Re: [Roll] processing of multiple SRH-6LoRH

"Pascal Thubert (pthubert)" <pthubert@cisco.com> Tue, 26 April 2016 11:22 UTC

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From: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
To: Michael Richardson <mcr+ietf@sandelman.ca>, "roll@ietf.org" <roll@ietf.org>
Thread-Topic: processing of multiple SRH-6LoRH
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Date: Tue, 26 Apr 2016 11:21:34 +0000
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Subject: Re: [Roll] processing of multiple SRH-6LoRH
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Hello Michael:



Sorry I failed to respond to this.





> Pascal,

>

> section 5.5 of routing-dispatch says:

>

>    Else, if there is a next SRH-6LoRH of a Type with a larger or equal

>       value, meaning a same or lesser compression yielding same or larger

>       compressed forms, then the SRH-6LoRH is removed.

>

> okay, so when the new SRH provides more bytes, we remove the consumed

> one.

>

>    Else, the first entry of the next SRH-6LoRH is popped from the next

>       SRH-6LoRH and coalesced with the first entry of this SRH-6LoRH.

>

> To get here, the next SRH-6LoRH must be of a higher level of compression, so

> it encodes addresses with fewer bytes.  What is the logic to making the next

> next 6LoRH smaller (popping), and keeping the larger current 6LoRH?



This is illustrated below:



[cid:image002.png@01D19FBE.5837F580]



The root sends a type 4 with the fill address of A (say that they do not share a same prefix)

When A receives the packet it must remove the first address in the SRH which is self.

As illustrated A pops B's compressed address from the next header (the type 3) and coalesces that in the first (type 4) to get the full address of B.



> Why not just drop the current 6loRH here and have fewer bytes, period?

If we had removed the type 4 then the first SRH would have been the type 3 and the prefix would be lost.



Makes sense?



Pascal