Re: [savi] Last Call: <draft-ietf-savi-dhcp-12.txt> (SAVI Solution for DHCP) to Proposed Standard

["Jun Bi" <[e-mail]>]

thanks!
Jun Bi

From: eric levy-abegnoli 
Sent: Thursday, April 12, 2012 3:47 PM
To: Guang Yao 
Cc: [e-mail] ; [e-mail] 
Subject: Re: [savi] Last Call: <draft-ietf-savi-dhcp-12.txt> (SAVI Solution for DHCP) to Proposed Standard

Hi Guang,
I realized I never acknowledged your responses. Sorry for the delay.
It does clear my concerns.
Thank you!
Eric
On 16/03/12 07:42, Guang Yao wrote: 
  Hi, Eric 

  Thank you for the comments. My replies are in the line. We have updated the text as the attachment. Sorry for it cannot be submitted because the submit window is closed.

  Best regards,
  Guang


  2012/3/13 eric levy-abegnoli <[e-mail]>

    Hi,
    here are my substantive comments
    Look for  [eric].
    Eric

    7.3.1. Timer Expiration Event

      EVE_ENTRY_EXPIRE: The lifetime of an entry expires

    [eric] 2 minutes sounds very long. DHCP client timeout is 1 sec for the first
    message. Then multiplied by 2, etc. What is the rational behind this value, which increase the window for DoS attacks?

  [guang]
  In RFC3315, it reads:
  "RT for the first message transmission is based on IRT:
      RT = IRT + RAND*IRT

   RT for each subsequent message transmission is based on the previous
   value of RT:

      RT = 2*RTprev + RAND*RTprev

   MRT specifies an upper bound on the value of RT (disregarding the
   randomization added by the use of RAND).  If MRT has a value of 0,
   there is no upper limit on the value of RT.  Otherwise:

      if (RT > MRT) RT = MRT + RAND*MRT"

  Here MRT is 120s. Based on this value, the maximum  retransmission time is in range of 120s(+-)12s. Thus, we think 120s is a favorable value to remove an entry. 
  The DoS in this window is a problem, but we think the binding number limitation on each binding anchor can mitigate the damage.

    8. Supplemental Binding Process
    [eric] This section is very unclear. The conditional SHOULD
      based on  "vendor ability" sounds like a "MAY" to me, which is not
      what I remember of the WG consensus. In addition, hosts are not
      required to (DHCP) re-configure upon link flapping, even when they
      are directly attached.  The text seems to indicate otherwise.
      In practice, in the absence of such mechanism, traffic will be blocked.


  [guang]
  We have removed the condition on "vendor ability" . Link flap is handled through keeping bindings for a period after binding anchor off-link. We have changed the text to make it clear.


    8.1. Binding Recovery Process
    [eric] It is unclear what the address is bound to. In the normal case,
        the entry is created upon receiving a message (i.e. REQUEST) from
        the client, and the anchor is stored by that time. You should
        specified where the anchor comes from in this scenario, and where
        was it stored (given that the section specifies the binding entry creattion on LQ Reply)

  [guang]
  We have changed the text, and specified each step. Tell me if it is still unclear.

    10. State Restoration
    [eric] Requiring non-volatile memory sounds wrong. Other techniques
    exists such as redundant boxes (switches) synchronizing states. I
    don't recall that non-volatile memory was discussed at length in the
    WG, especially given that it carries its own challenges: frequency
    for saving states, load incurred, etc)
    The one technique that was discussed in the WG was Binding Recovery
    process.  One solution should be enough.
  [guang]
  There can be a large number of bindings on the savi device. If only relying on the binding recovery process, there can be a large latency. Especially, the recovery in this mechanism requires querying the DHCP server. 
  Moreover, the storing in non-volatile memory is just recommended but not mandatory. Using redundant box can be  another suggestion. We have change the MUST to MAY in text.


    Eric 


    On 06/03/12 16:01, The IESG wrote:

      The IESG has received a request from the Source Address Validation
      Improvements WG (savi) to consider the following document:
      - 'SAVI Solution for DHCP'
        <draft-ietf-savi-dhcp-12.txt>  as a Proposed Standard

      The IESG plans to make a decision in the next few weeks, and solicits
      final comments on this action. Please send substantive comments to the
      [e-mail] mailing lists by 2012-03-20. Exceptionally, comments may be
      sent to [e-mail] instead. In either case, please retain the
      beginning of the Subject line to allow automated sorting.

      Abstract


         This document specifies the procedure for creating bindings between a
         DHCPv4 [RFC2131]/DHCPv6 [RFC3315] assigned source IP address and a
         binding anchor [I-D.ietf-savi-framework] on SAVI (Source Address
         Validation Improvements) device. The bindings can be used to filter
         packets generated on the local link with forged source IP address.




      The file can be obtained via
      http://datatracker.ietf.org/doc/draft-ietf-savi-dhcp/

      IESG discussion can be tracked via
      http://datatracker.ietf.org/doc/draft-ietf-savi-dhcp/ballot/


      No IPR declarations have been submitted directly on this I-D.


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