RE: Some RDDP attacks

DDP depends on ordering as well as reliability. So UDP (the
ultimate silent drop :) would be a double challenge.

Not that I want to go there. The "traditional" model is the
only one we need, IMO. What data-intensive protocols run
by default over unreliable, unordered transport?

Tom.

At 09:34 AM 7/8/2004, Jim Pinkerton wrote:
> 
>Abstracting it up a level, the current DDP/RDMAP IDs require a reliable 
>transport protocol underneath them. For example, the DDP ID is titled "DDP 
>over Reliable Transports". Silent drop is effectively corrupting the 
>reliable transport. 
> 
>Back when we were originally creating the DDP/RDMAP drafts, we spent a lot 
>of time trying to decide on whether the protocol was generic enough to run 
>over reliable and unreliable transports. When we dove in to it, there were 
>significant issues that were unique to the approach of running over an 
>unreliable transport (what is the programming model, how are completions 
>handled when things are lost, resolving holes in sequence space, etc). The 
>group was primarily interested in nailing reliable transports, since that 
>has been the traditional RDMA programming model. Thus the draft title got 
>"... over Reliable Transports" added to it to explicitly state the original 
>author's focus. 
> 
>I believe since the IDs were adopted by RDDP, that there has been wide 
>support for a focus on reliable transports as the first protocol suite to 
>come out of RDDP. Unreliable can come later. 
> 
> 
> 
>jim
> 
> 
>
>  _____  
>
>From: [email protected] on behalf of Talpey, Thomas
>Sent: Thu 7/8/2004 4:17 AM
>To: [email protected]
>Subject: Re: [rddp] Some RDDP attacks
>
>
>
>At 02:50 PM 7/5/2004, [email protected] wrote: 
>>I think that's actually indicative of a DDP problem, in that the current 
>>DDP draft is too quick to close a connection when receiving anything it 
>>doesn't expect.  Mandating "silent drop" rather than "tear down the 
>>connection" would make this attack significantly harder to pull off. 
>
>Silent drop would be a disastrous choice for DDP errors, especially 
>bad MSN or invalid STag! This would be like TCP ack'ing a hole in 
>sequence space or bad checksum. It would give the upper layers 
>on both sides of the connection an indication that messages had 
>been received when they had not. 
>
>Consider an RDMA Write with bad STag that was dropped at the 
>receiver. The subsequent Send, signalling the receipt, would then 
>pass upwards. Oops. Or consider a sender exceeding its credits 
>and losing a string messages in the middle, but not the end, of a 
>sequence. 
>
>Because it's an ack-less protocol, the only valid response DDP can 
>make is to send a Terminate and close the connection. Which it must. 
>
>Tom.

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