Re: Summary of responses so far and proposal moving forward[WasRe: [tcpm] Is this a problem?]
Mahesh Jethanandani <mahesh@cisco.com> Tue, 27 November 2007 23:21 UTC
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Date: Tue, 27 Nov 2007 15:21:39 -0800
From: Mahesh Jethanandani <mahesh@cisco.com>
Organization: Cisco Systems Inc.
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To: David Borman <david.borman@windriver.com>
Subject: Re: Summary of responses so far and proposal moving forward[WasRe: [tcpm] Is this a problem?]
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David Borman wrote: > Ok, I haven't chimed in yet on this conversation. I am glad you finally did :-) > > While I agree with the document on the identification of the problem, > I disagree with the proposed solution (changing TCP to time out > connections in persist state). Having a connection stay in persist > state for long periods of time (i.e., zero window probes continue to > be ACKed) by itself is not a bad thing. That is how TCP was designed > to work. Connections can survive through lots of adversity. If a > connection is stuck because it is waiting for user action and the user > walked away and went home for the day, he should be able to come back > the next morning and do what needs to be done, and then the connection > will continue. My understanding of rfc 1122 is and I quote from the rfc itself: > A TCP MAY keep its offered receive window closed > indefinitely. As long as the receiving TCP continues to > send acknowledgments in response to the probe segments, the > sending TCP MUST allow the connection to stay open. > > DISCUSSION: > It is extremely important to remember that ACK > (acknowledgment) segments that contain no data are not > reliably transmitted by TCP. If zero window probing is > not supported, a connection may hang forever when an > ACK segment that re-opens the window is lost. > This tells me that the concern was with ACK's getting lost in the network and that is why the need to keep the connection open. The point we bring up in the draft is in the case the ACK's are being received reliably then the need to keep the connection open just to make sure the ACK has made it to the other end goes away. That is why the request to change the language to say that *in case of reliable ACK*, TCP MAY tear the connection down if it is not able to service existing or new connections. We seem to agree on the user scenario you describe above. That is why we make it clear in the draft that we should not tear down a connection just because the connection is open for a long time. Where there is one or a few connections that are keeping the connection open, the solution will not tear the connection down. The problem happens is when lots of users (or attackers) do the same. > > As has already been stated, the issue is what should the OS do when it > runs out of resources. TCP implementations typically oversubscribe > their resources, and run into problems when all the open connections > try to use up all the resources that they've been told they can use. > In this situation, the OS has to figure out some way to free up > resources. There may be some things it can do without killing > connections (e.g., flush TCP resequencing queues), but usually that > won't be sufficient if you have a runaway or malicious source that is > causing the resource problem in the first place. In this situation, > anything the OS decides to do, including killing TCP connections, is > at the discretion of the OS, and I don't that view as violating any > RFC. You're out of resources, you have to do something. This is not > a TCP protocol issue, it is an OS implementation issue. True. But it was caused by TCP's insistence on keeping the connection open that causes the OS to even run out of resources, even if the reason to keep the connection open (unreliable ACKs) may not be true. I know there is very little support for this argument, but for a reader reading the rfc there is sufficient confusion on whether the connection can be cleared or not. Why not change the MUST to a MAY for reliable ACKs? People on this mailing list have been arguing on the point of if connections can even be cleared and this is tcpm mailing list!! Everybody is a TCP expert here. Is it not telling of a problem in the language of the rfc? /mahesh
_______________________________________________ tcpm mailing list tcpm@ietf.org https://www1.ietf.org/mailman/listinfo/tcpm
- [tcpm] Is this a problem? Mahesh Jethanandani
- RE: [tcpm] Is this a problem? Caitlin Bestler
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? Mahesh Jethanandani
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? MURALI BASHYAM
- Re: [tcpm] Is this a problem? Mahesh Jethanandani
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? Florian Weimer
- Re: [tcpm] Is this a problem? John Heffner
- Re: [tcpm] Is this a problem? MURALI BASHYAM
- Re: [tcpm] Is this a problem? speakeasy
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? Ethan Blanton
- Re: [tcpm] Is this a problem? Lloyd Wood
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? MURALI BASHYAM
- Re: [tcpm] Is this a problem? MURALI BASHYAM
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? MURALI BASHYAM
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? MURALI BASHYAM
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? MURALI BASHYAM
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? Ethan Blanton
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? Ethan Blanton
- Re: [tcpm] Is this a problem? Mahesh Jethanandani
- Re: [tcpm] Is this a problem? Ethan Blanton
- Re: [tcpm] Is this a problem? MURALI BASHYAM
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? MURALI BASHYAM
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? Mahesh Jethanandani
- Re: [tcpm] Is this a problem? Ted Faber
- RE: [tcpm] Is this a problem? Caitlin Bestler
- Re: [tcpm] Is this a problem? John Heffner
- Re: [tcpm] Is this a problem? Mark Allman
- Re: [tcpm] Is this a problem? Mark Allman
- Re: [tcpm] Is this a problem? MURALI BASHYAM
- Re: [tcpm] Is this a problem? Mark Allman
- Re: [tcpm] Is this a problem? MURALI BASHYAM
- Re: [tcpm] Is this a problem? Mark Allman
- Re: [tcpm] Is this a problem? Lloyd Wood
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? Mark Allman
- Re: [tcpm] Is this a problem? Chandrashekhar Appanna
- Re: [tcpm] Is this a problem? Ethan Blanton
- Re: [tcpm] Is this a problem? Mahesh Jethanandani
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? Ethan Blanton
- Re: [tcpm] Is this a problem? Chandrashekhar Appanna
- Re: [tcpm] Is this a problem? Mark Allman
- RE: Summary of responses so far and proposal movi… Anantha Ramaiah (ananth)
- Re: [tcpm] Is this a problem? Lloyd Wood
- Re: [tcpm] Is this a problem? Lloyd Wood
- Re: [tcpm] Is this a problem? Joe Touch
- Re: [tcpm] Is this a problem? Lloyd Wood
- Re: [tcpm] Is this a problem? Jakob Heitz
- Re: [tcpm] Is this a problem? Ethan Blanton
- Re: [tcpm] Is this a problem? Chandrashekhar Appanna
- Re: [tcpm] Is this a problem? Ted Faber
- Re: [tcpm] Is this a problem? Ted Faber
- Summary of responses so far and proposal moving f… Anantha Ramaiah (ananth)
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… Ted Faber
- Re: Summary of responses so far and proposal movi… John Heffner
- RE: Summary of responses so far and proposal movi… Anantha Ramaiah (ananth)
- RE: Summary of responses so far and proposal movi… Anantha Ramaiah (ananth)
- Re: Summary of responses so far and proposal movi… Ted Faber
- Re: Summary of responses so far and proposal movi… Mahesh Jethanandani
- Re: Summary of responses so far and proposal movi… Mahesh Jethanandani
- RE: Summary of responses so far and proposal movi… Anantha Ramaiah (ananth)
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… Ted Faber
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… Ted Faber
- RE: Summary of responses so far and proposal movi… Anantha Ramaiah (ananth)
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… Ted Faber
- RE: Summary of responses so far and proposal movi… Anantha Ramaiah (ananth)
- Re: Summary of responses so far and proposal movi… Ted Faber
- Re: Summary of responses so far and proposal movi… Ted Faber
- Re: Summary of responses so far and proposal movi… Joe Touch
- RE: Summary of responses so far and proposal movi… Anantha Ramaiah (ananth)
- Re: Summary of responses so far and proposal movi… Joe Touch
- RE: Summary of responses so far and proposal movi… Anantha Ramaiah (ananth)
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… Tom Petch
- RE: Summary of responses so far and proposal movi… Anantha Ramaiah (ananth)
- RE: Summary of responses so far and proposal movi… Anantha Ramaiah (ananth)
- Re: Summary of responses so far and proposal movi… Joe Touch
- RE: Summary of responses so far and proposal movi… Anantha Ramaiah (ananth)
- Re: Summary of responses so far and proposal movi… Joe Touch
- RE: Summary of responses so far and proposal movi… Anantha Ramaiah (ananth)
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… Mark Allman
- Re: Summary of responses so far and proposal movi… Mark Allman
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… Mark Allman
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… Mark Allman
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… Mark Allman
- Re: Summary of responses so far and proposal movi… John Heffner
- Re: Summary of responses so far and proposal movi… Ted Faber
- Re: Summary of responses so far and proposal movi… Lloyd Wood
- Re: Summary of responses so far and proposal movi… Mahesh Jethanandani
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… Lloyd Wood
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: Summary of responses so far and proposal movi… David Borman
- Re: Summary of responses so far and proposal movi… weddy
- Re: Summary of responses so far and proposal movi… Mahesh Jethanandani
- Re: Summary of responses so far and proposal movi… Mahesh Jethanandani
- Re: Summary of responses so far and proposal movi… Ethan Blanton
- Re: Summary of responses so far and proposal movi… Ethan Blanton
- Re: Summary of responses so far and proposal movi… David Borman
- Re: Summary of responses so far and proposal movi… Mahesh Jethanandani
- Re: Summary of responses so far and proposal movi… Joe Touch
- Re: [tcpm] Is this a problem? Mahesh Jethanandani
- Re: Summary of responses so far and proposal movi… Erik Nordmark