nanog mailing list archives
Re: MPLS in metro access networks
From: Eric Osborne <eosborne () cisco com>
Date: Fri, 30 Nov 2001 08:12:16 -0500
However, the proponents of MPLS based networks stress things like it's reliability, speed and simplicity, over existing, pure IP network designs.
We do? Not all of us...:) Reliability? I've never heard claims that MPLS is any more or less reliable than IP. Certainly there's fast reroute mechanisms so that a failure can be worked around pretty quickly, but we're talking about a failure at a lower level (link failure) or a box/LC failure (crash). The MPLS software implementation from a given vendor should be as reliable as the IP software; there's nothing fundamentally different in MPLS that makes it easier to code, or inherently bug-free or any of that stuff. Speed? Back in the early days, it was thought that a 20-bit label lookup would be faster than a 32-bit IP DA lookup. With the advent of fast hardware switching, this turns out not to be true. Speaking as I can for only one vendor, I can tell you that anyone from my company who claims MPLS is substantially faster at a switching lookup than IP needs to be beat with a clue stick. It turns out, on some platforms, that imposing a label stack is a wee bit slower than switching an IP packet and that swapping a label is a wee bit faster than switching an IP packet, but "wee bit" means something in the area of a few percent. And this does not apply to all platforms. Simplicitly? Possibly. It might be argued that no longer needing BGP in the core makes your network simpler. But IMHO a BGP-free core in and of itself is not enough of a reason to deploy MPLS. The things I think MPLS buys you are: - traffic engineering for your core - being able to forward traffic down a path other than the one your IGP would select, in a more granular method and less error-prone fashion than other tools to do such (static routes, GRE tunnels, juggling link costs, etc) - ability to carry edge services (L3VPN, L2VPN) across your network. And there's some QoS benefits in here, too, since you have a hierarchical set of labels. MPLS is not the *only* way to do these things, but what it can do has proven useful to lots of people.
My point, is that it is certain not faster, not any simpler, and, for many, has been considerably less reliable. I reiterate that the point of implimenting MPLS is to be able to provide the services it enables (of which, TE is a great example, along with VPNs).
Absolutely. Let me also add that reliability tends to correlate with maturity and deployment, so you'll only see existing implementations get better over time.
Of course, different levels of perceived reliability may be due to different depths of MPLS implimentation. A design consistint of fully meshed, explicit TE tunnels would probably be pretty reliable, by this point. A network with many L2VPNs and RFC2547 VPNs running over LSPs instantiated by LDP, might be less so, depending on the platform.
I think I agree with this. It's not that LDP is inherently any less reliable than TE, but that with FRR one can protect against lower-level failures. I think I prefer "availability" over "reliability" in this context, since that takes into account TE's ability to avoid some congestion that LDP (following the IGP path) can't. But that's just me. eric
- Daniel Golding-----Original Message----- From: Dave Siegel [mailto:dave () siegelie com] Sent: Wednesday, November 28, 2001 7:27 PM To: Daniel Golding Cc: Quibell, Marc; mcohen () thrupoint net; nanog () merit edu Subject: Re: MPLS in metro access networksMPLS is not useful in and of itself as a switching mechanism.However, it isuseful for TE, VPNs, etc. If you enable MPLS on your network toget "betterperformance", "faster speeds", or a "more reliable core", you will be disappointed in the end, as the performance is the same, speedis the same,and reliability is lower due to immature code.How old is your information? The company I'm working for has been using MPLS for some 2 years now (maybe more, maybe less, I forget). We have found the code to be quite stable, although that speaks as much to our vendors improved QA as it does to our internal QA and testing that takes place months before deployment. MPLS-TE is definitely a valuable feature. It was worth it for us to deploy it back in '99, and it's worth it now. MPLS-based VPN's are interesting in their own right. I would not consider MPLS to be bleeding edge anymore...and for us, it doesn't really feel cutting edge anymore either. It's the newer features still in the standards process that might be dangerous to deploy at this stage, but that's what labs are for (that would be an actual lab, not the "production lab" :-). That being said, I would love to see some quantifiable data showing the differences in switching latencies between labels and packets. %age increase in efficient use of network capacity will of course depend on your backbone design. Reliability, in the end, has more to do with organization processes for engineering and operating your network than the quality of a vendor's latest GA release of code. Dave- Daniel Golding -----Original Message----- From: owner-nanog () merit edu [mailto:owner-nanog () merit edu]On Behalf Of Quibell, Marc Sent: Thursday, November 15, 2001 1:04 PM To: 'mcohen () thrupoint net'; nanog () merit edu Subject: RE: MPLS in metro access networks I guess you answered your own question: "And I'm not sure what faster switching/routing has to do with MPLS:)" As far as CEF and such goes, I couldn't disagree with that (as I was not comparing MPLS to other optimized forwarding techniques),however, MPLS isnot a vendor-proprietary forwarding mechanism, which means thatI can deployit worldwide, or state-wide, whatever the case may be, in my network and have the benefit of using only ONE protocol with MPLS-enabled/aware routers/switches. A definate plus over the other proprietaryfast switchingtechniques you mentioned. Your last statement indicates "added services" have nothing todo with thethe fast switching processing of MPLS, when in fact theseservices dependupon the faster delivery of the non-proprietary fast switchingof MPLS. Asquoted from the rfc: "This memo presents an approach for building core Virtual Private Network (VPN) services in a service provider's MPLS backbone. This approach uses Multiprotocol Label Switching (MPLS) running in the backbone to provide premium services in addition to best effort services." Marc -----Original Message----- From: Michael Cohen [mailto:mcohen () thrupoint net] Sent: Thursday, November 15, 2001 11:20 AM To: nanog () merit edu Subject: RE: MPLS in metro access networks I still have to disagree that MPLS results in fasterswitching/routing inmodern service provider networks. Modern vendor cachingmechanisms are justas fast if not faster than MPLS processing. With the smalloverhead of MPLSlabels and LDP I highly doubt that you're getting anyperformance increaseover Cisco's CEF or Juniper's FPC architecture. I also doubtthat speed isa benefit that service providers consider when deciding whetheror not theywant to implement MPLS. Added services that run on top of MPLSlike VPNs,traffic engineering, and fast rerouting capabilities (allmentioned in theoriginal post) are more likely the benefits considered.Perhaps when labelswitching was first being marketed (Ipsilon and Cisco in 1996)there weresome speed benefits but now I think it's the services that useMPLS that arethe major benefit. -Michael Cohen -----Original Message----- From: Quibell, Marc [mailto:mquibell () icn state ia us] Sent: Thursday, November 15, 2001 10:59 AM To: 'mcohen () thrupoint net'; 'nanog () merit edu' Subject: RE: MPLS in metro access networks soooo...Label switching assigns labels to packet headers whichresults inless time and processing looking up routes, and instead reliesupon a labelindex for forwarding decisions? Hence my statement "fasterswitching/routingand less processing":) Marc -----Original Message----- From: Michael Cohen [mailto:mcohen () thrupoint net] Sent: Thursday, November 15, 2001 10:56 AM To: Quibell, Marc Subject: RE: MPLS in metro access networks I hope so:) -----Original Message----- From: Quibell, Marc [mailto:mquibell () icn state ia us] Sent: Thursday, November 15, 2001 10:46 AM To: 'mcohen () thrupoint net'; nanog () merit edu Subject: RE: MPLS in metro access networks Are we talking about Multiprotocol Label Switching? Marc -----Original Message----- From: Michael Cohen [mailto:mcohen () thrupoint net] Sent: Thursday, November 15, 2001 10:45 AM To: nanog () merit edu Subject: RE: MPLS in metro access networks And I'm not sure what faster switching/routing has to do with MPLS:) I believe one of the ideas behind MPLS benefiting metro access networks is using MPLS to deliver layer 2 VPNs across an MPLS enabled core thus simulating leased lines for access clients...but I'm sure somebody will correct me if I'm wrong. There seems to be some hype forMartini draft VPNsand large enterprise customers in metro areas. Cheers, -Michael Cohen -----Original Message----- From: owner-nanog () merit edu [mailto:owner-nanog () merit edu]On Behalf Of Quibell, Marc Sent: Thursday, November 15, 2001 10:20 AM To: 'srihari varada'; nanog () merit edu Subject: RE: MPLS in metro access networks I would think faster switching/routing and less processingwould be wantedin any mid-to-large sized network...I'm not sure what load balancing and fault restoration has to do with MPLS.... Marc -----Original Message----- From: srihari varada [mailto:varada () txc com] Sent: Thursday, November 15, 2001 10:12 AM To: nanog () merit edu Subject: MPLS in metro access networks Hello: I have heard some stressing the role of MPLS in metro access networks. It is difficult for me to visualize the need for it in them while it is not so difficult to understand the utility (load balancing and fault restoration etc.) of it in the metro backbone networks. To characterize metro access networks in the context, the following is provided: -- aggregates traffic from residential (arriving via broadband access links such as xDSL, Cable) and business consumers (arriving via broadband access links such as xDSL and high speed links such as Ethernet or SONET) -- funnels aggregated traffic to metro backbone networks for destination hosts in the local metro region or remote regions across the internet regional and backbone networks. Majority of such access networks are SONET/ATM based (I didn't come across any case of Gig Ethernet. However, I do not preculde it). Thus, there are two questions: -- Are there known RBOCs/ILECs and CLECs entrenching MPLS in the said network scope? (I do not see many major ILECs in the un-official MPLS service providers list being circulated but it may mean little) -- If so, what motivates them to do so? Any analysis of the driving forces is appreciated. Regards, Srihari Varada-- Dave Siegel HOME 520-877-2593 dave at siegelie dot com WORK 520-877-2628 dsiegel at gblx dot net Director, IP Engineering, Global Crossing
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Current thread:
- RE: MPLS in metro access networks, (continued)
- RE: MPLS in metro access networks Michael Cohen (Nov 15)
- RE: MPLS in metro access networks Quibell, Marc (Nov 15)
- RE: MPLS in metro access networks Michael Cohen (Nov 15)
- RE: MPLS in metro access networks Gary Blankenship (Nov 16)
- RE: MPLS in metro access networks Gary Blankenship (Nov 18)
- RE: MPLS in metro access networks Michael Cohen (Nov 15)
- RE: MPLS in metro access networks Daniel Golding (Nov 16)
- Re: MPLS in metro access networks Dave Siegel (Nov 28)
- Re: MPLS in metro access networks Leo Bicknell (Nov 28)
- Re: MPLS in metro access networks Dave Siegel (Nov 30)
- RE: MPLS in metro access networks Daniel Golding (Nov 29)
- Re: MPLS in metro access networks Eric Osborne (Nov 30)
- Re: MPLS in metro access networks srihari varada (Nov 15)
- Re: MPLS in metro access networks Eric Osborne (Nov 15)
- Re: MPLS in metro access networks Stephen Stuart (Nov 15)