Internet DRAFT - draft-shi-v6ops-caba
draft-shi-v6ops-caba
Internet Engineering Task Force Shi, Ed.
Internet-Draft Yang
Intended status: Informational Wang
Expires: August 28, 2017 Wu
Yin
Tsinghua Univ.
February 24, 2017
Classless AS-based Addressing
draft-shi-v6ops-caba-01
Abstract
Addressing is the foundation of routing and it impacts the routing
scalability. The IPv6 routing system will face severe scalability
issue if the IPv6 addresses are recklessly used without careful
aggregation strategy. This draft describes an addressing scheme and
the corresponding allocation scheme which can facilitate the
aggregation of IPv6 addresses and keep the IPv6 inter-domain routing
system from being overloaded.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Address format . . . . . . . . . . . . . . . . . . . . . . . 2
3. ASN allocation . . . . . . . . . . . . . . . . . . . . . . . 3
4. effects on the size of IPv6 inter-domain routing tables . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 5
8. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
IP address fragment is one of the most contributing factors that
cause scalability problems to the IPv4 inter-domain routing system.
The IPv6 routing system will face severe scalability issue if the
IPv6 addresses are recklessly used without careful aggregation
strategy. This document propose Classless AS-Based Addressing (CABA)
scheme, which embeds 32 bits AS number (ASN) into the IPv6 address.
If ASNs are properly allocated, CABA can facilitate aggregation of IP
addresses and reduce the size of inter-domain routing tables.
2. Address format
The Classless AS-Based address has five fields of fixed lengths, as
shown in Figure 1.
+---------+-------------+--------------+------------+--------/ /--------+
| IANA /8 | ASN Low /16 | ASN High /16 | Subnet /24 | Interface /64 |
+---------+-------------+--------------+------------+--------/ /--------+
Figure 1: Classless AS-Based address format
IANA /8 field should be allocated by IANA.
ASN Low /16 is the lower 16 bits of the AS number.
ASN High /16 is the higher 16 bits of the AS number.
Subnet /24 should be allocated by individual ASes according to their
intra-domain routing policies.
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Interface /64 is interface ID.
All ASNs are assumed as 32 bits long. For a legacy ASN of 16 bits,
the higher 16 bits are filled with 0. The document uses AS x.y to
denote an ASN whose higher part is x and lower part is y. For
example, AS 199081 (0x309a9 in hex) is denoted as AS 3.2473, and the
ASN Low /16 field and the ASN High /16 field are 0x09a9 and 0x0003
respectively, as shown in Figure 2.
+----------------+--------------------+----------------------------+
| ASN in decimal | ASN in hexadecimal | IPv6 Block |
+----------------+--------------------+----------------------------+
| AS 0.2473 | 0x9a9 | [xx]09:a900::/40 |
| AS 3.2473 | 0x309a9 | [xx]09:a900:300::/40 |
+----------------+--------------------+----------------------------+
Figure 2: ASN and IPv6 Block examples
In order to prevent routing scalability issues, any prefixes that are
more specific than the allocated /40 should not be advertised into
global routing system. Meanwhile, IPv6 operator must filter BGP
updates that contain information of more specific prefixes.
3. ASN allocation
To take advantage of this AS-based addressing scheme, this document
suggests to allocate ASNs in a way similar to provider-aggregatable
(PA) addresses, where each allocation is made by ASes instead of
RIRs.
Initially, a legacy 16-bit ASN is regarded as holding 65536 32-bit
ASNs. For example, AS 333 holds ASNs from 0.333 to 65535.333.
Existing 32-bit ASNs are regarded as holding only one 32-bit ASN and
it is not hold by any other AS. For example, if 2.333 exists, AS 333
holds ASNs 0.333, 1.333 and from 3.333 to 65535.333. And each AS can
use only one ASN for routing purpose and this ASN is the smallest
among all ASNs it holds.
When a new AS wants to obtain an ASN, it should choose a provider who
holds several ASNs and ask for a unrouted ASN. The provider should
response by allocating an ASN or a range of ASNs from its ASN pool
according to its policy. Each AS can have its own allocation policy
but must conform to the following guidelines:
1. The higher part of allocated ASNs should be successive.
2. The higher part of remained ASNs should be as successive as
possible (There might be holes due to historical reasons).
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For example, if AS 0.333 allocates 4 ASNs to its customer, it should
allocate ASNs from 65532.333 to 65535.333.
Therefore, an ASN can only decide the number of ASNs in each
allocation. As examples, there might be two kind of polices:
1. Allocating a fixed ratio of all ASNs currently hold by the AS.
2. Allocating a fixed number of ASNs.
For example, an AS who has ASNs from 0.100 to 65535.100 may choose to
allocate 1/4 of its ASNs (49152.1s00~65535.100) or 256 ASNs
(65280.100~65535.100). An AS can define its own allocation policy
provided the policy conforms to the above guidelines.
According to the allocation strategy above, we encode the ASN's lower
bits first. Thus ASNs who have the same lower part share a common
prefix. As Figure 2 shows, AS 0.2473 and AS 3.2473 share the same
prefix [xx]09:a900::/32 and their IPv6 blocks are more likely to be
aggregated by ASN allocator AS 0.2473. (xx denote the bits provided
by IANA). Therefore, any prefixes that are more specific than the
corresponding AS-Based prefix should not be advertised into global
routing system. As a result, IPv6 operator must filter the anomalous
BGP updates which contain information of more specific prefixes.
4. effects on the size of IPv6 inter-domain routing tables
For core routers in the Internet, their inter-domain routing tables
are usually large and complex. routing tables list the routes to
particular network prefixes and some metrics associated with those
routes. As there are so many prefixes spreading around the current
Internet, core routers' inter-domain routing tables become larger,
causing routing system overloaded.
In the current Internet, an AS usually announces several prefixes to
its neighbors. CABA scheme embeds 32-bit ASN into its IPv6 address.
If CABA is adopted in the Internet, the number of spreading prefixes
will reduce obviously. One AS deploying CABA can only announce one
prefix to other networks. Thus, the size of inter-domain routing
tables will never be more than the number of ASes. Figure 3 shows
the result of our simulation. The routes from inter-domain routing
tables are collected by Routeviews in August, 2016. We choose
different proportions of ASes in the Internet randomly to adopt CABA
scheme and count the size of inter-domain routing tables.
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+---------------+--------+--------+--------+--------+--------+-------+
| adoption rate | 0 | 20 | 40 | 60 | 80 | 100 |
+---------------+--------+--------+--------+--------+--------+-------+
| RIB size | 634050 | 515201 | 393595 | 280183 | 173500 | 53483 |
+---------------+--------+--------+--------+--------+--------+-------+
Figure 3: CABA deployment influences sizes of inter-domain routing
tables
In addition, since the allocation of ASNs facilitates aggregation of
IP addresses (providers can aggregate classless AS-Based addresses
which they allocate to customers), the size of routing tables will
reduce further.
5. IANA Considerations
IANA should allocate a /8 IPv6 address block for this purpose, which
is similar to 2002::/8 [RFC3068] used by 6to4. No IPv4 allocation
required.
6. Security Considerations
This document includes no request to security.
7. Conclusions
This draft describes an addressing scheme CABA (Classless AS-Based
Addressing) and an address allocation scheme which can facilitate
aggregation of addresses. CABA can solve the scalability problem of
IP address and reduce the size of core RIBs obviously.
8. Normative References
[RFC3068] Huitema, C., "An Anycast Prefix for 6to4 Relay Routers",
RFC 3068, DOI 10.17487/RFC3068, June 2001,
<http://www.rfc-editor.org/info/rfc3068>.
Authors' Addresses
Xingang Shi (editor)
Tsinghua Univ.
Beijing
CN
Email: shixg@cernet.edu.cn
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Yan Yang
Tsinghua Univ.
Beijing
CN
Email: yangyan15@mails.tsinghua.edu.cn
Zhiliang Wang
Tsinghua Univ.
Beijing
CN
Email: wzl@csnet1.cs.tsinghua.edu.cn
Jianping Wu
Tsinghua Univ.
Beijing
CN
Email: jianping@csnet1.cs.tsinghua.edu.cn
Xia Yin
Tsinghua Univ.
Beijing
CN
Email: yxia@csnet1.cs.tsinghua.edu.cn
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