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

[Jeff Tantsura <[e-mail]>]

Gyan,

I wrote this presentation ~3 years ago, so the numbers are not necessarily current.

Please see inline, hope this helps you to better understand the technology behind the terminology.
Let me know if anything is unclear.

Cheers,
Jeff
On Dec 17, 2019, 3:45 PM -0800, Gyan Mishra <[e-mail]>, wrote:
>
> Hi Ketan
>
> Is this the artificial boundary below for SR-TE from the document provided by Jeff.
>
>  MSD supported by different HW/SW differs widely :
> – Linux (kernel 4.10): 2 SID’s, some improvements recently (as of 4.11) – Low end off the shelf (merchant) silicon, e.g. BCM Trident2: 3-5 SID’s – High end off the shelf (merchant) silicon, e.g BCM Jericho1 : 4-7 SID’s – Vendor’ silicon, e.g. Juniper’ Trio, Nokia’ FP3: 4-10+ SID’s
>
> So if you are doing MPLS-TE w/o SR-TE policies reusing they MPLS data plane the label stack is identical to MPLS just with different label range for SRGB 16000-23999 for absolute or indexed label.
[jeff]SRGB is either configurable or a static label range, it doesn’t have to be identical with SR domain, indexing provides the abstraction (and there’s life outside of Cisco ;-))
> Label stack for SR-MPLS is identical to MPLS with single topmost label for label switching through the core and bottom of stack services label for L3 vpn services.
[jeff] NH in the VPN route is recursively resolved to a LSP (or policy in modern lingo) that could have 1 or more SID’s associated with it (). In MPLS case, without TE, would be the label/N-SID of the egress PE, the SID stack would grow any time you need to use Adj-SID’s to deviate from SPT. Specifically to SR, egress PE can also associate a particular path (color) with the route and signal to the ingress PE what path to take in order to reach it (NH).
>
> For clarity on nomenclature below please comment:
>
> Transport label - This is the SID label stack insertion at the ingress PE head end to the SR-MPLS domain performing SR-TE.  Each hop along the way hop the top SID label is popped until SL==0 at which time PHP default or UHP explicit null “pipe mode” is performed. (Similar to topmost in MPLS label switch world but now its a stack of labels  instead of a single label)
[jeff] There’s no SL field in MPLS header, there’s however BoS bit that should be set on the most bottom label (in this case - VPN label), PHP is explicitly signaled by the egress PE (P/NP-flag in Prefix-SID)
>
> Once you get past the transport label now you are on common ground with M-BGP overlay services
>
> Services label- L3 vpn service SID signaled.
> So with the service label that is signaled from ingress to egress PE for service.  Is this a single label like traditional L3 vpn aggregate label or more then one or many labels.
[jeff] there’s no differences with any other VPNoverFoo, service labels are signaled in exactly same way independently of the transport and are locally significant (that’s why LxVPN’s are such a great technology)
>
> The services label my guess should be fixed and not have any vendor specific boundary constraints.
[jeff] they are locally significant, in any implementation - label blocks are associated with particular functions and programmed in HW, so the service label would come out of the service range, which is significant to the device advertising it.
In modern OS’s the ranges are configurable, in older ones, it is static and there’s usually a header file that looks like:
#define MPLS_L3VPN_MIN_LABEL  0x40000
#define MPLS_L3VPN_MAX_LABEL 0x85FFF


> Gyan
>
> > On Tue, Dec 17, 2019 at 7:21 AM Ketan Talaulikar (ketant) <[e-mail]> wrote:
> > > Hi Nat,
> > >
> > > The MSD framework enables us to define more/new MSD types. If there is a real use-case and requirement (as you express) and the necessary MSD type(s) can be formally defined then perhaps the WG can evaluate it.
> > >
> > > Thanks,
> > > Ketan
> > >
> > > From: spring <[e-mail]> On Behalf Of Nat Kao
> > > Sent: 17 December 2019 17:16
> > > To: Robert Raszuk <[e-mail]>
> > > Cc: SPRING WG <[e-mail]>; Nat Kao <[e-mail]>
> > > Subject: Re: [spring] Different MSDs for different traffic types on the same headend.
> > >
> > > Hello, Robert.
> > > Surely the current BMI-MSD definition is sufficient for platforms without artificial boundaries.
> > > In this ideal case, maximum labels available for SR-TE policy can be inferred from BMI-MSD and VPN routes.
> > >
> > > However we have 3 different artificial boundaries across 3 different platforms now.
> > > Hardcoding these boundaries might not scale well. (Especially different OS versions may behave differently.)
> > > A standard mechanism to discover this boundary would greatly help constructing SR-TE policy candidate paths.
> > >
> > > Regards,
> > > Nat.
> > >
> > >
> > > On Tue, Dec 17, 2019 at 5:58 PM Robert Raszuk <[e-mail]> wrote:
> > > > Hi Nat,
> > > >
> > > > I am having a bit of difficulty understanding reasoning and the way you are separating transport from service labels.
> > > >
> > > > The processing label limit usually comes from data plane capabilities of the platform namely LFIB or hardware below.
> > > >
> > > > Such layer is function agnostic and it does not matter what role the label serves.
> > > >
> > > > Label lookup results in pointer to a adj. rewrite on the outbound side. It really does not matter if the adjacent peer is your P router, segment endpoint or CE.
> > > >
> > > > Of course there are number of processing exceptions - for example concept of aggregate VPN label, additional header modifications etc ...
> > > >
> > > > Likely some platforms put such artificial boundary between transport and service hence your request. But if so IMHO this is more of an issue with specific platform or its marketing message then IETF :).
> > > >
> > > > Many thx,
> > > > R.
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > On Tue, Dec 17, 2019 at 6:06 AM Nat Kao <[e-mail]> wrote:
> > > > > Hi, Jeff.
> > > > > Consider a headend that can perform 1 of the following 2 modes(but not both):
> > > > > 1) Plain IPv4: 6 transport labels + 0 service label => traffic can be steered into a 6-label SR-TE policy.
> > > > > 2) Any type of VPN: 3 transport labels + 1~3 service labels => traffic cannot be steered into a 6-label SR-TE policy.
> > > > > a) As defined in RFC8491, the BMI-MSD is 6 for this headend. Do we have a standardized way to signal the transport label depth in mode 2?
> > > > >    Maybe in a different MSD type?
> > > > > b) Since plain IPv4 and VPN routes can be steered into the same SR-TE policy, do we have a standardized headend behavior in this situation?
> > > > >    (Should I open a new thread to discuss this? It seems not quite MSD-relative.)
> > > > >
> > > > > Thanks...
> > > > > Nat
> > > > > >
> > > > > > On Tue, Dec 17, 2019 at 7:19 AM Jeff Tantsura <[e-mail]> wrote:
> > > > > > > Gyan,
> > > > > > >
> > > > > > > MSD is only relevant for a device that either imposes the label stack (head-end) or manipulates it (BSID anchor). There are some other constrains when it comes to entropy labels and ERLD, please read the respective drafts.
> > > > > > > In general, SID stack would grow when TE is in use (any time you need to use additional SID to deviate from SPT), another case is when additional SID’s are used for services on the nodes, other than the tail-end.
> > > > > > > That’s why we've designed MSD to be very flexible to accommodate all the different use cases, it is upto computational logic to decide how to deal with different constrains (MSD types)
> > > > > > >
> > > > > > > Cheers,
> > > > > > > Jeff
> > > > > > >
> > > > > > > P.S. you might want to see the NANOG MSD presentation I did some time ago.
> > > > > > > https://pc.nanog.org/static/published/meetings/NANOG71/1424/20171004_Tantsura_The_Critical_Role_v1.pdf
> > > > > > > On Dec 14, 2019, 11:59 PM -0800, Gyan Mishra <[e-mail]>, wrote:
> > > > > > >
> > > > > > > > Jeff
> > > > > > > >
> > > > > > > > With SR-MPLS with SR-TR let’s say if you use cSPF snd don’t have an ERO strict explicit path defined or is a loose path, then the for the cSPF would the transport labels be 1.  For loose would also be 1 also.  If the path were explicit defined to egress PE and was 7 hops from ingress to egress then transport would be 6.  And if L3 vpn service sid was signaled that would be 1 vpn label.
> > > > > > > >
> > > > > > > > Let me know if I have that right.
> > > > > > > >
> > > > > > > > In Nats scenario for IPv6 he has 3 vpnv6 labels.
> > > > > > > >
> > > > > > > > Why is that?
> > > > > > > >
> > > > > > > > With both SR-MPLS and SRv6 the L3 vpn AFI/SAFI MBGP services overlay single label sits on top off SR as if does today with MPLS so why 3 vpn labels.
> > > > > > > >
> > > > > > > > So with this draft with BGP-LS and BMI-MSD you can flood into the IGP the SID depth so all the nodes along the SR-TE path don’t go over the maximum which would result in an error.
> > > > > > > >
> > > > > > > > If you set your MTU high enough in the core like 9216, does that overcome the SID depth issues with SR-TE?
> > > > > > > >
> > > > > > > > Warm regards,
> > > > > > > >
> > > > > > > > Gyan
> > > > > > > >
> > > > > > > > On Sat, Dec 14, 2019 at 2:43 AM Nat Kao <[e-mail]> wrote:
> > > > > > > > > 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 <[e-mail]> 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 <[e-mail]>, 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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> > > > > > > > --
> > > > > > > > Gyan S. Mishra
> > > > > > > > IT Network Engineering & Technology
> > > > > > > > Verizon Communications Inc. (VZ)
> > > > > > > > 13101 Columbia Pike FDC1 3rd Floor
> > > > > > > > Silver Spring, MD 20904
> > > > > > > > United States
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> --
> Gyan S. Mishra
> IT Network Engineering & Technology
> Verizon Communications Inc. (VZ)
> 13101 Columbia Pike FDC1 3rd Floor
> Silver Spring, MD 20904
> United States
> Phone: [phone]
> Email: [e-mail]
> www.linkedin.com/in/networking-technologies-consultant
>
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