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Nov 5, 2025 at 16:24 comment added Barmar @grawity Perhaps that also suggests a poor design of MAC cache timeout. Don't just base it on receive times, also use send times.
Nov 5, 2025 at 12:48 comment added grawity @jcaron: I've heard of that happening with dedicated UDP syslog servers in particular.
Nov 5, 2025 at 12:39 comment added jcaron And even beyond the initial start up, a host receiving traffic is very unlikely to never respond: ARP requests will yield ARP replies, TCP connections will result in ACKs or RSTs, etc. It would be an extremely unusual setup where the host receives frames and never sends anything either before or after.
Nov 5, 2025 at 10:53 comment added psmears "a node starting up or activating a link is extremely likely to send something - a DHCP discovery, ARP request for its gateway or DNS server" - yes, and, conversely, a host that sends some packets to a given MAC address and doesn't ever get any response will probably stop sooner or later (eg because the connection attempt times out, or the ARP table entry ages out, etc...)
Nov 5, 2025 at 7:09 vote accept Peter
Nov 4, 2025 at 14:45 comment added Zac67 All good, that's what questions are for. Please don't change your question substantially as then the answer wouldn't fit very well any more. I took the liberty to shorten your answer to convert it to a comment as I think that was the intention.
Nov 4, 2025 at 14:16 comment converted from answer Peter I conflated "collision domain" with "filtering/separation of traffic between ports of a bridge". You're right that there's no meaningful distinction between how things worked with and without hubs. For a moment I thought I came up with a case where the difference mattered, but it's just that my intuition played tricks on me - a bunch of hosts behind a single hub seemed somewhat more "wrong" to pass traffic to the other side of the bridge when communicating solely among themselves that if each host were connected directly to a switch.
Nov 4, 2025 at 13:09 history edited Zac67 CC BY-SA 4.0
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Nov 4, 2025 at 11:05 history answered Zac67 CC BY-SA 4.0