Re: Comments on multi6dt documents

[Erik Nordmark <erik.nordmark@sun.com>]

Pekka Savola wrote:


> True .. but firewalls of today don't even have a _chance_ of skipping 
> over the extension header, even if they, or their administrators would 
> want that (well, if the extension header is in TLV format, maybe then, 
> because some firewalls assume the next ext headers are in TLV). 
> Destination options at least allow that possibility.

If any future extension headers follow the canonical format:

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Next Header  |  Hdr Ext Len  | ....
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

then one can build firewalls that are liberal in what they accept.
But I still think this is moot because firewalls by nature will be 
conservative in what they accept.


> Right out, I can't think of anything else than ICMP and multicast (which 
> you already mentioned), but that doesn't of course mean those kind of 
> protocols might not exist.  Therefore I think it would make sense to put 
> this sufficiently clearly in the document that people need to keep in 
> mind that there may be some protocols which might call for special 
> handling.

ok, I'll add some words.

> > Why do you wish to confuse things by calling it an ALG? It is a local 
> > matter for the implementation how it demuxes ICMP errors. ALGs and 
> > NATs make people think of middleboxes which perform transformations 
> > which can not be reversed.
>
>
> Sorry, I was just trying to figure out a term which says, "requires the 
> host's shim layer and possibly some weirder middleboxes (like stateful 
> firewalls, when they want to figure whether to pass this error in or 
> not) have knowledge of applications' semantics [and if there are new 
> such applications, requiring that this application knowledge to be 
> updated], to be able to mangle the addresses inside the payload correctly."

It isn't "applications" - it is what I'd call "IP signaling protocols" 
or something like it; protocols which are not end-to-end but involve the 
routers along the path. ICMP errors from the routers, or RSVP signaling 
is what we currently have as examples. NSIS falls here as well.

   Erik