Re: [middisc] TCP middlebox option requirements

["Anantha Ramaiah (ananth)" <[e-mail]>]

OUI as exists today is standardized and managed and provides unquiness.
If we were to define a 1 byte vendor it, it has all issues which Ron
mentioned below + the need for standardizing that space, I don't know
who is going to manage allocation and maintenance of that field. I don't
think IANA would do that.
 
I also wanted to understand the use case of having this option sent in
the middle of the connection. FWIW TCP options as exisits today are
either "negotiated" one time in the initial 3 way handshake (MSS, Window
scale, SACK permitted etc.,) or sent on every packet (TCP MD5,
TIMESTAMP etc.,) On demand sendind of the option is something new, so is
the concept of variable length TCP option (with the exception of SACK,
which itself needs to agreed upon using SACK PERMITTED option during the
3 way HS.
 
-Anantha


________________________________

	From: [e-mail] [mailto:[e-mail]]
On Behalf Of Ron Frederick
	Sent: Tuesday, May 25, 2010 5:52 PM
	To: Andrew Knutsen
	Cc: Ron Frederick; [e-mail]
	Subject: Re: [middisc] TCP middlebox option requirements
	
	
	On May 25, 2010, at 5:28 PM, Andrew Knutsen wrote:

		    It seems to me that if we do limit our goal here to
agreeing on an option number and vendor ID scheme, we haven't really
limited ourselves to autodiscovery except in the requirements we state
for getting a vendor ID (ie, agreements on use). Mostly this would
involve removing the requirement that the option only be present with
the SYN bit. We added this requirement primarily due to concerns about
reliable transmission, but in later discussions we came up with a
midstream discovery requirement and mechanism where that isn't an issue,
so I don't think we're particularly attached to it. Also, we probably
don't have to require everyone to encode the vendor-specific type
information in the same way.
		
		   Another implication of that goal is that we wouldn't
be making a standard per se; rather we'd be making a first step towards
a set of standards.  Thats the purpose of the "P" bit in the current
proposal, and the "standard vendor" codes in the proposal for removing
the OUI in my message below. The idea is that as the technology matures,
we can move towards a standard mechanism.
		
		   I'm not familiar with IPv6 options, but at this point
what we're doing sounds so simple it should work.
		
		   I'm getting the impression that to make this
alternate option useful to everyone here, we have to change the proposal
in a few ways, including:
		
		    1) Removing the OUI, and having a single byte of
vendor code. The option format would be vendor-specific.
		    2) Replacing the P bit with a "standard" vendor code
or codes -- perhaps one code per interoperable option format.
		    3) Removing the requirement that the option only be
present with the SYN bit set.
		    4) It sounds like the R bit may be redundant with
other, more complex schemes already implemented by some vendors.
		
		    This would mean the option format would only specify
a single byte of vendor ID after the option length. We would need some
stipulations on the option's use (making and maintaining tunnels,
perhaps). Vendors would have to agree to these stipulations to get a
code, so we aren't making a "catch-all" option.
		
		    Opinions?
		

	
	
	[Ron] A single byte for vendor ID clearly will not scale. There
can easily be more than 256 vendors our there who may eventually want to
use this option. I don't see any obvious way to do better space-wise
than what we proposed with the OUI if we want this to be truly
extensible to support all possible vendors.
	
	
	Regarding the P bit, I don't really understand what you mean. We
could have a single vendor code value for all the standard extensions,
but we'd still need another byte for which option it was. If we burn a
vendor code point for each interoperable option, we'd have even fewer
code points left to allow vendor extensibility. If we think we can live
with only 127 possible options (both for standard options and for each
vendor), we could potentially shorten the type field from 2 bytes to 1
byte, which would then become 4 bytes when you add the OUI when the P
bit is set, but I'm not sure the single byte of savings we get from that
is really worth the flexibility we lose by dropping from 32K options per
vendor to 127. Both of these numbers drop by a factor of 2 if we keep
the R bit, which makes it even more of a poor choice.
	
	
	I'm ok with dropping the requirement that these options are only
sent on the SYN and SYN-ACK, but I would prefer to see an example of
sending such an option mid-stream and some text which describes the
known issues with trying to send an option in such an unsyncrhonized
way.
	
	
	Regarding the R bit, I could potentially see folding that into
the vendor-specific data, but I would expect pretty much everyone to
need to deal with this issue, so it seems like it would be best if we
had a single general mechanism which did so.
	
	

		Mark Day wrote: 

			Two additional issues seem worth clarifying
since I'm not sure how others would view them.
			
			1. Are we concerned strictly with autodiscovery
options, or are we attempting to understand the requirements for options
usage generally among current symmetric middleboxes?  For example,
Riverbed uses a different option for some forms of addressing
information in situations after the two communicating peers have been
established by autodiscovery.  It wouldn't surprise me to learn that
other vendors have other similar schemes.
			
			2. Don't we also need to consider requirements
for autodiscovery options in IPv6 environments?  
			
			In both cases, I can see a pragmatic argument
for focusing narrowly vs. an architectural argument for considering
broader issues. IPv4 autodiscovery is the clear existing
interoperability/coexistence problem and may be solvable by simply
agreeing on an option number and vendor id scheme, while the other areas
might not yet have enough experience and implementations to justify a
standard.  And yet it feels to me like we might solve one option-related
problem just to trip across another similar one soon afterward.
			
			--Mark
			
			-----Original Message-----
			From: [e-mail]
[mailto:[e-mail]] On Behalf Of Andrew Knutsen
			Sent: Friday, May 21, 2010 2:23 PM
			To: [e-mail]
			Subject: Re: [middisc] TCP middlebox option
requirements
			
			
			    Thanks Ananth.
			
			    One possibility that Jamshid and I talked
about addresses concerns 
			about using 3 bytes for the OUI. We could skip
it (and the P bit), and 
			break up the 15 bits or so of "device
capability" into an IANA-assigned 
			vendor code of maybe 7 bits, leaving 8 bits (or
so) for vendor-specific 
			type. There could be one or more "standard"
vendor codes for 
			multi-vendor interoperability (ie, IANA-assigned
types), and an 
			extension code if we run out of room.
			
			    Perhaps we also need to define the
requirements for getting a vendor 
			code or a standard type -- for instance, we
might not want any 
			individual to be able to get a vendor code,
since they are limited; and 
			the standard types would need some
documentation, but perhaps not as 
			widely reviewed as for a top-level option kind.
			
			Andrew
			
			Anantha Ramaiah (ananth) wrote:
			  

				Hi,
				   I am just taking the liberty to post
the first email on this mailing
				list. During our last call there was
talk about the requirements of this
				TCP option. From our pov, the following
would be the general
				requirements of the TCP option.
				
				
				Reason for TCP option :
				
				- A standard TCP option is needed
because every vendor cannot have one
				option for the same purpose of
auto-discovery and capability exchange.
				By standardizing the TCP option,
firewalls etc., are aware of this
				option and problems can be avoided.
				
				Requirements of this TCP option :
				
				- There has to be a vendor ID (OUI)
which would identify the specific
				vendor. This is needed because every
vendors option format is going to
				be 
				different.
				
				- Already existing non-standardized
option numbers (TCP option 33,
				riverbed's options no's) for doing auto
discovery should not be
				allocated for this new TCP option. This
is to prevent any confusion.
				
				- The TCP option needs to be variable
length to permit multiple option
				formats since the option size may vary
depending on the vendor.
				
				- This TCP option should be advocated
for use only by middleboxes.
				
				
				My guess is that these requirements may
be common for all the vendors or
				there may be some additional
requirements not covered by this post. In
				either case we can continue the
discussion and come to some conclusions.
				
				-Anantha

	
	-- 
	Ron Frederick
	[e-mail]