Re: [manet-dlep-rg] Slight issue with Data items

Henning Rogge <hrogge@gmail.com> Mon, 10 March 2014 19:23 UTC

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From: Henning Rogge <hrogge@gmail.com>
Date: Mon, 10 Mar 2014 20:23:14 +0100
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To: "Stan Ratliff (sratliff)" <sratliff@cisco.com>
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Cc: "manet-dlep-rg@ietf.org Group, \(manet-dlep-rg@ietf.org\)" <manet-dlep-rg@ietf.org>, Rick Taylor <rick@tropicalstormsoftware.com>, "Taylor, Rick" <Rick.Taylor@cassidian.com>
Subject: Re: [manet-dlep-rg] Slight issue with Data items
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Don't we already have a list of "mandatory/optional" data items for each signal?

Maybe we should reword "unknown" into "neither defined as mandatory or
optional for a signal" ?

Henning Rogge

On Mon, Mar 10, 2014 at 6:52 PM, Stan Ratliff (sratliff)
<sratliff@cisco.com>; wrote:
>
> On Mar 10, 2014, at 1:25 PM, "Taylor, Rick" <Rick.Taylor@cassidian.com>; wrote:
>
>>
>>> I'll offer up a slight modification of the "London Rule" :  Experimental Data
>>> Items (and Vendor-specific TLVs) that are not supported by an
>>> implementation should be parsed (e.g. "stepped over') and silently dropped.
>>> Data Item TLVs that are not *understood* (e.g. TLV number not registered,
>>> or "reserved"), OR are out-of-context (like a Version TLV in a destination
>>> update message) should cause PEER_TERMINATION and closure of TCP
>>> session.
>>
>> That will rely on a clear list of every suitable data item TLV used with each signal, which might turn into an O(N^2) documentation nightmare.
>>
>> I was wondering about adding an 8bit context field to the TLV header: 8bit Type, 8bit Context, 16bit Length (seems to align nicely).
>>
>> Context: 1 = Discovery Data Item, 2 = Session Initiation/Termination Data Item, 3 = Peer Data Item, 4 = Link Data Item, plus the classic experimental and reserved spaces.
>>
>> This might be easier to specify, and reduces the London Rule to "Any data item received with a context field that does not match the context of the enclosing signal MUST result in PEER_TERMINATION", then all that is needed is to define the context of each signal, back to O(N) for those of you familiar with big-O notation.
>
> Hmmm... could be. Let me noodle on this a bit.
>
> Regards,
> Stan
>
>
>>
>> I know this seems like adding error checking to the protocol, but with Vendor Extensions and experimental TLVs a bit of error checking is no bad thing, just think of it as an FEC code...
>>
>> Alternatively you could consider Type and Context as one little endian 16bit value... or swap them around to make CTLV...
>>
>> Rick
>>
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