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 networks
MPLS is not useful in and of itself as a switching mechanism. However, it is useful for TE, VPNs, etc. If you enable MPLS on your network to get "better performance", "faster speeds", or a "more reliable core", you will be disappointed in the end, as the performance is the same, speed is 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 is not a vendor-proprietary forwarding mechanism, which means that I can deploy it 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 proprietary fast switching techniques you mentioned.
Your last statement indicates "added services" have nothing to do with the the fast switching processing of MPLS, when in fact these services depend upon the faster delivery of the non-proprietary fast switching of MPLS. As quoted 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 faster switching/routing in modern service provider networks. Modern vendor caching mechanisms are just as fast if not faster than MPLS processing. With the small overhead of MPLS labels and LDP I highly doubt that you're getting any performance increase over Cisco's CEF or Juniper's FPC architecture. I also doubt that speed is a benefit that service providers consider when deciding whether or not they want to implement MPLS. Added services that run on top of MPLS like VPNs, traffic engineering, and fast rerouting capabilities (all mentioned in the original post) are more likely the benefits considered. Perhaps when label switching was first being marketed (Ipsilon and Cisco in 1996) there were some speed benefits but now I think it's the services that use MPLS that are the 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 which results in less time and processing looking up routes, and instead relies upon a label index for forwarding decisions? Hence my statement "faster switching/routing and 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 for Martini draft VPNs and 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 processing would be wanted in 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