Re: [NSIS] I-D ACTION:draft-rahman-rtg-router-alert-dangerous-00.txt

Magnus,

It is not a question of the Value field.

Suppose the Value field is set to zero. That means "routers shall examine 
this packet further".

It is clear what they do if they examine the packet and decide it is for 
local processing (for example, they look at the IP Protocol field and see 
the payload is RSVP, and there is a local RSVP stack enabled on the 
interface).

It is unclear what they do if the payload is STII and there is no local 
stack.
Router alert says "pass it up for local processing" but there is no-one to 
pass it to.
Should it be dropped, forwarded on the slow path, or forwarded on the fast 
path?

The only evidence we have for the "correct" behavior is in 2205 where 
packets are send with RA and are expected to be able to pass through 
non-RSVP clouds.

Even the "silently ignore" for unrecognized Value fields is ambiguous. Does 
that mean drop the packet (ignore the packet) or forward it (ignore the RA 
option)?

Lastly, it is really unclear what should be done with a packet that carries 
RA and a protocol that *is* active on the router but which is not expecting 
router alert packets. For example, UDP. Should the packets be delivered 
there and then dropped (causing unnecessary processing) or should the 
protocol be expected to register as a router alert consumer with the fast 
path (requiring specifics of the implementation)?

These are all issues that could usefully be documented in Reshad's draft.

Cheers,
Adrian

----- Original Message ----- 
From: "Magnus Westerlund" <[email protected]>
To: "David Ward" <[email protected]>
Cc: "Roland Bless" <[email protected]>; "Adrian Farrel" <[email protected]>; 
"Reshad Rahman" <[email protected]>; "NSIS" <[email protected]>; 
<[email protected]>; "tsvwg" <[email protected]>
Sent: Monday, October 27, 2008 2:57 PM
Subject: Re: [NSIS] I-D 
ACTION:draft-rahman-rtg-router-alert-dangerous-00.txt


> David Ward skrev:
>> Roland -
>>
>> On Oct 21, 2008, at 3:35 AM, Roland Bless wrote:
>>
>>> Hi Magnus,
>>>
>>> Magnus Westerlund wrote:
>>>> I reacted on the following sentence from Section 4:
>>>>
>>>>    A router SHOULD inspect Router Alert packets before sending them to
>>>>    the "slow path" so that if the protocol to which a packet belongs is
>>>>    not enabled on the router or on the incoming interface (physical or
>>>>    virtual), then the packet is dropped.
>>>>
>>>> Isn't this preventing use of RAO completely unless all nodes between
>>>> source and destination supports RAO and that protocol? Isn't the right
>>>> answer to not kick it into the slow path and simply forward it?
>>>
>>> Yes, the behavior should be: simply forward the packet in case
>>> the router does not understand/intercept packets with this RAO value.
>>> Otherwise an efficient interception as we need it in NSIS is
>>> not possible.
>>> If the router is the destination of the packet and it doesn't
>>> understand the RAO, it probably could drop the packet.
>>>
>>
>> DW: The RSVP spec doesn't state this clearly thus the confusion.
>
>
> Why are we talking about RSVP here? RAO for IPv4 is RFC 2113 which says:
>
> 2.2  Semantics
>
>   Hosts shall ignore this option.  Routers that do not recognize this
>   option shall ignore it.  Routers that recognize this option shall
>   examine packets carrying it more closely (check the IP Protocol
>   field, for example) to determine whether or not further processing is
>   necessary.  Unrecognized value fields shall be silently ignored.
>
>   The semantics of other values in the Value field are for further
>   study.
>
> Maybe not 100% clear in regards to the value and that the packet simply
> should be forward for unrecognized value. But I think it is reasonable
> that your document helps clarify this.
>
> Cheers
>
> Magnus Westerlund
>
> IETF Transport Area Director & TSVWG Chair
> ----------------------------------------------------------------------
> Multimedia Technologies, Ericsson Research EAB/TVM
> ----------------------------------------------------------------------
> Ericsson AB                | Phone +46 8 4048287
> Färögatan 6                | Fax   +46 8 7575550
> S-164 80 Stockholm, Sweden | mailto: [email protected]
> ----------------------------------------------------------------------
>