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What's the maximum amount of MPLS VPNs a router can provide?

Is it 2^20 = ~1 million = the maximum amount of different MPLS labels?

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  • Why does this matter to you? How would you use the information? What kind of routers and os versions are they using? Apr 12, 2015 at 12:33
  • it would give me a better understanding of how MPLS works and what are the limits of it. Are the different customer VPNs separated by MPLS label at the service provider site? I would use this information to better understand how VPNs are isolated at the service provider site. I don't have a background in networking, I'm just learning. So there is no specific reason for this question was just wondering :P Apr 12, 2015 at 12:36
  • FYI, I took the liberty of modifying your question to be more on-topic; asking about other networks that you don't control is too broad / off-topic. Apr 12, 2015 at 14:09
  • Thanks although that changes the intent of my question a bit. I would still be specifically interested in how service providers handle the separation of different customer's MPLS VPN. Do they apply a different MPLS label to each different customer in the service provide MPLS core systems? And if so does that theoritically cause the maximum amount of MPLS VPNs provided to be 2^20? Apr 12, 2015 at 14:14

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What's the maximum amount of MPLS VPNs a router can provide?

Short answer:

"it depends". To be honest, it sounds like you're getting in way over your head, but I'll answer the question as best I can.

Long answer:

Sam said... I would still be specifically interested in how service providers handle the separation of different customer's MPLS VPN.

Why do you think that the answer is different when comparing how a router separates customers in an MPLS VPN vs a service provider separating customers in an MPLS VPN?

A router is the most basic building block for MPLS VPN network. Functionally, service providers use many routers to deploy MPLS VPNs. MPLS VPN customer separation can be implemented within the same router, or between different routers; it doesn't matter.

The difference in asking for how many VPNs a service provider can offer vs what a router can offer is: we can answer how many MPLS VPNs a router can offer in a normal-sized Stack Exchange answer.

If we start talking about how many VPNs a service provider can offer with many routers, that introduces too many variables... such as how many MPLS labels the service provider uses for other MPLS services (LDP, L2VPN, MPLS TE, etc...). This is relevant because you're asking about large numbers of VPNs, and large Service Providers offer all the aforementioned services.

What's the maximum amount of MPLS VPNs a router can provide?

Speaking practically, It depends on what hardware / software is providing the VPNs and how they are being used.

For instance, MPLS VPN under Cisco IOS binds labels per-VRF, and per-non-connected prefix so the total number of VPNs is reduced for every route you advertise into MPLS VPN from a CE router. There are features to bind labels per-VRF on some platforms. However, you did not tell us what hardware platform you're asking about, so this is all pointless other than to demonstrate that you're making far too many assumptions.

Is it 2^20 = ~1 million = the maximum amount of different MPLS labels?

That's not a practical constraint. There are theoretical numbers and real numbers; let's live in reality. Remember how MPLS VPN is used...

  • A unique MPLS VPN instance is bound to a router's physical interface or subinterface
  • MPLS VPNs can contain overlapping routes between each other, MPLS VPN makes those routes unique with Route Distinguishers

Because MPLS VPNs are bound to interface / subinterfaces; one possible limit is the number of possible interfaces / subinterfaces in the router. On Cisco platforms, the maximum number of subinterfaces is constrained by the max number of software IDBs. Consider the ASR1000, which supports up to 65,535 IDBs. This means any one router cannot terminate more than 64K MPLS VPNs.

Furthermore, it's possible to dump more routes in a router than the FIB can hold... some platforms are limited by memory required (particularly if you put full / partial BGP tables in a VRF... that explodes your memory requirements). If people are doing reasonable things (i.e. not dumping many thousands of routes into a single VPN), then this is not a big problem.

All that said, real per-router MPLS Scalability numbers are not constrained by:

  • Number of MPLS labels (as you mentioned, roughly 2**20)
  • Number of possible BGP Route Targets (2**48)Note 1

Note 1Routes are marked for inclusion in a specific MPLS VPN by setting a Route Target on the route; route targets are 48-bits wide, which gives you up to 2**48 possible route-targets

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  • great answer! "A router is the most basic building block for MPLS VPN network. Functionally, service providers use many routers to deploy MPLS VPNs. MPLS VPN customer separation can be implemented within the same router, or between different routers; it doesn't matter." Across the provider routers does the MPLS label have to stay globally unique? I thought that the top label added at the provider edge should stay the same until it get's stripped off at the provider edge again at destination. Based on ietf.org/proceedings/49/slides/ppvpn-7.pdf Apr 13, 2015 at 2:40

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