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   ✧✦Catherine✦✧ (whitequark@mastodon.social)'s status on Wednesday, 04-Jun-2025 12:46:41 JST ✧✦Catherine✦✧

   networking folks: the minimum Ethernet frame size is 64 octets, right? does that include the FCS?

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     ✧✦Catherine✦✧ (whitequark@mastodon.social)'s status on Wednesday, 04-Jun-2025 12:49:24 JST ✧✦Catherine✦✧

     in reply to

     i did look at the 802.3 spec and it says this, which doesn't clarify much

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     ✧✦Catherine✦✧ (whitequark@mastodon.social)'s status on Wednesday, 04-Jun-2025 13:50:59 JST ✧✦Catherine✦✧

     in reply to

     • Dan 🔓:afloppy:​:donor:, powered by sarcasm
     • Andrew Zonenberg

     @azonenberg @sycophantic so while I have your attention: in my Ethernet deframer (connected to output of PHY), how should I treat the preamble? do I just sync on the SFD and ignore all 55's before it? do I count the 55's?

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     Andrew Zonenberg (azonenberg@ioc.exchange)'s status on Wednesday, 04-Jun-2025 13:51:00 JST Andrew Zonenberg

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     • Dan 🔓:afloppy:​:donor:, powered by sarcasm

     @sycophantic @whitequark Interesting all of my MACs to date has just treated the 802.1q tag the same as an ethertype for the most part (only caring about the tag once i start making forwarding decisions) and my padding insertion logic pads the entire frame to 64.

     I haven't got to the point of adding outbound 802.1q tags on trunk ports yet but when I do, I'll probably need to patch my MAC code that does padding insertion to change the target frame length based on whether a tag is present

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     Andrew Zonenberg (azonenberg@ioc.exchange)'s status on Wednesday, 04-Jun-2025 13:51:01 JST Andrew Zonenberg

     in reply to

     @whitequark yes, 64 octets including src/dest MAC, 802.1q tag if present, ethertype/length, frame body, and FCS.

     Preamble/SFD and interframe gap do not count towards the 64

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     Dan 🔓:afloppy:​:donor:, powered by sarcasm (sycophantic@infosec.exchange)'s status on Wednesday, 04-Jun-2025 13:51:01 JST Dan 🔓:afloppy:​:donor:, powered by sarcasm

     in reply to

     • Andrew Zonenberg

     @azonenberg @whitequark 68 octets if a vlan tag is present. https://www.cisco.com/c/en/us/support/docs/lan-switching/8021q/17056-741-4.html

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     ✧✦Catherine✦✧ (whitequark@mastodon.social)'s status on Wednesday, 04-Jun-2025 13:56:02 JST ✧✦Catherine✦✧

     in reply to

     • Dan 🔓:afloppy:​:donor:, powered by sarcasm
     • Andrew Zonenberg

     @azonenberg @sycophantic right, that's exactly how I implemented it already

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     Andrew Zonenberg (azonenberg@ioc.exchange)'s status on Wednesday, 04-Jun-2025 13:56:03 JST Andrew Zonenberg

     in reply to

     • Dan 🔓:afloppy:​:donor:, powered by sarcasm

     @whitequark @sycophantic My own implementation looks for I think at least one 55 as a state machine trigger followed by a D5 and then goes to frame content. Do not count the 55s, some PHYs/protocols can remove some of them (e.g. 10baseT before bit sync is achieved)