Re: [v6ops] Extension Headers / Impact on Security Devices

[Joe Touch <[e-mail]>]

On 5/26/2015 4:02 PM, Brian E Carpenter wrote:
> On 20/05/2015 08:59, Joe Touch wrote:
...
>>> No. RFC 2460 makes it clear that hops don't modify extension headers
>>> (except for shuffling within a routing header).
>>
>> HBH headers are the exception and can be modified in-transit, which
>> would affect a transport-offset header.
> 
> I don't get where RFC 2460 allows that.

Section 4 states:

   With one exception, extension headers are not examined or processed
   by any node along a packet's delivery path, until the packet reaches
   the node (or each of the set of nodes, in the case of multicast)
   identified in the Destination Address field of the IPv6 header.
...

   The exception referred to in the preceding paragraph is the Hop-by-
   Hop Options header, which carries information that must be examined
   and processed by every node along a packet's delivery path, including
   the source and destination nodes.

In addition, RFC2460 defines a bit to handle when changes to such
options occurs en-route:

      1 - Option Data may change en-route

What is the purpose of that bit if the data can never change en-route?

Such changes can affect the content and *length* of these options.

Joe