Hi Aijun,
please see inline (##PP):
On 05/01/2022 13:01, Aijun Wang wrote:
Hi, Peter:
Thanks for your comments.
Please see replies inline.
Aijun Wang
China Telecom
On Jan 5, 2022, at 18:45, Peter Psenak
<[email protected]> wrote:
Hi,
I'm afraid the draft has some serious issues that would need to be
addressed if it is to become a WG document.
Below comments use ISIS as an example, but most of it applies to OSPF
as well.
1. The draft says:
"ISIS[RFC5316] defines the Inter-AS Reachability TLV to carry the TE
information about inter-AS links. This TLV can be used to transfer
the information about the stub link which is located at the boundary
of one AS. This document defines the Stub-Link sub-TLV within this
TLV to identify the stub link and transfer the associated attributes."
- there is an existing mechanisms to advertise inter-AS link. There is
existing mechanisms to advertise external prefix. What exactly is the
reason to define a new TLV?
It's still not clear to me what exactly is the use case for the new
TLVs defined in the document.
[WAJ] RFC 5392 and RFC 5316 defines the TLV to carry the information
about other endpoint for the inter-AS link, for example , the remote
ASBR ID, the remote AS etc.
Such information are normally derived from the manual configuration.
For stub link, there are situations that the above information can’t
easily be obtained or doesn’t exist, what we can get only the
information about the local end, not the information about the remote end.
##PP
All link related TLVs, including Inter-AS Reachability TLV share the
same Sub-TLV space, including Link Local/Remote Identifiers IPv4/IPv6
local/remote address, etc. What exactly is missing?
All you have defined is the prefix advertisement with the link? What is
the exact usage of the prefix that is advertised with the link?
Then It is better to use different TLV to differentiate the local
information from the remote information. Define the Stub-Link TLV to
contain such local obtained information is then the reasonable way.
##PP
I don't understand the above. We have existing sub-TLVs that include
both local and remote link data.
The use case of stub link can be referred at the introduction part of
the draft.
##PP
the description in the draft is very high level. Please provide an exact
use case for the prefix that is advertised with the link.
2. Looking at the proposed ISIS Stub-link Sub-TLV, which is a sub-TLV
of the existing Inter-AS Reachability TLV:
- it advertises prefix. The advertisement of the prefix and link
information is strictly decoupled in ISIS. Here the proposal is to
advertise the prefix inside the Inter-AS Reachability TLV, which is
advertising a link. Why do we need the prefix of the inter-AS link to
be advertised inside the link advertisement?
[WAJ]For stub link, what we can get is only the interface addresses of
the local end and its associated prefixes. The associated prefixes can
be used to match the two ends of the stub-link, it can also indicate the
server’s address as that described in
##PP
ok, so you want to use the prefix information of the Inter-AS
Reachability TLV to link the two endpoints of such link together?
Inter-AS Reachability TLV includes:
a) the "IPv4/v6 remote ASBR identifier" which identifies the remote
end-point and should carry the TE Router ID (see sections 3.3.2 and
3.3.3 of RFC5316).
b) The local end-point ID is advertised in the form of the "IPv4/IPv6
TE Router ID" in the IS-IS Router Capability TLV of the originator.
These two are sufficient to pair the two endpoints of the inter-AS link
together.
https://datatracker.ietf.org/doc/draft-dunbar-lsr-5g-edge-compute/
<https://datatracker.ietf.org/doc/draft-dunbar-lsr-5g-edge-compute/>.
2. The new ISIS Stub-link Sub-TLV includes sub-TLVs, the text says:
"Sub-TLVs: Existing sub-TLVs that defined within "Sub-TLVs for TLVs
22, 23, 25, 141, 222, and 223" can be included if necessary."
The parent Inter-AS Reachability TLV already has Sub-TLVs from the
exact same space. Not to mention that the new sub-TLV itself comes
from the same space.
[WAJ] 141(inter-AS reachability information) is mentioned in the above
sentence.
##PP
what you have is:
Inter-AS Reachability TLV
Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223
ISIS Stub-link Sub-TLV
Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223
where ISIS Stub-link Sub-TLV is part of the
"Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223"
3. Link Type in ISIS Stub-link Sub-TLV - what is it used for and why
do we need it?
[WAJ] There are different kinds of stub link. Differentiate them via the
link type can help the precise control and analyze these stub links.
##PP
exact use case please.
thanks,
Peter
thanks,
Peter
On 04/01/2022 07:58, Christian Hopps wrote:
Hi Folks,
This begins a 2 week WG Adoption Call for the following draft:
https://datatracker.ietf.org/doc/draft-wang-lsr-stub-link-attributes/
Please indicate your support or objections by January 18th, 2022.
Authors, please respond to the list indicating whether you are aware
of any IPR that applies to these drafts.
Thanks,
Chris.
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