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

"Stan Ratliff (sratliff)" <sratliff@cisco.com> Mon, 10 March 2014 17:52 UTC

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From: "Stan Ratliff (sratliff)" <sratliff@cisco.com>
To: "Taylor, Rick" <Rick.Taylor@cassidian.com>
Thread-Topic: [manet-dlep-rg] Slight issue with Data items
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Date: Mon, 10 Mar 2014 17:52:11 +0000
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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>
Subject: Re: [manet-dlep-rg] Slight issue with Data items
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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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