Dongjie,
On 20/04/18 11:00 , Dongjie (Jimmy) wrote:
Hi Peter,
Please see inline:
-----Original Message-----
From: Peter Psenak [mailto:[email protected]]
Sent: Friday, April 20, 2018 3:31 PM
To: Dongjie (Jimmy) <[email protected]>; Acee Lindem (acee)
<[email protected]>; [email protected]
Subject: Re: [Lsr] LSR Working Group Adoption Poll for Flex Algorithm Drafts
Hi Dongjie,
please see inline:
On 20/04/18 05:04 , Dongjie (Jimmy) wrote:
Hi Peter,
Thanks for the prompt response. Please see inline:
-----Original Message-----
From: Peter Psenak [mailto:[email protected]]
Sent: Thursday, April 19, 2018 4:28 PM
To: Dongjie (Jimmy) <[email protected]>; Acee Lindem (acee)
<[email protected]>; [email protected]
Subject: Re: [Lsr] LSR Working Group Adoption Poll for Flex Algorithm
Drafts
Hi Dongjie,
please see inline:
On 19/04/18 09:10 , Dongjie (Jimmy) wrote:
Hi,
Here are some comments on the Flex Algo drafts.
SR algorithm as defined in
draft-ietf-isis-segment-routing-extensions
is about the algorithm used for path calculation, such as SPF, strict SPF, etc.
In the Flex Algo drafts, the definition of algorithm is extended to
include topological constraints and the metric type used in
calculation, which makes its functionality analogous to
multi-topology routing
(MTR).
not really. MTR is defined on a per link basis and each MTR
participation needs to be advertised on a per link basis. There is no such
concept in flex-algo draft.
Both mechanisms have the capability to define a specific sub-topology in the
network, that's why I say they are analogous in functionality. Flex-algo uses
link
affinity to describe the constraints of the corresponding topology, which is
also
a link attribute and needs to be configured on a per-link basis.
The difference is in topology advertisement. In MTR a consistent topology is
constructed by each node advertising its own adjacent links in the topology.
While in flex-algo, the whole topology is advertised as part of the algorithm
definition by each node, and priority based selection is used to reach a
consistent view by all nodes.
Flex-algo works on top of existing IGP topologies.
Do you mean flex-algo can work on top of the default IGP topology, and can
also work on top of multiple IGP topologies created with MTR?
yes
In the latter case, it seems you would create sub-topologies on top of
a sub-topology (MTR) of the default topology,
no. We don't create any topologies with flex-algo. We compute constrained
based paths.
MTR is also used to compute constrained based path:) The constraint is
described as a sub-topology.
you are mixing two different things - topology and path computations,
these are two different things.
With flex-algo, you need to define the algorithm first, then the constrained
path can be computed according to the algorithm.
According to your presentation in IETF101, a flex-algo specifies:
a) Set of constraints - e.g affinity exclude-any, include-any, include-all
b) Metric type - IGP metric, Delay (RFC7810), TE metric (RFC5305), ...
c) Algorithm type - SPF, ...
As I see a) defines a constrained topology, or a sub-topology.
again, you are mixing "set of constraints" with a "topology", these are
two different things.
which sounds quite complicated. Maybe another way is to use MTR to create
the sub-topology needed, and define the metric type and computation
algorithm using a particular flex-algo?
what we propose is simple - compute multiple constrained based paths on top
of a given topology.
What you propose is indeed complicated - create as many topologies as many
constrained based paths you need. That solution does not scale.
Not exactly. Multiple constrained paths can be created in the same
sub-topology. You don't need as many topologies as the number of paths.
if you calculate multiple constrained paths on a single MT, you need to
agree what the constraints are for each calculation and that is what the
flex-algo draft is doing.
regards,
Peter
Section 4.1 of the Flex Algo drafts says "Flex-Algorithm definition
is topology independent", while in some places Flex Algo is
described as a "light weight alternative" to MTR.
there is no mention of MTR in the document.
I was referring to another relevant draft:
draft-wijnands-mpls-mldp-multi-topology-00. Sorry for the confusion caused. It
seems that draft considered MTR and flex-algo as comparable candidates for
creating sub-topology.
then please talk to the authors of that draft.
OK. It seems some sync up is needed to have consistent understanding of what
flex-algo means.
It would be necessary if the relationship between Flex-Algo and MTR
can be further clarified. Whether the two mechanisms are
complementary to each other, or Flex-Algo will be used to replace MTR?
they are orthogonal.
If as you said they are orthogonal, it would be better to avoid overlapping
functionalities in topology definition and creation.
orthogonal does not mean overlapping.
Right, in order to make them orthogonal, overlapping (if any) should be
resolved.
Best regards,
Jie
thanks,
Peter
Best regards,
Jie
thanks,
Peter
And if it is claimed that Flex-Algo is light weight than MTR, it
would be helpful to give a thorough comparison of the two mechanisms
somewhere.
Best regards,
Jie
*From:*Lsr [mailto:[email protected]] *On Behalf Of *Acee Lindem
(acee)
*Sent:* Tuesday, April 17, 2018 10:44 PM
*To:* [email protected]
*Subject:* [Lsr] LSR Working Group Adoption Poll for Flex Algorithm
Drafts
This begins a two-week adoption poll for the following Flex
Algorithm
drafts:
https://datatracker.ietf.org/doc/draft-hegdeppsenak-isis-sr-flex-alg
o/
https://datatracker.ietf.org/doc/draft-ppsenak-ospf-sr-flex-algo/
The adoption poll will end at 12:00 AM EST on May 2^nd , 2018.
Please indicate your support of opposition of the drafts.
Additionally, the authors are amenable to combining the drafts into
a single draft. If you have an opinion, please state that as well.
Thanks,
Acee
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