One document matched: draft-atlas-bryant-shand-lf-timers-01.txt

Differences from draft-atlas-bryant-shand-lf-timers-00.txt

INTERNET DRAFT     Synch of Loop Free Timer Values           Mar 2006 
 

 
                                                                      
Network Working Group                                        S. Bryant 
Internet Draft                                                M. Shand 
Expiration Date: September 2006                          Cisco Systems 
                                                                      
                                                              A. Atlas 
                                                            Google Inc 
                                                                      
                                                            March 2005 
                                                                      
              Synchronisation of Loop Free Timer Values 
             <draft-atlas-bryant-shand-lf-timers-01.txt> 
  
     
Status of this Memo  

  By submitting this Internet-Draft, each author represents that any    
  applicable patent or other IPR claims of which he or she is aware    
  have been or will be disclosed, and any of which he or she becomes    
  aware will be disclosed, in accordance with Section 6 of BCP 79. 

  Internet-Drafts are working documents of the Internet Engineering 
  Task Force (IETF), its areas, and its working groups.  Note that 
  other groups may also distribute working documents as        
  Internet-Drafts. 

  Internet-Drafts are draft documents valid for a maximum of six 
  months and may be updated, replaced, or obsoleted by other 
  documents at any time.  It is inappropriate to use Internet-Drafts 
  as reference material or to cite them other than as "work in 
  progress." 

  The list of current Internet-Drafts can be accessed at 
  http://www.ietf.org/1id-abstracts.html  

  The list of Internet-Draft Shadow Directories can be accessed at 
  http://www.ietf.org/shadow.html 

Abstract  
  This draft describes a mechanism that enables routers to agree on a 
  common convergence delay time for use in loop-free convergence.     

Conventions used in this document  
     
  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
  "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 
  this document are to be interpreted as described in RFC 2119 
  [RFC2119]. 


 
Atlas, Bryant, Shand      Expires Sept 2006                  [Page 1] 
 





INTERNET DRAFT     Synch of Loop Free Timer Values           Mar 2006 
 



1.     Introduction 

  Most of the loop-free convergence mechanisms [LFFWK] require one or 
  more convergence delay timers that MUST have a duration that is 
  consistent throughout the routing domain. This time is the worst 
  case time that any router will take to calculate the new topology, 
  and to make the necessary changes to the FIB. The timer is used by 
  the routers to know when it is safe to transition between the loop-
  free convergence states. 

  The time taken by a router to complete each phase of the loop-free 
  transition will be dependent on the size of the network and the 
  design and implementation of the router. It can therefore be 
  expected that the optimum delay will need to be tuned from time to 
  time as the network evolves. 

  Manual configuration of the timer is fraught for two reasons, 
  firstly it is always difficult to ensure that the correct value is 
  installed in all of the routers, and secondly, if any change is 
  introduced into the network that results in a need to change the 
  timer, for example due to a change in hardware or software version, 
  then all of the routers need to be reconfigured to use the new 
  timer value.  

  It is therefore desirable that a means be provided by which the 
  convergence delay timer can be automatically synchronized 
  throughout the network. 



2.    Required Properties 

  The timer synchronization mechanism MUST have the following 
  properties: 

     o The convergence delay time must be consistent amongst all 
       routers that are converging on the new topology. 

     o The convergence delay time must be the highest delay required 
       by any router in the new topology. 

     o The mechanism must increase the delay when a new router in 
       introduced to the network that requires a higher delay than is 
       currently in use. 

     o When the router that had the longest delay requirements is 
       removed from the topology, the convergence delay timer value 
       must, within some reasonable time, be reduced to the longest 
       delay required by the remaining routers. 


 
Atlas, Bryant, Shand      Expires Sept 2006                  [Page 2] 
 





INTERNET DRAFT     Synch of Loop Free Timer Values           Mar 2006 
 

     o It must be possible for a router to change the convergence 
       delay timer value that it requires. 

     o A router which is in multiple routing areas, or is running 
       multiple routing protocols may signal a different loop-free 
       convergence delay for each area, and for each protocol. 

  How a router determines the time that it needs to execute each 
  convergence phase is an implementation issue, and outside the scope 
  of this specification. However a router that dynamically determines 
  its proposed timer value must do so in such a way that it does not 
  cause the synchronized value to continually fluctuate.  



3.    Mechanism 

  The following mechanism is proposed.  

  A new information element is introduced into the routing protocol 
  that specifies the maximum time (in milliseconds) that the router 
  will take to calculate the new topology and to update its FIB as a 
  result of any topology change. 

  When a topology change occurs, the largest convergence delay time 
  required by any router in the new topology is used by the loop-free 
  convergence mechanism. 

  If a routing protocol message is issued that changes the 
  convergence delay timer value, but does not change the topology, 
  the new timer value MUST be taken into consideration during the 
  next loop-free transition, but MUST NOT instigate a loop-free 
  transition. 

  If a routing protocol message is issued that changes the 
  convergence timer value and changes the topology, a loop-free 
  transition is instigated and the new timer value is taken into 
  consideration. 

  The loop-free convergence mechanism should specify the action to be 
  taken if a timer change (only) message and a topology change 
  message are independently generated during the hold-off time. A 
  suitable action would be to take the same action that would be 
  taken if two uncorrelated topology changes occurred in the network. 

  All routers that support loop-free convergence MUST advertise a 
  loop-free convergence delay time. The loop-free convergence 
  mechanism MUST specify the action to be taken if a router does not 
  advertise a convergence delay time. 




 
Atlas, Bryant, Shand      Expires Sept 2006                  [Page 3] 
 





INTERNET DRAFT     Synch of Loop Free Timer Values           Mar 2006 
 

4.    Protocol Details 

  This section describes the protocol changes needed to implement the 
  timer synchronization function. 


4.1.     ISIS 

  The controlled convergence timer value will be carried in a new 
  Sub-TLV of the capability TLV as defined in [ISIS-CAP].  

  This draft defines one such SUB-TLV where the type is for the 
  worst-case FIB compute/install time, the value is 16 bits and is 
  specified in milliseconds; this gives a max value of about 65s.  

  The format of the Sub-TLV is as shown below. 

      Sub-TLV FIB-Convergence Timer  

      TYPE: <TBD>  

      Length: 2 octets  

      Value: <16-bit timer value expressed in milliseconds>  

  This MUST be carried in a capability TLV with the S-bit set to zero 
  (indicating that it MUST NOT be leaked between levels).  


4.2.     OSPF 

  A new type-10 opaque LSA (the controlled convergence LSA) will be 
  defined as part of OSPF changed needed to define the loop-free 
  convergence mechanism. This will consist of one or more TLVs.  This 
  draft defines one such TLV where the type is for the worst-case FIB 
  compute/install time, the value is 16 bits and is specified in 
  milliseconds; this gives a max value of about 65s. 



5.    IANA considerations 

  There will be IANA considerations that arise as a result of this 
  draft, but they are not yet determined. 



6.    Security Considerations 

  If an abnormally large timer value is proposed by a router, the 
  there is a danger that the loop-free convergence process will take 
  an excessive time. If during that time the routing protocol signals 
  the need for another transition, the loop-free transition will be 
 
Atlas, Bryant, Shand      Expires Sept 2006                  [Page 4] 
 





INTERNET DRAFT     Synch of Loop Free Timer Values           Mar 2006 
 

  abandoned and the default best case (traditional) convergence 
  mechanism used. 

  It is still undesirable that the routers select a convergence delay 
  time that has an excessive value. The maximum value that can be 
  specified in the LSP/LSA is limited through the use of a 16 bit 
  field to about 65 seconds. When sufficient implementation 
  experience is gained, an architectural constant will be specified 
  which sets the upper limit of the convergence delay timer.  



7.    Intellectual Property Statement 

 
  The IETF takes no position regarding the validity or scope of any   
  Intellectual Property Rights or other rights that might be claimed 
  to pertain to the implementation or use of the technology described 
  in this document or the extent to which any license under such 
  rights might or might not be available; nor does it represent that 
  it has made any independent effort to identify any such rights.  
  Information on the procedures with respect to rights in RFC 
  documents can be found in BCP 78 and BCP 79. 

  Copies of IPR disclosures made to the IETF Secretariat and any 
  assurances of licenses to be made available, or the result of an   
  attempt made to obtain a general license or permission for the use 
  of such proprietary rights by implementers or users of this 
  specification can be obtained from the IETF on-line IPR repository 
  at http://www.ietf.org/ipr. 

  The IETF invites any interested party to bring to its attention any 
  copyrights, patents or patent applications, or other proprietary 
  rights that may cover technology that may be required to implement 
  this standard.  Please address the information to the IETF at       
  ietf-ipr@ietf.org. 

 


8.     Full copyright statement 

  Copyright (C) The Internet Society (2006). This document is subject 
  to the rights, licenses and restrictions contained in BCP 78, and 
  except as set forth therein, the authors retain all their rights. 

  This document and the information contained herein are provided on 
  an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE 
  REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND 
  THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, 
  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT 
  THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR 

 
Atlas, Bryant, Shand      Expires Sept 2006                  [Page 5] 
 





INTERNET DRAFT     Synch of Loop Free Timer Values           Mar 2006 
 

  ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A 
  PARTICULAR PURPOSE. 



9.    Normative References 

  Internet-drafts are works in progress available from   
  <http://www.ietf.org/internet-drafts/> 

   [ISIS-CAP]     Vasseur JP. et al,  "IS-IS extensions for 
                  advertising router information",  draft-ietf-
                  isis-caps-03.txt , Work in Progress. 

 



10.     Informative References 

  Internet-drafts are works in progress available from   
  <http://www.ietf.org/internet-drafts/> 

  [LFFWK]       Bryant, S., Shand, M., A Framework for Loop-
                 free Convergence <draft-bryant-shand-lf-conv-
                 frmwk-01.txt>, (work on progress) 

 


11.    Acknowledgements 

  Our thanks to Stefano Previdi for his useful coments. 




















 
Atlas, Bryant, Shand      Expires Sept 2006                  [Page 6] 
 





INTERNET DRAFT     Synch of Loop Free Timer Values           Mar 2006 
 



12.    Authors' Addresses 

  Alia K. Atlas 
  1600 Amphitheatre Parkway 
  Mountain View CA 94043    Email: akatlas@gmail.com 
   
  Stewart Bryant 
  Cisco Systems, 
  250, Longwater, 
  Green Park, 
  Reading, RG2 6GB, 
  United Kingdom.            Email: stbryant@cisco.com 

  Mike Shand 
  Cisco Systems, 
  250, Longwater, 
  Green Park, 
  Reading, RG2 6GB, 
  United Kingdom.            Email: mshand@cisco.com 

   

   




























 
Atlas, Bryant, Shand      Expires Sept 2006                  [Page 7]