Hi Chris,
On 24/08/16 20:31 , Chris Bowers wrote:
Peter,
The text that you propose corresponds to part of the text that I proposed, and
it seems good to me.
However, the last sentence of the text that I proposed in not addressed.
------
If router B does not advertise the
SR-Algorithm TLV for algorithm X, then other routers should not
forward traffic destined for a prefix-SID for algorithm X advertised by
some router D using a path that would require router B to forward traffic using
algorithm X.
------
Is this an oversight?
not that I disagree with the statement that you want to add.
The question is whether that belongs to the IGP SR draft, or whether
that should be specified in a different draft.
There is already some text regarding the forwarding for a SR algorithm
in draft-ietf-spring-segment-routing section 3.2.1., which may not be
aligned with what you have in mind:
"The ingress node of an SR domain validates that the path to a prefix,
advertised with a given algorithm, includes nodes all supporting the
advertised algorithm. In other words, when computing paths for a
given algorithm, the transit nodes MUST compute the algorithm X on
the IGP topology, regardless of the support of the algorithm X by the
nodes in that topology. As a consequence, if a node on the path does
not support algorithm X, the IGP-Prefix segment will be interrupted
and will drop packet on that node. It's the responsibility of the
ingress node using a segment to check that all downstream nodes
support the algorithm of the segment."
Maybe we should add/modify the text in draft-ietf-spring-segment-routing
section 3.2.1, rather then adding anything to the OSPF/ISIS SR drafts.
thanks,
Peter
Thanks,
Chris
-----Original Message-----
From: Peter Psenak [mailto:[email protected]]
Sent: Monday, August 22, 2016 2:32 AM
To: Chris Bowers <[email protected]>; OSPF List <[email protected]>
Subject: Re: [OSPF] OSPFv2 SR draft
Chris,
what about this to be added in the Section 3.1:
"A router receiving a Prefix-SID (defined in section 5) from a remote node and with
an SR algorithm value that such remote node has not advertised in the SR-Algorithm
sub-TLV MUST ignore the Prefix-SID sub-TLV."
thanks,
Peter
On 19/08/16 23:33 , Chris Bowers wrote:
Peter,
Please share the updated text that you plan to use with the WG, since this is a
reasonably significant clarification.
Thanks,
Chris
-----Original Message-----
From: Peter Psenak [mailto:[email protected]]
Sent: Tuesday, August 16, 2016 10:02 AM
To: Chris Bowers <[email protected]>; OSPF List <[email protected]>
Subject: Re: [OSPF] OSPFv2 SR draft
Hi Chris,
I'll update the draft along those lines.
thanks,
Peter
On 16/08/16 16:02 , Chris Bowers wrote:
Peter,
I suggest changing the paragraph to read as below to make this clearer.
=====
The SR-Algorithm Sub-TLV is optional. It MAY only be advertised once
in the Router Information Opaque LSA. If the SID/Label Range TLV, as
defined in Section 3.2, is advertised, then the SR-Algorithm TLV MUST
also be advertised. If a router C advertises a Prefix-SID sub-TLV for
algorithm X
but does not advertise the SR-Algorithm Sub-TLV with algorithm X, then
a router receiving that advertisement MUST ignore the Prefix-SID
advertisement from router C. If router B does not advertise the
SR-Algorithm TLV for algorithm X, then other routers should not
forward traffic destined for a prefix-SID for algorithm X advertised by
some router D using a path that would require router B to forward traffic
using
algorithm X.
=====
Thanks,
Chris
-----Original Message-----
From: Peter Psenak [mailto:[email protected]]
Sent: Monday, August 15, 2016 6:40 AM
To: Chris Bowers <[email protected]>; OSPF List <[email protected]>
Subject: Re: [OSPF] OSPFv2 SR draft
Hi Chris,
sorry for the delay, I was on PTO during last two weeks.
Please see inline:
On 03/08/16 16:45 , Chris Bowers wrote:
Peter,
Taking a looking at the whole paragraph into this sentence was
added, I am not sure how to interpret it.
The SR-Algorithm Sub-TLV is optional. It MAY only be advertised once
in the Router Information Opaque LSA. If the SID/Label Range TLV, as
defined in Section 3.2, is advertised, then the SR-Algorithm TLV MUST
also be advertised. If the SR-Algorithm TLV is not advertised by the
node, such node is considered as not being segment routing capable.
Is this sentence intended to imply that if a router does not
advertise the SR-Algorithm TLV including algorithm X, then any
prefix-SIDs for algorithm X advertised by that router will be ignored by other
routers?
in OSPF we do not have the SR capability TLV. We use SR-Algorithm TLV
for that purpose. So if a router does not advertise the SR-Algorithm
TLV for algorithm X, other routers should not send any SR traffic
using SIDs that were advertised for algorithm X.
If the router does not advertise any SR Algorithm TLV, then the node
is not SR capable and no SR traffic should be forwarded to such a node.
thanks,
Peter
If this is the intention, then it would be better to state is more explicitly.
If not, then the intended meaning should be clarified.
Thanks,
Chris
-----Original Message-----
From: OSPF [mailto:[email protected]] On Behalf Of Peter Psenak
Sent: Friday, July 22, 2016 3:30 AM
To: OSPF List <[email protected]>
Subject: [OSPF] OSPFv2 SR draft
Hi All,
following text has been added in the latest revision of the OSPFv2
SR draft, section 3.1.
"If the SR-Algorithm TLV is not advertised by node, such node is
considered as not being segment routing capable."
Please let us know if there are any concerns regarding this addition.
thanks,
Peter
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