Re: [Isis-wg] WG adoption for draft-tantsura-isis-segment-routing-msd

<> Wed, 02 November 2016 15:37 UTC

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To: Hannes Gredler <>, "" <>, Christian Hopps <>
Thread-Topic: [Isis-wg] WG adoption for draft-tantsura-isis-segment-routing-msd
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Date: Wed, 02 Nov 2016 15:36:59 +0000
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Subject: Re: [Isis-wg] WG adoption for draft-tantsura-isis-segment-routing-msd
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Hi all,

I have read and support.
"MSD" is a useful info to be advertised. While I would a priori assume that it's mainly useful for the PCE (hence defined in draft-ietf-pce-segment-routing) I can understand that one want to also have it advertised in the IGP.

Please find some below some comments:

- I'd like the draft to expand and specify the interaction with the entropy labels.
e.g. is msd the maximum number of label that can be pushed, i.e. including entropy labels?
Currently draft talks about SID; IMO entropy labels are not SIDs; should we understand that the node is capable of pushing MSID + 2 (EL) labels?

- To a lesser extent, it would be good to clarify the interaction with service labels.
e.g. if the SID list/SR tunnel is (also) to be used by VPN traffic, who need to account for this additional label? (the sender or the receiver of the MSD?)

- I assume that the MSD is "incoming protocol independent" i.e. applies to any type of incoming/received packets: IPv4, IPv6, MPLS (i.e. the "SWAP" operation counts as a PUSH)
Please clarify in the doc.

- MSD 0
I note that in the PCE draft, the MSD value 0 means "no default limitation" while in the IGP draft it means " lack of the ability to push MSD of any depth".
IOW, their meaning is opposite.
While this is technically possible, this seems counter intuitive and open misunderstandings, at least for human beings.
Could the authors of both draft work to harmonize this?

- "Node MSD is the lowest MSD supported by the node"
Open question: an alternative would be to advertise the lowest MSD supported by the IS-IS enabled interfaces of this node. As possibly, customer/peer facing interfaces could be of a different hardware type, possibly not supporting MPLS at all.
Alternative 2: :s/ IS-IS enabled interfaces/ MPLS enabled interfaces
Alternative 3: :s/ IS-IS enabled interfaces/ Segment Routing enabled interfaces

- Nits: " Length is 1 bytes"
Do you mean the length of the "length field" or the length of the value/MSD field? Especially since this line is below " The Type (1 byte)" where "1 byte" is the length or the "Type" field.
"Node MSD is a number in the range of 0-254" is "254" a typo or do you have a plan for 255 to have a special meaning (and if so, please specify)

-- Bruno
 > -----Original Message-----
 > From: Isis-wg [] On Behalf Of Hannes Gredler
 > Sent: Monday, October 24, 2016 11:07 AM
 > To:
 > Cc: Christian Hopps
 > Subject: [Isis-wg] WG adoption for draft-tantsura-isis-segment-routing-msd
 > WG,
 > the authors of draft-tantsura-isis-segment-routing-msd have requested
 > adoption as a WG item.
 > opinions/comments appreciated.
 > thanks,
 > /hannes & chris
 > _______________________________________________
 > Isis-wg mailing list


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