DHC Working Group Sheng Jiang
Internet Draft Huawei Technologies Co., Ltd
Intended status: Informational October 22, 2012
Expires: April 23, 2013
A Framework for Semantic IPv6 Prefix and Gap Analysis
draft-jiang-semantic-prefix-02.txt
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Abstract
Some Internet Service Providers and enterprises desire to be aware of
more information about each packet, so that packets can be treated
differently and efficiently. Packet-level differentiating can also
enable flow-level and user-level differentiating.
IPv6, with a large address space, allows semantics to be embedded
into addresses. Routers can easily apply relevant operations
accordingly.
This document describes a framework that embeds semantics into IPv6
prefixes, so that network devices can treat packets based on these
explicit semantics. This document also analyzes on the technical gaps
for embedding complex semantics.
This informational document only discusses usage of semantics in a
Semantic Prefix Domain. It does NOT intent or suggest to standardize
any common global semantics.
Table of Contents
1. Introduction ................................................ 3
2. Terminology ................................................. 4
3. Why Prefix .................................................. 4
4. The Semantic Prefix Domain .................................. 5
5. The Embedded Semantics ...................................... 5
6. Applicability ............................................... 6
6.1. An ISP semantic prefix example ......................... 6
6.2. An enterprise semantic prefix example .................. 7
7. Benefits .................................................... 7
8. Gaps ........................................................ 8
9. Security Considerations ..................................... 9
10. IANA Considerations......................................... 9
11. Change log ................................................. 9
12. References ................................................. 9
12.1. Normative References .................................. 9
12.2. Informative References ............................... 10
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1. Introduction
While the global Internet increases explosively, more and more
differentiated requirements are raised for the packet delivery of
networks. Internet Service Providers and enterprises desire to be
aware of more information about each packet, such as
destination/source location, user types, service types, applications,
security requirements, traffic identity types, quality requirements,
etc. Based on these informations, network operators could treat
packets differently and efficiently. Packet-level differentiating can
also enable flow-level and user-level differentiating.
However, except for destination/source location, almost of
abovementioned information is not expressed explicitly. Hence, it is
difficult for network operators to identify.
Two passive and indirect technologies are already developed to
distinguish the packets. Deep Packet Inspection (DPI) has been used
by ISPs to learn the characters of packets. But DPI is expensive for
both operational costs and process latency. Its time delay is too
much to be able to be used for real time traffic control. Overlay
networks are constructed in order to permit routing of packets to
destinations not specified by IP addresses. But still, the overlay
has no control over how packets are routed in the underlying network
between two overlay nodes. Although tunnel or label forwarding may
operate the traffic path, they introduce extra overhead while they
depend on indirect information sources.
An initiative solution, Quality of Service (QoS) and DiffServ
[RFC2474] was also developed. It specifies a simple, scalable and
coarse-grained mechanism for classifying and managing network
traffic. However, the DiffServ fields set by the packet senders are
not trustable by the network operators. In the real user case, ISPs
deploy "remarking" points at the edge network, which classify each
received packet and rewrite its DiffServ field according to user
information learned from AAA or VLAN.
The abovementioned solutions are mainly developed in IPv4 era, in
which IP address is only locator, nothing else, giving the limited
space. Although DiffServ was developed identically for IPv4 and IPv6,
it inherits the same limitation.
IPv6 has broken such limitation with its very large address space. It
allows certain semantics to be embedded into addresses. ISPs or
Enterprises can proactively embed pre-defined information into
addresses so that intermediate devices can easily apply relevant
operations on packet since addresses are the most explicit element in
a packet. It provides an easy access and trustable fundamental for
packet differentiated treatment. The technical fact that IPv6 allow
multiple addresses on a single interface also provides precondition
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for the approach that user chooses addresses differently for
different purposes/usages.
This document describes a framework that embeds semantics into IPv6
prefixes, so that network devices can treat packets based on these
explicit 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 networks may have very different choose for the most
important semantics. Pre-defined semantic definitions are only
meaningful locally. Therefore, standardizing a general semantic is
almost an impossible job. This informational document only discusses
usage of semantics in a Semantic Prefix Domain. It does NOT intent or
suggest to standardize any common global semantics.
This document also analyzes the technical gaps to maximum the
benefits of semantics prefix approach, for which complex semantics
may need to be embedded. For now, this document only discusses
unicast address within IPv6 Addressing Architecture [RFC4291].
2. Terminology
Semantic Prefix: a flexible-length IPv6 prefix that was embedded
certain semantics.
Semantic Prefix Domain: a portion of the Internet over which a
consistent set of semantic prefix policies are administered in a
coordinated fashion.
3. Why Prefix
Although interface identifier of IPv6 address has arbitrary bits and
extension header can carry much more information, they are not
trustable by network operators. Selfish 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.
Prefix is almost the only thing a network operator can trust in an IP
packet because it is delegated by the network and the network can
detect any undesired modifications, then, filter the packet. If one
gets the destination address wrong, the packet would not reach; if it
gets the source address wrong, the return packet would not arrive.
This also would allow enterprise semantics to be able to traverse ISP
networks.
The prefix concept here refers the most left bits in IP addresses,
that are delegated by the network management plane. It could be
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longer than 64, 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 - SLACC [RFC4862] cannot be used).
Although IPv6 address space is plentiful, it should not be wasted.
This argument can be dealt with by ensuring that only a small number
of traffic classes are identified within a given user's traffic, so
only a few bits in the prefix are needed.
4. The Semantic Prefix Domain
A Semantic Prefix Domain, analagous to a Differentiated Services
Domain [RFC2474], is a portion of the Internet over which a
consistent set of semantic prefix policies are administered in a
coordinated fashion. A Semantic Prefix Domain can represent different
administrative domains or autonomous systems, different trust
regions, different network technologies, hosts and routers, different
user groups, different services, different traffic groups, different
applications, etc. An enterprise Semantic Prefix Domain may span
several physical networks, traversing ISP networks.
The selections of semantics are various among different Semantic
Prefix Domains. Network operators should choose semantics according
to their needs for network management and services management. If an
ISP has several discontinuous address blocks, it may be organized as
a single Semantic Prefix Domain if the same semantic definition
shared among these discontinuous address blocks. If these address
blocks have different prefix lengths, their Semantic Prefix Domains
may be distinguished each other by minimum differences of semantic
definition.
A Semantic Prefix Domain has a set of pre-defined semantic
definitions, which are only meaningful locally. Without an efficient
semantics notification or exchanging mechanism or service agreement,
the definitions of semantics are only meaningful within local
Semantic Prefix Domain. The semantics notification or exchanging does
not have to through protocols. 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.
5. The Embedded Semantics
As mentioned in Section 1, much information regarding to packets is
useful for network operators. But, the prefix bits that can be used
for embedded semantics are very limited. Therefore, only the
selected, most useful semantics can be embedded in the prefix. Note,
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however, that DiffServ provides a very rich QoS semantic with only 6
bits. The available bits increase largely in the strictly managed
network by DHCPv6.
The following are some semantics may be useful by network operators
beside source/destination location: user types, service types,
applications, security requirements, traffic identity types, quality
requirements, etc. When used, all of them should be restricted in a
highly abstracted way. Larger granularity of semantics may provide
better aggregation and extensibility. This document does not intend
to define or give recommendations on choose of semantics for
embedding in prefix.
In a given Semantic Prefix Domain, multiple semantics can be used
combinatorially. To use the limited bits efficiently, bits semantics
should be pre-defined very carefully. The network operators should be
very careful to plan and manage the semantic field. The network
operators should self-restrict NOT to put too many semantic into
prefixes, in order to avoid to be trapped into very complicated
management issues. Too many semantics make management for prefix
delegation become very complicated and hosts would not be able to
handle.
An important principle is to avoid semantic overlap for packet though
semantic overlap for devices/hosts is fine. Any potential scenarios
that a given packet may be mapped two or more semantic prefixes are
considered harmful.
6. Applicability
6.1. An ISP semantic prefix example
The current ISP network is mainly aggregated according to locator.
The below ISP semantic prefix example uses the most left bits of
prefix for locator function and lower bits for semantics. In other
scenarios, if the network operator would like to organize network
aggregation by semantic prior, using higher bits for semantics is
also possible. Mixed aggregation model can be reached by put
semantics or part of semantics bits in the middle of locator bits.
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|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: An ISP semantic prefix example
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In this example, the Semantic Prefix Domain has a /20 IPv6 address
space. The 28 most-left (roughly 26 million of /64 prefixes) bits are
allocated as locator. It serves network aggregation of topology
based. The 8 most-right bits are subscriber bits. It means /56 prefix
is assigned to subscribers. 8 bits (from bit 44 to 51) are assigned
as semantic field.
6.2. An enterprise semantic prefix example
The below enterprise semantic prefix example also uses the most left
bits of prefix for locator function and lower bits for semantics.
However, the locator function of IP address in enterprise networks
may not be as important as in ISP networks. The enterprise network
operator may prefer to organize network by semantic prior.
A multiple-site enterprise may receive several prefixes that have
different lengths. The semantic bits should be based on the longest
prefix. The shorter prefix can use extra available bits for locators.
It is compatible that shorter prefixes serve bigger networks with
more users.
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 | Locator | Semantic Field|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: An enterprise semantic prefix example
In this example, an enterprise have received a 38/ address block for
one site A and a /44 for another site B (semantic prefix shown in
Figure 2). They can be organized in a same Semantic Prefix Domain.
The most-left 18 (site A) / 12 (site B, as shown in Figure 2) bits
are allocated as locator. It serves network aggregation of topology
based. The most-right 8 bits (from bit 56 to 63) are assigned as
semantic field.
7. Benefits
This section presents some, definitely not all, benefits. Depending
on embedded semantics, various beneficial scenarios can be expected.
- Easy measurement and statistic
The semantic prefix provides explicit identifiers for measurement and
statistic. They are as simple as checking certain bits of address in
each packets.
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- Easy flow control
By applying policies according to certain bit value, it is easy to
control packets that have the same semantics.
- Policy aggregation
Semantic prefix allows many policies to be aggregated according to
the same semantics in the policy based routing system [RFC1104].
- Application-aware routing
Embedding application information into IP addresses is the simplest
way to realize application aware routing.
8. Gaps
The simplest model of semantic prefix is only embedded abstracted
user type semantic into the prefix. It can be supported with the
current network architecture because each subscriber is still
assigned one prefix, while they are not notified the semantic within
it.
The more semantics embedded into prefix, the more complicated
functions are needed for prefix delegation, host notification and
address selections.
- Associate semantics with prefix delegation
When DHCPv6-PD [RFC3633] delegates a prefix, the associated semantics
should be bounded.
- Notify prefix semantics to hosts
When a host connects to network, it should be assign a short prefix
locator with some enabled semantics rules.
- Address selection according to semantics on hosts
In practice, a host may belong to several semantics. It means several
IPv6 addresses are available on a single physical interface. A
certain packet would only serve a certain semantic. The IPv6 stack on
that host must know and understand these semantics and its
correspondent bits 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]). Then the
application responses the one it attached.
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In this architecture, hosts have to be intelligent enough to choose
its source address according to its given information. In some
complicated scenarios, choosing destination address may also need
further supporting functions.
The current address selection algorithms and address selection API
[RFC5014] are too simple to support this architecture. More
complicated functions and intelligence are needed.
9. 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.
10. IANA Considerations
This document has no IANA considerations.
11. Change log
draft-jiang- semantic-prefix-02: Removed detailed examples and
recommendations for semantics bits, 2012-10-22.
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. References
12.1. Normative References
[RFC1104] H.W. Braun, "Models of policy based routing", RFC 1104,
June 1989.
[RFC2474] K. Nichols, S. Blake, F. Baker, and D. Black, "Definition
of the Differentiated Services Field (DS Field) in the IPv4
and IPv6 Headers", RFC 2474, December 1998
[RFC3315] R. Droms, et al., "Dynamic Host Configure Protocol for
IPv6", RFC 3315, July 2003.
[RFC3633] O. Troan, and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC4862] S. Thomson, T. Narten, and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
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[RFC4291] R. Hinden, and S. Deering, "IP Version 6 Addressing
Architecture", RFC4291, February 2006.
12.2. Informative References
[RFC5014] E. Nordmark, S. Chakrabarti, J. Laganier, "IPv6 Socket API
for Source Address Selection", RFC 5014, September 2007.
Author's Addresses
Sheng Jiang
Huawei Technologies Co., Ltd
Q14, Huawei Campus
No.156 Beiqing Road
Hai-Dian District, Beijing 100095
P.R. China
EMail: jiangsheng@huawei.com
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