draft-ietf-idr-aggregation-framework-04.txt   rfc2519.txt 
INTERNET-DRAFT Enke Chen Network Working Group E. Chen
<draft-ietf-idr-aggregation-framework-04.txt> Cisco Request for Comments: 2519 Cisco
John W. Stewart, III Category: Informational J. Stewart
Juniper Juniper
December 1998 February 1999
A Framework for Inter-Domain Route Aggregation A Framework for Inter-Domain Route Aggregation
<draft-ietf-idr-aggregation-framework-04.txt>
Status of this Memo Status of this Memo
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Please check the abstract listing contained in each Internet-Draft Copyright (C) The Internet Society (1999). All Rights Reserved.
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Draft.
Abstract Abstract
This document presents a framework for inter-domain route aggregation This document presents a framework for inter-domain route aggregation
and shows an example router configuration which 'implements' this and shows an example router configuration which 'implements' this
framework. This framework is flexible and scales well as it framework. This framework is flexible and scales well as it
emphasizes the philosophy of aggregation by the source, both within emphasizes the philosophy of aggregation by the source, both within
routing domains as well as towards upstream providers, and it also routing domains as well as towards upstream providers, and it also
strongly encourages the use of the 'no-export' BGP community to strongly encourages the use of the 'no-export' BGP community to
balance the provider-subscriber need for more granular routing balance the provider-subscriber need for more granular routing
skipping to change at page 2, line 20 skipping to change at page 1, line 48
and memory) required to process routing information is reduced and and memory) required to process routing information is reduced and
route calculation is sped up. Another benefit of route aggregation route calculation is sped up. Another benefit of route aggregation
is that route flaps are limited in number, frequency and scope, which is that route flaps are limited in number, frequency and scope, which
saves resources and makes the global Internet routing system more saves resources and makes the global Internet routing system more
stable. stable.
Since CIDR (Classless Inter-Domain Routing) [2] was introduced, Since CIDR (Classless Inter-Domain Routing) [2] was introduced,
significant progress has been made on route aggregation, particularly significant progress has been made on route aggregation, particularly
in the following two areas: in the following two areas:
- Formulation and implementation of IP address allocation policies by - Formulation and implementation of IP address allocation policies
the top registries that conform to the CIDR principles [1]. This by the top registries that conform to the CIDR principles [1].
policy work is the cornerstone which makes efficient route aggrega-
tion technically possible.
- Route aggregation by large (especially "Tier 1") providers. To This policy work is the cornerstone which makes efficient route
date, the largest reductions in the size of the routing table have aggregation technically possible.
resulted from efficient aggregation by large providers.
However, the ability of various levels of the global routing system to - Route aggregation by large (especially "Tier 1") providers. To
implement efficient aggregation schemes varies widely. As a result, the date, the largest reductions in the size of the routing table
size and growth rate of the Internet routing table, as well as the asso- have resulted from efficient aggregation by large providers.
ciated route computation required, remain major issues today. To sup-
port Internet growth, it is important to maximize the efficiency of
aggregation at all levels in the routing system.
Because of the current size of the routing system and its dynamic However, the ability of various levels of the global routing system
nature, the first step towards this goal is to establish a clearly- to implement efficient aggregation schemes varies widely. As a
defined framework in which scaleable inter-domain route aggregation can result, the size and growth rate of the Internet routing table, as
be realized. The framework described in this document is based on the well as the associated route computation required, remain major
predominant and current experience in the Internet. It emphasizes the issues today. To support Internet growth, it is important to
philosophy of aggregation by the source, both within routing domains as maximize the efficiency of aggregation at all levels in the routing
well as towards upstream providers. The framework also strongly encour- system.
ages the use of the "no-export" BGP community to balance the provider-
subscriber need for more granular routing information with the Inter-
net's need for scalable inter-domain routing. The advantages of this
framework include the following:
- Route aggregation is done in a distributed fashion, with emphasis Because of the current size of the routing system and its dynamic
on aggregation by the party or parties injecting the aggregatable nature, the first step towards this goal is to establish a clearly
routing information into the global mesh. defined framework in which scaleable inter-domain route aggregation
can be realized. The framework described in this document is based
on the predominant and current experience in the Internet. It
emphasizes the philosophy of aggregation by the source, both within
routing domains as well as towards upstream providers. The framework
also strongly encourages the use of the "no-export" BGP community to
balance the providersubscriber need for more granular routing
information with the Internet's need for scalable inter-domain
routing. The advantages of this framework include the following:
- The flexibility of a routing domain to be able to inject more gran- - Route aggregation is done in a distributed fashion, with
ular routing information to an adjacent domain to control the emphasis on aggregation by the party or parties injecting the
resulting traffic patterns, without having an impact on the global aggregatable routing information into the global mesh.
routing system.
In addition to describing the philosophy, we illustrate it by presenting - The flexibility of a routing domain to be able to inject more
sample configurations. IPv4 prefixes, BGP4 and ASs are used in exam- granular routing information to an adjacent domain to control
ples, though the principles are applicable to inter-domain route aggre- the resulting traffic patterns, without having an impact on the
gation in general. global routing system.
Address allocation policies and technologies to renumber entire net- In addition to describing the philosophy, we illustrate it by
works, while very relevant to the realization of successful and sus- presenting sample configurations. IPv4 prefixes, BGP4 and ASs
tained inter-domain routing, are not the focus of this document. The are used in examples, though the principles are applicable to
references section contains pointers to relevant documents [8, 9, 11, inter-domain route aggregation in general.
12].
Address allocation policies and technologies to renumber entire
networks, while very relevant to the realization of successful
and sustained inter-domain routing, are not the focus of this
document. The references section contains pointers to relevant
documents [8, 9, 11, 12].
2. Route Aggregation Framework 2. Route Aggregation Framework
The framework of inter-domain route aggregation we are proposing can be The framework of inter-domain route aggregation we are proposing can
summarized as follows: be summarized as follows:
- Aggregation from the originating AS - Aggregation from the originating AS
That is, in its outbound route announcements, each AS aggregates That is, in its outbound route announcements, each AS aggregates
the BGP routes originated by itself, by dedicated AS and by pri- the BGP routes originated by itself, by dedicated AS and by
vate-ASs [10]. ("Routes originated by an AS" refers to routes private-ASs [10]. ("Routes originated by an AS" refers to
which have that AS first in the AS path attribute. For example, routes which have that AS first in the AS path attribute. For
routes statically configured and injected into BGP fall into this example, routes statically configured and injected into BGP fall
category.) into this category.)
This framework does not depend on "proxy aggregation" which refers This framework does not depend on "proxy aggregation" which
to route aggregation done by an AS other than the originating AS. refers to route aggregation done by an AS other than the
This preserves the capability of a multi-homed site to control the originating AS. This preserves the capability of a multi-homed
granularity of routing information injected into the global routing site to control the granularity of routing information injected
system. Since proxy aggregation involves coordination among multiple into the global routing system. Since proxy aggregation involves
organizations, the complexity of doing proxy aggregation increases coordination among multiple organizations, the complexity of
with the number of parties involved in the coordination. The doing proxy aggregation increases with the number of parties
complexity, in turn, impacts the practicality of proxy aggregation. involved in the coordination. The complexity, in turn, impacts
the practicality of proxy aggregation.
An AS shall always originate via a stable mechanism (e.g., static An AS shall always originate via a stable mechanism (e.g.,
route configuration) the BGP routes for the large aggregates from static route configuration) the BGP routes for the large
which it allocates addresses to customers. This ensures that it is aggregates from which it allocates addresses to customers. This
safe for its customers to use BGP "no-export". ensures that it is safe for its customers to use BGP "no-
export".
- Using BGP community "no-export" toward upstream providers - Using BGP community "no-export" toward upstream providers
That is, in its route announcements toward its upstream provider,
an AS tags the BGP community "no-export" to routes it originates
that do not need to be propagated beyond its upstream provider
(e.g., prefixes allocated by the upstream provider).
This framework is illustrated in Figure 1. A "Tier 1" provider does not That is, in its route announcements toward its upstream
use "no-export" in its announcement as it does not have an upstream provider, an AS tags the BGP community "no-export" to routes it
provider. However, it shall aggregate the routes it originates in its originates that do not need to be propagated beyond its upstream
outbound announcements towards both peer providers and customers. An AS provider (e.g., prefixes allocated by the upstream provider).
with an upstream provider shall aggregate the routes it originates and
use "no-export" toward its upstream provider for routes that do not need
to be propagated beyond its provider's AS. This recursion shall apply
to all levels of the routing hierarchy.
Tier 1 This framework is illustrated in Figure 1. A "Tier 1" provider does
+-- Provider <--+ not use "no-export" in its announcement as it does not have an
| | upstream provider. However, it shall aggregate the routes it
o aggregates routes | | o announces customer routes originates in its outbound announcements towards both peer providers
it originates | | o aggregates routes it originates and customers. An AS with an upstream provider shall aggregate the
| ^ o uses "no-export" if appropriate routes it originates and use "no-export" toward its upstream provider
| for routes that do not need to be propagated beyond its provider's
+---> Tier 2 <--+ AS. This recursion shall apply to all levels of the routing
Provider | hierarchy.
V |
| |
o aggregates routes | | o announces customer routes
it originates | | o aggregates routes it originates
| | o uses "no-export" if appropriate
| |
| ^
-> Customer AS
Figure 1 Tier 1
+-- Provider <--+
| |
o aggregates routes | | o announces customer routes
it originates | | o aggregates routes it originates
| ^ o uses "no-export" if appropriate
|
+---> Tier 2 <--+
Provider |
V |
| |
o aggregates routes | | o announces customer routes
it originates | | o aggregates routes it originates
| | o uses "no-export" if appropriate
| |
| ^
-> Customer AS
This framework scales well as aggregation is done at all levels of the Figure 1
routing system. It is flexible because the originating AS controls
whether routes of finer granularity are injected to, and/or propagated
by, its upstream provider. It facilitates multi-homing without compro-
mising route aggregation.
This framework is detailed in the following sections. This framework scales well as aggregation is done at all levels of
the routing system. It is flexible because the originating AS
controls whether routes of finer granularity are injected to, and/or
propagated by, its upstream provider. It facilitates multi-homing
without compromising route aggregation.
This framework is detailed in the following sections.
3. Aggregation from the Originating AS 3. Aggregation from the Originating AS
It has been well recognized that address allocation and address renum- It has been well recognized that address allocation and address
bering are keys to containing the growth of the Internet routing table renumbering are keys to containing the growth of the Internet routing
[1, 2, 8, 9, 11, 12]. table [1, 2, 8, 9, 11, 12].
Although the strategies discussed in this document do not assume a per- Although the strategies discussed in this document do not assume a
fect address allocation, it is strongly urged that an AS receive alloca- perfect address allocation, it is strongly urged that an AS receive
tion from its upstream service providers' address block. allocation from its upstream service providers' address block.
3.1 Intra-Domain Aggregation 3.1 Intra-Domain Aggregation
To reduce the number of routes that need to be injected into an AS, To reduce the number of routes that need to be injected into an AS,
there are a couple of principles that shall be followed: there are a couple of principles that shall be followed:
- Carry in its BGP table the large route block allocated from its - Carry in its BGP table the large route block allocated from its
upstream provider or an address registry (e.g., InterNIC, RIPE, upstream provider or an address registry (e.g., InterNIC, RIPE,
APNIC). This can be done by either static configuration of the APNIC). This can be done by either static configuration of the
large block or by aggregating more specific BGP routes. The former large block or by aggregating more specific BGP routes. The
is recommended as it does not depend on other routes. former is recommended as it does not depend on other routes.
- Allocate sub-blocks to the access routers where further allocation - Allocate sub-blocks to the access routers where further
is done. That is, the address allocation shall be done such that allocation is done. That is, the address allocation shall be
only a few, less specific routes (instead of many more, specific done such that only a few, less specific routes (instead of many
ones) need to be known to the other routers within the AS. more, specific ones) need to be known to the other routers
within the AS.
For example, a prefix of /17 can be further allocated to different For example, a prefix of /17 can be further allocated to
access routers as /20s which can then be allocated to customers different access routers as /20s which can then be allocated to
connected to different interfaces on that router (as shown in Fig- customers connected to different interfaces on that router (as
ure 2). Then in general only the /20 needs to be injected into the shown in Figure 2). Then in general only the /20 needs to be
whole AS. Exceptions need to be made for multi-homed static routes. injected into the whole AS. Exceptions need to be made for
multi-homed static routes.
access router access router
+------------+ +------------+
| x.x.x.x/20 | | x.x.x.x/20 |
+------------+ +------------+
| | | | | |
| | | | | |
/24 /22 /25 /24 /22 /25
Figure 2 Figure 2
It is noted that rehoming of customers without renumbering even within It is noted that rehoming of customers without renumbering even
the same AS may lead to injection of more specific routes. However, in within the same AS may lead to injection of more specific routes.
general the more-specifics do not need to be advertised outside of that However, in general the more-specifics do not need to be advertised
AS. Such routes can either be tagged with the BGP community "no-export" outside of that AS. Such routes can either be tagged with the BGP
or filtered out by a prefix-based filter to prevent them from being community "no-export" or filtered out by a prefix-based filter to
advertised out. prevent them from being advertised out.
3.2 Inter-Domain Aggregation 3.2 Inter-Domain Aggregation
There are at least two types of routes that need to be advertised by an There are at least two types of routes that need to be advertised by
AS: routes originated by the AS and routes originated by its BGP cus- an AS: routes originated by the AS and routes originated by its BGP
tomers. An AS may need to advertise full routes to certain BGP cus- customers. An AS may need to advertise full routes to certain BGP
tomers, in which case the routing announcements include routes origi- customers, in which case the routing announcements include routes
nated by non-customer ASs. Clearly an AS can, and should, safely aggre- originated by non-customer ASs. Clearly an AS can, and should,
gate the routes originated by itself and by its BGP customers multi- safely aggregate the routes originated by itself and by its BGP
homed only to it (using, e.g., the dedicated-AS and by the private-AS customers multi-homed only to it (using, e.g., the dedicated-AS and
mechanism [10]) in its outbound announcement. But it is far more dan- by the private-AS mechanism [10]) in its outbound announcement. But
gerous to aggregate routes originated by customer ASs due to multi-hom- it is far more dangerous to aggregate routes originated by customer
ing. ASs due to multi-homing.
However, there are several cases in which a route originated by a BGP However, there are several cases in which a route originated by a BGP
customer (other than using the dedicated AS or private AS) does not need customer (other than using the dedicated AS or private AS) does not
to be advertised out by its upstream providers. For example, need to be advertised out by its upstream providers. For example,
- The route is a more-specific of the upstream provider's block. - The route is a more-specific of the upstream provider's block.
However, the customer is either singly homed; or its connection to However, the customer is either singly homed; or its connection
this particular upstream provider is used for backup only. to this particular upstream provider is used for backup only.
- The more-specifics of a larger block are announced by the customer - The more-specifics of a larger block are announced by the
in order to balance traffic over the multiple links to the upstream customer in order to balance traffic over the multiple links to
provider. the upstream provider.
Our approach to suppress such routes is to give control to the ASs that Our approach to suppress such routes is to give control to the ASs
originate the more-specifics (as seen by its upstream providers) and let that originate the more-specifics (as seen by its upstream providers)
them tag the BGP community "no-export" to the appropriate routes. and let them tag the BGP community "no-export" to the appropriate
routes.
The BGP community "no-export" is a well known BGP community [6, 7]. A The BGP community "no-export" is a well known BGP community [6, 7].
route with this attribute is not propagated beyond an AS boundary. So, A route with this attribute is not propagated beyond an AS boundary.
if a route is tagged with this community in its announcement to an So, if a route is tagged with this community in its announcement to
upstream provider and is accepted by the upstream provider, the route an upstream provider and is accepted by the upstream provider, the
will not be announced beyond the upstream provider's AS. This achieves route will not be announced beyond the upstream provider's AS. This
the goal of suppressing the more-specifics in the upstream provider's achieves the goal of suppressing the more-specifics in the upstream
outbound announcement. provider's outbound announcement.
In this framework, the BGP community "no-export" shall be tagged to In this framework, the BGP community "no-export" shall be tagged to
routes that are to be advertized to, but not propagated by, its upstream routes that are to be advertized to, but not propagated by, its
provider. They may include routes allocated out of its upstream upstream provider. They may include routes allocated out of its
provider's block or the more specific routes announced to its upstream upstream provider's block or the more specific routes announced to
provider for the purpose of load balancing. This aggregation strategy its upstream provider for the purpose of load balancing. This
can be implemented via prefix-based filtering as shown in the example of aggregation strategy can be implemented via prefix-based filtering as
Section 5. shown in the example of Section 5.
For its own protection, a downstream AS shall announce only its own For its own protection, a downstream AS shall announce only its own
routes and its customer routes to its upstream providers. Thus, the routes and its customer routes to its upstream providers. Thus, the
outbound routing announcement and aggregation policy can be expressed as outbound routing announcement and aggregation policy can be expressed
follows: as follows:
For routes originated by itself/dedicated-AS/private-AS: For routes originated by itself/dedicated-AS/private-AS:
tag with "no-export" when appropriate, and advertise the tag with "no-export" when appropriate, and advertise the
large block and suppress the more-specifics large block and suppress the more-specifics
For routes originated by customer ASs: For routes originated by customer ASs:
advertise to upstream ASs advertise to upstream ASs
For any other routes: For any other routes:
do not advertise to upstream ASs do not advertise to upstream ASs
This approach is flexible and scales well as it gives control to the This approach is flexible and scales well as it gives control to the
party with the special needs, distributes the workload and avoids the party with the special needs, distributes the workload and avoids the
coordination overhead required by proxy aggregation. coordination overhead required by proxy aggregation.
4. Aggregation by a Provider 4. Aggregation by a Provider
A provider shall aggregate all the routes it originates, as documented A provider shall aggregate all the routes it originates, as
in Section 3. The only difference is that the provider may be providing documented in Section 3. The only difference is that the provider
full routes to certain BGP customers where no outbound filtering is may be providing full routes to certain BGP customers where no
presently in place. Experience has shown that inconsistent route outbound filtering is presently in place. Experience has shown that
announcement (e.g., aggregate at the interconnects but not toward cer- inconsistent route announcement (e.g., aggregate at the interconnects
tain customers) can cause serious routing problems for the Internet as a but not toward certain customers) can cause serious routing problems
whole because of longest-match routing. In certain cases announcing the for the Internet as a whole because of longest-match routing. In
more-specifics to customers might provide for more accurate IGP metrics certain cases announcing the more-specifics to customers might
and could be useful for better load-balancing. However, the potential provide for more accurate IGP metrics and could be useful for better
risk seems to outweigh the benefit, especially given the increasing com- load-balancing. However, the potential risk seems to outweigh the
plexity of connectivity that a customer may have. As a result, every benefit, especially given the increasing complexity of connectivity
effort shall be made to ensure consistent route aggregation for all BGP that a customer may have. As a result, every effort shall be made to
peers. This means deploying filters for the BGP peers which receive ensure consistent route aggregation for all BGP peers. This means
full routes. deploying filters for the BGP peers which receive full routes.
In summary, the aggregation strategy for a provider shall be: In summary, the aggregation strategy for a provider shall be:
- In announcing customer routes: - In announcing customer routes:
For routes originated by itself/dedicated-AS/private-AS: For routes originated by itself/dedicated-AS/private-AS:
tag with "no-export" when appropriate, and advertise the tag with "no-export" when appropriate, and advertise the
large block and suppress the more-specifics large block and suppress the more-specifics
For routes originated by other customer ASs: For routes originated by other customer ASs:
advertise advertise
For any other routes: For any other routes:
do not advertise do not advertise
- In announcing full routes: - In announcing full routes:
For routes originated by itself/dedicated-AS/private-AS: For routes originated by itself/dedicated-AS/private-AS:
tag with "no-export" when appropriate, and advertise the tag with "no-export" when appropriate, and advertise the
large block and suppress the more-specifics large block and suppress the more-specifics
For any other routes: For any other routes:
advertise advertise
5. An Example 5. An Example
Consider the example shown in Figure 3 where AS 1000 is a "Tier 1" Consider the example shown in Figure 3 where AS 1000 is a "Tier 1"
provider with two large aggregates 208.128.0.0/12 and 166.55.0.0/16, and provider with two large aggregates 208.128.0.0/12 and 166.55.0.0/16,
AS 2000 is a customer of AS 1000 with a "portable address" 160.75.0.0/16 and AS 2000 is a customer of AS 1000 with a "portable address"
and an address 208.128.0.0/19 allocated from AS 1000. Assume that 160.75.0.0/16 and an address 208.128.0.0/19 allocated from AS 1000.
208.128.0.0/19 does not need to be propagated beyond AS 1000. Assume that 208.128.0.0/19 does not need to be propagated beyond AS
1000.
+----------------+ +----------------+
| AS 1000 | | AS 1000 |
| 208.128.0.0/12 | | 208.128.0.0/12 |
| 166.55.0.0/16 | | 166.55.0.0/16 |
+----------------+ +----------------+
| |
| BGP | BGP
| |
| |
+----------------+ +----------------+
| AS 2000 | | AS 2000 |
| 208.128.0.0/19 | | 208.128.0.0/19 |
| 160.75.0.0/16 | | 160.75.0.0/16 |
+----------------+ +----------------+
Figure 3 Figure 3
Then, based on the framework presented, AS 1000 would Then, based on the framework presented, AS 1000 would
- originate and advertise the BGP routes 208.128.0.0/12 and - originate and advertise the BGP routes 208.128.0.0/12 and
166.55.0.0/16, and suppress more-specifics originated by 166.55.0.0/16, and suppress more-specifics originated by
itself/private-ASs/dedicated-ASs itself/private-ASs/dedicated-ASs
- advertise the routes received from the customer AS 2000 - advertise the routes received from the customer AS 2000
and AS 2000 would and AS 2000 would
- originate BGP route 208.128.0.0/19 and 160.75.0.0/16 - originate BGP route 208.128.0.0/19 and 160.75.0.0/16
- advertise both 160.75.0.0/16 and 208.128.0.0/19 to its provider AS - advertise both 160.75.0.0/16 and 208.128.0.0/19 to its provider
1000 and suppress the more specifics originated by itself/private- AS 1000 and suppress the more specifics originated by
AS/dedicated-AS, tagging the route 208.128.0.0/19 with "no-export" itself/private-AS/dedicated-AS, tagging the route 208.128.0.0/19
with "no-export"
- advertise both 160.75.0.0/16 and 208.128.0.0/19 to its BGP cus- - advertise both 160.75.0.0/16 and 208.128.0.0/19 to its BGP
tomers (if any) and suppress the more-specifics originated by customers (if any) and suppress the more-specifics originated by
itself/private-AS/dedicated-AS, plus any other routes the customers itself/private-AS/dedicated-AS, plus any other routes the
may desire to receive customers may desire to receive
The sample configuration which implement these policies (in Cisco syn- The sample configuration which implement these policies (in Cisco
tax) is given in Appendix A. syntax) is given in Appendix A.
6. Acknowledgments 6. Acknowledgments
The authors would like to thank Roy Alcala of MCI for a number of inter- The authors would like to thank Roy Alcala of MCI for a number of
esting hallway discussions related to this work. The IETF's IDR Working interesting hallway discussions related to this work. The IETF's IDR
Group also provided many helpful comments and suggestions. Working Group also provided many helpful comments and suggestions.
7. References 7. References
[1] Rekhter, Y., Li, T., "An Architecture for IP Address Allocation with [1] Rekhter, Y. and T. Li, "An Architecture for IP Address Allocation
CIDR", RFC 1518, September 1993. with CIDR", RFC 1518, September 1993.
[2] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless Inter- [2] Fuller, V., Li, T., Yu, J. and K. Varadhan, "Classless Inter-
Domain Routing (CIDR): an Address Assignment and Aggregation Strategy", Domain Routing (CIDR): an Address Assignment and Aggregation
RFC 1519, September 1993. Strategy", RFC 1519, September 1993.
[3] Rekhter, Y., and Li, T., "A Border Gateway Protocol 4 (BGP-4)", [3] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP-4)",
RFC1771, March 1995. RFC 1771, March 1995.
[4] Rekhter, Y., and Gross, P., "Application of the Border Gateway Pro- [4] Rekhter, Y. and P., Gross, "Application of the Border Gateway
tocol in the Internet", RFC1772, March 1995. Protocol in the Internet", RFC 1772, March 1995.
[5] Rekhter, Y., "Routing in a Multi-provider Internet", RFC1787, April [5] Rekhter, Y., "Routing in a Multi-provider Internet", RFC 1787,
1995. April 1995.
[6] Chandra, R., Traina, P., and Li, T., "BGP Communities Attribute", [6] Chandra, R., Traina, P. and T. Li, "BGP Communities Attribute",
RFC 1997, August 1996. RFC 1997, August 1996.
[7] Chen, E., and Bates, T., "An Application of the BGP Community [7] Chen, E. and T. Bates, "An Application of the BGP Community
Attribute in Multi-home Routing", RFC 1998, August 1996. Attribute in Multi-home Routing", RFC 1998, August 1996.
[8] Ferguson, P., Berkowitz, H., "Network Renumbering Overview: Why [8] Ferguson, P. and H. Berkowitz, "Network Renumbering Overview: Why
would I want it and what is it anyway?", RFC 2071, January 1997. would I want it and what is it anyway?", RFC 2071, January 1997.
[9] Berkowitz, H., "Router Renumbering Guide", RFC 2072, January 1997. [9] Berkowitz, H., "Router Renumbering Guide", RFC 2072, January
1997.
[10] Stewart, J., Bates, T., Chandra, R., and Chen, E., "Using a [10] Stewart, J., Bates, T., Chandra, R., and Chen, E., "Using a
Dedicated AS for Sites Homed to a Single Provider", RFC2270, January, Dedicated AS for Sites Homed to a Single Provider", RFC 2270,
1998. January 1998.
[11] Carpenter, B., Crowcroft, J., Rekhter, Y., "IPv4 Address Behaviour [11] Carpenter, B., Crowcroft, J. and Y. Rekhter, "IPv4 Address
Today", RFC 2101, February 1997. Behaviour Today", RFC 2101, February 1997.
[12] Carpenter, B., Rekhter, Y., "Renumbering Needs Work", RFC 1900, [12] Carpenter, B. and Y. Rekhter, "Renumbering Needs Work", RFC
February 1996. 1900, February 1996.
[13] Cisco systems, Cisco IOS Software Version 10.3 Router Products Con- [13] Cisco systems, Cisco IOS Software Version 10.3 Router Products
figuration Guide (Addendum), May 1995. Configuration Guide (Addendum), May 1995.
8. Authors' Addresses 8. Authors' Addresses
Enke Chen Enke Chen
Cisco Systems Cisco Systems
170 West Tasman Drive 170 West Tasman Drive
San Jose, CA 95134-1706 San Jose, CA 95134-1706
Phone: +1 408 527 4652
email: enkechen@cisco.com Phone: +1 408 527 4652
EMail: enkechen@cisco.com
John W. Stewart, III
Juniper Networks, Inc.
385 Ravendale Drive
Mountain View, CA 94043
Phone: +1 650 526 8000
EMail: jstewart@juniper.net
John W. Stewart, III
Juniper Networks, Inc.
385 Ravendale Drive
Mountain View, CA 94043
phone: +1 650 526 8000
email: jstewart@juniper.net
A. Appendix A: Example Cisco Configuration A. Appendix A: Example Cisco Configuration
This appendix lists the Cisco configurations for AS 2000 of the examples This appendix lists the Cisco configurations for AS 2000 of the
presented in Section 5. The configuration here uses the AS-path for examples presented in Section 5. The configuration here uses the
outbound filtering although it can also be based on BGP community. Sev- AS-path for outbound filtering although it can also be based on BGP
eral route-maps are defined that can be used for peering with the community. Several route-maps are defined that can be used for
upstream provider, and for peering with customers (announcing full peering with the upstream provider, and for peering with customers
routes or customer routes). (announcing full routes or customer routes).
!!# inject aggregates !!# inject aggregates
ip route 160.75.0.0 255.255.0.0 Null0 254 ip route 160.75.0.0 255.255.0.0 Null0 254
ip route 208.128.0.0 255.255.224.0 Null0 254 ip route 208.128.0.0 255.255.224.0 Null0 254
! !
router bgp 2000 router bgp 2000
network 160.75.0.0 mask 255.255.0.0 network 160.75.0.0 mask 255.255.0.0
network 208.128.0.0 mask 255.255.224.0 network 208.128.0.0 mask 255.255.224.0
neighbor x.x.x.x remote-as 1000 neighbor x.x.x.x remote-as 1000
neighbor x.x.x.x route-map export-routes-to-provider out neighbor x.x.x.x route-map export-routes-to-provider out
skipping to change at line 503 skipping to change at page 13, line 4
route-map export-customer-routes permit 20 route-map export-customer-routes permit 20
match as-path 20 match as-path 20
! !
!!# route-map with BGP customers that desire full routes !!# route-map with BGP customers that desire full routes
route-map export-full-routes permit 10 route-map export-full-routes permit 10
match as-path 10 match as-path 10
match ip address 102 match ip address 102
route-map export-full-routes permit 20 route-map export-full-routes permit 20
match as-path 1 match as-path 1
! !
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