Minutes interim-2020-lsr-02: Wed 10:00
|Meeting Minutes||Link State Routing (lsr) WG|
|Title||Minutes interim-2020-lsr-02: Wed 10:00|
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LSR Interim Agenda Chairs: Acee Lindem Chris Hopps Secretary: Yingzhen Qu WG Status Web Page: http://tools.ietf.org/wg/lsr/ Session #2 Date: Wednesday, 29 April 2020 Start Time: 10:00 America/New_York Bruno Decraene - IS-IS Flooding Speed Parameters Advertisement https://datatracker.ietf.org/doc/draft-decraene-lsr-isis-flooding-speed/ Acee: Can you disclose the implementations used in your tests. Bruno: I don’t want to disclose the implementations. If we have two senders, that’s something we can do but there are synchronization issues. Chris H: We can talk offline. Acee: That’s interesting. If you have somebody who has a naive assumption that faster is better, they’re actually going to get three times slower flooding than the optimal. Chris H: Does TCP support dynamic receiver window resizing? Bruno: I don’t know. But from protocol standpoint, you can change but you’re not supposed to reduce. Chris H: There is lots of information, flow control, congestion control and modifications of the protocol. I have different ideas of flow control and congestion control, not necessarily correct here. Really congestion control is about loss, it can happen in the network and in the router. I want to bring up that we have flow control of saying stop sending, it’s more active. The point is we should explore the idea, it might be a simple solution. The dynamic receive window size is 2nd order, it’s almost modifying the congestion control algorithm. It’s worth investigating, but seems complex. Bruno: It could be simple. It’s already available on some implementation. Chris H: You’re talking about burst rate. It’s more like a buffer size. It won’t help speed up. Bruno: You might send back to back. Chris H: That’s a bit different. Tony Li: We’ve been flexible in the draft. Not all knobs are useful, and this allows flexible implementations. People can play with the knobs and see what happens. Les Ginsberg - IS-IS Flooding Scale Considerations https://datatracker.ietf.org/doc/draft-ginsberg-lsr-isis-flooding-scale/ Chris H: I’d be surprised to see that ISIS traffic is not separated from data traffic on the line card, other than all control plane traffic. Les: So be shocked. I talked to some implementations, and in some cases, this is the case. There are implementations with the separation, but there are some without. Chris H: These might be barriers. It doesn’t mean we need to engineer to it. It’s not hard to do, considering IS-IS is coming in as ISO, it’s separated early generally. Let’s not throw out a solution yet. Tony P: from practical implementation, the transmitter-based is very useful and works well, but the receiver needs high frequency which we don’t have. You have to go through TCP, etc. If you start running faster timers, you can’t get decent feedback. You can put it in, and it may fly in the future. Chris H: What do you say to my idea of having an ISIS queue in the line card? If it’s not draining, I send a pause. Tony P: Now you need line card to generate ISIS packets. It’s pretty challenging. Chris H: Just add an ISIS queue, if it’s 80% full, send a pause. Tony P: But your line card starts to generate a packet and your implementation knows nothing about it. Or the line card needs to report back. Those are not easy to build. Les: Your proposal is only taking one point from the chain. Even if we agree to do what you suggested, it doesn’t cover the case where the PDU might be dropped. Tony P: For ISIS, everything is in LSP. It’s more difficult, not like OSPF. Chris H: I just don’t want to throw this out so quickly. It might be an add-on solution. I’m not convinced it’s too hard to put it in the line card. Tony P: This is decent idea. Something to think about. Chris H: If we can flood without loss, why should we care whether one interface floods faster than the other? Les: For any event, left side of network can converge faster than the right side. Chris H: We want to converge as fast as possible. Why should I wait for the slowest router in the network? Les: If you look at your network, if there are one or two routers that are slower then it’s a problem of your network. The analogy is like some SPF is running at 5s interval while others at 15s. Chris: I want my network to converge as fast as possible. John Scudder: Typically the answer to why you don’t want one part of your network to converge faster is because you create forwarding loops. I agree in general faster convergence is better, but it’s not always. Chris H: We talked about good and bad information before. If your network is broken, you want reconverge as fast as possible because it’s black holing. If you’re bringing up alternate routes, and you’re creating loops then that good information becomes bad propagating at different rate. John Scudder: Black holing traffic consumes one transmission on the link, micro-looping consumes many transmission on that link. Chris H: That’s a good point. Bruno: Agree with micro loops, you have LSDB inconsistency. Les: We want to decide whether we want to do transmit-side or receive-side flow control. Let’s not get lost in other issues. Bruno: I think you’re mixing flow control and congestion control. If you want to do flow control, it’s end to end. Tony Li: Question to Les, have you done any experiments? Les: The data Bruno presented reinforces the point. We published an algorithm, but you haven’t. Tony Li: We’re not trying to publish an algorithm, we’re trying to set up some experimentations. How about we stop trying to decide without evidence. Let’s do some coding and put the evidence on the table. Les: If we were try to implement the receiver-side algorithm what we have to do. I need to do changes from the platform side. Tony Li: I’m asking you to implement your proposal. Les: That’s fine. We can do that. Tony P: The algorithm is a simplified version of what we run in RIFT, the receiver-side also provides some sort of back pressure, something along the line. Tony Li: Can we see some numbers? Tony P: What numbers? It’s platform dependent. Tony Li: I’d like to see two implementations, flooding 10K LSPs. Tony P: So give me the other one. Tony Li: I agree. Let’s get some numbers. Peter: It looks to me both drafts are trying to do flow control, and it needs to be done from the sending side. The only difference is where to get the parameters, buffer size, number of LSPs that can be flooded, etc. For the rest it looks to me the same thing. Tony Li: I agree. Peter: If we’re going to use static value, I can configure it on the sender side as well. If we’re to tie the value to platform dependent receiver and send it in Hello packets, it’s problematic. Chris H: As WG member, why don’t we talk about more why a solution works better? Instead of why the other one not working? Les: It’s a mis-statement. I’m not saying it’s bad, but it's difficult to implement. Tony Li: If we can get to 99% with transmit-side, there is no reason not. Les: I agree. Peter: The results will be the same with static value, whether it’s from the sender or receiver. Chris H: Why don’t we get some numbers from the transmitter-side solution? Peter: What Bruno presented already proved that. We can debate what’s the best algorithm from the sender side to get the best result. Chris H: We can do that. Tony Li: If we have to configure static numbers everywhere, the users won’t be happy. Peter: We don’t want that, we want it to behave the same. Tony Li: You have interoperability issue, different implementations, different router capabilities. Peter: For less capable router, I will slow down immediately. Tony Li: You don’t know how to slow down, you don’t have feedback. Peter: I have unacked LSPs. Tony Li: That means some implementations have to speed up, that means we’re changing the protocol, and we have to agree on that. Les: We’re not changing the protocol here. Tony Li: You are, you’re changing behavior. Les: We’re changing behavior, but not the protocol. If the algorithm is sound, and the receiver is capable of processing the packets, there is no interoperability issue. Chris H: Whether we’ve changing the behavior, or the protocol on the wire, it’s not the point. We’re trying to solve a problem. Les: The concern we raised about dynamic algorithm, not static. If we agree that it doesn’t require significant changes to platform and protocol, that’s a plus. Chris H: that’s a selling point. Ketant Talaulikar: In Bruno’s presentation, all those numbers from receiver-based implementation? Acee: No. Ketant: If so, how can it say one algorithm is better than the other? Tony Li: That serves as baseline to show default parameters is not good. Ketant: So we need proofs from both proposals. Tony Li: Agree. Chris H: I don’t think these two drafts are in conflict. I can do both. No reason to pick one against the other. Ketant: I just got the impression that we have numbers from one approach. To be fair, we need number from both. From simplicity point of view, the 2nd proposals seems easy to roll out and gets deployed in mixed environment. While the other proposal needs change on the wire. Chris H: if it works. Peter: if the 2nd one doesn’t work, the first doesn’t work either. Chris H: Let’s get some numbers. Not changing something on the wire is preferable. Les: the point we’re making is in order to make the receiver based algorithm work, it requires changes on the platform. Tony Li: If that hard work is necessary then we should do it. No question about that. Acee: speaking as chair, we will need further implementation and provide data. Possible another meeting on this. Comments from Chat: From Henk to Everyone: 8:51 AM The problem is that a "sender-only" algorithm isn't really send-only. The sender makes guesses, based on what it sees. Part of what is sees are the PSNPs. And the behaviour of the receiver when and how to send the PSNPs is not 100% the same in all implementations. If you want to a "sender-only" algorithm, you need to specify PSNPs in more detail. How long to wait, what intervals, how many acks to pack in one PSNP, etc. from Les Ginsberg (Cisco) to Everyone: 8:53 AM Henk - I do not agree. Tx based works on what was actually sent and what was actually acknowledged. We do not care whether an LSP was dropped at ingress or in some queue on it's way to IS-IS. from henk to Everyone: 8:54 AM Not only what was acknowledged, also the speed at which the acks come in. And how acks are grouped, and when they are sent, are implementation specific. I'll send an email to the list later today or tomorrow. from Bruno Decraene (Guest) to Everyone: 8:54 AM +1 thanks Henk Peter: Read the comments, I agree. It’s not completely from the transmitter because we’re based on the acks. This is just terminology. Chris H: That’s a great point. The proposal only covers p2p, and it need to cover LAN. If it proves to be working, then we can look at the ACK mechanism. Xuesong Geng: If we want to do the tests, how do we do the tests? Tony Li: Bruno showed a straightforward test, taking 5000 LSPs and send from point to point. I believe he’s using TCP dump and looking at it from the wire and observing retransmissions and whether the transmitter has sync'ed the entire LSDB. Xuesong: So we can see the retransmission times and judge which one is better? Chris H: You can also look at the sequence number. Tony Li: You can also watch PSNPs coming from the other router. Xuesong: I just want to figure out what parameters to capture to determine which is better? What numbers to look at? Chris H: you can send an email on the list and ask. Les: I’m not against testing, but it’s not going to be so easy and compare the results. There are many variables. Chris H: You’re right, we have to believe the results. Xuesong: Agree with Les, the answers might not be straightforward. In TCP congestion control, we can only say one is more agressive than the other. Chris H: It’s a deterministic result, I send one LSP from one side, and when I receive it on the other side. Acee: Let’s keep this discussion going. Chris H: I don’t see a conflict here. We don’t have to pick one. Discussion from the chat window: From Tony P to Everyone: 8:56 AM The only thing that matters is really, do you get ACKs in a timely manner ... If you RTX it means _something_ went wrong, PSNP didn't get produced, got lost of the wire etc. all the same to the transmitter, it means From Tony P to Everyone: 8:56 AM Basicaly, back-off From Tony PWorking Group to Everyone: 8:57 AM That's why the RX trying to do something is hairy. Now what? we'll start to send empty PSNPs to indicate that we can process more now? Every 200msecs like TCP? From Peter Psenak to Everyone: 8:58 AM Who is "BIER Working Group"? from John Scudder to Everyone: 9:00 AM It would be nice if somebody had a graduate student group who wanted to drop both options into their simulator, instead of two groups of partisans running a beauty contest. From Ketan Talaulikar to Everyone: 9:00 AM +1 to John From Tony Li to Everyone: 9:00 AM I don’t trust simulators. From John Scudder to Everyone: 9:00 AM Somebody could get a nice publication out of it, I’m totally serious. from Tony Li to Everyone: 9:01 AM But implementations, yes. From Bruno Decraene (Guest) to Everyone: 9:01 AM +1 to John From John Scudder to Everyone: 9:01 AM Tony Li, fair enough. It does provide an apples-to-apples comparison, though. From Fohn Scudder to Everyone: 9:01 AM Also, what’s the difference between a simulator and someone’s virtualized control plane software? From Bruno Decraene (Guest) to Everyone: 9:01 AM Does anyone know such a team? From Les Ginsberg (Cisco) to Everyone: 9:01 AM IS-IS on the RX side is not guaranteed to know what has been dropped - so you cannot depend on IS-IS Rx side to know when to send "sned me more/faster". From Tony Li to Everyone: 9:02 AM John, no diff. From John Scudder to Everyone: 9:02 AM But yet we field those things. From Tony P to Everyone: 9:02 AM "If" you assume that you can get the RX size on the reciever side and assume you can send very fast to the transmitter that information, the RX will perform better. But you knnow what assumptions made of you and me ;-) From John Scudder to Everyone: 9:03 AM Bruno, Cisco used to fund research groups, I don’t know if they still do, but it might be that people there have access.