draft-ietf-ospf-abr-alt-02.txt   draft-ietf-ospf-abr-alt-03.txt 
Network Working Group Alex Zinin Network Working Group Alex Zinin
Internet Draft Cisco Systems Internet Draft Cisco Systems
Expiration Date: January 2001 Acee Lindem Expiration Date: July 2001 Acee Lindem
File name: draft-ietf-ospf-abr-alt-02.txt Redback Networks File name: draft-ietf-ospf-abr-alt-03.txt Redback Networks
Derek Yeung Derek Yeung
Procket Networks Procket Networks
July 2000 November 2000
Alternative OSPF ABR Implementations Alternative OSPF ABR Implementations
draft-ietf-ospf-abr-alt-02.txt draft-ietf-ospf-abr-alt-03.txt
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet Drafts are working documents of the Internet Engineering Internet Drafts are working documents of the Internet Engineering
Task Force (IETF), its Areas, and its Working Groups. Note that other Task Force (IETF), its Areas, and its Working Groups. Note that other
groups may also distribute working documents as Internet Drafts. groups may also distribute working documents as Internet Drafts.
skipping to change at page 5, line 29 skipping to change at page 5, line 29
Active Backbone Connection: Active Backbone Connection:
A router is considered to have an active backbone connection if A router is considered to have an active backbone connection if
the backbone area is actively attached and there is at least one the backbone area is actively attached and there is at least one
fully adjacent neighbor in it. fully adjacent neighbor in it.
Area Border Router (ABR): Area Border Router (ABR):
Cisco Systems Interpretation: Cisco Systems Interpretation:
A router is considered to be an ABR if it has more than one area A router is considered to be an ABR if it has more than one area
Configured and the backbone area Actively Attached. Actively Attached and one of them is the backbone area.
IBM Interpretation: IBM Interpretation:
A router is considered to be an ABR if it has more than one A router is considered to be an ABR if it has more than one
Actively Attached area and the backbone area Configured. Actively Attached area and the backbone area Configured.
2.2 Implementation Details 2.2 Implementation Details
The following changes are made to the base OSPF, described in [Ref1]: The following changes are made to the base OSPF, described in [Ref1]:
1. The algorithm of Type 1 LSA (router-LSA) origination is changed 1. The algorithm of Type 1 LSA (router-LSA) origination is changed
skipping to change at page 7, line 40 skipping to change at page 7, line 40
The behavior described in this document requires special processing The behavior described in this document requires special processing
when the router's ABR status or backbone connection status changes. when the router's ABR status or backbone connection status changes.
3.1 ABR status change 3.1 ABR status change
The router's ABR flag can change due to the following events: The router's ABR flag can change due to the following events:
For Cisco ABR definition: For Cisco ABR definition:
1. A new area has been configured. The router becomes an ABR 1. The state machine of an OSPF-enabled interface in an area has
if the new area is the first non-backbone area and the router transitioned to a state higher than Down. (The router becomes
has the backbone area Actively Attached. an ABR if the area becomes Actively Attached and the ABR
condition is met.)
2. An area has been deconfigured. The router stops being an ABR 2. The state machine of an OSPF-enabled interface in an area has
if only one configured area has left or the area in question transitioned to the state Down. (The router stops being an ABR
is the backbone. if the area stops being Actively Attached and the ABR
condition is not met.)
3. The state machine of an OSPF-enabled interface in the backbone
area has transitioned to a state higher than Down. The router
becomes an ABR if there is at least one non-backbone area
Configured.
4. The state machine of an OSPF-enabled interface in the backbone 3. An area has been deconfigured. (The router stops being an
area has transitioned to the state Down. The router stops the area is the backbone or if it was Actively Attached the
being an ABR if the interface in question was the last one in ABR condition is not met.)
the backbone area.
For IBM ABR definition: For IBM ABR definition:
1. A new area has been configured. The router becomes an ABR 1. A new area has been configured. (The router becomes an ABR
if the new area is the backbone and the router is Actively if the new area is the backbone and the router is Actively
Attached to two or more areas. Attached to two or more areas.)
2. An area has been deconfigured. The router stops being an ABR 2. An area has been deconfigured. The router stops being an ABR
if only one configured area has left or the area in question if only one configured area has left or the area in question
is the backbone. is the backbone.
3. The state machine of an OSPF-enabled interface transitions 3. The state machine of an OSPF-enabled interface transitions
into a state higher than Down, an area becomes Actively into a state higher than Down, an area becomes Actively
Attached. If this is the second actively attached area and Attached. If this is the second actively attached area and
the backbone area is Configured the router becomes an ABR. the backbone area is Configured the router becomes an ABR.
skipping to change at page 12, line 9 skipping to change at page 12, line 4
to N will cross the areas directly via R3 and, in this example, will to N will cross the areas directly via R3 and, in this example, will
not use a more optimal path through the backbone. not use a more optimal path through the backbone.
Note that this problem is not caused by the fact that R3 uses the Note that this problem is not caused by the fact that R3 uses the
alternative approach. The reason for attracting the attention to it alternative approach. The reason for attracting the attention to it
is that R3 is not really functioning as an ABR in case this new is that R3 is not really functioning as an ABR in case this new
behavior is used, i.e., it does not inject summary-LSAs into the behavior is used, i.e., it does not inject summary-LSAs into the
attached areas, but inter-area traffic can still go through it. attached areas, but inter-area traffic can still go through it.
7 Security Considerations 7 Security Considerations
The alternative ABR behavior specified in this document does not The alternative ABR behavior specified in this document does not
raise any security issues that are not already covered in [Ref1]. raise any security issues that are not already covered in [Ref1].
8 Acknowledgements 8 Acknowledgements
Authors would like to thank Alvaro Retana and Russ White for their Authors would like to thank Alvaro Retana, Russ White, and Liem
review of the document. Nguyen for their review of the document.
9 Disclaimer 9 Disclaimer
This document describes OSPF ABR implementations of respective This document describes OSPF ABR implementations of respective
vendors "as is", only for informational purposes, and without any vendors "as is", only for informational purposes, and without any
warranties, guarantees or support. Also, authors do not have any warranties, guarantees or support. Also, authors do not have any
intention to keep this document in sync with actual implementations. intention to keep this document in sync with actual implementations.
10 References 10 References
 End of changes. 

This html diff was produced by rfcdiff 1.23, available from http://www.levkowetz.com/ietf/tools/rfcdiff/