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When/why would a device send a frame with ethertype 0x86dd (IPv6) but it's actually an IPv4 packet?

I've been playing around with packet captures on my local network, and I ran into an odd behavior that seems to crop up occasionally. When establishing a TCP connection to an IPv4 host, I caught my iPhone sending an Ethernet frame with type 0x86dd but encapsulating an IPv4 packet (Frame no. 3 in pcap dump). Wireshark flags this as an undecodable mess, since the IPv6 version field is set to 4. If I manually override it to decode as IPv4, then sure enough it's a valid, correct IPv4 packet.

Is this something my network should be able to handle? What should my router do with such a packet?

wolak's avatar
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wolak
asked 2017-11-27 04:17:38 +0000
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It seems that we don´t have the permissions to view your shared file.

Christian_R's avatar Christian_R (2017-11-27 15:17:11 +0000) edit
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Whoops! Fixed.

wolak's avatar wolak (2017-11-27 16:44:42 +0000) edit
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Looks totally strange to me. And no, your network should not be able to handle this packet (IMHO). I expect that the packet gets dropped at the next layer 3 hop (router).

Uli's avatar Uli (2017-11-28 19:18:34 +0000) edit
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Wow, I've never seen this behaviour before. I'm not aware of any protocol or RFC mentioning this. I'm quite sure that this is an error. Interestingly, your router did NOT discard but forwarded it, since your TCP handshake took place correctly.

webernetz's avatar
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webernetz
answered 2022-11-03 11:28:37 +0000
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