Subject: Re: [lisp] Benjamin Kaduk's No Objection on draft-ietf-lisp-gpe-12: (with COMMENT)

From: "Fabio Maino (fmaino)" <[email-masked]>
Date: Mon, 6 Jan 2020 22:37:15 +0000

Hi Ben, 
Thanks for your comments, and happy new year! 

Please see below. 

On 12/30/19, 11:49 AM, "Benjamin Kaduk via Datatracker" <[email-masked]> wrote:

    Benjamin Kaduk has entered the following ballot position for
    draft-ietf-lisp-gpe-12: No Objection
    
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    ----------------------------------------------------------------------
    COMMENT:
    ----------------------------------------------------------------------
    
    Thanks for the updates in -10 through -12 to leave nonce/versioning to
    additional shim headers/extensions; that does alleviate the concerns that
    left me balloting Abstain on the -09.
    
    I do have some (new) comments on the -12.
    
    Section 3
    
    Conceptually, I'm thinking about this document as allocating the 'P' bit in
    the header and specifying its format when the P bit is set to 1; I don't
    expect it to be making changes to generic non-GPE LISP behavior.  So it's
    a little surprising to see that bits 0-3 are now marked as Reserved (though
    that could probably be wordsmithed away, and the existing Section 2 probably
    sets the reader up to do the right thing already), and fairly surprising to
    see the following in the P-Bit description:
    
          If the P-bit is clear (0) the LISP header is bit-by-bit equivalent
          to the definition in [I-D.ietf-lisp-rfc6830bis] with bits N, L, E
          and V set to 0.
    
    Is the claim that once an implementation supports GPE, it will never use the
    non-shim-header versions of echo-nonce, map-versioning, etc?  If not, then I
    don't think it's appropriate to say "with bits N, L, E, and V set to 0"
    here.
    
[FM] I think you make a good point, especially that we don't want to alter the behavior of the protocol when P=0. We can re-word the document accordingly: we leave NLEV bits in the header definition, and we limit the document to specify the behavior for the case when P=1. 

    I'm also not sure I fully understand the motivation for pulling out
    the Locator-Status-Bits, as that field's width is unchanged from stock
    6830bis.  Leaving them to a TBD shim-header does prevent the conflict with
    the Instance ID field, and perhaps the current usage patterns justify such a
    shift, so this may be more of a side note than an indication of a flaw in
    the document.

[FM] Indeed, there isn't a strong rationale to prevent the use of LSBs with GPE. Following your suggestion of specifying GPE as "allocating the P bit in LISP" we can leave that feature available even when P=1. 

    Section 7
    
       LISP-GPE, as many encapsulations that use optional extensions, is
       subject to on-path adversaries that by manipulating the g-Bit and the
       packet itself can remove part of the payload.  Typical integrity
    
    Is "g-Bit" supposed to be "P-Bit"?  I am failing to remember what the g-Bit
    is, at least...

[FM] yes, typo. Will fix in next rev. 
    
       With LISP-GPE, issues such as data-plane spoofing, flooding, and
       traffic redirection may depend on the particular protocol payload
       encapsulated.
    
    I'd consider adding another clause, "noting that an attacker that is
    spoofing LISP-GPE traffic can claim to encapsulate any protocol payload
    type" -- the risk here is based on what types the receiver's implementation
    supports, not just what the legitimate sender is encapsulating.

[FM] Ok, we will address this in the next rev. 

I'll post an updated version to reflect the comments above asap. 

Thanks,
Fabio

---

From: "Fabio Maino (fmaino)" <[email-masked]>
Date: Mon, 6 Jan 2020 23:34:49 +0000

Hi Ben, 
I have just posted -rev 13 (https://www.ietf.org/id/draft-ietf-lisp-gpe-13.txt) that should address your comments as described in my previous email. 

Please, find attached the diff with -rev 12. 

Thanks again,
Fabio

On 1/6/20, 2:37 PM, "Fabio Maino (fmaino)" <[email-masked]> wrote:

    Hi Ben, 
    
    Please see below. 

        

        

        
        Section 3

        

    

        Section 7

    

    

    Thanks,
    Fabio