Yes, I admit it is tricky, but I think that we have to be honest with the reader, since as we both agree this only solves part of the problem.
Incremental metrics is certainly one local solution that can be deployed, and if the metric of the link is low that need not take many cycles to complete.
The key point for me is that the text needs to describe the shortfall of the solution, and whilst ideally it should provide mitigation if it cannot do that, it needs to be clear on the consequences of not providing it so that those not schooled in the detail of IPFRR understand what will happen to their network when they deploy this.
Something that Benoit has been encouraging people to write for a while is an Operational Considerations section, which would be an ideal place to put this discussion.
- Stewart On 27/09/2017 09:19, stephane.litkowski@xxxxxxxxxx wrote:
Hi Stewart, Thanks for your comment. Managing the link up is more tricky than the link down. We had a proposal to tweak the flooding in the first versions of the draft but there was not a good support of that as it touches an important component of the protocol, so it was removed to keep the solution simple but yes it reduces the benefit. There is nothing that we can really do to prevent the impact of the link up. Even if the operator implements an interface dampening mechanism to ensure that the link is stable, the link will eventually goes up and may create a microloop. Now keeping the link down until a quiet time is theorically doable but practically it is not. When a link is down, there are two situations: the operator has lost some capacity that leads to a congestion somewhere or if there is no congestion, the network becomes at risk as if another component fails, there will be not enough capacity. So practically, we want the link to go back up as soon as possible. Other approaches like using "incremental" metrics may be used for the up case to prevent the uloop. Brgds, -----Original Message----- From: Stewart Bryant [mailto:stewart.bryant@xxxxxxxxx] Sent: Thursday, September 21, 2017 10:21 To: ietf@xxxxxxxx Cc: rtgwg-chairs@xxxxxxxx; akatlas@xxxxxxxxx; draft-ietf-rtgwg-uloop-delay@xxxxxxxx; rtgwg@xxxxxxxx Subject: Re: Last Call: <draft-ietf-rtgwg-uloop-delay-06.txt> (Micro-loop prevention by introducing a local convergence delay) to Proposed Standard The draft states that " The proposed mechanism is limited to the link down event in order to keep the mechanism simple." Since a link that goes down will normally also come up again, the draft ought to provide some guidance to the operator on how they should handle that situation. Applications that care about the disruption caused by microloops presumably have no care as to whether they are cause by link up or link down, and so would prefer a complete elimination of that disruption. However I accept that complete elimination has wider network impact and that this approach which is really microloop mitigation has utility. The advice might be as simple as keeping the link out of service until a quiet time, or the loss of connectivity has moved to the network to a state of fragility such that disruption is acceptable. - Stewart On 20/09/2017 19:44, The IESG wrote:The IESG has received a request from the Routing Area Working Group WG (rtgwg) to consider the following document: - 'Micro-loop prevention by introducing a local convergence delay' <draft-ietf-rtgwg-uloop-delay-06.txt> as Proposed Standard The IESG plans to make a decision in the next few weeks, and solicits final comments on this action. Please send substantive comments to the ietf@xxxxxxxx mailing lists by 2017-10-04. Exceptionally, comments may be sent to iesg@xxxxxxxx instead. In either case, please retain the beginning of the Subject line to allow automated sorting. Abstract This document describes a mechanism for link-state routing protocols to prevent local transient forwarding loops in case of link failure. This mechanism proposes a two-step convergence by introducing a delay between the convergence of the node adjacent to the topology change and the network wide convergence. As this mechanism delays the IGP convergence it may only be used for planned maintenance or when fast reroute protects the traffic between the link failure time and the IGP convergence. The proposed mechanism is limited to the link down event in order to keep the mechanism simple. Simulations using real network topologies have been performed and show that local loops are a significant portion (>50%) of the total forwarding loops. The file can be obtained via https://datatracker.ietf.org/doc/draft-ietf-rtgwg-uloop-delay/ IESG discussion can be tracked via https://datatracker.ietf.org/doc/draft-ietf-rtgwg-uloop-delay/ballot/ The following IPR Declarations may be related to this I-D: https://datatracker.ietf.org/ipr/2565/_________________________________________________________________________________________________________________________ Ce message et ses pieces jointes peuvent contenir des informations confidentielles ou privilegiees et ne doivent donc pas etre diffuses, exploites ou copies sans autorisation. Si vous avez recu ce message par erreur, veuillez le signaler a l'expediteur et le detruire ainsi que les pieces jointes. Les messages electroniques etant susceptibles d'alteration, Orange decline toute responsabilite si ce message a ete altere, deforme ou falsifie. Merci. This message and its attachments may contain confidential or privileged information that may be protected by law; they should not be distributed, used or copied without authorisation. If you have received this email in error, please notify the sender and delete this message and its attachments. As emails may be altered, Orange is not liable for messages that have been modified, changed or falsified. Thank you.