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

[<[e-mail]>]

I think this may have implications beyond SR but it seems there are other areas where LAGs (aka, link-bundles) have permeated into L3 (e.g., BFD - RFC 7130). 

[SLI] Fully agree, IMO, we must not let the doors wide open to this kind of permeation. 


-----Original Message-----
From: Acee Lindem (acee) [mailto:[e-mail]] 
Sent: Thursday, August 06, 2015 14:53
To: LITKOWSKI Stephane SCE/IBNF; Ebben Aries; [e-mail] list ([e-mail])
Subject: Re: [Isis-wg] draft-ginsberg-isis-l2bundles

Hi Stephane, 


On 8/6/15, 4:01 AM, "[e-mail]"
<[e-mail]> wrote:

>Hi Acee,
>
>Some comments inline
>
>-----Original Message-----
>From: Acee Lindem (acee) [mailto:[e-mail]]
>Sent: Wednesday, August 05, 2015 19:24
>To: LITKOWSKI Stephane SCE/IBNF; Ebben Aries; [e-mail] list
>([e-mail])
>Subject: Re: [Isis-wg] draft-ginsberg-isis-l2bundles
>
>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.
>[SLI] Yes, and IMO, that's bad.



>- I still have some doubt on the reason to split LAGs for TE and 
>keeping bundles for other protocols.
>- Regarding TE, I don't really see how BW use cases can work with this, 
>as there may be some TE tunnels using the bundle and some using 
>specific link, so evaluating the remaining BW per link and for the bundle is hard.
>- This "breaks" layers, IGP exposes Layer 3 topology by design, not 
>layer
>2 ... if we want to expose layer 2, that's not an issue, it's a kind of 
>multilayer TE approach and BGP-LS may so come in the picture and is a 
>good candidate to retrieve topological information. I do not want to 
>see IS-IS or OSPF becoming a topology discovery protocol for everything :
>while it's related to the Layer 3 topology it's fine to me to keep it 
>in the IGP for other informations, may be we need to find another way.
>
>
> 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.
>[SLI] Agree but I don't see this as a negative point, as I think most 
>networks running TE, already have a BGP controlplane that can be reused.

If there is BGP-LS peering on all the routers, then I agree that this would work given the right local policy to specify what BGP-LS information each router advertises.

Thanks,
Acee 




>
>     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).
>[SLI] Agree there is a need of correlation, but correlation is required 
>in all cases (in the current proposal, we advertise some parent link 
>information).
>
>Additionally, any time the information is coming from multiple sources, 
>you are likely to trigger path computation more frequently.
>[SLI] I would say that's implementation dependent.
>
>
>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
>>> 
>>>  
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Orange decline toute responsabilite si ce message a ete altere, deforme ou falsifie. Merci.

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they should not be distributed, used or copied without authorisation.
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As emails may be altered, Orange is not liable for messages that have been modified, changed or falsified.
Thank you.