Subject: Re: [manet] #3: Use msg-hop-count in RFC 5444 header to limit # of hops

From: "manet issue tracker" <[email-masked]>
Date: Wed, 12 Jun 2013 22:41:40 -0000

#3: Use msg-hop-count in RFC 5444 header to limit # of hops

Comment (by [email-masked]):

 ----
 From: Thomas Heide Clausen 11/1/2012 5:18 AM --
 That would be a direct violation of the definition of <msg-hop-limit> and
 <msg-hop-count> in RFC5444, and would render any generic
 demultiplexing/dispatching/forwarding framework inapplicable.

 This proposal is, therefore, not acceptable under any circumstances.

 ----
 From: Dearlove, Christopher (UK) 11/1/2012 6:50 AM ----

 Let's consider an RREQ message, which is flooded. The issue is, does it
 mutate on its travels? If not, I don't see why we can't use the 5444 hop
 limit. If it does, then that is not technically an issue for 5444, but
 does have two bad effects:
 - There is a general processing/forwarding engine described in OLSRv2. In
 an ideal world this is another thing that should be in a separate draft.
 It is designed for wider use (hence its inclusion of message type). There
 are reasons I would find that a good model for what I'm going to call son-
 of-AODV, whatever that ends up being based on and called.
 - Unmutated (other than hop count/limit) messages work well with message
 signatures described in 6622 for end to end verification. Mutating
 messages are a bigger headache. They need either new signatures each hop,
 in which case let's just not bother signing messages, but let's sign
 packets - a valid choice, but loses a tool - or some sort of difference
 collecting and aggregating signature that I know nothing about, and may
 not even exist.

 -------
 From: Charles E. Perkins 11/1/2012 10:43 AM -------

 RFC 5444 has this:

    o  <msg-hop-count> field, if present, contains the number of hops on
       which the packet has traveled across the MANET.  The <msg-hop-
       count> is set to 0 by the message originator and is used to
       prevent messages from endlessly circulating in a MANET. When
       forwarding a message, a MANET router should increase <msg-hop-
       count> by 1 and should discard the message when <msg-hop-count>
       reaches 255.

 From this, I conclude that the purpose of the field is to count the
 number of hops a message has traversed.

 -------
 From: Henning Rogge 11/1/2012 10:45 AM -------

 If DYMO changes the content of a message, its not the same message
 anymore. At least thats how I understand this field.

 You could not put a signature on it "end to end" for example.

 -------
 From: Charles E. Perkins 11/1/2012 11:04 AM -------
 RFC 5444 also says this:

    o  For forwarded messages where the message is unchanged by
       forwarding MANET routers, end-to-end authentication and integrity
       MAY be implemented, between MANET routers with an existing
       security association, by including a suitable Message TLV
       containing a cryptographic signature in the message.  Since <msg-
       hop-count> and <msg-hop-limit> are the only fields that should be
       modified when such a message is forwarded in this manner, this
       signature can be calculated based on the entire message, including
       the Message Header, with the <msg-hop-count> and <msg-hop-limit>
       fields set to 0, if present.

 I think this means that the msg-hop-count can be incremented while
 the other content of the message remains the same.

 -------

 On 11/1/2012 12:17 PM, Abdussalam Baryun wrote:

 I agree with the proposal, it seems with advantages, but there maybe
 disadvantages (i.e. violation to rfc5444) that need to be fixed. I don't
 think it is flexible to use only the hop-limit for rfc5444 messages for
 better dissimination, using other fields will give advantages. It may be
 considered to modify RFC5444 in future to accomodate reactive protocols
 advantages.

 -------

-- 
-----------------------------------+------------------------------
 Reporter:  [email-masked]  |       Owner:  Charlie Perkins
     Type:  enhancement            |      Status:  new
 Priority:  major                  |   Milestone:
Component:  dymo                   |     Version:
 Severity:  Active WG Document     |  Resolution:
 Keywords:  hop count, hop limit   |
-----------------------------------+------------------------------

Ticket URL: <http://trac.tools.ietf.org/wg/manet/trac/ticket/3#comment:1>
manet <http://tools.ietf.org/manet/>

---

From: "Charles E. Perkins" <[email-masked]>
Date: Wed, 12 Jun 2013 17:09:47 -0700

Hello folks,

I have collected the previous discussion about issue #3 and
posted the the technical parts of the discussion to the issue tracker,
as reproduced before.  If I have missed any points of the discussion,
please let me know and I will similarly post those points also to
the issue tracker.

While the technical matters involved with issue #3 may still be of
interest and open to discussion, I think that the discussion is no
longer relevant to the working group document, because there isn't
much motivation to make the necessary protocol changes to
utilize the idea.  For this reason, I propose to close the issue without
making any changes to the document.

Regards,
Charlie P.

PS. My plan is to similarly collect the technical discussions related
       to the other issues, and to propose a resolution for each one,
       according to the current state of the AODVv2 document, based
       on the points raised during the discussion.

-- 
Regards,
Charlie P.