Hi Markku,
Markku Savela wrote:
>> From: Suresh Krishnan <[EMAIL PROTECTED]>
>
>> If I add the word intermediate in the text in order to read
>>
>> " This document proposes that all IPv6 extension headers be encoded in
>> a consistent TLV format so that it is possible for intermediate nodes
>> to skip over unknown extension headers and continue to further
>> process the header chain."
>
> But, but... how can intermediate skip over "unknown extension header",
> if it doesn't know the header.
>
> The part of draft, that proposes new extension headers follow the TLV
> format is OK. Although, I have always assumed that this was already
> implicit or even specified. If not, the draft could be seen as an
> emendation to the existing drafts.
I am glad you are OK with this. This was neither implicit or specified.
That is what this draft is trying to fix.
>
> What irks me, is the talk of intermediates skipping "unknowns", which
> depends on them somehow recognizing the header as "extension
> header". But, if they recognize it, it is not *unknown* anymore. Seems
> to be a "thought loop".
OK. I will think out loud on this one. This is how I feel it can be
done. We allocate a single IP protocol number for IPv6 extension
headers. Say 141 (Generic IPv6 extension header). All new extension
headers need to use this in the first octet. The second octet contains a
specific extension header type (this identifies the actual extension
header). The third octet contains the length. Everything else is
type-specific.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Specific Type | Hdr Ext Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. Header Specific Data .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header 8-bit selector. Identifies the type of header
immediately following the Extension header.
Uses the same values as the IPv4 Protocol
field.
Specific Type 8-bit unsigned integer. The actual IPv6
extension header type. This will be allocated
from a new IANA registry.
Hdr Ext Len 8-bit unsigned integer. Length of the
Extension header in 8-octet units, not
including the first 8 octets.
Header Specific Variable length. Fields specific to the
Data extension header
At this point we can say that anything where the EH type is 141 and
specific type not recognized is an unknown extension header. Anything
else is an upper layer protocol (that does not follow the format).
Thanks
Suresh
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