Re: I-D Action: draft-herbert-6man-eh-limits-00.txt

I think the basic proposal is to limit extension headers to a total of 64 bytes, if outside a limited domain (TL;DR: see page 9 of the draft).

Now, I'm well aware that shim6 (RFC5533) is not used; the main reason being that the Internet is largely opaque to its extension headers. Nevertheless, shim6 is a fully worked out use case for extension headers that would need to cross the open Internet.

I wrote in 2016 as part of the RFC2460bis discussion that "I was surprised a while back to discover that a legal shim6 extension header could in fact exceed a kilobyte, specifically it is only limited to 1240 bytes by the standard." More to the point, a typical "large" shim6 extension header would be 40 bytes between dual-homed hosts. If hosts were more-than-dual-homed and therefore needed to exchange more addresses, the extension header would increase by 16 bytes per extra address.

So, if we prescribed a 64 byte limit, we would also limit what extension headers can achieve.

Regards
   Brian

On 23-Jun-21 13:01, internet-drafts@ietf.org wrote:
> 
> A New Internet-Draft is available from the on-line Internet-Drafts directories.
> 
> 
>         Title           : Limits on Sending and Processing IPv6 Extension Headers
>         Author          : Tom Herbert
> 	Filename        : draft-herbert-6man-eh-limits-00.txt
> 	Pages           : 18
> 	Date            : 2021-06-22
> 
> Abstract:
>    This specification defines various limits that may be applied to
>    receiving, sending, and otherwise processing packets that contain
>    IPv6 extension headers.  The need for such limits is pragmatic to
>    facilitate interoperability amongst hosts and routers in the presence
>    of extension headers and thereby increasing the feasibility of
>    deployment of extension headers.
> 
> 
> The IETF datatracker status page for this draft is:
> https://datatracker.ietf.org/doc/draft-herbert-6man-eh-limits/
> 
> There is also an htmlized version available at:
> https://datatracker.ietf.org/doc/html/draft-herbert-6man-eh-limits-00
> 
> 
> Internet-Drafts are also available by anonymous FTP at:
> ftp://ftp.ietf.org/internet-drafts/
> 
> 
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