Re: [tcpm] New version of TCP Option for Transparent Middlebox Discovery available

[Caitlin Bestler <cait at asomi.com>]

On Sep 23, 2009, at 7:12 PM, Andrew Knutsen wrote:

>  This version addresses Wesley's comments and questions, and also  
> has a re-organized "Operation" section addressing off-list comments.  
> This version should not have any substantive changes to the option.  
> It is available at <http://www.ietf.org/internet-drafts/draft-knutsen-tcpm-middlebox-discovery-01.txt 
> >.
>
>  Again, your time reviewing this document is appreciated.
>
> Andrew

The applicability of this proposed option needs more explanation and  
justification.

The part that makes perfect sense is the desire to have a middle-box  
discovery probe that follows
the same path that a TCP packet would.

What is not clear is why the probe is based on OUI-specific secret  
handshakes.

1) Why not simply probe for "first middlebox that sees this once the  
TTL is less than or equal to X"?
     That would enable discovering all middleboxes that understood  
this option, no matter who
     made them. Once identified SNMP can be used to obtain vendor  
specific information.
2) If vendor X has *two* middleboxes on the path from A to B, is there  
any way to control
     who answers?

One further question, what is the correct handling of redundant SYN- 
ACKs from different
sources? This could happen if a middle-box takes longer than the  
initiator anticipates
and the retransmission follows a different path due to intermittent  
failures and/or
load balancing.






--
Caitlin Bestler
cait at asomi.com
http://www.asomi.com/CaitlinBestlerResume.html