Subject: Re: IPv6 extension header privileges

From: Sowmini Varadhan <[email-masked]>
Date: Fri, 20 May 2016 21:56:04 -0400

On (05/21/16 02:20), Hannes Frederic Sowa wrote:
> 
> There are some options inherently protocol depending like the jumbo
> payload option, which should be under control of the kernel, or the
> router alert option for igmp, which causes packets to be steered towards
> the slow/software path of routers, which can be used for DoS attacks.
> 
> Setting CALIPSO options in IPv6 on packets as users would defeat the
> whole CALIPSO model, etc.
> 
> The RFC3542 requires at least some of the options in dst/hop-by-hop

"requires" is a strong word. 3542 declares it as a  "may" (lower case).
The only thing required strongly is IPV6_NEXTHOP itself.

I suspect 3542 was written at a time when hbh and dst opt were loosely
defined and the "may" is just a place-holder (i.e., it's not even a MAY)

> 
> AFAIK people worried about the parsing overhead and thus decided to
> block it for ordinary users.

That's probably more likely, esp for hbh options. It may also be 
interesting to find out what BSD does in these cases. 

--Sowmini