Difference between revisions of "RFC1397"
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Request for Comments: 1397 Bolt Beranek and Newman, Inc. | Request for Comments: 1397 Bolt Beranek and Newman, Inc. | ||
January 1993 | January 1993 | ||
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Default Route Advertisement In | Default Route Advertisement In | ||
BGP2 And BGP3 Versions Of The Border Gateway Protocol | BGP2 And BGP3 Versions Of The Border Gateway Protocol | ||
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Status of this Memo | Status of this Memo | ||
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This RFC specifies an IAB standards track protocol for the Internet | This RFC specifies an IAB standards track protocol for the Internet | ||
community, and requests discussion and suggestions for improvements. | community, and requests discussion and suggestions for improvements. | ||
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Standards" for the standardization state and status of this protocol. | Standards" for the standardization state and status of this protocol. | ||
Distribution of this memo is unlimited. | Distribution of this memo is unlimited. | ||
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Abstract | Abstract | ||
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This document specifies the recommendation of the BGP Working Group | This document specifies the recommendation of the BGP Working Group | ||
on default route advertisement support in BGP2 [1] and BGP3 [2] | on default route advertisement support in BGP2 [1] and BGP3 [2] | ||
versions of the Border Gateway Protocol. | versions of the Border Gateway Protocol. | ||
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This recommendation only applies to BGP2 and BGP3 versions of the | This recommendation only applies to BGP2 and BGP3 versions of the | ||
Border Gateway Protocol since starting with the BGP4 [3] version a | Border Gateway Protocol since starting with the BGP4 [3] version a | ||
default route advertisement capability is built in the protocol. | default route advertisement capability is built in the protocol. | ||
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== Overview == | == Overview == | ||
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The purpose of the default route advertisement capability is to | The purpose of the default route advertisement capability is to | ||
advertise the IP address of a border gateway which can be used as the | advertise the IP address of a border gateway which can be used as the | ||
default next hop to destinations that are not listed explicitly in | default next hop to destinations that are not listed explicitly in | ||
the BGP peer's routing table. | the BGP peer's routing table. | ||
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This capability will allow routers, that are unable to maintain a | This capability will allow routers, that are unable to maintain a | ||
complete routing table (e.g., due to its size) to learn a border | complete routing table (e.g., due to its size) to learn a border | ||
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preference for one over the other. It also reduces the need to | preference for one over the other. It also reduces the need to | ||
configure default routes in routers. | configure default routes in routers. | ||
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== Default Route Advertisement == | == Default Route Advertisement == | ||
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A default route is advertised in an UPDATE message that carries | A default route is advertised in an UPDATE message that carries | ||
reachability information for network 0.0.0.0. A Network field of | reachability information for network 0.0.0.0. A Network field of | ||
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indication that it carries a default route. The NEXT_HOP path | indication that it carries a default route. The NEXT_HOP path | ||
attribute of such a message provides the IP address of a border | attribute of such a message provides the IP address of a border | ||
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should be constructed according to the same rules that apply to a | should be constructed according to the same rules that apply to a | ||
conventional network advertisement. | conventional network advertisement. | ||
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If multiple default routes are advertised by a BGP speaker, the | If multiple default routes are advertised by a BGP speaker, the | ||
INTER-AS-METRIC path attribute can be included in the corresponding | INTER-AS-METRIC path attribute can be included in the corresponding | ||
UPDATE messages to express preference levels for entry points to the | UPDATE messages to express preference levels for entry points to the | ||
same AS. | same AS. | ||
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The UNREACHABLE path attribute is used to indicate that a previously | The UNREACHABLE path attribute is used to indicate that a previously | ||
advertised default route has become unreachable. | advertised default route has become unreachable. | ||
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UPDATE messages containing the default route advertisements should be | UPDATE messages containing the default route advertisements should be | ||
handled according to the rules that apply to all other UPDATE | handled according to the rules that apply to all other UPDATE | ||
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route is selected according to the local policies adopted by this BGP | route is selected according to the local policies adopted by this BGP | ||
speaker. | speaker. | ||
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References | References | ||
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[1] Lougheed, K., and Y. Rekhter, "A Border Gateway Protocol (BGP)", | [1] Lougheed, K., and Y. Rekhter, "A Border Gateway Protocol (BGP)", | ||
| − | + | RFC 1163, cisco Systems, T.J. Watson Research Center, IBM Corp., | |
June 1990. | June 1990. | ||
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[2] Lougheed, K., and Y. Rekhter, "A Border Gateway Protocol 3 (BGP- | [2] Lougheed, K., and Y. Rekhter, "A Border Gateway Protocol 3 (BGP- | ||
| − | 3)", | + | 3)", RFC 1267, cisco Systems, T.J. Watson Research Center, IBM |
Corp., October 1991. | Corp., October 1991. | ||
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[3] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP-4)", | [3] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP-4)", | ||
Work in Progress, T.J. Watson Research Center, IBM Corp., cisco | Work in Progress, T.J. Watson Research Center, IBM Corp., cisco | ||
Systems, December 1992. | Systems, December 1992. | ||
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Security Considerations | Security Considerations | ||
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Security issues are not discussed in this memo. | Security issues are not discussed in this memo. | ||
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Author's Address | Author's Address | ||
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Dimitry Haskin | Dimitry Haskin | ||
Bolt, Beranek & Newman | Bolt, Beranek & Newman | ||
150 Cambridge Park Drive | 150 Cambridge Park Drive | ||
Cambridge, MA 02140 | Cambridge, MA 02140 | ||
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Phone: 617-873-8609 | Phone: 617-873-8609 | ||
Email: [email protected] | Email: [email protected] | ||
Revision as of 07:13, 23 September 2020
Network Working Group D. Haskin Request for Comments: 1397 Bolt Beranek and Newman, Inc.
January 1993
Default Route Advertisement In
BGP2 And BGP3 Versions Of The Border Gateway Protocol
Status of this Memo This RFC specifies an IAB standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited. Abstract This document specifies the recommendation of the BGP Working Group on default route advertisement support in BGP2 [1] and BGP3 [2] versions of the Border Gateway Protocol. This recommendation only applies to BGP2 and BGP3 versions of the Border Gateway Protocol since starting with the BGP4 [3] version a default route advertisement capability is built in the protocol.
Overview
The purpose of the default route advertisement capability is to advertise the IP address of a border gateway which can be used as the default next hop to destinations that are not listed explicitly in the BGP peer's routing table. This capability will allow routers, that are unable to maintain a complete routing table (e.g., due to its size) to learn a border gateway that is ready to handle the default traffic. Also, in contrast to static defaults, if there is more than one default gateway, this would make it possible for a BGP speaker to express a preference for one over the other. It also reduces the need to configure default routes in routers.
Default Route Advertisement
A default route is advertised in an UPDATE message that carries reachability information for network 0.0.0.0. A Network field of such an UPDATE message must contain the IP address 0.0.0.0 as the indication that it carries a default route. The NEXT_HOP path attribute of such a message provides the IP address of a border
gateway that can be used as a default next hop to destinations that are not listed in the BGP peer's routing table. The value of the ORIGIN attribute should be 2 (INCOMPLETE). The AS_PATH attribute should be constructed according to the same rules that apply to a conventional network advertisement. If multiple default routes are advertised by a BGP speaker, the INTER-AS-METRIC path attribute can be included in the corresponding UPDATE messages to express preference levels for entry points to the same AS. The UNREACHABLE path attribute is used to indicate that a previously advertised default route has become unreachable. UPDATE messages containing the default route advertisements should be handled according to the rules that apply to all other UPDATE messages. If multiple default route are acquired by a BGP speaker, a route is selected according to the local policies adopted by this BGP speaker. References [1] Lougheed, K., and Y. Rekhter, "A Border Gateway Protocol (BGP)",
RFC 1163, cisco Systems, T.J. Watson Research Center, IBM Corp., June 1990.
[2] Lougheed, K., and Y. Rekhter, "A Border Gateway Protocol 3 (BGP-
3)", RFC 1267, cisco Systems, T.J. Watson Research Center, IBM Corp., October 1991.
[3] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP-4)",
Work in Progress, T.J. Watson Research Center, IBM Corp., cisco Systems, December 1992.
Security Considerations Security issues are not discussed in this memo. Author's Address Dimitry Haskin Bolt, Beranek & Newman 150 Cambridge Park Drive Cambridge, MA 02140 Phone: 617-873-8609 Email: [email protected]
