draft-ietf-rtgwg-ordered-fib-11.txt   draft-ietf-rtgwg-ordered-fib-12.txt 
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Expires: November 25, 2013 S. Previdi Expires: November 25, 2013 S. Previdi
C. Filsfils C. Filsfils
Cisco Systems Cisco Systems
P. Francois P. Francois
Institute IMDEA Networks Institute IMDEA Networks
O. Bonaventure O. Bonaventure
Universite catholique de Louvain Universite catholique de Louvain
May 24, 2013 May 24, 2013
Framework for Loop-free convergence using oFIB Framework for Loop-free convergence using oFIB
draft-ietf-rtgwg-ordered-fib-11 draft-ietf-rtgwg-ordered-fib-12
Abstract Abstract
This document describes an illustrative framework of a mechanism for This document describes an illustrative framework of a mechanism for
use in conjunction with link state routing protocols which prevents use in conjunction with link state routing protocols which prevents
the transient loops which would otherwise occur during topology the transient loops which would otherwise occur during topology
changes. It does this by correctly sequencing the forwarding changes. It does this by correctly sequencing the forwarding
information base (FIB) updates on the routers. information base (FIB) updates on the routers.
This mechanism can be used in the case of non-urgent (management This mechanism can be used in the case of non-urgent (management
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5.2. Link or Router Up or Metric Decrease . . . . . . . . . . 10 5.2. Link or Router Up or Metric Decrease . . . . . . . . . . 10
6. Acceleration of Ordered Convergence . . . . . . . . . . . . . 10 6. Acceleration of Ordered Convergence . . . . . . . . . . . . . 10
6.1. Construction of the waiting list and notification list . 11 6.1. Construction of the waiting list and notification list . 11
6.1.1. Down events . . . . . . . . . . . . . . . . . . . . . 11 6.1.1. Down events . . . . . . . . . . . . . . . . . . . . . 11
6.1.2. Up Events . . . . . . . . . . . . . . . . . . . . . . 11 6.1.2. Up Events . . . . . . . . . . . . . . . . . . . . . . 11
6.2. Format of Completion Messages . . . . . . . . . . . . . . 12 6.2. Format of Completion Messages . . . . . . . . . . . . . . 12
7. Fall back to Conventional Convergence . . . . . . . . . . . . 12 7. Fall back to Conventional Convergence . . . . . . . . . . . . 12
8. oFIB state machine . . . . . . . . . . . . . . . . . . . . . 12 8. oFIB state machine . . . . . . . . . . . . . . . . . . . . . 12
8.1. OFIB_STABLE . . . . . . . . . . . . . . . . . . . . . . . 13 8.1. OFIB_STABLE . . . . . . . . . . . . . . . . . . . . . . . 13
8.2. OFIB_HOLDING_DOWN . . . . . . . . . . . . . . . . . . . . 13 8.2. OFIB_HOLDING_DOWN . . . . . . . . . . . . . . . . . . . . 14
8.3. OFIB_HOLDING_UP . . . . . . . . . . . . . . . . . . . . . 14 8.3. OFIB_HOLDING_UP . . . . . . . . . . . . . . . . . . . . . 15
8.4. OFIB_ONGOING . . . . . . . . . . . . . . . . . . . . . . 16 8.4. OFIB_ONGOING . . . . . . . . . . . . . . . . . . . . . . 16
8.5. OFIB_ABANDONED . . . . . . . . . . . . . . . . . . . . . 16 8.5. OFIB_ABANDONED . . . . . . . . . . . . . . . . . . . . . 17
9. Management Considerations . . . . . . . . . . . . . . . . . . 17 9. Management Considerations . . . . . . . . . . . . . . . . . . 17
10. IANA considerations . . . . . . . . . . . . . . . . . . . . . 17 10. IANA considerations . . . . . . . . . . . . . . . . . . . . . 17
11. Security considerations . . . . . . . . . . . . . . . . . . . 17 11. Security considerations . . . . . . . . . . . . . . . . . . . 17
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
13. Informative References . . . . . . . . . . . . . . . . . . . 17 13. Informative References . . . . . . . . . . . . . . . . . . . 18
Appendix A. Candidate Methods of Safely Abandoning Loop-Free Appendix A. Candidate Methods of Safely Abandoning Loop-Free
Convergence (AAH) . . . . . . . . . . . . . . . . . 18 Convergence (AAH) . . . . . . . . . . . . . . . . . 18
A.1. Possible Solutions . . . . . . . . . . . . . . . . . . . 18 A.1. Possible Solutions . . . . . . . . . . . . . . . . . . . 19
A.2. Hold-down timer only . . . . . . . . . . . . . . . . . . 18 A.2. Hold-down timer only . . . . . . . . . . . . . . . . . . 19
A.3. AAH messages . . . . . . . . . . . . . . . . . . . . . . 20 A.3. AAH messages . . . . . . . . . . . . . . . . . . . . . . 20
A.3.1. Per Router State Machine . . . . . . . . . . . . . . 20 A.3.1. Per Router State Machine . . . . . . . . . . . . . . 20
A.3.2. Per Neighbor State Machine . . . . . . . . . . . . . 22 A.3.2. Per Neighbor State Machine . . . . . . . . . . . . . 22
Appendix B. Synchronisation of Loop Free Timer Values . . . . . 23 Appendix B. Synchronisation of Loop Free Timer Values . . . . . 24
B.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 23 B.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 24
B.2. Required Properties . . . . . . . . . . . . . . . . . . . 24 B.2. Required Properties . . . . . . . . . . . . . . . . . . . 24
B.3. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . 24 B.3. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . 25
B.4. Security Considerations . . . . . . . . . . . . . . . . . 25 B.4. Security Considerations . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
1. The Purpose of this Document 1. The Purpose of this Document
This document describes an illustrative framework of a mechanism for This document describes an illustrative framework of a mechanism for
use in conjunction with link state routing protocols which prevents use in conjunction with link state routing protocols which prevents
the transient loops which would otherwise occur during topology the transient loops which would otherwise occur during topology
changes. It does this by correctly sequencing the forwarding changes. It does this by correctly sequencing the forwarding
information base (FIB) updates on the routers. information base (FIB) updates on the routers.
At the time of publication there is no demand to deploy this At the time of publication there is no demand to deploy this
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Compute rank with respect to the event, as defined in Section 5. Compute rank with respect to the event, as defined in Section 5.
Store Waiting List and Notification List for X--Y obtained from Store Waiting List and Notification List for X--Y obtained from
the rank computation. the rank computation.
EVENT : Reception of a link-state packet describing an event of the EVENT : Reception of a link-state packet describing an event of the
type link X--Y up or metric decrease which to be processed using type link X--Y up or metric decrease which to be processed using
oFIB. oFIB.
ACTION :
Set state to OFIB_HOLDING_UP.
Start Hold_down_timer.
ofib_current_common_set = {X,Y}.
Compute rank with respect to the event, as defined in Section 5.
Store Waiting List and Notification List for X--Y obtained from
the rank computation.
8.2. OFIB_HOLDING_DOWN 8.2. OFIB_HOLDING_DOWN
OFIB_HOLDING_DOWN is the state of a router that is collecting a set OFIB_HOLDING_DOWN is the state of a router that is collecting a set
of link down or metric increase link-state packets to be processed of link down or metric increase link-state packets to be processed
together using controlled convergence. together using controlled convergence.
EVENT : Reception of a link-state packet describing an event of the EVENT : Reception of a link-state packet describing an event of the
type link up or metric decrease which in itself can be processed type link up or metric decrease which in itself can be processed
using oFIB. using oFIB.
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processed using oFIB. processed using oFIB.
ACTION : ACTION :
ofib_current_common_set = ofib_current_common_set =
intersection(ofib_current_common_set,{A,B}). intersection(ofib_current_common_set,{A,B}).
If ofib_current_common_set is empty, then there is no longer a If ofib_current_common_set is empty, then there is no longer a
node in common in all the pending link-state changes. node in common in all the pending link-state changes.
Set state to OFIB_ABANDONED Set state to OFIB_ABANDONED.
Reset Hold_down_timer Reset Hold_down_timer.
Trigger AAH mechanism. Trigger AAH mechanism.
If ofib_current_common set is not empty, update waiting list and If ofib_current_common set is not empty, update waiting list and
notification list as defined in Section 5. Note that in the case notification list as defined in Section 5. Note that in the case
of a single link event, the link-state packet received when the of a single link event, the link-state packet received when the
router is in this state describes the state change of the other router is in this state describes the state change of the other
direction of the link, hence no changes will be made to the direction of the link, hence no changes will be made to the
waiting and notification lists. waiting and notification lists.
EVENT : Hold_down_timer expires. EVENT : Hold_down_timer expires.
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type link A--B up or metric decrease to be processed using oFIB. type link A--B up or metric decrease to be processed using oFIB.
ACTION : ACTION :
ofib_current_common_set = ofib_current_common_set =
intersection(ofib_current_common_set,{A,B}). intersection(ofib_current_common_set,{A,B}).
If ofib_current_common_set is empty, then there is no longer a If ofib_current_common_set is empty, then there is no longer a
common node in the set of pending link-state changes. common node in the set of pending link-state changes.
Set state to OFIB_ABANDONED. Set state to OFIB_ABANDONED.
Reset Hold_down_timer. Reset Hold_down_timer.
Trigger AAH mechanism. Trigger AAH mechanism.
If ofib_current_common set is not empty, update waiting list and If ofib_current_common set is not empty, update waiting list and
notification list as defined in Section 5. Note that in the case notification list as defined in Section 5. Note that in the case
of a single link event, the link-state packet received when the of a single link event, the link-state packet received when the
router is in this state describes the state change of the other router is in this state describes the state change of the other
direction of the link, hence no changes will be made to the direction of the link, hence no changes will be made to the
waiting and notification lists. waiting and notification lists.
EVENT : Reception of a completion message EVENT : Reception of a completion message
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