Re: [spring] Different MSDs for different traffic types on the same headend.

Nat Kao <lekao@pyxisworks.org> Sat, 14 December 2019 07:43 UTC

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From: Nat Kao <lekao@pyxisworks.org>
Date: Sat, 14 Dec 2019 15:42:48 +0800
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To: Jeff Tantsura <jefftant.ietf@gmail.com>, spring@ietf.org
Cc: Nat Kao <lekao@pyxisworks.org>
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Subject: Re: [spring] Different MSDs for different traffic types on the same headend.
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Hi, Jeff.

Thanks for the BMI-MSD reference. If I understand correctly:

BMI-MSD = Transport Label Depth + Service Label Depth
Only former can be utilized by SR-TE policies.

Currently do we have any method to determine the composition of BMI?
We need to know the transport label depth when doing service route
per-destination steering.

This problem arises when trying to steer a plain IPv4 route and a VPN
service route into the same SR-TE policy that exceeds the transport label
depth of the service route. I'm trying to figure out the standard behavior
in this case since the headend we use currently produces some interesting
results.

Regards,
Nat.

On Sat, Dec 14, 2019 at 2:42 AM Jeff Tantsura <jefftant.ietf@gmail.com>
wrote:

> Hi Nat,
>
> Please read https://tools.ietf.org/html/rfc8491#section-5
> Currently defined MSD types are:
> 1: BMI
> 2: ERLD
>
> Specifically to BMI:
> Base MPLS Imposition MSD (BMI-MSD) signals the total number of MPLS labels
> that can be imposed, including all service/transport/special labels.
> The answer to your question is 6
>
> Cheers,
> Jeff
> On Dec 13, 2019, 3:42 AM -0800, Nat Kao <lekao@pyxisworks.org>rg>, wrote:
>
> Hello, SPRING WG.
>
> How do we deal with an SR-TE policy headend with different MSDs for
> different types of traffic?
> For example, a headend H can impose:
> 6 transport labels for plain IPv4 packets;
> 5 transport labels + 1 IPv6 ExpNull label for plain IPv6 packets;
> 3 transport labels + 3 VPN  labels for VPN packets.
>
> a) For a plain IPv4 route R4 and a VPN route Rv both steered into the
> SR-TE policy P1 with SID list <S1, S2, S3, S4, S5>, what will H perform in
> this situation?
> b) What is the MSD of H? 6, 5 or 3?
>
> Thanks,
> Nat.
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