Re: [Int-area] Proxy function for PTB messages on the tunnel end

[Joseph Touch <[e-mail]>]

Hi, Eduard,

> On Mar 23, 2021, at 8:47 AM, Vasilenko Eduard <[e-mail]> wrote:
> 
> Hi Joseph,
> Please, show any except (or section number) from any RFC that push vendor to use 1500B buffer for reassembly in the data plane on the transit node? (or any other number on the transit node)

The Internet defines:
	- nodes that create or consume IP packets are hosts
	- nodes that relay IP packets are routers

RFC1122/1123 summarizes host requirements. RFC1812 summarizes router requirements. - both for IPv4. For IPv6, the former is largely in the IPv6 spec RFC8200 and RFC8504 and the latter in RFC8200, though there are some useful observations in RFC7084.

To your question, assuming you’re speaking of IPv6, RFC8200 requires nodes that consume IPv6 packets to support 1500B reassembly.
RFC791 requires that nodes that consume IPv4 packets support 576B reassembly.

> Please, show any evidence (or just claim if you could not disclose) that any vendor has 1500B (or less) for reassembly in the data plane (on transit node).

I neither know nor care. That’s a compliance issue, not a standards issue.

> Please, show the evidence that the fragmentation problem exists.

This is described in detail in:
	RFC1858
	RFC4459
	RFC4944
	RFC6946
	RFC6980
	RFC7588
	RFC8021
	RFC8900
	
As well as nearly any tunnel protocol description.

> All your discussions for EMTU_R are not relevant – it is for *host* reassembly buffer.

See above; you need to understand that the Internet defines HOST as any device that creates or consumes IP packets.

> Data Plane on the transit node has not been regulated before – It was not needed. Vendors have chosen big enough numbers that did not affect anybody so far.

See above; that’s not correct.

> It was effectively 1 MTU restriction per 1 virtual interface, not 2.
>  
> I do not accept this:
> That’s just the case where pathMTU == EMTU_R.
> That means the EMTU_R is not needed *in practice*, but in principle it still exists.
> If particular tunneling technology does not have a reassembly buffer (reject fragmentation in principle) – we could not talk about it like it exists.

I don’t see why you’re stuck on this issue. You don’t have to implement a separate reassembly buffer to have an implementation behave exactly as if there was one with the same size as the pathMTU. The effect is the same - no reassembly. 

> If you would look to microcode – you would not find it. We could go very far with such logic.

I don’t take my cues from others’ implementations.

Joe