From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: mail.toke.dk; spf=pass smtp.mailfrom=; dkim=pass header.d=gmx.de header.i=moeller0@gmx.de; arc=none (Message is not ARC signed); dmarc=pass (Used From Domain Record) header.from=gmx.de policy.dmarc=quarantine Received: from mout.gmx.net (mout.gmx.net [212.227.15.18]) by mail.toke.dk (Postfix) with ESMTPS id 0F93470D748 for ; Tue, 30 Sep 2025 08:09:58 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmx.de; s=s31663417; t=1759212598; x=1759817398; i=moeller0@gmx.de; bh=n5uz1RcbPXVUR03Dn1WSJ/fYA7BKLOzc+R36ouoRFZU=; h=X-UI-Sender-Class:Content-Type:Mime-Version:Subject:From: In-Reply-To:Date:Cc:Content-Transfer-Encoding:Message-Id: References:To:cc:content-transfer-encoding:content-type:date:from: message-id:mime-version:reply-to:subject:to; b=Hud5PwpfH7L43TG02Svxs7p+tlXR/ZzF1QdaXjll0RJH1yywdozjXW9UD62j882h U/pQfCcvOBBCZKe0AX8UZqAI2/Uh2DnsELtfrNeuddOYj4PRNSvng4WZ8CFfbGnKr 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max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.10 Precedence: list Subject: [Cake] Re: help request for cake on a large network List-Id: Cake - FQ_codel the next generation Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: Hi Jonathan... thanks for commenting on the details. > On 30. Sep 2025, at 07:18, Jonathan Morton = wrote: >=20 >> On 28 Sep, 2025, at 8:07 pm, dave seddon = wrote: >>=20 >> cakeConfig =3D { >> Bandwidth =3D "990M"; # We currently have 1Gb/s, so this is our = limit >> OverheadBytes =3D 38; # Ethernet overhead (preamble + inter-frame = gap + FCS) >> MPUBytes =3D 84; # Minimum packet unit for Ethernet >> NAT =3D true; >> FlowIsolationMode =3D "triple"; >> PriorityQueueingPreset =3D "besteffort"; >> }; >=20 > It's perhaps worth talking about these parameters a bit. >=20 > You probably realise that the overhead compensation should be set up = for the physical bottleneck link. Not everything is, or behaves exactly = like, an Ethernet cable, even if the connection between your router and = the transceiver for that link physically is one. Or it might really be = Ethernet, but with extra headers patched into each Ethernet frame (in a = domestic context, that's what PPPoE partially is, but VLANs add an extra = couple of words to a frame too). If in doubt, err on the side of = assuming there's more overhead than you know about. These parameters = are, however, completely inadequate to describe wireless links, = especially WiFi. +1; over estimating the true overhead (or MPU) slightly has negligible = cost (a small reduction in potential maximum throughput), = underestimating however can result in noticeable latency under load = increases. Some years ago, I retested my assumed de-bloated DSL link = (after a few months of uneventful operation) because somewhat felt just = not right under load, and lo and behold, my ISP had increased the = overhead by 4 bytes (a VLAN tag) in the interim invalidating my overhead = settings by 4 bytes... (That was with an ATM/AAL5 link, where measuring = the actual overhead is achievable for end-users). Long story, short: if in doubt rather add a small safety margin to your = best overhead estimate... sqm-scripts came down on recommeding 44 bytes = as default. Will not cover all possibilities, but goes a long way in = covering those encapsulation seen often on ebd user internet access = links. >=20 > I'd also like to remind everyone what "triple" flow isolation is. = It's a way to get something like host-and-flow isolation when you're not = certain which side of the link the hosts that want isolating from each = other are; there's a heuristic which effectively decides, dynamically = for each flow, whether to treat it as being src-host or dst-host = isolated. I put it in mainly to serve as a sensible default, since = blindly choosing one or the other would get it wrong exactly half the = time. I don't really like seeing it in a config file that someone's = actually worked on. Mmmh, we might want to tweak the tc-cake man page then to make this = clearer? ATM it reads: dual-srchost Flows are defined by the 5-tuple, and fairness is applied first over source addresses, then over individual flows. Good for use on egress traffic from a LAN to the internet, where it'll prevent any one LAN host from monopolising the uplink, regardless of the number of flows they use. dual-dsthost Flows are defined by the 5-tuple, and fairness is applied first over destination addresses, then over individual flows. Good for use on ingress traffic to a LAN from the internet, where it'll prevent any one LAN host from monopolising the downlink, regardless of the number of flows they use. triple-isolate (default) Flows are defined by the 5-tuple, and fairness is applied over source *and* destination addresses intelligently (ie. not merely by host-pairs), and also over individual flows. Use this if you're not certain whether to use dual-srchost or dual-dsthost; it'll do both jobs at once, preventing any one host on *either* side of the link from monopolising it with a large number of flows. Reading this I would have the impression that selecting triple even on a = bespoke config would be fine, no? >=20 > It's better to explicitly configure this rather than using the = heuristic. The tc-cake keywords are "dual-srchost" if the hosts to be = isolated are upstream of Cake, and "dual-dsthost" if they are = downstream. In a typical installation where two instances of Cake are = managing both directions of traffic, one will be configured each way. >=20 > It's also possible to disable host-isolation entirely, using the = "flows" keyword to provide the same kind of flow-isolation as fq_codel = (or most other forms of FQ) does. Cake can also provide only host = isolation, relying entirely on statistical multiplexing (and the = beneficience of AQM) for managing flows to each host; the keywords are = then "srchost" and "dsthost" with the same meaning as above. If you are = seriously worried about the number of active users at critical moments, = this could be a useful option for you; the number of hosts Cake can = fully handle in this mode is the same as the number of flows it can = handle in the normal flow-isolation modes. I would really like to see some tc -s qdisc output from this network = under load, as that should be informative if any twaeks are necessary at = all. >=20 > - Jonathan Morton > _______________________________________________ > Cake mailing list -- cake@lists.bufferbloat.net > To unsubscribe send an email to cake-leave@lists.bufferbloat.net