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

"Les Ginsberg (ginsberg)" <ginsberg@cisco.com> Mon, 17 August 2015 14:41 UTC

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From: "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
To: "stephane.litkowski@orange.com" <stephane.litkowski@orange.com>, "Ahmed Bashandy (bashandy)" <bashandy@cisco.com>, "Acee Lindem (acee)" <acee@cisco.com>, Ebben Aries <exa@fb.com>, "isis-wg@ietf.org list (isis-wg@ietf.org)" <isis-wg@ietf.org>
Thread-Topic: [Isis-wg] draft-ginsberg-isis-l2bundles
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Date: Mon, 17 Aug 2015 14:40:52 +0000
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Subject: Re: [Isis-wg] draft-ginsberg-isis-l2bundles
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Stephane –

Your new column is already covered by Ahmed’s column #3: “L2 bundles as unnumbered interfaces in ISIS”

Problem is – the two of you disagree on what is +/- for a number of rows.

I don’t think assigning addresses for a much larger set of interfaces (e.g. if there are 128 bundle members this is 128 * the number of L3 interfaces) should be considered easy to do – which is why Ahmed suggested using unnumbered.

Perhaps you could explain why you disagree with Ahmed’s assessment of the rows for his column #3??

    Les


From: Isis-wg [mailto:isis-wg-bounces@ietf.org] On Behalf Of stephane.litkowski@orange.com
Sent: Monday, August 17, 2015 1:41 AM
To: Ahmed Bashandy (bashandy); Acee Lindem (acee); Ebben Aries; isis-wg@ietf.org list (isis-wg@ietf.org)
Subject: Re: [Isis-wg] draft-ginsberg-isis-l2bundles


You can add in the table as a new solution : establish L3 adjacency on each link in addition to the LAG.


Establish L3 adjacencies on each link in addition to on LAG

Scalability

-1

Mandate the deployment of a protocol that was not deployed before

No (+1)

Impact on basic routing functionality

Minimal (+1)

Works for both P2P and LAN

Simple (+1)

Using 1 protocol for diverse functionilities

Yes (+1)

Exposing L2 info in L3 protocol

No (+1)

Protocol change

No (+1)

Risk

Small (Minimal impact on baseline functionality and managements tools while not deploying any new protocol) (+1)

Sum

6


As for the layer 3 bundles, for the scaling part, it adds some adjacencies, but honestly I don’t think today this is an issue with controlplane resources we have and multithreading.

In the table, you can also add  a section regarding failure detection :
As for solution #1 (L2 bundles in ISIS) and solution #2 (BGP-LS), you need a mechanism outside the protocol to monitor the status on each individual link and report it to the protocol which requires to implement something in addition (it does not work by itself), solution#3 and #4 (see above) : ISIS hellos are doing the job if fast detection is not required.


Regarding the risk :
What is the risk to deploy BGP-LS ? It’s an operational cost (and you already count it before) but there is no risk associated.


For solution #3, what is the impact on the base routing ?


Regarding the criteria : “Using 1 protocol for diverse functionalities”, This is always counted in “Mandate the deployment of a protocol that was not deployed before” moreover using IMO, 1 protocol to do everything is never good … (like using a single router to do every features ☺ )


Best Regards,


From: Ahmed Bashandy (bashandy) [mailto:bashandy@cisco.com]
Sent: Tuesday, August 11, 2015 02:05
To: LITKOWSKI Stephane SCE/IBNF; Acee Lindem (acee); Ebben Aries; isis-wg@ietf.org<mailto:isis-wg@ietf.org> list (isis-wg@ietf.org<mailto:isis-wg@ietf.org>)
Subject: Re: [Isis-wg] draft-ginsberg-isis-l2bundles

Folks

In attempt to provide a relatively quantitative measurement of the proposed solutions to the problem at hand, I thought I would prepared a small comparison table between ISIS for L2 bundles, BGP-LS for L2 bundles, and changing all L2 bundles members to L3 links as unnumbered interfaces. I put +1 for (IMHO) what looks like an advantage, -1 for (IMHO) what looks like a disdavantage, and (0) what looks like a minor disadvantage or advantage

ISIS to advertise L2 bundles

BGP-LS to advertise L2 bundle

L2 bundles as unnumbered interfaces in ISIS

Scalability

Minimal scale overheard (+1)

Minimal scale overhead (+1)

Significant scale overhead (-1)

Mandate the deployment of a protocol that was not deployed before

No (+1)

Yes (-1)

No (+1)

Impact on basic routing functionality

Minimal (+1)

Minimal (+1)

Significant (-1)

Works for both P2P and LAN

Simple (+1)

Simple (+1)

Difficult (unnumbered not easy with LANs) (-1)

Using 1 protocol for diverse functionilities

Yes (+1)

No (-1)

Yes (+1)

Exposing L2 info in L3 protocol

Yes (-1)

Yes (-1)

No (+1)

Protocol change

Yes (-1)

Yes (-1)

No (+1)

Risk

Small (Minimal impact on baseline functionality and managements tools while not deploying any new protocol) (+1)

Medium (Have to deploy BGP-LS everywhere) (0)

Significant (Have to make sure that baseline functionality on all routers as well as management and monitoring tools are not impacted by the sharp scale increase) (-1)

Sum

5

-1

-2



One Important point, I agree with Ebben that BGP-LS is not an alternative to using ISIS but rather a complementary solution to be used by networks that do not use ISIS and OSPF. If we assume that BGP-LS will be used by networks that already employ BGP, then using ISIS and BGP-LS will have almost the same score


Thanks

Ahmed


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