You are actually right Ron. Thanks for the explanation.
L. From: Ron Bonica <[email protected]> Sent: Friday, July 11, 2025 2:38 PM To: Luigi IANNONE <[email protected]>; Eric Vyncke (evyncke) <[email protected]>; [email protected] Cc: [email protected]; xiao.min2 <[email protected]> Subject: Re: AD review of draft-ietf-intarea-icmp-exten-hdr-len-01 Luigi, In section 4, I say: "Legacy implementation do not recognize messages that rely on the ICMP Extension Header length field. This is because when the document was published, the IETF had not yet standardized any messages that rely on ICMP Extension Header length field." Here, ICMP messages are defined by their type (e.g., Destination Unreachable, Time Exceeded). So, let's say that in the future, the IETF Standardizes the ICMP Network Happiness Message and that message relies on the ICMP Extension Header length field. A legacy implementation won't recognize the message because of its type. It won't examine the messages content at all. So, no reference to the extension structure or extension objects is required. Ron Juniper Business Use Only ________________________________ From: Luigi IANNONE <[email protected]<mailto:[email protected]>> Sent: Friday, July 11, 2025 7:57 AM To: Eric Vyncke (evyncke) <[email protected]<mailto:[email protected]>>; Ron Bonica <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]> <[email protected]<mailto:[email protected]>> Cc: [email protected]<mailto:[email protected]> <[email protected]<mailto:[email protected]>>; xiao.min2 <[email protected]<mailto:[email protected]>> Subject: RE: AD review of draft-ietf-intarea-icmp-exten-hdr-len-01 [External Email. Be cautious of content] ### Section 4 Even if the text is better in -02, the operational considerations / backward compatibility are still vague. As I said in my review, on this point I think that Section 7 of RFC 4884 applies: In particular the text: Having received an ICMP message with extensions, application software MAY process selected objects while ignoring others. The presence of an unrecognized object does not imply that an ICMP message is malformed. I interpret it as "unrecognized objects" are ignored by implementations that respect 4884. My 2cts Ciao L.
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