Re: [spring] Different MSDs for different traffic types on the same headend.
Gyan Mishra <hayabusagsm@gmail.com> Thu, 19 December 2019 02:12 UTC
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From: Gyan Mishra <hayabusagsm@gmail.com>
Date: Wed, 18 Dec 2019 21:12:17 -0500
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To: Jeff Tantsura <jefftant.ietf@gmail.com>
Cc: "Ketan Talaulikar (ketant)" <ketant@cisco.com>, Nat Kao <lekao@pyxisworks.org>, Robert Raszuk <robert@raszuk.net>, SPRING WG <spring@ietf.org>
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Subject: Re: [spring] Different MSDs for different traffic types on the same headend.
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Thank you Jeff for taking the time for the detailed response!! Cheers & Happy Holidays!! Gyan On Wed, Dec 18, 2019 at 7:13 PM Jeff Tantsura <jefftant.ietf@gmail.com> wrote: > Pleasure, see inline > /*somewhat philosophical ;-) > > Cheers, > Jeff > On Dec 17, 2019, 10:28 PM -0800, Gyan Mishra <hayabusagsm@gmail.com>, > wrote: > > > Thanks Jeff!! > > Kind regards > > I have a personal Cisco VIRL server server which I just finished building > out the SP topology with two SP SR domains. Cisco XRv supports SRv6 in > 6.6.1 so I have loaded the latest image 7.0.1 so hopefully have all > features. Plan to get it all up and running tomorrow. > > Question- Since SR-MPLS uses an IPv4 data plane and since SRv6 uses IPv6 > data plane is it possible to run SRv6 as an overlay both SR-MPLS and SRv6 > together as two ships in the night. Would save on having to go back and > forth between simulations if they can both live together so I can test > both simultaneously. > > [jeff] I’m not sure what you mean by overlay, just run ipv4+mpls for > SR-MPLS and ipv6 for SRv6, perhaps different interfaces rather than dual > stack > > > In-line questions follow up > > On Tue, Dec 17, 2019 at 8:41 PM Jeff Tantsura <jefftant.ietf@gmail.com> > wrote: > >> 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 <hayabusagsm@gmail.com>, >> 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). >> > > [gyan] So if you are running just SR-MPLS using SPF path and don’t > deviate from that then with prefix/node SID which I believe is like the > egress PE ibgp NH loopback FEC destination, that you have a SID label > binding for your LSP to build topmost reusing the MPLS data plane. In the > case described there would be only 1 transport label. Correct? > > [jeff] yes, the only difference with LDP/RSVP would be the “globally > significant label” (N-SID of egress PE), so there’s no swap (there is but > to the same value) > > > You would only have an Adj-SID if you are doing SR-TE. Correct? In that > case if you had one Adj-SID in the middle of the path like a loose explicit > route object ERO, then would still be only 1 transport label in the stack > as if you were not doing SR-TE. Or would it be 2 labels, not sure. > > [jeff] if Adj-SID is locally significant (L flag not set) (default in most > implementation) is must be evaluated only by the node that it is local to, > which should result in 2 label construct (N-SID,Adj-SID), there are ways to > optimize but this is the idea. > > > So let’s say If your SR-TE path deviated from the spf along 10 hops, so > then you would have 10 Adj-SIDs and so 10 labels in the stack. So this is > where MSD and BGP-LS IGP extensions come into play to signal back to the > head end that the maximum SID depth has exceeded resulting in an error. At > that point the > SR-TE LSP would be broken and you would have to manually build policy with > less strict hops. > > [jeff] depends on implementation, it could as well be 20. No, this is > other way around - (simplified version) BGP-LS distributes SR related data > to the PCE and then PCE computes a path that meets the constrains, MSD > being one of them, in other words - if PCE can’t compute a path to a > destination that meets the constrains, it will not be instantiated > > > I guess If you were using PCEP centralized controller that would signal > MSD exceeded but I think you would still be in a broken LSP state. The > pcep controller would have to be sitting next to the head end for the SR-TE > policy for the LSP to fix automatically. Is that correct? > > [jeff]see previous answer, if MSD (or any other) constrains can’t be met, > the path is not going to be instantiated > PCEP is the protocol between PCE and PCC and has little to do with > computation logic, PCE could compute a path but use for example RESTCONF to > communicate with the head-end > > > So for SR-TE due to the MSD issues and SID depth asic limitations even > with the latest asic, you really have to deploy a pcep controller based > architecture near the head end with SR-MPLS if using SR-TE. If you are not > using SR-TE then I believe there is really no benefit of going to SR-MPLS. > > > [jeff] you mean PCE controller. I disagree with you, reducing number of > protocols in the network is a great goal (reduces complexity and number of > interactions between them). Look at RSVP - there are many people using it > but a only little part of them is actually doing TE, most use it for FRR > and tactical TE. > To cite a great book ;-) - complexity doesn’t disappear, it moves to > different places. In SR we have significantly reduced amount of state and > complexity associated with maintaining it in the network, but it is still > there, it has just moved to a controller. In RSVP for example, you could do > in-band BW reservations, in SR it is “soft” controller has to do it and > then network gets configured. Multicast works in IP because there’s enough > state to compute loop-free MDT and so forth > > > You agree. > > I guess you save on having to maintain ldp state on each node. Thats not > a big deal or business justification to switch to SR-MPLS as for operators > “MPLS” is their bread & butter they are use to so why change. > > [jeff] No, I don’t agree - the value is not in removing LDP state but > reducing overall complexity, interactions between IGPs and LDP are complex > and error prone, over the time resulted in 100’s of high severity bugs and > broken networks (if you are old enough you should remember :)) > > > I think the big benefit for both SR-MPLS and SRv6 is individual coloring > of vpn flows. Cisco calls it per-VRF TE, but it’s ugly to configure and > manage. > > [jeff] well, complain to your account, building networking features is > quite different from intuitive interfaces ;-) color is a piece of metadata > associated with a route, on itself not directly related to SR, nothing > prevents you of signaling a RSVP LSP or similar, there’s some work on > generalization of colored path advertisement which I find very valuable > (draft-chan-idr-bgp-lu2/ draft-szarecki-idr-bgp-lcu-traffic-steering) > > > So SR-MPLS and SRv6 is the future solution for operators that need the per > vpn coloring. > > [jeff] different people have different requirements, our job here is to > build technology that is flexible enough to address them at scale while > manageable. > > > Given the issues with SR-TE with SID depth asic limitations is it possible > to use traditional RSVP TE. > > [jeff] I don’t think you are right, while limitations are there, there are > solvable, by a better silicon (or trading off capacity for functionality - > looping/recycling packets), by a more clever computation, by brining some > of the state back (take a look > at draft-chunduri-lsr-isis-preferred-path-routing) > > > I am going to try in my virl setup as that could be a good workaround for > SR-TE hardware limitations until the hardware is up to snuff to handle very > long explicit paths. > > I believe their is a draft with teas in the works for IP TE to use rsvp > bandwidth signaling path and reserve messages with both SR-MPLS and SRv6. > > [jeff] good engineering is always a right balance of trade-offs, > extremities on either side (no state/all the state in a packet) (OpenFlow > is a great example) are rigid and won’t survive when deployed at scale. > > > >> 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) < >> ketant@cisco.com> 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 <spring-bounces@ietf.org> *On Behalf Of* Nat Kao >>> *Sent:* 17 December 2019 17:16 >>> *To:* Robert Raszuk <robert@raszuk.net> >>> *Cc:* SPRING WG <spring@ietf.org>; Nat Kao <lekao@pyxisworks.org> >>> *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 <robert@raszuk.net> 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 <lekao@pyxisworks.org> 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 <jefftant.ietf@gmail.com> >>> 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 <hayabusagsm@gmail.com>, >>> 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 <lekao@pyxisworks.org> 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 <jefftant.ietf@gmail.com >>> <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>, 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. >>> >>> _______________________________________________ >>> spring mailing list >>> spring@ietf.org >>> https://www.ietf.org/mailman/listinfo/spring >>> >>> _______________________________________________ >>> spring mailing list >>> spring@ietf.org >>> https://www.ietf.org/mailman/listinfo/spring >>> >>> -- >>> >>> Gyan S. Mishra >>> >>> IT Network Engineering & Technology >>> >>> Verizon Communications Inc. (VZ) >>> >>> 13101 Columbia Pike >>> <https://www..google.com/maps/search/13101+Columbia+Pike?entry=gmail&source=g> >>> FDC1 3rd Floor >>> >>> Silver Spring, MD 20904 >>> >>> United States >>> >>> Phone: 301 502-1347 >>> >>> Email: gyan.s.mishra@verizon.com >>> >>> www.linkedin.com/in/networking-technologies-consultant >>> >>> >>> >>> _______________________________________________ >>> spring mailing list >>> spring@ietf.org >>> https://www.ietf.org/mailman/listinfo/spring >>> >>> _______________________________________________ >>> spring mailing list >>> spring@ietf.org >>> https://www.ietf.org/mailman/listinfo/spring >>> >> -- >> >> Gyan S. Mishra >> >> IT Network Engineering & Technology >> >> Verizon Communications Inc. (VZ) >> >> 13101 Columbia Pike >> <https://www.google.com/maps/search/13101+Columbia+Pike?entry=gmail&source=g> >> FDC1 3rd Floor >> >> Silver Spring, MD 20904 >> >> United States >> >> Phone: 301 502-1347 >> >> Email: gyan.s.mishra@verizon.com >> >> www.linkedin.com/in/networking-technologies-consultant >> >> _______________________________________________ >> spring mailing list >> spring@ietf.org >> https://www.ietf.org/mailman/listinfo/spring >> >> -- > > Gyan S. Mishra > > IT Network Engineering & Technology > > Verizon Communications Inc. (VZ) > > 13101 Columbia Pike > <https://www.google.com/maps/search/13101+Columbia+Pike?entry=gmail&source=g> > FDC1 3rd Floor > > Silver Spring, MD 20904 > > United States > > Phone: 301 502-1347 > > Email: gyan.s.mishra@verizon.com > > www.linkedin.com/in/networking-technologies-consultant > > -- Gyan S. Mishra IT Network Engineering & Technology Verizon Communications Inc. (VZ) 13101 Columbia Pike FDC1 3rd Floor Silver Spring, MD 20904 United States Phone: 301 502-1347 Email: gyan.s.mishra@verizon.com www.linkedin.com/in/networking-technologies-consultant
- [spring] Different MSDs for different traffic typ… Nat Kao
- Re: [spring] Different MSDs for different traffic… Jeff Tantsura
- Re: [spring] Different MSDs for different traffic… Nat Kao
- Re: [spring] Different MSDs for different traffic… Gyan Mishra
- Re: [spring] Different MSDs for different traffic… Gyan Mishra
- Re: [spring] Different MSDs for different traffic… Jeff Tantsura
- Re: [spring] Different MSDs for different traffic… Gyan Mishra
- Re: [spring] Different MSDs for different traffic… Nat Kao
- Re: [spring] Different MSDs for different traffic… Robert Raszuk
- Re: [spring] Different MSDs for different traffic… Nat Kao
- Re: [spring] Different MSDs for different traffic… Ketan Talaulikar (ketant)
- Re: [spring] Different MSDs for different traffic… Gyan Mishra
- Re: [spring] Different MSDs for different traffic… Jeff Tantsura
- Re: [spring] Different MSDs for different traffic… Jeff Tantsura
- Re: [spring] Different MSDs for different traffic… Jeff Tantsura
- Re: [spring] Different MSDs for different traffic… Nat Kao
- Re: [spring] Different MSDs for different traffic… Gyan Mishra
- Re: [spring] Different MSDs for different traffic… Jeff Tantsura
- Re: [spring] Different MSDs for different traffic… Gyan Mishra
- Re: [spring] Different MSDs for different traffic… Nat Kao