Juliusz,
I understand that this is a complex feature that would require quite a bit of work to get right. There would also be work involved in standardizing the IS-IS autoconf and IS-IS source-specific routing extensions. In addition, we might want/need to standardize a mechanism for running IS-IS over IP. That would be considerable amount of work. I don't think it is likely to be a lot of work, though, compared to the effort to standardize Babel which would include: - Starting an IETF WG to do the work, and understanding that the WG would have change control over Babel. - Substantial work to bring the spec up to the level of detail/clarity required for and IETF protocol. - Consideration of many IETF requirements, perhaps most notably security requirements. - Finding a second set of people who are willing to do a complete, independent, fully-interoperable implementation. Personally, I think that Babel is an interesting Routing Protocol with substantially different applicability than IS-IS, OSPF or BGP, and it might be good to standardize it, whether Homenet adopts it or not. However, I think that the time to do that would be a serious problem for Homenet because of the time pressure to finalize a standard for Homenet. Margaret On Mar 24, 2015, at 2:32 PM, Juliusz Chroboczek <[email protected]> wrote: > Dear all, > > At todays meeting, the claim was made (at least twice) that adding > dynamically computed metrics to IS-IS is "just a feature". I strongly > disagree with this assessment -- it's an open research problem, and > a difficult one at that. > > Any interesting metric (packet loss, delay, etc.) will cause a negative > feedback loop, which will lead to oscillations. In Babel, there are three > mechanisms that cope with the oscillations caused by feedback loops: > > 1. the protocol is loop-avoiding, which means that even when oscillations > happen they don't normally cause packets to be lost; > 2. the protocol uses delayed updates, which means that even when a metric > is varying the amount of network traffic remains controlled; > 3. the protocol uses a hysteresis mechanism which limits the frequency of > oscillations. > > IS-IS is fundamentally based on the notion that a topology change is > propagated throughout the network in a timely manner and SPF is recomputed > by all nodes -- it has no loop-avoidance mechanism other then timely > reconvergence. If implemented naively, a dynamically computed metric will > cause repeated flooding, repeated SPF computation, and repeated transient > loops. > > I'm sure these issues can be solved, and I'm pretty confident that Henning > can tell you how; at any rate, it would be a very interesting research > project. However, it is a difficult one, and the three techniques used in > Babel do not apply directly to a link-state protocol. > > -- Juliusz > > _______________________________________________ > homenet mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/homenet _______________________________________________ homenet mailing list [email protected] https://www.ietf.org/mailman/listinfo/homenet
