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:ppse...@cisco.com]
Sent: Thursday, April 19, 2018 4:28 PM
To: Dongjie (Jimmy) <jie.d...@huawei.com>; Acee Lindem (acee)
<a...@cisco.com>; lsr@ietf.org
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.
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.
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.
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.
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:lsr-boun...@ietf.org] *On Behalf Of *Acee Lindem
(acee)
*Sent:* Tuesday, April 17, 2018 10:44 PM
*To:* lsr@ietf.org
*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-algo/
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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