As per Relevance of the word provider, we have this rfc below:
Network Working Group J.
Request for Comments: 2270
Category: Informational T.
R.
E.
January 1998
Using a Dedicated AS for Sites Homed to a Single
Status of this
This memo provides information for the Internet community. It
not specify an Internet standard of any kind. Distribution of
memo is unlimited
Copyright
Copyright (C) The Internet Society (1998). All Rights Reserved
With the increased growth of the Internet, the number of
using BGP4 has grown significantly. RFC1930 outlines a set
guidelines for when one needs and should use an AS. However,
customer and service provider (ISP) are left with a problem as
result of this in that while there is no need for an allocated
under the guidelines, certain conditions make the use of BGP4 a
pragmatic and perhaps only way to connect a customer homed to
single ISP. This paper proposes a solution to this problem in
with recommendations set forth in RFC1930.
1.
With the increased growth of the Internet, the number of
using BGP4 [1],[2] has grown significantly. RFC1930 [4] outlines
set of guidelines for when one needs and should use an AS. However
the customer and service provider (ISP) are left with a problem as
result of this in that while there is no need for an allocated
under the guidelines, certain conditions make the use of BGP4 a
pragmatic and perhaps only way to connect a customer homed to
single ISP. These conditions are as follows
1) Customers multi-homed to single
Stewart, et. al. Informational [Page 1]
RFC 2270 Dedicated AS January 1998
Consider the scenario outlined in Figure 1 below
+-------+ +-------+
+----+ | | |
+------+ | | ISP A +------+ ISP B |
| Cust.+---+ | | | |
| X +--------+ | | |
+------+ ++-----++\ +-------+
| | \
| | \ +--------+
++-----++ +-| |
| Cust. | | ISP C |
| Y | | |
+-------+ +--------+
Figure 1: Customers multi-home to a single
Here both customer X and customer Y are multi-homed to a
provider, ISP A. Because these multiple connections are "localized
between the ISP A and its customers, the rest of the routing
(ISP B and ISP C in this case) doesn't need to see
information for a single multi-homed customer any differently than
singly-homed customer as it has the same routing policy as ISP
relative to ISP B and ISP C. In other words, with respect to
rest of the Internet routing system the organization is singly-homed
so the complexity of the multiple connections is not relevant in
global sense. Autonomous System Numbers (AS) are identifiers used
routing protocols and are needed by routing domains as part of
global routing system. However, as [4] correctly outlines
organizations with the same routing policy as their upstream
do not need an AS
Despite this fact, a problem exists in that many ISPs can
support the load-sharing and reliability requirements of a multi
homed customer if that customer exchanges routing information
BGP-4 which does require an AS as part of the protocol
2) Singly-homed customers requiring dynamic advertisement of NLRI'
While this is not a common case as static routing is
used for this purpose, if a large amount of NLRI's need to
advertised from the customer to the ISP it is
administratively easier for these prefixes to be advertised
a dynamic routing protocol. Today, the only exterior
protocol (EGP) that is able to do this is BGP. This leads to
same problem outlined in condition 1 above
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RFC 2270 Dedicated AS January 1998
As can be seen there is clearly a problem with the
set forth in [4] and the practice of using BGP4 in the
above. Section 2 proposes a solution to this problem with
sections describing the implications and application of the
solution
It should also be noted that if a customer is multi-homed to
than one ISP then they are advised to obtain an official allocated
from their allocation registry
2.
The solution we are proposing is that all BGP customers homed to
same single ISP use a single, dedicated AS specified by the ISP
Logically, this solution results in an ISP having many peers with
same AS, although that AS exists in "islands" completely
from one another
Several practical implications of this solution are discussed in
next section
3.
3.1 Full Routing Table
The solution precludes the ability for a BGP customer using
dedicated AS to receive 100% full routes. Because of routing
detection of AS path, a BGP speaker rejects routes with its own
number in the AS path. Imagine Customer X and Customer Y
BGP peers with Provider A using AS number N. Then, Customer X
not be able to received routes of Customer Y. We do not believe
this would cause a problem for Customer X, though, because Customer
and Customer Y are both stub networks so default routing is adequate
and the absence of a very small portion of the full routing table
unlikely to have a noticeable impact on traffic patterns guided
MEDs received
A BGP customer using the dedicated AS must carry a default
(preferably receiving from its provider via BGP).
3.2 Change of External
The dedicated AS specified by a provider is purely for use in
between its customers and the provider. When a customer using
dedicated AS changes its external connectivity, it may be
for the customer to reconfigure their network to use a different
number (either a globally unique one if homed to multiple providers
Stewart, et. al. Informational [Page 3]
RFC 2270 Dedicated AS January 1998
or a dedicated AS of a different provider).
3.3
As BGP customers using this dedicated AS are only homed to one ISP
their routes allocated from its providers CIDR block do not need
be announced upstream by its provider as the providers will
be originating the larger block. [6].
3.4 Routing
The Internet Routing Registry (IRR) [5] is used by providers
generate route filtering lists. Such lists are derived
from the "origin" attribute of the route objects. The "origin"
the AS that originates the route. With multiple customers using
same AS, finer granularity will be necessary to generate the
route filtering. For example, the "mntner" attribute or
"community" attribute of a route object can be used along with
"origin" attribute in generating the filtering lists
4.
The AS number specified by a provider can either be an AS from
private AS space (64512 - 65535) [4], or be an AS
allocated to the provider. With the former, the dedicated AS
all other private AS's should be stripped from its AS path while
route is being propagated to the rest of the Internet routing system
5. Security
The usage of AS numbers described in this document has no
security impact. Acceptance and filtering of AS numbers
customers is an issue dealt with in other documents
6.
The authors would like to thank Roy Alcala of MCI and
Boonkongchuen for their input to this document. The members of
IDR Working Group also provided helpful comments
7.
[1] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP-4)",
RFC 1771, March 1995.
[2] Rekhter, Y., and P. Gross, "Application of the Border
Protocol in the Internet", RFC 1772, March 1995.
Stewart, et. al. Informational [Page 4]
RFC 2270 Dedicated AS January 1998
[3] Rekhter, Y., "Routing in a Multi-provider Internet", RFC 1787,
April 1995.
[4] Hawkinson, J., and T. Bates, "Guidelines for creation, selection
and registration of an Autonomous System (AS)", RFC 1930, March 1996.
[5] Bates, T., Gerich, E., Joncheray, L., Jouanigot, J-M, Karrenberg
D., Terpstra, M., and J. Yu., "Representation of IP Routing
in a Routing Registry (ripe-81++)", RFC 1786, March 1995.
[6] Chen, E., and J. Stewart., "A Framework for Inter-Domain
Aggregation", Work in Progress
8. Authors'
John
USC/
4350 North Fairfax
Suite 620
Arlington, VA 22203
EMail: jstewart@isi.
Tony
Cisco Systems, Inc
170 West Tasman
San Jose, CA 95134
EMail: tbates@cisco.
Ravi
Cisco Systems, Inc
170 West Tasman
San Jose, CA 95134
EMail: rchandra@cisco.
Enke
Cisco Systems, Inc
170 West Tasman
San Jose, CA 95134
EMail: enkechen@cisco.
Stewart, et. al. Informational [Page 5]
RFC 2270 Dedicated AS January 1998
9. Full Copyright
Copyright (C) The Internet Society (1998). All Rights Reserved
This document and translations of it may be copied and furnished
others, and derivative works that comment on or otherwise explain
or assist in its implementation may be prepared, copied,
and distributed, in whole or in part, without restriction of
kind, provided that the above copyright notice and this paragraph
included on all such copies and derivative works. However,
document itself may not be modified in any way, such as by
the copyright notice or references to the Internet Society or
Internet organizations, except as needed for the purpose
developing Internet standards in which case the procedures
copyrights defined in the Internet Standards process must
followed, or as required to translate it into languages other
English
The limited permissions granted above are perpetual and will not
revoked by the Internet Society or its successors or assigns
This document and the information contained herein is provided on
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
Stewart, et. al. Informational [Page 6]
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