Liaison statement
ASON Routing Loop Prevention Mechanism
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State | Posted |
---|---|
Submitted Date | 2007-09-03 |
From Group | ccamp |
From Contact | Adrian Farrel |
To Group | ITU-T-SG-15-Q14 |
To Contacts | Greg Jones <greg.jones@itu.int> |
Cc | Kam Lam <hklam@alcatel-lucent.com> Stephen Trowbridge <sjtrowbridge@alcatel-lucent.com> Ross Callon <rcallon@juniper.net> David Ward <dward@cisco.com> Scott Bradner <sob@hardward.edu> CCAMP Mailing List <ccamp@ops.ietf.org> |
Response Contact | Adrian Farrel <adrian@olddog.co.uk> Deborah Brungard <dbrungard@att.com> |
Technical Contact | Adrian Farrel <adrian@olddog.co.uk> Deborah Brungard <dbrungard@att.com> |
Purpose | In response |
Attachments | (None) |
Body |
The IETF CCAMP working group thanks you for your continued interest in the loop-prevention mechanism contained in our OSPF-based solution to the routing requirements as described in RFC 4258. This liaison is in response to your liaison COM15-169-E issued from your June plenary. A separate liaison will report on the status and progress of our OSPF ASON solution. We disagree with your statement that the rationale we explained "does not utilize the hierarchical nature defined by ASON." Quite to the contrary, the solution addresses the issues introduced by the hierarchical routing nature of ASON while utilizing the benefits. At the same time, since the protocol mechanisms are extensions to OSPF, it is only natural that "the rationale provided takes into account the considerations of how OSPF traditionally operates." You are right to observe that other mechanisms could have been selected, and would also have been functional. This is often the case in protocol design. However, a choice has to be made, and unless there are technical reasons to suggest that the choice is wrong, there seems to be no particular motivation to make a change. You say: While we recognise it is possible to identify the propagation direction based on the Area ID of the source, it does require that all redistribution mechanisms in the network understand the relative location of source areas given the area hierarchy (i.e. are they up or down the hierarchy from the evaluation point). We cannot identify in the existing proposal any mechanism (i.e. new LSA format) defined to provide this information. We note that the requirement is not to know the direction of propagation of information, but to detect routing advertisement loops. According to the strict hierarchical nature of ASON (as you describe in your liaison) the use of Area IDs is sufficient to detect advertisement loops. There is no definition of any new mechanism or LSA in this Internet-Draft: the use of a new LSA or changes to the processing rules for existing LSAs would inhibit the integration of ASON routing developments within the IETF routing family and, while this may not be an objective of the ASON architecture, it is an objective of the IETF. You suggest that the use of Area ID in the LSAs will inhibit re-configuration of AREA IDs. We do not believe that this is the case, and we will add text to the draft to describe the necessary processing for this important, but uncommon case. Please note that the scope of this work (including the loop-prevention mechanisms) is limited by the requirements expressed in RFC 4258. A separate liaison to you has requested a further review of RFC 4258. In the event that substantive modifications to the requirements are made as a result of your review, it will be necessary to consider updating the solutions work. Such a process of publication and revision is similar to the procedure applied within the ITU. Note also that the scope of this work (that is, of this current Internet-Draft) is extensions to the OSPFv2 protocol. The CCAMP working group would welcome contributions in the form of Internet-Drafts from anyone who is interested in addressing the same problem space through the IS-IS protocol. Thank you for your continued support of this work. Regards, Deborah Brungard and Adrian Farrel IETF CCAMP Working Group Co-Chairs |