As a result, DPI is difficult for
large-scale deployment and its usage is often limited to specific
functions at the edge of the network.
Despite this, "shallow DPI" is commonplace in routers today as they
examine the five-tuple of source address, destination address,
payload protocol, source port, and destination port to perform a hash
function for ECMP purposes (a form of policy-based routing).
5.1.2. Differentiated Services
Quality of Service (QoS) based on and Differentiated Services
[RFC2474] is a widely deployed framework specifying a simple and
scalable coarse-grained mechanism for classifying and managing
network traffic. However, in a service providers network, DiffServ
codepoint (DSCP) values cannot be trusted when they are set by the
customer, and may have different meanings as packets are passed
between networks.
In real-world scenarios, Service Providers deploy "remarking" points
at the edges of their network, re-classifying received packets by
rewriting the DSCP field according to local policy using information
such as the source/destination address, IP protocol number, transport
layer source/destination ports, and possibly applying DPI as
described in Section 5.1.1.
The traffic classification process and node-by-node processing leads
to increased packet processing overhead and complexity at the edge of
the Service Providers network.
5.1.3. IPv6 Extension Headers
[RFC8200] defines the IPv6 header and also a number of extension
headers. These extension headers can be used to carry additional
information that may be used by transit routers (the hop-by-hop
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options header) or by the destination identified by the destination
address field (the destination options header). These extension
headers could be used to encode additional semantics that could be
used to perform routing and to determine what functions and
operations should be performed on a packet.
[RFC7872] and [I-D.ietf-v6ops-ipv6-ehs-packet-drops] provide some
discussions about the operational problems of using IPv6 extension
headers especially in multi-domain environments, while
[I-D.bonica-6man-ext-hdr-update] proposes to update RFC 8200 with
guidance regarding the processing, insertion and deletion of IPv6
extension headers.
5.2. Semantic Overlays
An overlay network is built on top of an underlay or transport
network. Packets are encapsulated with the header for the overlay
network to carry the additional information needed to provide the
desired function, and then the packets are encapsulated for transport
through the underlay network. In this case, no changes are made to
the meaning of the IP addresses in the underlay, but the destination
address identifies the next hop in the overlay network rather than
the ultimate destination of the packet. In this way, packets can be
steered through different overlay nodes where routing decisions can
be made.
5.2.1. Application-Layer Traffic Optimization
Application-Layer Traffic Optimization (ALTO) [RFC7285] is an
architecture and protocol. ALTO defines abstractions and services to
provide simplified network views and network services to guide the
application usage of network resources, including cost.
An ALTO server gathers information about the network and answers
queries from an ALTO client that wants to find a suitable path for
traffic. ALTO responses are typically used to route whole flows (not
individual packets) either to suitable destinations (such as network
functions) or onto paths that have specific qualities.
5.2.2. Multipath TCP
Multipath TCP (MPTCP) [RFC8684] enables the use of TCP in a multipath
network using multiple host addresses. A Multipath TCP connection
provides a bidirectional bytestream between two hosts communicating
like normal TCP and thus does not require any change to the
applications. However, Multipath TCP enables the hosts to use
different paths with different IP addresses to exchange packets
belonging to the MPTCP connection.
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MPTCP it increases the available bandwidth, and so provides shorter
delays; it increases fault tolerance, by allowing the use of other
routes when one or more routes become unavailable; and it enables
traffic engineering and load balancing.
5.2.3. Service Function Chaining
Service Function Chaining (SFC) [RFC7665] is the process of sending
traffic through an ordered set of abstract service functions. This
may be achieved using an overlay encapsulation such as the Network
Service Header (NSH) [RFC8300] or MPLS [RFC8596] that rely on
tunneling through an underlay without any additional semantics
applied to the IP addresses.
Alternatively, SFC can be performed by adding semantics to the
addresses, for example, as in Section 5.3.3.
5.2.4. Path Computation Element
The Path Computation Element (PCE) [RFC4655] is an architecture and
protocol [RFC5440] that can be used to assist with network path
selection. A PCE is an entity capable of computing paths for a
single or set of services. A PCE might be a network node, network
management station, or dedicated computational platform that is
resource-aware and has the ability to consider multiple constraints
for sophisticated path computation. PCE applications compute label
switched paths for MPLS and GMPLS traffic engineering, but the PCE
has been extended for a variety of additional traffic engineering
problems.
5.3. Semantic Addressing
In semantic addressing, additional information or meaning is placed
into the IP address, and this is used to route packets within the
network.
5.3.1. Locator/ID Separation Protocol (LISP)
The Locator/ID Separation Protocol (LISP) [RFC6830] was published by
the IETF as an Experimental RFC in 2013 and is now being moved to the
Standards Track [I-D.ietf-lisp-rfc6830bis] and
[I-D.ietf-lisp-rfc6833bis]. LISP separates IP addresses into two
numbering spaces: Endpoint Identifiers (EIDs) and Routing Locators
(RLOCs). The former, the EIDs, are used to identify communication
end-points (as the name states) as well as local routing and
forwarding in the edge network. The latter, RLOCs, are used to
locate the EIDs in the Internet topology end are usually the address
of ASBRs (Autonomous System Border Routers). IP packets addressed
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with EIDs are encapsulated with RLOCs for routing and forwarding over
the Internet.
As end-to-end packet forwarding includes both EIDs and RLOCs an
additional control-plane is needed. This control plane provides a
mapping system and basic traffic engineering capabilities.
Multihoming becomes easier because one EID can be associated to more
than one RLOC or even to a local network address prefix.
5.3.2. Identifier-Locator Network Protocol
The Identifier-Locator Network Protocol (ILNP) [RFC6740] is an
experimental network protocol designed to separate the two functions
of network addresses: identification of network endpoints, topology
or location information. Differently from LISP, ILNP encodes both
locator and identifier in the IPv6 address format (128 bits). More
specifically, the most significant 64 bits of the 128 bits IPv6
address is the locator, while the less significant 64 bits form the
identifier. Upon reaching the destination network, a cache is used
to find the corresponding node. Furthermore, DNS can be dynamically
updated, which is essential for mobility and also for provider-
independent addresses. Similar to LISP, multihoming can be set by
assigning multiple locators to the same identifier. In addition,
identifiers can also be encrypted for privacy reasons. It was
intended that ILNP should be backwards-compatible with existing IP,
and is incrementally-deployable.
5.3.3. Segment Routing
Segment Routing (SR) [RFC8402] leverages the source routing paradigm.
A node steers a packet through an ordered list of instructions,
called "segments". A segment can represent any instruction,
topological or service based. A segment can have a semantic local to
an SR node or global within an SR domain. SR provides a mechanism
that allows a flow to be restricted to a specific topological path,
while maintaining per-flow state only at the ingress node(s) to the
SR domain.
In SR for IPv6 networks (SRv6) segment routing functions are used to
achieve a networking objective that goes beyond packet routing, in
order to provide "network programming"
[I-D.ietf-spring-srv6-network-programming]. The network program is
expressed as a list of instructions, which are represented as 128-bit
segments, called Segment Identifiers (SID) - encoded and presented in
the form of an IPv6 address. The first instruction of the network
program is placed in the Destination Address field of the packet. If
the network program requires more than one instruction, the remaining
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list of instructions is placed in the Segment Routing Extension
Header (SRH)[RFC8754].
An SRv6 instruction can represent any topological or service-based
instruction. The SRv6 domain is the service provider domain where
SRv6 services are built to transport any kind of customer traffic
including IPv4, IPv6, or frames. SRv6 is the instantiation of
Segment Routing deployed on the IPv6 data plane. Therefore, in order
to support SRv6, the network must first be enabled for IPv6.
For nodes forwarding traffic, the SRH in the IPv6 header is only
processed if the destination address identifies the local node. In
this case, the node must take several actions, including reading the
SRH, performing any node-specific actions identified by the
destination address or the next SIDs in the SRH, and re-writing the
IPv6 destination address field using information from the SRH before
forwarding the packet.
5.3.4. Preferred Path Routing
Preferred Path Routing (PPR)
[I-D.chunduri-lsr-isis-preferred-path-routing] is a proposed routing
protocol mechanism where alternate forwarding state is installed for
a set of different preferred paths. Each preferred path is described
as an ordered linear list of nodes, links, and network functions, and
the path is identified by a network-global preferred path identifier.
If a packet is marked with preferred path identifier, it is forwarded
according to the preferred path that has been installed on the
router. If a packet is not marked or if the preferred path is not
installed on the router, the packet is forwarded using the normal
shortest path first algorithm.
In PPR, the preferred path identifier is encoded in an IP address,
but the address is only used in an encapsulation of the end-to-end
packet. This approach is a hybrid in that it is applying a different
meaning to the IP addresses, using that meaning in an encapsulation,
but routing the packets through an existing IP network.
5.3.5. Information-Centric Networking
Information-Centric Networking (ICN) [ICNref] is an approach to
evolve the Internet infrastructure away from a host-centric paradigm,
based on perpetual connectivity and the end-to-end principle, to a
network architecture in which the focal point is information (or
content or data) that is assigned specific identifiers.
Several scenarios exist for semantic-based networking, providing
reachability based on Content Routing [CONTENTref] and Name Data
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Networking [NDNref]. The technology area of ICN is now reaching
maturity, after many years of research and commercial investigation.
A technical discussion into the deployment and operation of ICNs
continues in the IETF: [RFC8763] provides several important
deployment considerations for facilitating ICN and practical
deployments.
Although ICN is primarily an overlay technology, a more recently
concept, Hybrid-Information-Centric Networking (hICN), has been
introduced [HICNref]. In an hICN environment the ICN aspect is
integrated into the IPv6 architecture, reusing existing IPv6 packet
formats with the intention of maintaining compatibility with existing
and deployed IP network technology without creating overlays that
might require a new packet format or additional encapsulations. The
work is described in [I-D.muscariello-intarea-hicn].
This document does not promote or endorse specific ICN solutions: we
focus on the potential routing challenges faced by these types of new
networks, and highlight key areas of research interest.
5.3.6. Connectionless Network Protocol
The Connectionless Network Service (CLNP) [CLNPref] is a network
layer encoding that supports variable length, hierarchical
addressing. It is widely deployed in many communications networks
and is the ITU-T's standardised encoding for packets in the
management plane for Synchronous Digital Hierarchy (SDH) networks.
For a while, CLNP was considered in competition with IP as the
network layer encoding for the Internet, but IP (in conjunction with
TCP) won out.
Many of the considerations for semantic addressing can be handled
using CLNP, and it is particularly well suited to applications that
demand variable length addresses or that structure addresses
hierarchically for routing or geo-political reasons.
Routing for CLNP can be achieved using the IS-IS routing protocol in
its full form as documented in [ISISref] rather than its IP-only form
[RFC1195]. While this may make it possible to use CLNP alongside IP
in some routed networks, it does not integrate the use of IP
addresses with additional semantics with the historic use of IP
addresses except in "ships that pass in the night" fashion.
Alternatively, [RFC1069] explains how to carry regular IP addresses
in CLNP.
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5.4. Group Semantics
A mayor enhanced addressing semantic in IP is called "group
semantics". Here, an IP address identifies more than one individual
interface or node. This facilitates the delivery of a packet to any
one of a group of destinations, or to all members of a group.
5.4.1. Anycast
The first instance of group semantics to see deployment was what is
now called "anycast". This approach comes for "free" as part of
normal IP routing for unicast addresses. An anycast address can be
assigned to multiple interfaces on different nodes, and packets
carrying such a destination address are routed toward the instance
closest to the sender of the packet.
While duplicate identical addresses might have been considered a
configuration error, it now forms the basis of service redundancy in
IP networks. Multiple instances of services acting as responders use
the same IP address so that a consumer has a high chance of finding
the service even after network failures. IPv6 [RFC4291] formalizes
this semantic, following practices already used in before in IPv4 for
anycast. [RFC7094] discusses the architecture.
Anycast presents a problem because not all the packets in a sequence
sent to the same anycast address will necessarily arrive at the same
destination. This situation can arise even in stable routing
systems. Solutions to this are not standardised as generic
mechanisms, and depend on a higher layer protocol performing an
initial discovery phase and then directing all subsequent packets
using unique unicast addresses.
There are also additional complexities for security when anycast is
used because security associations are best formed as one-to-one
relationships.
5.4.2. Prioritycast
A modifications to anycast that can be instantiated by additional
engineering in the routing system is has been called "prioritycast".
Instead of relying on the shortest path forwarding semantic,
prioritycast directs all traffic to the anycast address instance that
is reachable and has the highest priority. This approach only
requires small modifications to routing protocols so that priorities
are advertized along side the addresses.
Prioritycast was originally introduced as a recommended operational
practice for deployments of Bidirectional PIM (Bidir-PIM) [RFC8736]
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which requires a single active instance of its Rendezvous Point (RP)
service. The RP is the root of a bidirectional tree and prioritycast
addresses for RP allow fast failover without additional redundancy
protocols beside the routing protocol, which would otherwise be
necessary for such a redundancy service.
5.4.3. Multicast
Multicast address semantics support delivery to all members of a
group of destinations. This is a controlled variant of broadcasting
where packets are delivered to all possible receivers in a particular
(static) scope such as a multi-access link. Membership of a
multicast link is dynamically signalled by the group members, and a
group is identified by a specific address.
IP multicast [RFC1112], based on the protocol and service definition
aspects of Steve Deering's PhD, is widely deployed for IPv4. It is
equally adopted and used in IPv6 using the addressing architecture
specified in [RFC4291]. In IP multicast (any Source Multicast - ASM)
any node can send to the multicast group and have its packets
delivered to all members of the group.
Research deployments in the 1990s (the so called 'MBone' [MBONEref])
indicated that IP multicast gave rise to a number of issues related
to address assignment, implementation, scale, and security. The
problem of allocation and management of IP multicast (group)
addresses led to several proposals including Multicast Address
Dynamic Client Allocation Protocol (MADCAP) [RFC2730], the Multicast
Address Allocation Architecture (MALLOC) [RFC6308], the Multicast
Address-Set Claim Protocol (MASC) [RFC2909], and the Multicast-Scope
Zone Announcement Protocol (MZAP) [RFC2776], but none was widely
adopted. Attempts to create a complete routing protocol suite for IP
multicast service model within the IETF resulted in the Multicast
Source Discovery Protocol (MSDP) being published as an experimental
RFC [RFC3618].
The popularity of multicast as a concept and the widespread
deployment of commercial IPv4 multicast led to the development of
"Source Specific Multicast" service (SSM) [RFC4607]. In SSM, the
combination of the Source and Group addresses (S,G) of an IP
multicast packet form a so-called SSM channel address, which
identifies group of receivers and implies a single permitted sender.
Receivers subscribe to every SSM channel.
From the perspective of a service user, SSM solves the security issue
(only valid sources can send traffic) and the address assignment
issue (all group addresses are relative to the source address). For
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the operator, SSM also eliminates the complex operational
requirements of ASM.
5.4.4. Automatic Multicast Tunneling
Automatic Multicast Tunneling (AMT) [RFC7450] is a protocol for
delivering multicast traffic from sources in a multicast-enabled
network to receivers that lack multicast connectivity to the source
network. The protocol uses UDP encapsulation and unicast replication
to provide this functionality as a hybrid solution using both
multicast routing and an overlay approach.
5.4.5. Bit Index Explicit Replication
The IETF standardized or otherwise deployed protocol solutions in
support of ASM and SSM in about 2015 relied all on per-hop, per ASM-
group/per-SSM-channel stateful hop-by-hop forwarding/replication.
Service Provider at that time were starting to removing or reduce
heavy-weight control and per-hop forwarding processing in unicast
caused by MPLS LDP/RSVP-TE driven designs, replacing it with more
lightweight MPLS-SR and later SRv6 forwarding and associated control
planes. But to reduce the cost for multicast service, the only
transit-hop stateless solution available was ingres-replication,
tunnel multicast across unicast, hence trading hop-by-hop state (and
its control and management plane cost) in the network against traffic
overhead and (under congestion) higher latency.
SSM and MPLS multicast solutions require relatively complex protocols
and state management in routers in the network. The only alternative
to this was "ingress replication" which placed large amounts of
traffic into the network.
Bit Index Explicit Replication (BIER) [RFC8279] addresses these
problems. BIER does not contain the notion of ASM or SSM groups.
Instead, a sender enumerates the set of receivers to which the packet
is to be delivered. The network routers forward packets and
replicate them onto the shortest paths to the destinations. As the
packets are replicated, so the enumeration of the receivers is pruned
on each copy of the packet.
BIER is able to use existing routing protocols without modification,
but requires enhancements in the forwarding plane to encode, parse,
and act on the set of receivers. The BIER information is carried in
new encapsulations [RFC8296] that is carried hop-by-hop in IP. Thus,
the additional semantic is in an overlay.
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6. Overview of Current Routing Research Work
Several recent techniques for improving IP-based routing have been
proposed, some of these are highlighted below.
6.1. Path Aware Networking
The IRTF's Path Aware Networking Research Group [PANRGref] aims to
support research in bringing path aware techniques into use in the
Internet. This research overlaps with many past and existing IETF
and IRTF efforts including multipath transport protocols, congestion
control in multiply-connected environments, traffic engineering, and
alternate routing architectures.
[I-D.irtf-panrg-path-properties] offers a vocabulary of path
properties. By doing so it gives some clarity of the distinction
between path aware routing and semantic routing as considered in this
document.
[I-D.irtf-panrg-what-not-to-do] provides a catalog and analysis of
past efforts to develop and deploy Path Aware techniques. Most, but
not all, of these mechanisms were considered at higher levels,
although some apply at the IP routing and forwarding layer.
6.2. Clean Slate Approaches
Incremental updates to the current Internet is seen as suboptimal and
an undesirable long-term solution [CLEANSLATEref].
A clean slate redesign of inter-domain routing would provide many
benefits and could reuse existing legacy routing protocols for intra-
domain communication. The following subsections outline current
proposals for clean slate inter-domain Internet routing.
6.2.1. Scalability, Control, and Isolation on Next-Generation Networks
The SCION (Scalability, Control, and Isolation on Next-Generation
Networks) [SCIONref] inter-domain network architecture has been
designed to address security and scalability issues and provides an
alternative current Border Gateway Protocol (BGP) solutions. The
SCION proposal combines a globally distributed public key
infrastructure, a way to efficiently derive symmetric keys between
any network entities, and the forwarding approach of packet-carried
forwarding state.
SCION End-hosts fetch viable path segments from the path server
infrastructure, and construct the exact forwarding route themselves
by combining those path segments. The architecture ensures that a
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variety of combinations among the path segments are feasible, while
cryptographic protections prevent unauthorized combinations or path-
segment alteration. The architecture further enables path
validation, providing per-packet verifiable guarantees on the path
traversed.
6.2.2. Non IP Approaches
6.2.2.1. Recursive InterNetwork Architecture
Recursive Inter Network Architecture (RINA) [RINAref] builds upon the
principle that applications communicate through Inter-process
Communication (IPC) facilities. For an application to communicate
through the distributed IPC facility, it only needs to know the name
of the destination application and to use the IPC interface to
request communication.
By leveraging IPC concepts RINA allows two processes to communicate,
IPC requires certain functions such as locating processes,
determining permission, passing information, scheduling, and managing
memory. Similarly, two applications on different end-hosts should
communicate by utilizing the services of a distributed IPC facility
(DIF). A DIF is an organizing structure, generally referred to as a
"layer".
The scope and functions provided by the different IPC facilities may
vary given the different type of network and performance goals.
Moreover, an IPC layer may recursively request services from other
IPC layers. The idea of recursively using multiple inter-process
communication services creates a multilayer structure repeated until
an IPC facility can fit well for physical technologies, e.g., wired
or wireless networks.
6.2.2.2. Expedited Internet Bypass Protocol
The Expedited Internet Bypass Protocol (EIBP) [EIBPref] is a clean
slate approach to routing and forwarding in the Internet using the
Internet infrastructure, but bypassing the Internet Protocol (IP).
The EIBP method may be deployed in current routers and when invoked
for a specific end to end IP hosts or networks, EIBP bypasses the
heavy traffic and security challenges faced at Layer-3. EIBP does
not require routing protocols, instead it abstracts network
structural (physical or logical) information into intelligent
forwarding addresses that are acquired by EIBP routers automatically.
The Forwarding tables used by EIBP are proportional to the
connectivity (degree) at a routing device making the protocol
scalable. The EIBP routing system does not require network-wide
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dissemination. Topology change impacts are local and thus
instabilities on topology changes are minimal. EIBP is a low
configuration protocol, which can be deployed in an AS and extended
to multiple ASes independently. EIBP evaluations were conducted
using GENI testbeds and compared to IP using Open Shortest Path First
and Border Gateway Protocol. Significant performance improvements in
terms of convergence and churn rates highlight the capabilities of
EIBP.
6.3. Hybrid Approaches
Some research work is engaged in examining the emerging set of new
requirements that exceed the network and transport services of the
current Internet, which only delivers "best effort" service. This
work aims to determine what features can be built on top of existing
solutions by adding additional new components or features. A
starting point for this discussion can be found in
[I-D.bryant-arch-fwd-layer-ps].
6.4. Approaches that Modify Existing Routing Protocols
Some routing solutions to support semantic addressing may be possible
by applying small changes to existing routing protocols. These
modifications may be:
o Backward compatible with the pre-existing protocol enabling
insertion into existing networks.
o Compatible with forwarding existing IP packets enabling support of
legacy traffic.
o Applicable only to deployment within a limited domain
(Section 4.1.1).
6.4.1. Dynamic Anycast
Dyncast (Dynamic anycast) addresses the problem of directing traffic
from a client to one service instance among several available, while
considering decision metrics beyond shortest path when doing so.
Those service instances are therefore possible destinations for a
specific service demand. [I-D.liu-dyncast-ps-usecases] outlines
several use cases where such traffic steering requirement is
desirable and may occur, such as in edge computing scenarios but also
in distribution of video content in scenarios like autonomous
driving. The draft also outlines problems with existing solutions,
most notably latency in changing relations from one service instance
to another due to a change in metric, which defines that decision
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(e.g., load in servers, latency, or a combination of several such
metrics).
Key to the proposed dyncast [I-D.li-dyncast-architecture]
architecture is to build on the notion of (IP) anycast, while
changing the addressing semantic from a locator-based addressing to a
service-oriented one. Here, the initial "service demand" packet is
being identified through a service identifier as destination address.
This identifier is then mapped onto a binding IP (locator-based)
address at the ingress of the network, allowing for locator-based
routing to be used throughout the network. The ingress-based
architecture is designed in such a way that ingress nodes upon
arrival of a new service demand can determine which instance (i.e.,
which binding IP to use) considering both network- and service-
related metrics. These metrics can be distributed among ingress
nodes in various ways, including over a routing protocol solution.
The overall forwarding decision is the adherence with what terms
"instance affinity", i.e., the need to adhere to a previous routing
decision for more than one packet, unlike IP forwarding on locator
addresses. This affinity is created, by means of a binding table on
the ingress nodes, since often more than one packet is needed for the
overall service-level transaction with a specific service instance.
For instance, HTTP requests may span more than one routed packet.
Also, a service instance may also create ephemeral state, which
requires the client to continue communicating with this instance for
the duration of this state. While the affinity is entirely defined
by the application layer protocol, the network layer takes the
affinity marking as input into the decision to renew its routing
decision.
6.5. No Changes Needed
It is entirely possible that some forms of modified address semantic
will work perfectly well with existing routing protocols and
mechanisms either across the whole Internet or within limited and
carefully controlled domains. Claims for this sort of functionality
need to be the subject of careful research and analysis as the
existing protocols were developed with a different view of the
meaning of IP addresses, and because routing systems are notoriously
fragile.
7. Challenges for Internet Routing Research
The techniques and architectures discussed in this document have
established very different strategies for semantic routing, and the
evolution of the Internet. The first being with incremental updates
and deployment, the second is based on clean slate proposals. If
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applied to the Internet as a whole, the later strategy faces the
considerable challenge of how to drastically change the Internet with
minimal or no service disruption, while if applied to specific
controlled domains it raises the question of how nodes in those
domains can communicate across the Internet to nodes that are outside
the domain.
It may not be possible to embrace all emerging scenarios outlined in
this document with a single approach or solution. Requirements such
as 5G mobility, near-space-networking, and networking for outer-
space, may need to be handled using separate network technologies.
Therefore, developing a new Internet architecture that is both
economically feasible and which has the support of the networking
equipment vendors, is a significant challenge in the immediate future
of the Internet.
Improving IP-based network capabilities and capacity to scale, and
address a set of growing requirements presents significant research
challenges, and will require contributions from the networking
research community.
7.1. Routing Research Questions to be Addressed
As research into the scenarios and possible uses of semantic
addressing progresses, a number of questions need to be addressed in
the scope of routing. These questions go beyond "Why do we need this
function?" and "What could we achieve by carrying this additional
semantic in an IP address?" The questions are also distinct from
issues of how the additional semantics can be encoded within an IP
address. All of those issues are, of course, important
considerations in the debate about semantic addressing, but they form
part of the essential groundwork of research into semantic addressing
itself.
This section sets out some of the concerns about how the routing
system might be impacted by the use of semantic addressing. These
questions need to be addressed in separate research work or folded
into the discussion of each semantic addressing proposal.
1. What is the scope of the semantic address proposal? This
question may be answered as:
* Global: It is intended to apply to all uses of IP addresses.
* Backbone: It is intended to apply to IP-based network
connectivity.
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* Overlay: It is to be used as an overlay network over previous
uses of IP or other underlay technologies using tunneling.
* Gateway: The semantic addressing will be used within a limited
domain, and communications with the wider Internet will be
handled by a protocol or application gateway.
* Domain: The use of the semantic addressing is entirely limited
to within a domain or private network.
Underlying this issue is a broader question about the boundaries
of the use of IP, and the limit of "the Internet". If a limited
domain is used, is it a semantic prefix domain [RFC8799] where a
part of the IP address space identifies the domain so that an
address is routable to the domain but the additional semantics
are used only within the domain, or is the address used
exclusively within the domain so that the external impact of the
routability of the address that carries additional semantics is
not important?
2. What will be the impact on existing routing systems? What would
happen if an address with additional semantics was released
according to normal operations, accidentally, or maliciously?
How would the existing routing systems react? For example: how
are cryptographically generated addresses made routable; how are
the semantic parts of an address distinguished from the routable
parts; is there an impact on the size and maintenance of routing
tables due to the addition of semantics to addresses?
3. What path characteristics are needed for the routed paths? Since
one of the purposes of adding semantics to IP addresses is to
cause special processing by routers, it is important to
understand what behaviors are wanted. Such path characteristics
include (but are not limited to):
* Quality: expressed in terms of throughput, latency, jitter,
drop precedence, etc.
* Resilience: expressed in terms of survival of network failures
and delivery guarantees;
* Destination: How is a destination address to be interpreted if
it encodes a choice of actual destinations?
In these cases, how do the routing protocols utilize the address
semantics to determine the desired characteristics? What
additional information about the network does the protocol need
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to gather? What changes to the routing algorithm is needed to
deliver packets according to the desired characteristics?
4. Can we solve these routing challenges with existing routing tools
and methods? We can break this question into more detailed
questions.
* Is new hardware needed? Existing deployed hardware has
certain assumptions about how forwarding is carried out based
on IP addresses and routing tables.
* Do we need new routing protocols? We might ask some
subsidiary questions:
+ Can we make do with existing protocols, possibly by tuning
configuration parameters or using them out of the box?
+ Can we make simple backward-compatible modifications to
existing protocols such that they work for today's IP
addresses as well as enhanced-semantic addresses?
+ Do we need entirely new protocols or radically evolutions
of existing protocols in order to deliver the functions
that we need?
+ Should we focus on the benefits of optimized routing
solutions, or should we attempt to generalize to enable
wider applicability?
Do we need new management tools and techniques? Management of
the routing system (especially diagnostic management) is a
crucial and often neglected part of the problem space.
5. What is the scalability impact for routing systems? Scalability
can be measured as:
* Routing table size. How many entries need to be maintained in
the routing table? Some approaches to semantic addressing may
be explicitly intended to address this problem.
* Routing performance. Routing performance may be considered in
terms of the volume of data that has to be exchanged both to
establish and to maintain the routing tables at the
participating routers. It may also be measured in terms of
how much processing is required to derive new routes when
there is a change in the network routing information.
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* Routing convergence is the time that it takes for a routing
protocol to discover changes (especially faults) in the
network, to distribute the information about any changes to
the network, and to reach a stable state across the network
such that packets are routed consistently.
For all questions of routing scalability, research that presents
real numbers based on credible example networks is highly
desirable.
6. To what extent can multicast be developed:
* To support programmable SDN systems such as P4 [BIER-P4]?
* To satisfy end-to-end applications?
* To apply per-packet multicasting to develop new services?
* As a separate network layer distinct from IP or by encoding
group destinations into IP addresses?
7. What aspects need to be standardised? It is really important to
understand the necessity of standardization within this research.
What degree of interoperability is expected between devices and
networks? Is the limited domain so constrained (for example, to
a single equipment vendor) that standardization would be
meaningless? Is the application so narrow (for example, in niche
hardware environments) such that interoperability is best handled
by agreements among small groups of vendors such as in industry
consortia?
8. Security Considerations
TBD
This section should summarize the novel security issues raised for
routing by semantic routing. It does not need to cover all other
security considerations for semantic routing.
9. IANA Considerations
This document makes no requests for IANA action.
10. Acknowledgements
Thanks to Stewart Bryant for useful conversations. Luigi Iannone,
Robert Raszuk, Dirk Trossen, and Ron Bonica made helpful comments.
The text on Dyncast is based on suggestions from Dirk Trossen, Luigi
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Iannone, and Yizhou Li. Toerless Eckert suggested text for the
multicast sections.
This work is partially supported by the European Commission under
Horizon 2020 grant agreement number 101015857 Secured autonomic
traffic management for a Tera of SDN flows (Teraflow).
11. Contributors
TBD
12. Informative References
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Evaluation of Scalable and Resilient Multicast with BIER
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hdr-update-04 (work in progress), August 2020.
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L., and Y. Qu, "Preferred Path Routing (PPR) in IS-IS",
draft-chunduri-lsr-isis-preferred-path-routing-06 (work in
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[I-D.ietf-lisp-rfc6830bis]
Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
Cabellos-Aparicio, "The Locator/ID Separation Protocol
(LISP)", draft-ietf-lisp-rfc6830bis-36 (work in progress),
November 2020.
[I-D.ietf-lisp-rfc6833bis]
Farinacci, D., Maino, F., Fuller, V., and A. Cabellos-
Aparicio, "Locator/ID Separation Protocol (LISP) Control-
Plane", draft-ietf-lisp-rfc6833bis-30 (work in progress),
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[I-D.ietf-spring-srv6-network-programming]
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Matsushima, S., and Z. Li, "SRv6 Network Programming",
draft-ietf-spring-srv6-network-programming-28 (work in
progress), December 2020.
[I-D.ietf-v6ops-ipv6-ehs-packet-drops]
Gont, F., Hilliard, N., Doering, G., Kumari, W., Huston,
G., and W. LIU, "Operational Implications of IPv6 Packets
with Extension Headers", draft-ietf-v6ops-ipv6-ehs-packet-
drops-03 (work in progress), January 2021.
[I-D.irtf-panrg-path-properties]
Enghardt, T. and C. Krahenbuhl, "A Vocabulary of Path
Properties", draft-irtf-panrg-path-properties-01 (work in
progress), September 2020.
[I-D.irtf-panrg-what-not-to-do]
Dawkins, S., "Path Aware Networking: Obstacles to
Deployment (A Bestiary of Roads Not Taken)", draft-irtf-
panrg-what-not-to-do-16 (work in progress), December 2020.
[I-D.jia-scenarios-flexible-address-structure]
Jia, Y., Li, G., and S. Jiang, "Scenarios for Flexible
Address Structure", draft-jia-scenarios-flexible-address-
structure-00 (work in progress), October 2020.
[I-D.jiang-semantic-prefix]
Jiang, S., Qiong, Q., Farrer, I., Bo, Y., and T. Yang,
"Analysis of Semantic Embedded IPv6 Address Schemas",
draft-jiang-semantic-prefix-06 (work in progress), July
2013.
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[I-D.li-dyncast-architecture]
Li, Y., Iannone, L., Trossen, D., and P. Liu, "Dynamic-
Anycast Architecture", draft-li-dyncast-architecture-00
(work in progress), February 2021.
[I-D.liu-dyncast-ps-usecases]
Liu, P., Willis, P., and D. Trossen, "Dynamic-Anycast
(Dyncast) Use Cases and Problem Statement", draft-liu-
dyncast-ps-usecases-01 (work in progress), February 2021.
[I-D.muscariello-intarea-hicn]
Muscariello, L., Carofiglio, G., Auge, J., Papalini, M.,
and M. Sardara, "Hybrid Information-Centric Networking",
draft-muscariello-intarea-hicn-04 (work in progress), May
2020.
[ICNref] Barbera, D., Xylomenos, G., Ververidis, C., Siris, V., and
N. Fotiou, "A Survey of information-centric networking
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<https://www.scopus.com/record/
display.uri?eid=2-s2.0-84901242669>.
[IOTSURVEYref]
Sheng, Z., Yang, S., Vasilakos, A., Mccann, J., and K.
Leung, "A Survey on the IETF Protocol Suite for the
Internet of Things: standards, challenges, and
opportunities", Paper IEEE Wireless Communications, vol.
20, no. 6, Dec 2013, 2014,
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routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode network service", standard ISO/IEC
10589, 2002, <https://standards.iso.org/ittf/
PubliclyAvailableStandards/
c030932_ISO_IEC_10589_2002(E).zip>.
[ITUNET2030ref]
"Network 2030 Architecture Framework", Technical
Specification ITU-T Focus Group on Technologies for
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T/focusgroups/net2030/Documents/Network_2030_Architecture-
framework.pdf>.
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[MBONEref]
Savetz, K., Randall, N., and Y. Lepage, "MBONE:
Multicasting Tomorrow's Internet", Book IDG, 1996,
<https://www.savetz.com/mbone/>.
[MULTICAST-SRref]
Jia, W. and W. He, "A Scalable Multicast Source Routing
Architecture for Data Center Networks", Paper IEEE
Journal on Selected Areas in Communications, vol. 32, no.
1, pp. 116-123, January 2014, 2014,
<https://ieeexplore.ieee.org/document/6799682>.
[NDNref] Zhang, L., Afanasyev, A., and J. Burke, "Named Data
Networking", Paper ACM SIGCOMM Computer Communication,
Review 44(3): 66-73, 2014, 2014.
[OPENSRNref]
Ren, P., Wang, X., Zhao, B., Wu, C., and H. Sun, "OpenSRN:
A Software-defined Semantic Routing Network Architecture",
Paper IEEE Conference on Computer Communications Workshops
(INFOCOM WKSHPS), Hong Kong, 2015, 2015,
<https://www.researchgate.net/
publication/308827498_OpenSRN_A_software-
defined_semantic_routing_network_architecture>.
[PANRGref]
"Path Aware Networking Research Group", RG Path Aware
Networking Research Group,
<https://datatracker.ietf.org/rg/panrg/about>.
[RESEARCHFIAref]
Pan, J., Paul, S., and R. Jain, "A Survey of the Research
on Future Internet Architectures", Paper IEEE
Communications Magazine, vol. 49, no. 7, July 2011, 2014,
<https://ieeexplore.ieee.org/document/5936152>.
[RFC1069] Callon, R. and H. Braun, "Guidelines for the use of
Internet-IP addresses in the ISO Connectionless-Mode
Network Protocol", RFC 1069, DOI 10.17487/RFC1069,
February 1989, <https://www.rfc-editor.org/info/rfc1069>.
[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, DOI 10.17487/RFC1112, August 1989,
<https://www.rfc-editor.org/info/rfc1112>.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>.
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[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[RFC2730] Hanna, S., Patel, B., and M. Shah, "Multicast Address
Dynamic Client Allocation Protocol (MADCAP)", RFC 2730,
DOI 10.17487/RFC2730, December 1999,
<https://www.rfc-editor.org/info/rfc2730>.
[RFC2776] Handley, M., Thaler, D., and R. Kermode, "Multicast-Scope
Zone Announcement Protocol (MZAP)", RFC 2776,
DOI 10.17487/RFC2776, February 2000,
<https://www.rfc-editor.org/info/rfc2776>.
[RFC2909] Radoslavov, P., Estrin, D., Govindan, R., Handley, M.,
Kumar, S., and D. Thaler, "The Multicast Address-Set Claim
(MASC) Protocol", RFC 2909, DOI 10.17487/RFC2909,
September 2000, <https://www.rfc-editor.org/info/rfc2909>.
[RFC3618] Fenner, B., Ed. and D. Meyer, Ed., "Multicast Source
Discovery Protocol (MSDP)", RFC 3618,
DOI 10.17487/RFC3618, October 2003,
<https://www.rfc-editor.org/info/rfc3618>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
<https://www.rfc-editor.org/info/rfc4607>.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[RFC4984] Meyer, D., Ed., Zhang, L., Ed., and K. Fall, Ed., "Report
from the IAB Workshop on Routing and Addressing",
RFC 4984, DOI 10.17487/RFC4984, September 2007,
<https://www.rfc-editor.org/info/rfc4984>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
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[RFC6308] Savola, P., "Overview of the Internet Multicast Addressing
Architecture", RFC 6308, DOI 10.17487/RFC6308, June 2011,
<https://www.rfc-editor.org/info/rfc6308>.
[RFC6740] Atkinson, RJ. and SN. Bhatti, "Identifier-Locator Network
Protocol (ILNP) Architectural Description", RFC 6740,
DOI 10.17487/RFC6740, November 2012,
<https://www.rfc-editor.org/info/rfc6740>.
[RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
Locator/ID Separation Protocol (LISP)", RFC 6830,
DOI 10.17487/RFC6830, January 2013,
<https://www.rfc-editor.org/info/rfc6830>.
[RFC7094] McPherson, D., Oran, D., Thaler, D., and E. Osterweil,
"Architectural Considerations of IP Anycast", RFC 7094,
DOI 10.17487/RFC7094, January 2014,
<https://www.rfc-editor.org/info/rfc7094>.
[RFC7285] Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
"Application-Layer Traffic Optimization (ALTO) Protocol",
RFC 7285, DOI 10.17487/RFC7285, September 2014,
<https://www.rfc-editor.org/info/rfc7285>.
[RFC7450] Bumgardner, G., "Automatic Multicast Tunneling", RFC 7450,
DOI 10.17487/RFC7450, February 2015,
<https://www.rfc-editor.org/info/rfc7450>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<https://www.rfc-editor.org/info/rfc7665>.
[RFC7872] Gont, F., Linkova, J., Chown, T., and W. Liu,
"Observations on the Dropping of Packets with IPv6
Extension Headers in the Real World", RFC 7872,
DOI 10.17487/RFC7872, June 2016,
<https://www.rfc-editor.org/info/rfc7872>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
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[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.
[RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
"Network Service Header (NSH)", RFC 8300,
DOI 10.17487/RFC8300, January 2018,
<https://www.rfc-editor.org/info/rfc8300>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8596] Malis, A., Bryant, S., Halpern, J., and W. Henderickx,
"MPLS Transport Encapsulation for the Service Function
Chaining (SFC) Network Service Header (NSH)", RFC 8596,
DOI 10.17487/RFC8596, June 2019,
<https://www.rfc-editor.org/info/rfc8596>.
[RFC8684] Ford, A., Raiciu, C., Handley, M., Bonaventure, O., and C.
Paasch, "TCP Extensions for Multipath Operation with
Multiple Addresses", RFC 8684, DOI 10.17487/RFC8684, March
2020, <https://www.rfc-editor.org/info/rfc8684>.
[RFC8736] Venaas, S. and A. Retana, "PIM Message Type Space
Extension and Reserved Bits", RFC 8736,
DOI 10.17487/RFC8736, February 2020,
<https://www.rfc-editor.org/info/rfc8736>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8763] Rahman, A., Trossen, D., Kutscher, D., and R. Ravindran,
"Deployment Considerations for Information-Centric
Networking (ICN)", RFC 8763, DOI 10.17487/RFC8763, April
2020, <https://www.rfc-editor.org/info/rfc8763>.
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[RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet
Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
<https://www.rfc-editor.org/info/rfc8799>.
[RINAref] Day, J., "Patterns in Network Architecture: A Return to
Fundamentals", Book Prentice Hall, 2008.
[SCIONref]
Barbera, D., Chaut, L., Perrig, A., Reischuk, R., and P.
Szalachowski, "Patterns in Network Architecture: A Return
to Fundamentals", Paper The ACM, vol. 60, no. 6, June
2017, 2017,
<https://icnp20.cs.ucr.edu/Slides/NIPAA/D-3_invited.pptx>.
[SEMANTICRTG]
Strassner, J., Sung-Su, K., and J. Won-Ki, "Semantic
Routing for Improved Network Management in the Future
Internet", Book Chapter Springer, Recent Trends in
Wireless and Mobile Networks, 2010, 2010,
<https://link.springer.com/
chapter/10.1007/978-3-642-14171-3_14>.
[TERASTREAMref]
Zaluski, B., Rajtar, B., Habjani, H., Baranek, M., Slibar,
N., Petracic, R., and T. Sukser, "Terastream
implementation of all IP new architecture", Paper 36th
International Convention on Information and Communication
Technology, Electronics and Microelectronics (MIPRO),
2013, 2013,
<https://ieeexplore.ieee.org/document/6596297>.
Authors' Addresses
Daniel King
Lancaster University
Email: d.king@lancaster.ac.uk
Joanna Dang
Huawei Technologies
Email: dangjuanna@huawei.com
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Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
King, et al. Expires August 26, 2021 [Page 39]