An Introduction to Semantic Routing
draft-farrel-irtf-introduction-to-semantic-routing-00
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draft-farrel-irtf-introduction-to-semantic-routing-00
IRTF A. Farrel
Internet-Draft Old Dog Consulting
Intended status: Informational D. King
Expires: May 12, 2022 Lancaster University
November 8, 2021
An Introduction to Semantic Routing
draft-farrel-irtf-introduction-to-semantic-routing-00
Abstract
Many proposals have been made to add semantics to IP packets by
placing additional information existing fields, by adding semantics
to IP addresses, or by adding fields to the packets. The intent is
to facilitate enhanced routing decisions based on these additional
semantics to provide differentiated paths for different packet flows
distinct from simple shortest path first routing. The process is
known as Semantic Routing.
This document provides a brief introduction to Semantic Routing.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Objectives and Scope . . . . . . . . . . . . . . . . . . . . 4
3. Approaches to Semantic Routing . . . . . . . . . . . . . . . 5
3.1. Packet and Service Routing . . . . . . . . . . . . . . . 7
4. Semantic Routing Information . . . . . . . . . . . . . . . . 7
4.1. Address Space Partitioning . . . . . . . . . . . . . . . 7
4.2. Prefix-based Contextual Address Usage . . . . . . . . . . 8
4.3. Semantic Addressing . . . . . . . . . . . . . . . . . . . 8
4.4. Flow Marking . . . . . . . . . . . . . . . . . . . . . . 8
4.5. Deep Packet Inspection . . . . . . . . . . . . . . . . . 8
4.6. Semantic Field Overloading . . . . . . . . . . . . . . . 9
4.7. IPv6 Extension Headers . . . . . . . . . . . . . . . . . 9
4.8. New Extensions . . . . . . . . . . . . . . . . . . . . . 9
5. Architectural Considerations . . . . . . . . . . . . . . . . 9
5.1. Isolated Domains . . . . . . . . . . . . . . . . . . . . 10
5.2. Bridged Domains . . . . . . . . . . . . . . . . . . . . . 10
5.3. Semantic Prefix Domains . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 11
10. Informative References . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
Historically, the meaning of an IP address has been to identify an
interface on a network device. Network routing protocols were
initially designed to determine paths through the network toward
destination addresses so that IP packets with a common destination
address converged on that destination. Anycast and multicast
addresses were also defined, and these new address semantics
necessitated variations to the routing protocols, and in some casese
the development of new protocols.
Over time, routing decisions were enhanced to route packets according
to additional information carried within the packets and dependent on
policy coded in, configured at, or signaled to the routers. Perhaps
the most obvious example is Equal-Cost Multipath (ECMP) where a
router makes a consistent choice for forwarding packets over a number
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of parallel links or paths based on the values of a set of fields in
the packet header.
Upper-layer applications are placing increasingly sophisticated
demands on the network for better quality, more predictability, and
increased reliability. Some of these applications are futuristic
predictions (for example, haptic augmented reality multiplayer 3D
worlds), some are new ideas on the threshold of roll-out (such as
holographic conferencing), and many are rapidly developing sectors
with established revenue streams (such as multiplayer immersive
gaming).
At the same time, lower-layer network technologies are advancing
rapidly providing increased bandwidth to the home and to mobile hand-
held devices. These advances create an environment that enables the
potential of advanced applications being run by very many end-users.
This coincides with a growing trend to extend end-to-end
communications to include machines and services, and to introduce
routing and addressing behaviors and semantics specific to a
particular use case and set of requirements applied within a limited
region or domain of the Internet. Examples of these three
developments include 5G, predicted wireless evolutions, IoT and
vehicular connectivity, space-terrestrial communication, industrial
networks, cloud computing, service function chaining and network
functions virtualization, digital twins, and data-centric data
brokerage platforms.
Despite this plurality of communication scenarios, IP-based
addressing and network layer routing have remained focused on
identifying locations of communication and determining paths between
those locations. This has previously depended on higher-layer
capabilities (e.g., for name-to-location resolution) to support those
comprehensive communication scenarios, but that approach introduces
latency and dependencies (e.g., changing locator assignments may
depend on the capabilities of the upper-layer capability that are
outside the core addressing and routing system). Furthermore, multi-
layer lookups and interactions may impact the efficacy of
communication scenarios, particularly those that employ different
routing and addressing approaches beyond just locators.
"Semantic Routing" places the support for advanced routing and
location functions directly at the packet routing layer, such as
through extensions to the identification properties of addresses (so
that the address indicates more than just the network location) or
through performing routing functions on an extended set of inputs
(for example, other fields carried in packet headers). Such an
approach should preserve the Internet architecture as it is today
while enabling additional routing function.
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This document provides a brief introduction to semantic routing and
outlines the possible approaches that might be taken. A separate
document ([I-D.king-irtf-semantic-routing-survey]) makes a start at a
survey of pre-existing work in this area, while
[I-D.king-irtf-challenges-in-routing] sets out some of the issues
that should be considered when researching, developing, or proposing
a semantic routing scheme.
2. Objectives and Scope
As with all advances in Internet protocols, semantic routing may be
considered for Internet-wide deployment or may be restricted
(possibly only initially) to well-defined and contained networks
referred to as "limited domains" (see [RFC8799]). The information
used for semantic routing may be opaque within the network (in other
words, the additional information is not visible to the routers), may
be transparent (so that routers may see the information, but their
processing does not need to be changed to accommodate the information
or its encoding), or may be active (so that semantic routing is fully
enabled).
Semantic routing may select paths in one domain that are not
consistent with the paths selected in other domains.
In any case, concern and consideration must be coexistence with, and
backward compatibility to, existing routing and addressing schemes
that are widely deployed.
A strategic objective of semantic routing, and associated semantic
enhancements, is to enable Service Providers to modify the default
forwarding behaviour to be based on other information present in the
packet and policy configured or dynamically programmed into the
routers and devices. This is aimed to cause new and alternative path
processing by routers, including:
o Determinism of quality of delivery in terms of throughput,
latency, jitter, drop precedence.
o Determinism of resilience in terms of survival of network failures
and delivery degradation.
o Determinism of routing performance in terms of the volume of data
that has to be exchanged both to establish and to maintain the
routing tables.
o Deployability in terms of configuration, training, development of
new hardware/software, and interaction with pre-existing network
technologies and uses.
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o Efficiency of manageability in terms of:
1. diagnostic management
2. management of Service KPIs with/without guarantees
3. dynamic and controlled instantiation of management information
in the packets.
Issues of security and privacy have been largely overlooked within
the routing systems. However, there is increasing concern that
attacks on routing systems can not only be disruptive (for example,
causing traffic to be dropped), but may cause traffic to be routed
via inspection points that can breach the security or privacy of the
payloads. While semantic routing may offer tools for increasing
security and privacy, it is possible that semantic routing and the
additional information that may be carried in packets to enable
semantic routing may provide vectors for attacks or compromise
privacy. This must be examined by any semantic routing proposals.
3. Approaches to Semantic Routing
Typically, in an IP-based network packets are forwarded using the
least-cost path to the destination IP address. Service Providers may
also use techniques to modify the default forwarding behavior based
on other information present in the packet and configured or
programmed into the routers. These mechanisms, sometimes called
semantic routing techniques include "Preferential Routing", "Policy-
based Routing", and "Flow Steering".
Examples of existing semantic routing usage in IP-based networks
include the following.
o Using addresses to identify different device types so that their
traffic may be handled differently [SEMANTICRTG].
o Expressing how a packet should be handled, prioritized, or
allocated network resources as it is forwarded through the network
[TERASTREAMref].
o Deriving IP addresses from the lower layer identifiers and using
addresses depending on the underlying connectivity (for example,
[RFC6282].
o Indicating the application or network function on a destination
device or at a specific location; or enable Service Function
Chaining (SFC).
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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 Content-based routing (CBR), forwarding of the packet based on
message content rather than the destination addresses
[OPENSRNref].
o Identifying hierarchical connectivity so that routing can be
simplified [EIBPref].
o Providing geographic location information within addresses
[GEO-IPref].
o Using cryptographic algorithms to mask the identity of the source
or destination, masking routing tables within the domain, while
still enabling packet forwarding across the network
[BLIND-FORWARDINGref].
A more comprehensive list of existing implementations and research
projects can be found in [I-D.king-irtf-semantic-routing-survey].
Semantic routing, operates to forward packets dependent on
information carried in the packets and rules present in the routers.
Those rules could be:
o Built into the routers
o Configured network-wide in the routers
o Configured per-router in a relatively static way
o Programmed to the routers in a dynamic way, for example, through
software defined networking (SDN)
o Distributed dynamically through the network using routing or
signalling protocols
Semantic routing will also require information about network state
and capabilities just as existing shortest path first routing systems
do. That may require information (such as link delays or other
qualitative attributes) to be collected by network nodes and
distributed between routers by routing protocols. Alternatively,
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this information could be collected centrally by a network controller
and used to derive the rules installed in the routers.
Forwarding by the router is based on a look-up of the semantic
routing information carried in the packet (see Section 4) and
forwarding instructions programmed into the forwarding element. The
actions to perform may be derived by the router based on the rules
and information that the router has collected, or may be programmed
directly from the network controller.
3.1. Packet and Service Routing
Routing is the process of selecting a path for traffic in a network
or between or across multiple networks. For example, IP routing uses
IP addresses for source and destination identification and is
typically used for packet networks, such as the Internet. IP routing
assumes that network addresses are structured and facilitates routing
entries in a routing table entry to represent a group of IP capable
devices.
Service routing and information-centric networking (ICN) use an
overlay approach that creates a layer on top of the IP network.
Control of the overlay necessitates augmentation of existing routing
mechanisms, or entirely new discovery, propagation and resource
management protocols and procedures.
IP Routing and service routing are not the same thing.
4. Semantic Routing Information
The subsections below describe some of the common techniques to
enable semantic routing in more detail. The sections are unordered
and no meaning should be assigned to how one approach is presented
before another. They are not a complete list of possible approaches.
The approaches described here have many advantages and disadvantages.
The purpose here is not to determine which approach is best or most
appropriate, and so those advantages and disadvantages are not
discussed. The reader will inevitably have a preference and see
drawbacks.
4.1. Address Space Partitioning
In some cases, an address prefix is assigned a special purpose and
meaning. When such an address appears in the packet's address field,
a router can know from the prefix that particular routing/forwarding
actions are required. An example of this approach is seen in
multicast addressing.
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4.2. Prefix-based Contextual Address Usage
The owner of a prefix to use the low-order bits of an address for
their own purposes.
The semantics of such an approach might be coordinated between prefix
owners, or could be indicated through information that is part of the
encoding, and is standardised.
4.3. Semantic Addressing
Semantic addressing is a term applied to any approach that adds
semantics to IP addresses. This includes the mechanisms described in
Section 4.1 and Section 4.2. Other semantic addressing proposals
suggest variable address lengths, hierarchical addresses, or a
structure to addresses so that they can carry additional information
in a common way.
In any case, semantic addressing intends to facilitate routing
decisions based solely on the address and without the need to find
and process information carried in other fields within the packets.
4.4. Flow Marking
Flow marking is a way of indicating, in a simple field in the packet
header, the treatment that the packet should receive in the network.
In IPv4 the six-bit DSCP field is commonly used for this purpose. In
IPv6, while the Traffic Class field could be used, it is generally
recommended that the Flow Label field should serve this and a more
general purpose.
4.5. Deep Packet Inspection
The term "deep packet inspection" (DPI) is used here to mean that the
router examines various packet fields, including those beyond the IP
packet header. For example, many router processes may look at the
"five-tuple" consisting of:
o source address
o destination address
o next protocol
o transport protocol source port
o transport protocol destination port
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4.6. Semantic Field Overloading
"Overloading" is a term applied to placing additional semantics on
the contents of a field beyond how it is specified. This is
relatively hard to do in an IPv6 header because the number of fields
is small, and all fields have specific meanings that are needed in
all cases. In IPv4 there may be more opportunity to use some fields
in very controlled situations to carry additional semantics that can
be used for semantic routing.
4.7. IPv6 Extension Headers
IPv6 defines extension headers explicitly for carrying information
that may be used by routers along the path. This information can be
used to instruct all routers, only the router indicated by the
destination address, or by the ultimate destination of the packet.
Extension headers may carry any information to enable semantic
routing.
4.8. New Extensions
Another approach is to define a new protocol extension to carry
information on which semantic routing can be performed. Such an
extension could be in the form of a new extension header (see
Section 4.7) or as a new shim encapsulation immediately after the IP
header.
5. Architectural Considerations
Some semantic routing 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.
Semantic data 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. An overlay may
be achieved in a higher protocol 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 thereby joining
together those nodes that use the semantic data.
The application of semantics may also be constrained to within a
limited domain. In some cases, such a domain will use IP, but be
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disconnected from Internet (see Section 5.1). 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 (see Section 5.2). And in still another
case traffic from the domain is routed across the Internet to other
nodes and this requires backward-compatible routing approaches (see
Section 5.3).
5.1. Isolated Domains
Some IP network domains are entirely isolated from the Internet and
other IP-based networks. In these cases, there is no risk to
external networks from any semantic routing schemes carried out
within the domain.
Many approaches in isolated domains will utilize environment-specific
routing protocols. For example, those suited to constrained
environments (for IoT) or mobile environments (for smart vehicles).
Such routing protocols can be optimized for the exchange of
information specific to semantic routing.
5.2. Bridged Domains
In some deployments, it will be desirable to connect together a
number of isolated domains to build a larger network. These domains
may be connected (or bridged) over an IP network or even over the
Internet.
Ideally, the function of the bridged domains should not be impeded by
how they are connected, and the operation of the IP network providing
the connectivity should not be compromised by the act of carrying
traffic between the domains. This can generally be achieved by
tunneling the packets between domains using any tunneling technique,
and this will not require the IP network to know about the semantic
routing used by the domains.
An alternative to tunneling is achieved using gateway functionality
where packets from a domain are mapped at the domain boundary to
produce regular IP packets that are sent across the IP network to the
boundary of the destination domain where they are mapped back into
packets for use within that domain.
5.3. 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. This is achieved by
assigning a routable address prefix (or a set of prefixes) for use
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with semantic addressing and routing so that packets may be routed
through the regular IP network (or the Internet) using the prefix and
without encountering or having to use any semantic addressing. Once
delivered to the semantic prefix domain, a packet can be subjected to
whatever semantic routing is enabled in the domain.
6. Security Considerations
Semantic routing must give full consideration to the security and
privacy issues that are introduced by these mechanisms. Placing
additional information into packet header fields might reveal details
of what the packet is for, what function the user is performing, who
the user is, etc. Furthermore, in-flight modification of the
additional information might not directly change the destination of
the packet, but might change how the packet is handled within the
network and at the destination.
It should also be considered how packet encryption techniques that
are increasingly popular for end-to-end or edge-to-edge security may
obscure the semantic information carried in some fields of the packet
header or found deeper in the packet. This may render some semantic
routing techniques impractical and may dictate other methods of
carrying the necessary information to enable semantic routing.
7. IANA Considerations
This document makes no requests for IANA action.
8. Acknowledgements
TBD
9. Contributors
TBD
10. Informative References
[BLIND-FORWARDINGref]
Simsek, I., "On-Demand Blind Packet Forwarding",
Paper 30th International Telecommunication Networks and
Applications Conference (ITNAC), 2020, 2020,
<https://www.computer.org/csdl/proceedings-article/
itnac/2020/09315187/1qmfFPPggrC>.
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[CONTENT-RTG-MOBILEref]
Liu, H. and W. He, "Rich Semantic Content-oriented Routing
for mobile Ad Hoc Networks", Paper The International
Conference on Information Networking (ICOIN2014), 2014,
2014, <https://ieeexplore.ieee.org/document/6799682>.
[EIBPref] Shenoy, N., "Can We Improve Internet Performance? An
Expedited Internet Bypass Protocol", Presentation 28th
IEEE International Conference on Network Protocols, 2020,
<https://icnp20.cs.ucr.edu/Slides/NIPAA/D-3_invited.pptx>.
[GEO-IPref]
Dasu, T., Kanza, Y., and D. Srivastava, "Geotagging IP
Packets for Location-Aware Software-Defined Networking in
the Presence of Virtual Network Functions", Paper 25th ACM
SIGSPATIAL International Conference on Advances in
Geographic Information Systems (ACM SIGSPATIAL 2017),
2017, <https://about.att.com/ecms/dam/sites/labs_research/
content/publications/
AI_Geotagging_IP_Packets_for_Location.pdf>.
[I-D.jiang-semantic-prefix]
Jiang, S., Sun, 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.
[I-D.king-irtf-challenges-in-routing]
King, D. and A. Farrel, "Challenges for the Internet
Routing Infrastructure Introduced by Changes in Address
Semantics", draft-king-irtf-challenges-in-routing-03 (work
in progress), June 2021.
[I-D.king-irtf-semantic-routing-survey]
King, D. and A. Farrel, "A Survey of Semantic Internet
Routing Techniques", draft-king-irtf-semantic-routing-
survey-02 (work in progress), June 2021.
[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>.
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[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>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.
[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>.
[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
Adrian Farrel
Old Dog Consulting
UK
Email: adrian@olddog.co.uk
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Daniel King
Lancaster University
UK
Email: d.king@lancaster.ac.uk
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