Network Working Group S. Jiang, Ed.
Internet-Draft Huawei Technologies Co., Ltd
Intended status: Informational Q. Sun
Expires: August 3, 2013 China Telecom
I. Farrer
Deutsche Telekom AG
January 30, 2013
A Framework for Semantic IPv6 Prefix and Gap Analysis
draft-jiang-semantic-prefix-04
Abstract
Some Internet Service Providers and enterprises require detailed
information about the payload of traffic, so that packets can be
treated differently and efficiently. Packet-level differentiation
can also enable flow-level and user-level differentiation.
With its large address space, IPv6 allows semantics to be embedded
into addresses by assigning additional significance to specific bits
within the prefix. Using these semantics, routers and other
intermediary devices can easily apply relevant policies as required.
This document describes a framework for such an approach. It also
analyses the technical advantages and limitations associated with
such an approach.
This informational document only discusses the usage of semantics
within a single network, or group of interconnected networks which
share a common addressing policy, referred to as a Semantic Prefix
Domain.
The document is NOT intended to suggest the standardization of any
common global semantics.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 3, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Existing Approaches to Traffic Differentiation . . . . . . . . 4
2.1. Differentiated Services . . . . . . . . . . . . . . . . . 4
2.2. Deep Packet Inspection . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Justifcation for Semantics with the IPv6 Prefix . . . . . . . 5
5. The Semantic Prefix Domain . . . . . . . . . . . . . . . . . . 6
6. The Embedded Semantics . . . . . . . . . . . . . . . . . . . . 7
7. Applicability Examples . . . . . . . . . . . . . . . . . . . . 8
7.1. An ISP Semantic Prefix Example . . . . . . . . . . . . . . 8
7.2. A Semantic Prefix for Security Domains . . . . . . . . . . 9
7.3. A Multi-Prefix Semantic . . . . . . . . . . . . . . . . . 9
8. Semantic Prefix Benefits . . . . . . . . . . . . . . . . . . . 9
9. Gaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Semantic Relevant Operations in Networks . . . . . . . . . 11
9.2. Semantic Relevant Interactions with Hosts . . . . . . . . 11
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
11. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 12
12. Security Considerations . . . . . . . . . . . . . . . . . . . 12
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
14.1. Normative References . . . . . . . . . . . . . . . . . . . 13
14.2. Informative References . . . . . . . . . . . . . . . . . . 13
Appendix A. Appendix A: Topics for Future Extention . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
As the global Internet expands, it is being used for an increasingly
diverse range of services. These services place differentiated
requirements upon packet delivery networks meaning that Internet
Service Providers and enterprises need to be aware of more
information about each packet in order to best meet a specific
service's needs.
Within a specific prefix, source/destination location information is
used for routing decisions. However, user types, service types,
applications, security requirements, traffic identity types, quality
requirements and other criteria may also be relevant parameters which
a network operator may wish to use to treat packets differently and
efficiently. Packet-level differentiation can also be used for flow-
level and user-level differentiation.
However, almost all of the above mentioned criteria are not expressed
explicitly within an packet. Hence, it is difficult for network
operators to identify from packet level.
2. Existing Approaches to Traffic Differentiation
There are several existing approaches which have been developed that
can assist operators in identifying and marking traffic. These
solutions were mainly developed in the IPv4 era, where the IP address
is used as a host locator and little else. The limited capacity of a
32-bit IPv4 address provides very little room for encoding additional
information. Correspondingly, these approaches are indirect,
inefficient and expensive for operators.
2.1. Differentiated Services
Quality of Service (QoS) based on and Differentiated Services
[RFC2474] is a widely deployed framework specifying a simple,
scalable and coarse-grained mechanism for classifying and managing
network traffic. But in a service provider's network, DiffServ
codepoint (DSCP) values cannot be trusted when they are set by the
customer as these are arbitrary values.
In real-world scenarios, ISPs deploy "remarking" points at the
customer edge 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 and
transport layer source/destination ports.
The traffic classification process leads to increased packet
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processing overhead and complexity at the edge of the service
provider's network.
The DSCP in the IPv6 header traffic class field allows 6-bits for
encoding service provider specific information related to the
contents of the packet. Whilst this is a useful part of an overall
packet differentiation architecture, the relative small number of
available bits (when compared to the available number of bits within
the service providers prefix) means that it cannot be used in
isolation.
2.2. Deep Packet Inspection
Deep Packet Inspection (DPI) may also be used by ISPs to learn the
characteristics of users packets. This involves looking into the
packet well beyond the network-layer header to identify the specific
application traffic type. Once identified, the traffic type can be
used as an input for setting the packet's DSCP or other actions.
But DPI is expensive both in processing costs and latency. The
processing costs means that dedicated infrastructure is necessary to
carry out the function. The incurred latency may be too much for use
with any delay/jitter sensitive applications. As a result, DPI is
difficult for large-scale deployment and it's usage is usually
limited to small and specific functions in the network.
3. Terminology
The following terms are used throughout this document:
Semantic Prefix: A flexible-length IPv6 prefix which embeds certain
semantics.
Semantic Prefix Domain: A portion of the Internet over which a
consistent semantic-prefix based policy is in operation.
Semantic Prefix Policy: [IF - I think that this could simplify
wording elsewhere in the document] Write this
4. Justifcation for Semantics with the IPv6 Prefix
The IPv6 address can remove such limitations due to its large address
space. This can be used by service provides to embed certain pre-
defined semantics into an address so that intermediate devices can
easily apply relevant forwarding operations each packet based solely
on network layer source and destination address information.
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Using semantic prefix information for this function also makes it
possible for the service provider to increase the level of trust in a
customer-generated packet. If the packet has an incorrectly set
source or destination address, then a session will simply fail to
establish.
This document describes a framework for embedding semantics into IPv6
prefixes so that network devices can process and forward packets
based on these semantics. This approach diverts much network
complexity to the planning and management of IPv6 address and IP
address based policies. It indeed simplifies the management of ISP
networks.
Different service providers may make very different choices regarding
the specific semantics which are relevant to their networks.
Semantic prefix definitions are only meaningful within a domain which
implements a single policy. Therefore, it is not possible or
desirable to attempt to standardize a general semantic prefix policy.
Although the interface identifier portion of an IPv6 address has
arbitrary bits and extension headers can carry significantly more
information, these fields can not be trusted by network operators.
Users may easily change the setting of interface identifier or
extension header in order to obtain undeserved priorities/privileges,
while servers or enterprise users may be much more self-restricted
since they are charged accordingly.
The prefix can offer a higher level of trust for the network operator
because it is delegated by the network and therefore the network is
better able to detect any undesired modifications and filter the
packet accordingly. If a user manipulated the destination address,
the packet will never arrive at the desired service; if the source
address is altered, then the return packet will not be received.
5. The Semantic Prefix Domain
A Semantic Prefix Domain is analagous to a Differentiated Services
Domain [RFC2474]. It can be described as a portion of the Internet
over which a consistent set of semantic-prefix-based policies are
administered in a coordinated fashion. Some of the characteristics
of a single Semantic Prefix Domain could represent include:
o Administrative domains
o Autonomous systems
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o Trust regions
o Network technologies
o Hosts
o Routers
o User groups
o Services
o Traffic groups
o Applications
An enterprise Semantic Prefix Domain may span several physical
networks and traverse ISP networks. However, when an interim network
is traversed (such as when an intermediary ISP is used for
interconnectivity), the relevance of the semantics is limited to
network domains that share a common Semantic Prefix Policy.
The selection of semantics vary between different Semantic Prefix
Domains. Network operators should choose semantics according to
their network and service management needs. If an ISP has several
non-contiguous address blocks, they may be organized as a single
Semantic Prefix Domain if the same Semantic Prefix Policy is shared
across these non-contiguous address blocks.
A Semantic Prefix Domain has a set of pre-defined semantic
definitions, which are only meaningful locally. Without an efficient
semantics notification, exchanging mechanism or service agreement,
the definitions of semantics are only meaningful within local
Semantic Prefix Domain. Manual interactions between network
operators may also work out. However, this may involve trust models
among network operators.
Sharing semantic definition among Semantic Prefix Domains enables
more semantic based network operations.
6. The Embedded Semantics
The size of the operator assigned prefix means that there is
potentially much more scope for embedding semantics than has
previously been possible. The following list describes some
suggested semantics which may be useful to network operators besides
source/destination location:
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o User types
o Applications
o Security domain
o Traffic identity types
o Quality requirements
Consideration must also be given to the complexity that is created
within the semantic prefix policy. Whilst it may be desirable to
encode as much information within the prefix so that it is possible
to have a high level of granularity, this can come at the expense of
future addressing flexibility and could also lead to a high amount of
address wastage. In the same time, embedding too many semantics may
waste addressing space and induce semantic overlap. It should be
taken into careful consideration on semantics definition.
7. Applicability Examples
The following sections provide some examples of how semantics
prefixes could be applied in different use cases. The network
operators could also choose to combine ideas from the following
examples, or create their own as best suits their requirements.
7.1. An ISP Semantic Prefix Example
Current ISP networks are mainly aggregated by using the IP prefix as
a geographical locator. The ISP semantic prefix example below uses
the left most bits of the prefix for the locator function and lower
bits for semantics.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IANA assigned block | locator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| locator (Cont.) | Semantic Field|Subscriber bits|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An ISP semantic prefix example
In this example, the service provider has been allocated a /20
prefix. This means that the Semantic Prefix Domain is potentially up
to 44-bits long. The 28 left-most bits (starting at bit-20) are
allocated for use as geographical locators. These provide the
facility for topolgy based network aggregation. The semantic prefix
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is assigned to bits 48 to 55. The remaining /56 is delegated as
prefixes for subscribers.
7.2. A Semantic Prefix for Security Domains
In some networks, the locator function of the IP address may be
considered to be secondary to the geographical locator function. An
example application could be where an operator wishes to use the
semantic field to separate services across their entire network to
create security domains.
Implementing the semantic field in the left-most bits means that a
single, simple access-control list implemented across all networking
devices would be enough to enforce effective traffic segregation.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ISP assigned block |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ISP assigned block | Security Domain Bits | Locator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An Semantic Prefix example for Security Domains
7.3. A Multi-Prefix Semantic
A multiple-site enterprise may have been assigned several prefixes of
different lengths by its upstream ISPs. In this situation, in order
to create a single, contiguous Semantic Prefix Domain, it is
necessary to base the semantic prefix policy on the longest assigned
prefix to ensure that there in enough addressing space to encode a
consistent set of semantics across all of the assigned prefixes.
In this example, an enterprise has received a /38 address block for
one site (A) and a /44 for a second site (B) . They can be organized
in the same Semantic Prefix Domain. The most-left 18 (site A) and 12
(site B) bits are allocated as locator. It provides topology based
network aggregation. The 8 right-most bits (from bits 56 to 63) are
assigned as the semantic field. In this design, the multiple-site
enterprise that has been assigned two prefixes of different lengths
can be organized as the same Semantic Prefix Domain.
8. Semantic Prefix Benefits
This section describes some of the benefits associated with the
semantic prefix approach, depending on the semantics which are
embedded.
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- Simplified measurement and statistics gathering
The semantic prefix provides explicit identifiers which can be used
for measurement and statistical information collection. This can be
achieved by checking certain bits of the source and/or destination
address in each packet.
- Simplified flow control
By applying policies according to certain bit values, packets
carrying the same semantics in their source/destination addresses
can.
- Service Segregation
When service related information is encoded within the semantic
prefix, this can be used to create simple access-control lists which
can be applied uniformly across all network devices. This means that
it is easy to
- Policy aggregation
The semantic prefix allows many policies to be aggregated according
to the same semantics within the policy based routing system
[RFC1104].
- Easy dynamic reconfiguration of semantic oriented policy
Network operators may want to dynamically change the policy actions
that are operated on certain semantic packets. The semantic prefix
allows such changes be operated easily, as only a small number of
consistent policy rules need to be updated on all devices within the
semantic prefix domain.
- Application-aware routing
Embedding application information into IP addresses is the simplest
way to realize application aware routing.
- Easy virtualization
Virtual network based on any semantics can be easily deployed using
the semantic prefix mechanism.
9. Gaps
The simplest semantic prefix model is to embed only abstracted user
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type semantics into the prefix. Current network architectures can
support this as each subscriber is still assigned a single prefix,
while they are not notified the semantic within it.
In order to maximise the benefits of the semantic prefix design,
additional functions are needed to allow semantic relevant operations
in networks and semantic relevant interactions with hosts.
IPv6 provides a facility for multiple addresses to be configured on a
single interface. This creates a precondition for the approach that
user chooses addresses differently for different purposes/usages.
9.1. Semantic Relevant Operations in Networks
In order to manage semantic prefixes and their relevant network
actions, the network should provide the following semantic relevant
functions:
- Notification of semantics within the managed network
When an prefix is delegated using a DHCPv6 IA_PD [RFC3633], the
associated semantics should also be propogated to the requesting
router. This is particularly useful for autonomic process when a new
device is connected.
9.2. Semantic Relevant Interactions with Hosts
The more that semantics are embedded into a prefix, the more that
complicated functions are needed for semantic relevant interactions
between hosts and the network, such as prefix delegation, host
notification and address selections, etc.
In practice, a single host may belong to multiple semantics. This
means that several IPv6 addresses are configured on a single physical
interface and should be selected for use depending on the service
that a host wishes to access. A certain packet would only serve a
certain semantic.
The host's IPv6 stack must have a mechanism for understanding these
semantics in order to choose right source address when forming a
packet. If the embedded semantic is application relevant,
applications on the hosts should also be involved in the address
choosing process: the host IPv6 stack reports multiple available
addresses to the application through socket API (one example is "IPv6
Socket API for Source Address Selection" [RFC5014]). The application
then needs to apply the semantic logic so that it can correctly
select from the offered candidate addresses.
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Although [RFC6724] provides an algorithm for source address
selection, some semantic prefix policies may conflict with this
algorithm. In this case, the source address selection mechanism may
also further supporting functions to be developed.
10. IANA Considerations
This document has no IANA considerations.
11. Change Log
draft-jiang-semantic-prefix-04: new coauthor and re-organize the
content, 2013-1-31.
draft-jiang-semantic-prefix-03: add the concept of hierarchical
Semantic Prefix Domain and more gap analysis, 2012-10-22.
draft-jiang-semantic-prefix-02: resubmitted to v6ops WG. Removed
detailed examples and recommendations for semantics bits, 2012-10-15.
draft-jiang-semantic-prefix-01: added enterprise considerations and
scenarios, emphasizing semantics only for local meaning and no intend
to standardize any common global semantics, 2012-07-16.
draft-jiang-semantic-prefix-00: original version, 2012-07-09
12. Security Considerations
Embedding semantics in prefix is actually exposing more information
of packets explicit. These informations may also provide convenient
for malicious attackers to track or attack certain type of packets.
When networks announce their local prefix semantics to their peer
networks, it may increase the vulnerable risk.
Prefix-based filters should be deployed, in order to protect against
address spoofing attacks or denial of service for packets with forged
source addresses.
13. Acknowledgements
Useful comments were made by Erik Nygren, Nick Hilliard, Ray Hunter,
David Farmer, and other participants in the V6OPS working group.
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14. References
14.1. Normative References
[RFC1104] Braun, H., "Models of policy based routing", RFC 1104,
June 1989.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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,
December 1998.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, September 2012.
14.2. Informative References
[RFC5014] Nordmark, E., Chakrabarti, S., and J. Laganier, "IPv6
Socket API for Source Address Selection", RFC 5014,
September 2007.
[RFC5401] Adamson, B., Bormann, C., Handley, M., and J. Macker,
"Multicast Negative-Acknowledgment (NACK) Building
Blocks", RFC 5401, November 2008.
Appendix A. Appendix A: Topics for Future Extention
There are several areas in which the semantic prefix could be
extended in order to increase the usefulness and applicability of the
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concept. They are complementarity besides the main framework. These
are being described here as topics for possible future work. Each of
them may deserve a separated document for technical details.
- Dynamic Policy Configuration
Dynamic policy configuration would simplify the distribution of
policy across devices in the semantic prefix domain. New functions
or protocol extension are needed to enable dynamic changes to the
policy actions in operation on certain semantic packets.
- Semantics Announcements to peer networks
A network may announce all, or some of its Semantic Prefix Policy to
connected peer networks. This could be used to enable more dynamic
configuration and enable traffic from different semantic prefix
domains to traverse different networks whilst having the same
semantic prefix policy applied. Again, this would require new
functions or protocol extensions to realise.
This also would allow enterprise semantics to be able to traverse ISP
networks.
- Extension of Prefix Semantics beyond the left-most 64-bits
The prefix concept refers here to the left-most bits in the IP
addresses delegated by the network management plane. The prefix
could be longer than 64-bits if the network operators strictly manage
the address assignment by using Dynamic Host Configuration Protocol
for IPv6 (DHCPv6) [RFC3315] (but in this case standard Stateless
Address Autoconfiguration - SLAAC [RFC4862] cannot be used).
Authors' Addresses
Sheng Jiang (editor)
Huawei Technologies Co., Ltd
Q14, Huawei Campus, No.156 Beijing Road
Hai-Dian District, Beijing, 100095
P.R. China
Email: jiangsheng@huawei.com
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Qiong Sun
China Telecom
Room 708, No.118, Xizhimennei Street
Beijing 100084
P.R. China
Email: sunqiong@ctbri.com.cn
Ian Farrer
Deutsche Telekom AG
Bonn 53227
Germany
Email: ian.farrer@telekom.de
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