Re: Question: Hop-by-Hop Header and Router Alert

On Mon, 26 May 2008, Suresh Krishnan wrote:
>> Second question:
>>
>> What will happen if a router doesn?t recognize the value in the
>> router alert?s value field? Will it continue parsing the datagram
>> and then forward the packet to the next hop (two MSB in the
>> Hop-by-Hop option type field set to ?00?), or will it immediately
>> stop parsing and forward the received IPv6 packet to the next
>> hop (two MSB in the Hop-by-Hop option type field set to ?00?)?
>
> The router code will not see this as an error. It will forward the
> packet through as if nothing happened. This is required for incremental
> deployment(e.g. non RSVP routers among RSVP routers)

FWIW, I share Suresh's sentiments about Hop-by-Hop and Router Alert 
options :-)

FYI, here is discussion on what Linux does (which is a bit different 
given that there is no strict fast/slow path separation).  An 
application running on the router needs to set IPV6_ROUTER_ALERT 
sockopt with value of the desired RA option it wants to see.  Other 
messages are not delivered to the application and are forwarded as 
normal.  If some application gets the packet, it is responsible for 
re-injecting a new packet:

http://www.mail-archive.com/netdev@vger.kernel.org/msg50634.html

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings
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