Re: [Isis-wg] draft-ginsberg-isis-l2bundles

["Acee Lindem (acee)" <[e-mail]>]

Hi Stephane, 
I think the IS-IS advertisement is merely a consequence of the fact that
we are satisfying the requirement of incorporating these L2 links in the
segment routing path. If we limit advertisement to BGP-LS, it will have
the following impact:

     1. All routers in the IS-IS domain that use link-bundles will need
some form of BGP LS peering, either to the controller directly or through
some intermediary.
     2. Since the link-bundle itself is an IS-IS L3 link, one would need
to correlate the information with the corresponding IS-IS link state
information (assuming not every IS-IS router advertises the entire LSDB).
Additionally, any time the information is coming from multiple sources,
you are likely to trigger path computation more frequently.

I don’t think this added complexity warrants omitting them from the IGPs
if we do, in fact, accept link bundle adjacency steering as a requirement.

Thanks,
Acee 


On 8/5/15, 4:12 AM, "Isis-wg on behalf of [e-mail]"
<[e-mail] on behalf of [e-mail]>
wrote:

>Hi,
>
>Pls find some inline comments.
>
>-----Original Message-----
>From: Ebben Aries [mailto:[e-mail]]
>Sent: Wednesday, August 05, 2015 01:39
>To: LITKOWSKI Stephane SCE/IBNF; [e-mail] list ([e-mail])
>Subject: Re: [Isis-wg] draft-ginsberg-isis-l2bundles
>
>I see BGP-LS extensions complementing this, not necessarily as a
>replacement.  
>[SLI] It's for sure an option, but my point is do we need to continue to
>add extensions to both IGP and BGP LS ?
>Moreover I still have an issue with propagating L2 informations into
>layer 3 routing protocol  (not technically ... more from a design
>perspective).
>Let's say that tomorrow, you would like to advertise some L1 information
>under your layer 2 information ... ?? As we are breaking layers, if you
>want to advertise some underlay topology, I would be in favor to not
>doing it in IGP.
>
>For a use-case of a central entity learning these underlying l2
>attributes to then do whatever you wish (impose label stacks, etc..) -
>BGP-LS is a natural fit.
>[SLI] Nothing prevents to use BGP-LS in a distributed computation model.
>
>For this to remain in the IGP, a consideration could be the propagation
>of these L2 attributes to then be included in TEDs for additional logic
>from headend nodes (network elements within the IGP domain) - e.g.
>control packet per member from a remote endpoint overriding remote
>hashing either by some policy/SLA or dynamic based off of per member
>utilization, etc..
>
>[SLI] Even if TED was previously populated only by IGP (because there was
>nothing else), this is not the case anymore. TED is also populated by
>BGP-LS and we may be able to create also new processes to populate the
>TED. So you can imagine having your process managing LAGs to add those L2
>TE information into the TED and then being able to export it through
>BGP-LS to other nodes through the BGP controlplane, so every one will
>have the same content in the TED.
>
>
>On 08/03/2015 07:02 AM, [e-mail] wrote:
>> Hi,
>> 
>>  
>> 
>> Thinking again about this draft, I wondering why not using BGP-LS for
>> that purpose ?
>> 
>> I mean, the goal here is just to provide some topological information
>> that are not related to IGP, as you want to keep L2 bundles and so a
>> single IP link. If you want to expose the underlaying topology, you
>> may be able to do it in BGP-LS rather than adding this in the IGP as
>> the information you want to expose is not necessary for the IGP to run.
>> 
>>  
>> 
>> Thx
>> 
>>  
>> 
>> Orange logo
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