Re: [v6ops] [IPv6] Why folks are blocking IPv6 extension headers? (Episode 1000 and counting) (Linux DoS)

It depends on your position in the network.

A) Transit AS:
Should transparently pass all traffic and not look beyond the 40-byte IPv6 header.

With the exception of NH=0.
Let’s have that discussion if there ever is a HBH option with “transit AS applicability”.

B) Limited Domain

C) Modern application
With modern applications, it has become blurry where the application ends and the network starts.
Where the “application” is disaggregated, embeds a custom network stack for it’s purpose.
Has a set of IP addresses representing the “service”, but those addresses does in no way represent an interface on a host.
That “cluster” of services is only going to support the functions that the application needs.
An EH would essentially be a side channel here.

D) Enterprises
What Fernando says.

It’s somewhat ironic that 25 years in, this debate is still hypothetical.
“What if we ever got an EH that has Internet wide applicability”
(and for the sake of argument I’ve rebranded ESP to a tunnel encap).

O.

> On 21 May 2023, at 23:28, Brian E Carpenter <brian.e.carpenter@gmail.com> wrote:
> 
> On 21-May-23 21:33, Fernando Gont wrote:
>> Hi, Tom,
>> On 18/5/23 15:27, Tom Herbert wrote:
>> [....]
>>>>> 
>>>>> So, I’m not really happy with the all or nothing approach the two of you
>>>>> seem to be offering for IPv6 extension headers, is there something in
>>>>> between? If not, then maybe that is what we need to be working towards.
>>>> 
>>>> FWIW, I[m not arguing for a blank "block all", but rather "just allow
>>>> the ones you really need" -- which is a no brainer.
>>> 
>>> Fernando,
>>> 
>>> I'm not sure how that's a no brainer, who decides "the ones you really
>>> need"?
>> Typically. whoever runs the destination AS or network. Or the transit
>> AS, if the packets will affect the transit AS.
> 
> And there's the problem. The operator of a large network cannot possibly
> know which extension headers every host on the network needs. It's
> called permissionless innovation, and is supposed to be one of the main
> success factors for the Internet.
> 
>>> If everyone independently makes that decision then we wind up
>>> with an Internet that can't evolve and is perpetually stuck in the
>>> status quo.
>> Well, yes, there's no big brother making decisions about mine or your
>> networks' policies.... hence everyone makes decisions independently.
> 
> From the point of view of hosts, there is an anonymous Big Brother, the
> moment that any upstream operator blocks a wanted extension header.
> 
>> (IN a way that's why QUIC runs on top of UDP ... although in the case of
>> QUIC, I bet it has more to do with NATs thatn with explicit firewalling)
> 
> It's to do with *any* barrier to IP layer transparency. This is a very
> basic tussle in the architecture.
> 
>   Brian
> 
>>>> The list you need
>>>> is, maybe Frag and, say, IPsec at the global level? (from the pov of
>>>> most orgs).
>>>> 
>>>> (yeah... HbH and the like are mostly fine for the local link (e.g. MLD).
>>>> 
>>> It might be productive if you suggested a more concrete direction
>>> here. Maybe a proposed BCP suggesting the EHs that you believe should
>>> be universally blocked and the rationalization for that and why the
>>> problems with them can't be fixed.
>> Are your referring to the "transit AS" case, the "dest AS/network" case,
>> or both?
>> In any case, my comment was simply a two-liner email comment, as opposed
>> to full-fledged advice.
>> Thanks!
>> Regards,
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