Hey Rahul, Cenk, Koen,
> 6lo frag is not a good option to use and should be avoided as far as possible. right, but as we all know it cannot be achieved all the time. > Supporting target aggregation in DAO without depending on 6lo frag I think that would be the right direction for mitigating the symptom of sending elidable redundant information in DAOs options, which exceed the MTU. I don't remember exactly if the rfc6550 et al. restrict the behaviour of constructing and distributing DAO transit/target options to parents in solely a single packet. If splitting the downward information does not violate the RFCs, then taking the MTU into account up to a cetrain degree, would be just an implementation specific detail and probably the way to go (again). But I would always prefer letting the underlying layer to provide fragmentation over an customized approach. Best regards, Martin ________________________________ Von: devel [devel-boun...@riot-os.org]" im Auftrag von "Koen Zandberg [k...@bergzand.net] Gesendet: Donnerstag, 19. Oktober 2017 08:19 An: devel@riot-os.org Betreff: Re: [riot-devel] RPL DAO target concat from fib Hey Rahul, Unfortunately I don't have time right now to read and comment on your email in depth :( About the ETX metrics for RPL, please have a look at #6873 and #7450. I want to take a better look at your ideas and proposal in the weekend. Regards, Koen Zandberg #6873: https://github.com/RIOT-OS/RIOT/pull/6873 #7450: https://github.com/RIOT-OS/RIOT/pull/7450 On 10/19/2017 07:46 AM, Rahul Jadhav wrote: Thanks Cenk for giving a clear picture. Some comments inline... In general, I feel this is important to be handled, since even in small network this would result in DAO fragmentation and will impact its performance. Also there are some other points i wanted to understand/clarify: 1. Currently RIOT does not handle L2 ACK for determining whether L2 send was successful or not. This feedback is not used at RPL/6lo layer. Scenario: A node receives a DIO from parent and sends a DAO. But lets say this DAO could not reach the parent. In this case L2 ACK would have failed and the child node could have handled it to switch parent. Even if K bit is set in the DAO, and if DAO-ACK is not received, the child node wont come to know since there is no state/timer maintained to handle this. Essentially this will lead to child node believing that it is connected to the network but the downstream path is never actually established. 2. RIOT does not handle L2 retry-count feedback to maintain RPL metric (for e.g. ETX). Pls correct if i m wrong. Thanks, Rahul On 19 October 2017 at 01:00, Cenk Gündoğan <list-r...@cgundogan.de<mailto:list-r...@cgundogan.de>> wrote: Hey Rahul, you are correct. The current RPL DAO building routine does not take into account the MTU size, which is IMO the appropriate approach, because on that level (ICMPv6) there is usually no knowledge about the link-layer in use. [RJ] True. If I understand you correctly, then you basically want to move the fragmentation from the 6lowpan layer up to the ICMPv6/RPL layer (and only for DAOs). [RJ] Thats exactly what I had in mind. I think in one of the older iterations of our RPL implementation we once had a functionality to limit the number of Target Options in the DAO to a specific number (configurable on compile-time). [RJ] This would have been a real nice feature. Supporting target aggregation in DAO without depending on 6lo frag. In the future, proposing/implementing prefix eliding (the way 6loRH does for SRH or by simply using 6lo CID) between target containers and standardising it would make sense ! Considering that DAO consumes the most amount of RPL control traffic, i feel this can be fairly important. But with the addition of a proper 6lowpan fragmentation, we dropped that functionality. [RJ] 6lo frag is not a good option to use and should be avoided as far as possible. I may take a look at it during the weekend. If I remember correctly, then we used to have a further parameter to the "send_DAO" function that tracked the number of already sent Target Options. Further calls to "send_DAO" would then add the next Target Options. If such functionality is needed (@bergzand, @BytesGalore, @smlng any comments on this?) then we should aim to come up with an unintrusive approach to activate / deactivate such a behaviour with compile flags. [RJ] Wouldn't a simple compile-time flag such as DAO_TARGET_CONCAT_NUM=X be sufficient, where X could be 0 (no concat, send only 1 target container which will be node self IP addr), -1(for full concat, current implementation), and anything else which means non-self target container count. The other way to define such a flag would be DAO_TARGET_CONCAT_SZ=Ybytes ... which defines number of bytes instead of target count. Cheers, Cenk Gündoğan On 17-10-19 00:00:34, Rahul Jadhav wrote: > Hello RIOT team, > > While experimenting with RIOT i found the RPL module implementation > behaviour which sort of stops my network from building up. > > Scenario: > If i have a RIOT 6lr node and it has an FIB with, let's say, 10 active > entries, then when the 6lr next sends DAO, it concatenates multiple target > containers (from multiple FIB entries) in the same DAO message. This > results in a packet size crossing link MTU limit (127 in my case) and for > my case i do not have 6lo fragmentation enabled. Thus the DAO is getting > dropped. > > I skimmed through the code but could not find a way to send DAO with max x > target containers, where x is predefined. > > To reiterate, if the FIB active entries are more, then RIOT aggregates all > the entries into the same DAO as target containers and forwards it. While > aggregating if the packet crosses MTU boundary and if the 6lo frag is not > on then it (6lo module) will drop the packet. Thus the network wont form. > (i do not want 6lo fragmentation to happen for RPL control packets). > > Just want to understand, is there any way to handle this situation without > turning on 6lo frag? > > Thanks, > Rahul > > --------------[log snippet]------- > > RPL: Send DAO - building internal transit > > RPL: Send DAO - building target fd00::302:304:506:3/128 > > RPL: Send DAO - building target fd00::302:304:506:8/128 > > RPL: Send DAO - building target fd00::302:304:506:d/128 > > RPL: Send DAO - building target fd00::302:304:506:10/128 > > RPL: Send DAO - building target fd00::302:304:506:11/128 > > RPL: Send DAO - building target fd00::302:304:506:12/128 > > RPL: Send DAO - building target fd00::302:304:506:e/128 > > RPL: Send DAO - building target fd00::302:304:506:9/128 > > RPL: Send DAO - building target fd00::302:304:506:4/128 > > RPL: Send DAO - building target fd00::302:304:506:6/128 > > :::::::: > > 6lo: iface->max_frag_size = 127 for interface 6 > > 6lo: packet too big (254 > 127) > > 6lo: waiting for incoming message. > > :::::::: > > -----------[end of log]------------ > _______________________________________________ > devel mailing list > devel@riot-os.org<mailto:devel@riot-os.org> > https://lists.riot-os.org/mailman/listinfo/devel -- Cenk Gündoğan Hamburg University of Applied Sciences Dept. of Computer Science / Internet Technologies Group Berliner Tor 7, 20099 Hamburg, Germany Fon: +49 40 42875 - 8426 Mail: cenk.guendo...@haw-hamburg.de<mailto:cenk.guendo...@haw-hamburg.de> Web: https://www.inet.haw-hamburg.de/ _______________________________________________ devel mailing list devel@riot-os.org<mailto:devel@riot-os.org> https://lists.riot-os.org/mailman/listinfo/devel _______________________________________________ devel mailing list devel@riot-os.org<mailto:devel@riot-os.org> https://lists.riot-os.org/mailman/listinfo/devel
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