Hi Bruno,
Many thanks for your valuable comments and see in line
Cheers,
Jeff
-----Original Message-----
From: <bruno.decra...@orange.com>
Date: Wednesday, December 20, 2017 at 02:10
To: "draft-ietf-isis-segment-routing-...@ietf.org"
<draft-ietf-isis-segment-routing-...@ietf.org>
Cc: "isis-...@ietf.org" <isis-...@ietf.org>, "isis-wg@ietf.org"
<isis-wg@ietf.org>, Christian Hopps <cho...@chopps.org>
Subject: RE: [Isis-wg] WG Last Call for draft-ietf-isis-segment-routing-msd-07
Resent-From: <alias-boun...@ietf.org>
Resent-To: <jefftant.i...@gmail.com>, <uma.chund...@huawei.com>,
<aldrin.i...@gmail.com>, <ginsb...@cisco.com>
Resent-Date: Wed, 20 Dec 2017 02:10:57 -0800 (PST)
Hi authors,
Please find below WGLC comments on this document.
Major:
-----
"the provisioned MSD
of the router originating the Router Capability TLV. Node MSD is the
lowest MSD supported by the node of any interface and can be
provisioned in IS-IS instance."
I don't see the MSD as a provisioned value, but as a hardware capability.
(Note that as a network operator, I'd be happy to be able to provision this
capability without changing the hardware/software, but that has not been my
experience so far.)
Let's not put the burden on the network operator to configure this, while
the node should know the value better. (as a priori, in the absence this
extension, the node would report an error if instructed to push more labels
than it is capable of). Especially for WAN routers, when Line Card may be
changed (e.g. upgraded), so this would requires the network operator to keep
track of all Line card change and update the MSD capability accordingly.(in
which case, it may be just simpler to configure it directly on the controler,
rather than requiring IS-IS, OSPF, BGP-LS protocol extensions, plus new
features on all (involded) nodes)
[jeff] In ideal situation, the MSD capabilities should come from the HW SDK,
while in a vertically integrated device, it might be vendor provisioned,
however in a disaggregated case (HW and SW are from different vendors), ability
to query HW for its MSD capabilities becomes crucial.
I have brought this point and discussed with BCM, Barefoot and few other HW
vendors:
everyone agreed that would be a useful functionality, and would require quite
simple API to add. Now it is up to their customers to demand an implementation,
CP is standardized here, and, as usual, HW vendors have preference for a formal
specification, that is stable.
For the time being, while there are no implementations we need to provide means
to configure the value
Please also note, MSD configuration is covered by SR YANG model, in case the
MSD value is communicated from HW(ro), it would go into operational data store
-----
"the provisioned MSD of the interface associated with the link."
Please explicit whether the controller/reader need to use the MSD of the
incoming link or of the outgoing link.
If you believe this may be hardware dependent, this need to be signaled.
[jeff] always from outgoing link prospective, so the internals
(ingress/egress/spitted MSD imposition) of a device are not of importance
==============
Minor:
"MSD of type 1 (IANA Registry), called Base MSD, is used to signal the
total number of SIDs a node is capable of imposing,"
I think that this is limited to MPLS-SID. It would be good to state this
somewhere. e.g. :s/SIDs/MPLS SIDs
[jeff] No, it doesn’t have to, IPv6 data plane could be covered as well,
however topic for future and would be done thru a separate draft.
----
"MSD: Maximum SID Depth"
IMHO, I'm not a big fan of the term "depth".
I find that it can be mislead with RLD (Readable Label Depth Capability). I
don't feel that pushing N SID requires looking/going deep into the packet.
Looking at the surface of the incoming label looks enough.
Obviously, the comment is late.
[jeff] Let’s agree to disagree on this one, the draft explicitly mentions RLD
and spells out the difference.
Related comment: I don't find the definition to be explicit enough. e.g.
You now need to define what "SID depth" is or provide or reference.
[jeff] Point taken, will include in the terminology section – would definition
such as “ SID depth is a number of SID’s a node or a link on a node is capable
of imposing” work? Any text you would like to propose?
-----
1.1.1. Terminology
Given that the term are very very briefly explained, may be adding a
reference to the RFC defining/explaining them.
---
"In order, for BGP-LS to signal MSD for
the all nodes and links in the network MSD is relevant, MSD
capabilites SHOULD be distributed to every IS-IS router in the
network."
I don't think that the "SHOULD" is related to interoperability. Hence a
"should" is probably enough.
[jeff] agreed, will change
-----
"Value field consists of a 1 octet sub-type (IANA Registry) and 1 octet
value."
I don't see the value (sic) to hard code the legnth of the "sub-value":
- this restrict the use of future MSD Sub-type Codepoints
- if we hard code it, there is no use of the "length" field. (and "Length
is variable " becomes not true)
-----
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Sub-Type and Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
"Value field consists of a 1 octet sub-type (IANA Registry) and 1
octet value."
Text and figure do not match: the value field is either 'Sub-Type and
value" as per the text, or just "value without the Sub-type" as per the figure.
[jeff]point taken, will update
*2 (link and node MSD)
---
§ MSD Advertisement
" Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD
of the router originating the corresponding TLV's 22, 23, 141, 222,
and 223. Link MSD is a number in the range of 0-254. 0 represents
lack of the ability to impose MSD stack of any depth; any other value
represents that of the particular link MSD value."
It's not clear whether the text related to the MSD value is specific to the
Sub-type 1 or to the whole Link MSD Advertisment. (i.e. would restrict the
usage of future sub-Types). May be using two sections would help: one defining
the Link MSD, one defining Sub-type 1. In which case the last paragraph of the
introduction may be move to this new sub-type 1 section.
[jeff]point taken, will update
*2 (link and node MSD)
-----
" Other Sub-types other than defined above are reserved for future
extensions. This sub-TLV is optional."
It's not clear whether you mean this sub-TLV 1, or any sub-TLV n, or the
presence of a sub-TLV.
[jeff]point taken, will update
----
"the ability to impose MSD stack of any depth"
Were are not imposing an "MSD stack", but SID stack. Actually the SR
architecture tends to use the term "list of segments" (or "ordered list of
segments")
[jeff] agreed, will correct
----
" This document describes a mechanism to signal Segment Routing MSD
supported at node and/or link granularity through IS-IS LSPs and does
not introduce any new security issues."
Improved fingerprinting capability would be one. Which may help target the
right vulnerability of the advertising router.
[jeff] I don’t see how exposing MSD would increase the risk, please elaborate
==============
Nits:
"supported by a node at node and/or link granularity"
May be NEW: supported by a node or link
[jeff] declined, both could be signaled at the same time
"In order, for BGP-LS to signal MSD for
the all nodes and links in the network MSD is relevant, MSD
capabilites SHOULD be distributed to every IS-IS router in the
network."
In my understandind:
:s/the all nodes/all the nodes
:s/distributed to every IS-IS router/advertised by every IS-IS router
[jeff] agreed, will correct
---
"A new sub-TLV within the body of IS-IS Router Capability TLV
[RFC7981], Node MSD sub-TLV is defined to carry the provisioned MSD
of the router originating the Router Capability TLV. ""
May be the following would be easier to read
A new sub-TLV "Node MSD sub-TLV" is defined within the body of IS-IS
Router Capability TLV
[RFC7981], to carry the provisioned MSD
of the router originating the Router Capability TLV.
[jeff] agreed will correct
-----
"Sub-Type 1 (IANA Section), MSD and the Value field contains Link MSD
of the router originating the corresponding TLV's 22, 23, 141, 222,
and 223. Link MSD is a number in the range of 0-254."
Please use two paragraphs. One for "Sub-type" field, one for "MSD value"
field.
[jeff] agreed will correct
-----
"0 represents lack of the ability to impose MSD stack of any depth "
May be NEW: "0 represents lack of the ability to impose any SID"
----
"Maximum MSD"
NEW: MSD
("M" already stands for Maximum)
Multiple times in the doc, with "Maximum" or "maximum"
[jeff] agreed will correct
----
The document has 2 "Terminology" sections. You should probably merge them.
[jeff] agreed will correct
Thanks
Regards,
--Bruno
> -----Original Message-----
> From: Isis-wg [mailto:isis-wg-boun...@ietf.org] On Behalf Of Christian
Hopps
> Sent: Wednesday, December 20, 2017 9:33 AM
> To: isis-wg@ietf.org
> Cc: isis-...@ietf.org; draft-ietf-isis-segment-routing-...@ietf.org
> Subject: [Isis-wg] WG Last Call for
draft-ietf-isis-segment-routing-msd-07
>
>
> The authors have asked for and we are starting a WG Last Call on
>
> https://datatracker.ietf.org/doc/draft-ietf-isis-segment-routing-msd/
>
> which will last an extended 4 weeks to allow for year-end PTO patterns.
>
> An IPR statement exists:
>
>
https://datatracker.ietf.org/ipr/search/?submit=draft&id=draft-ietf-isis-segment-routing-msd
>
> Authors please reply to the list indicating whether you are aware of any
> *new* IPR.
>
> Thanks,
> Chris.
>
> _______________________________________________
> Isis-wg mailing list
> Isis-wg@ietf.org
> https://www.ietf.org/mailman/listinfo/isis-wg
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