Wireshark mailing list archives
pcapng decoding error when preamble is shortened
From: Timmy Brolin <tib () hms se>
Date: Tue, 9 Feb 2021 10:21:39 +0000
Hi, It seems Wireshark fails to decode captured packets with shortened preamble? Normally Ethernet packets have a preamble and SFD like this: 55555555555555D5 But during transmission over Ethernet, sometimes the preamble arrives slightly shorter at the receiving end. Some bytes, or even half a byte(!), at the start of the preamble can go missing for various technical reasons. This is considered normal, and all Ethernet MACs are required to properly decode packets with shortened preamble, as well as packets where the preamble is a non-integer number of bytes. But it seems Wireshark does not? Decoding failure when preamble is shortened: [cid:image002.png@01D6FED5.BB3DFFA0] Normal preamble, decoding successful: [cid:image003.png@01D6FED5.BB3DFFA0] I have attached a pcapng file with these two packets. Timmy Brolin M.SC. Computer Systems Engineering HMS Industrial Networks AB Stationsgatan 37, Box 4126 300 04 Halmstad, Sweden Email: tib () hms se<mailto:tib () hms se> Direct: +46 35 17 29 32 [cid:image001.png@01D6FED3.ADC71BB0] HALMSTAD | BARCELONA | BEIJING | BOSTON | BUCHEN | CHICAGO | COVENTRY | DUBAI | HEDEL | IGUALADA | KARLSRUHE | MILAN | MULHOUSE | NIVELLES | PUNE | RAVENSBURG | SEOUL | SINGAPORE | TOKYO | WETZLAR www.hms-networks.com
Attachment:
shortened_preamble.pcapng
Description: shortened_preamble.pcapng
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Current thread:
- pcapng decoding error when preamble is shortened Timmy Brolin (Feb 09)
- Re: pcapng decoding error when preamble is shortened Jaap Keuter (Feb 13)
- Re: pcapng decoding error when preamble is shortened Timmy Brolin (Feb 13)
- Re: pcapng decoding error when preamble is shortened Jaap Keuter (Feb 15)
- Re: pcapng decoding error when preamble is shortened Timmy Brolin (Feb 16)
- Re: pcapng decoding error when preamble is shortened Guy Harris (Feb 16)
- Re: pcapng decoding error when preamble is shortened Timmy Brolin (Feb 16)
- Re: pcapng decoding error when preamble is shortened Timmy Brolin (Feb 16)
- Re: pcapng decoding error when preamble is shortened Timmy Brolin (Feb 17)
- Re: pcapng decoding error when preamble is shortened Guy Harris (Feb 18)
- Re: pcapng decoding error when preamble is shortened Timmy Brolin (Feb 18)
- Re: pcapng decoding error when preamble is shortened Timmy Brolin (Feb 13)
- Re: pcapng decoding error when preamble is shortened Jaap Keuter (Feb 13)