Re: Usable extension headers [Re: New Version Notification for draft-voyer-6man-extension-header-insertion-08.txt]

[Brian E Carpenter <[e-mail]>]

Hi Bert,
On 28-Nov-19 16:34, Manfredi (US), Albert E wrote:
> -----Original Message-----
> From: ipv6 <[e-mail]> On Behalf Of Brian E Carpenter
> 
>> As I experienced years ago when my Ph.D. student was making real-world experiments with SHIM6, and as RFC7872 reported too, it's an observed fact that the Internet isn't transparent to packets with extension headers, not even to currently standardised ones. The same appears to have been true for IPv4 Options for at least 25 years. So, to be honest, I have no idea how to change that for the open Internet. We seem to be stuck with a lowest common denominator network layer.
> 
> Isn't the problem that routers must mostly not mess with these extension headers?

"Mostly" isn't good enough. It needs to be 100%. It only takes one router or middlebox on the path to be allergic to extension headers, and that's what we see in practice.

   Brian

> Even hop-by-hop headers can be ignored by routers (unless specifically configured not to ignore)?
> 
> So, you have a layer 3 extension option, but the boxes which do the heavy lifting at layer 3 must never mess with. On the other hand, end systems, which can play with IP extension headers, have virtually no knowledge of the network topology details.
> 
> Router manufacturers seem to prefer the simplest possible routing mechanization. Hosts don't typically have a clue how best to use the knob. My impression has always been that people are as discouraged to use layer 3 extension headers, as they are to use packet fragmentation. One of those things you want to avoid, unless you're a glutton for punishment? Not so?
> 
> Happy Thanksgiving, for those to whom this applies.
> 
> Bert
> 
>