Speaking as WG Member and longstanding steward of the OSPF protocol:
Hi Aijun,
As I stated during the LSR meeting, one of the main changes between OSPFv3 and
OSPFv2 is that the addressing semantics are removed from the router and network
LSAs. Refer to section 2.2 in RFC 5340.
o Router-LSAs and network-LSAs no longer contain network addresses,
but simply express topology information. See Section 2.8 for
details.
The OSPFv2 stub link was somewhat of a hack to advertise local prefixes and it
was removed in OSPFv3 as prefixes are advertised in separate LSAs. We certainly
don’t want to revert this behavior and definitely not for a questionable use
case outside the OSPF protocol itself.
Additionally, the example you state of the prefixes already being advertised
ambiguously is not flawed in the that the Link-LSA and Intra-area-prefix-LSA
are advertised at different flooding scopes (link-scope versus area-scope).
The attributes that you want to convey throughout the area domain are relevant
to the prefix itself and not a link that has any topological significance to
OSPF. This should be reflected in the draft and the advertisement should be
proposed for prefixes as opposed to adding the stub-link concept.
Hence, I don’t think there should be an adoption call for this document in its
current form.
Thanks,
Acee
From: <[email protected]> on behalf of Aijun Wang
<[email protected]>
Date: Saturday, July 31, 2021 at 8:48 AM
To: Aijun Wang <[email protected]>
Cc: Acee Lindem <[email protected]>, Gyan Mishra <[email protected]>,
"[email protected]"
<[email protected]>, "[email protected]"
<[email protected]>
Subject: Re: [Lsr] [Stub-Link-Attributes] Comments on "Passive Interface
Attribute" - draft-wang-lsr-passive-interface-attribute
Hi, All:
I have uploaded the updated draft with the new name
“draft-wang-lsr-stub-link-attributes” at
https://datatracker.ietf.org/doc/draft-wang-lsr-stub-link-attributes/, which
replaces the previous passive interface draft.
Any comments are welcome.
We think it is ready for WG adoption call.
Aijun Wang
China Telecom
On Jul 31, 2021, at 10:35, Aijun Wang <[email protected]> wrote:
Hi, Acee:
Regarding to your comments on the meetings that where to put the attributes of
these stub-link attributes, I had reviewed again the previous discussions on
the mail list. Please see it at
https://mailarchive.ietf.org/arch/msg/lsr/LbsiUl9iL_9zTXnxtuAnKVpfmGs/. Then
putting it into link related attributes is more reasonable.
Regarding your concerns for the associated prefixes to be advertised in
different places, I checked also
https://datatracker.ietf.org/doc/html/rfc8362#section-3.7 and we can see for
Intra-Area-Prefix TLV, it can also be included in two different places. The
redundancy information has no influence for any other aspects, just used for
easy correlation.
And, based on the discussion along with 5G edge use case and the ASLA
attributes(please see
https://mailarchive.ietf.org/arch/msg/lsr/0Lk8IPxsD1BJYT9D-NcRQJEnwHU/ ). It is
then more reasonable to put these attributes into link related TLV, that is,
the newly defined Stub-Link TLV/Sub-TLV.
If there is no other comments/argues on this draft, we will update the draft in
recent days, change the name to “draft-wang-lsr-stub-link-attributes” and ask
for WG adoption.
Thanks in advance.
Aijun Wang
China Telecom
On Jul 31, 2021, at 06:45, Aijun Wang <[email protected]> wrote:
Hi, Acee:
Thanks for your comments.
Please see the replies inline.
Aijun Wang
China Telecom
On Jul 31, 2021, at 01:00, Acee Lindem (acee) <[email protected]> wrote:
Hi Gyan,
See brief inlines.
From: Gyan Mishra <[email protected]>
Date: Thursday, July 29, 2021 at 10:24 PM
To: Acee Lindem <[email protected]>
Cc: "[email protected]"
<[email protected]>, "[email protected]"
<[email protected]>
Subject: Re: [Lsr] Comments on "Passive Interface Attribute" -
draft-wang-lsr-passive-interface-attribute
Hi Acee
In-line
On Thu, Jul 29, 2021 at 4:24 PM Acee Lindem (acee)
<[email protected]<mailto:[email protected]>> wrote:
Speaking as WG member:
Authors,
I think this draft is still flawed. Regarding the terminology, I don’t think it
should refer to passive interfaces at all since they aren’t referenced in
protocol documents. Rather, you should use stub-link consistently – including
the title. However, I don’t think this makes any difference as I think you need
to “go back to the drawing board”.
Gyan> Agreed. We will change any references to passive to stub.
Why do other routers in the domain need to know the link if it isn’t connected
to any other routers? The stub-link is an artifact of OSPFv2 used to advertise
local prefixes. As you noticed, it was removed in OSPFv3 and local prefixes are
advertised in Intra-Area-Prefix LSAs (and E-Inter-Area-Prefix-LSAs). I really
think you are trying to advertise attributes of a prefix and not a link. In
fact, in OSPFv3 there is no address associated with the link – I see you have
attempted to remedy this by adding a sub-TLV to advertise the prefix associated
with the link ;^). So, now this local prefix will be advertised two different
ways?
Gyan>(We did remedy as you asked) Per yours and I believe Peters a d others
recommendation with OSPFV2 update RFC 7684 change from fixed format LSA to TLV
based similar to OSPFV3 RFC 8362 which the other big change was the breakout of
“topological” construct from the prefix creating separate router links LSA for
“topological” and prefix LSA for prefixes. As the passive or stub concept as
you have reiterated to the authors is really topological and of prefix based
to use router links and not router prefix to add the new stub TLV so that is
what we did for both OSPFV2 and OSPFV3 and added new top level stub TLV for
ISIS.
I’m glad you didn’t modify the base LSAs. However, my question is why the
entity you are trying to describe isn’t just a local prefix – why do we need to
create a stub-link?
[WAJ] There are other attributes need to be associated and advertised with
these stub links. Please refer to the discussion at
https://mailarchive.ietf.org/arch/msg/lsr/0Lk8IPxsD1BJYT9D-NcRQJEnwHU/ for 5G
edge computation use case.
Specifically, what is BGP controller going to do with the stub link
advertisement that it couldn’t do with a prefix advertisement? Also, why can’t
the AS boundary router report the inter-AS prefix via BGP-LS? The other routers
in the IGP domain have no use for this information.
Gyan> From a use case perspective the goal is to make this new stub TLV
generic so it can be used for any use case where you have a stub LSA that is
advertised that can be tracked by the PCE controller for the NB BGP-LS building
of the topological graphs and being able to distinguish any stub nets from
transit nets with neighbors.
What is the use-case for knowing that a prefix is associated with a loopback?
We already have the N-Flag (Node) for prefixes… What is your loopback use case?
Gyan> When NBI BGP-LS builds the topological graphs it’s any stub link which
could be inter-as or loopbacks or any interfaces so they can be differentiated
when the LSDB is build for the TEDs database.
Also, what is the Vlan interface use case? What possible use could other
routers in the domain have for this information?
Gyan> I believe vlan is just another example but it’s really any interface that
is a stub link with no neighbors can be treated differently by the NBI BGP-LS,
when the topological graph is built.
I don’t see why this attribute can’t be associated with a prefix and why we
need a link. Furthermore, I don’t see any of the types as being useful other
than inter-AS. And for inter-AS, it can be advertised in BGP-LS. Clearly, if
there is an inter-AS interface, the router is running BGP.
[WAJ] As stated above, there are other attributes that should be associated
with the stub links. There are also other use cases for theses information on
the controller. For example, the controller can deploy network boundaries
security policy once it knows which interfaces are facing the external world.
It can also release the operator from deploying BGP-LS on every border router
for inter-AS use case.
The 5G edge computation that described in
https://datatracker.ietf.org/doc/draft-dunbar-lsr-5g-edge-compute/ is another
use case for these stub links on IGP routers.
Thanks,
Acee
Thanks,
Acee
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Gyan Mishra
Network Solutions Architect
Email [email protected]<mailto:[email protected]>
M 301 502-1347
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