Routing protocol for MPLS


A bit confuse with MPLS, Please help on this:

1) is ATM or FR use in MPLS? 2) what' s the routing protocol used? I know it used label switching by adding label on the header to aids in the routing of packets. 3) which layer does MPLS falls in OSI model , L2 or L3 ? 4) is MPLS considered a true leased line (Private line)?


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With my limited understanding, here are my answers:

1) No, it replaces ATM and FR. 2) Any interior routing protocol can be used. IS-IS, EIGRP, OSPF, RIP, etc. 3) I'd say it's layer 2. 4) Yes. I think you are referring to the popular product MPLS VPN. In which case, MPLS traffic can be designated as belonging to a specific customer.

Regards, Steve

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there are 2 basic flavours of MPLS. 1 is cell based and often uses the same hardware as ATM. The much more common flavour is packet based and is more about labels used as a "shim" layer between IP and the underlying layer 2.

labels are only used in the core network.

ATM / FR can be used as a transport - MPLS doesnt care what is under the IP layer at the edge.

my employer uses Frame relay encapsulation over E1 and n* 64k links to allow multiple VPNs to CE router.

theres a bunch of different bits that uses routing protocols

you need an IP routing protocol in the core (often IS-IS), a label distribution protocol, and protocols to distribute routes for different VPNs, often MP-BGP.

then you need routing from the edge (CE) routers into the label switching domain (PE routers) - we allow a mix here, including statics, BGP, EIGRP and RIP - the choice depends on the customer, the resilience requirements,and whether dynamic routes are needed in other bits - e.g. for links to other carriers.

you could argue both or neither. MPLS can carry IP, ATM, Frame, Ethernet traffic - which makes it layer 2 or lower - but it also has route style management, which makes it layer 3.

In reality it is sort of sideways on to the "customer" protocol stack, since it is there to allow multiple networks to share a common backbone. Similar arguments apply to an ATM switch core - the protocol standards are about the interfaces to devices at the cloud edge, not how the cloud operates internally.

No - but it can use a leased line.

Given some of the assumptions in these Qs - you need to go and find a good background on MPLS

an intro

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a bunch of cisco info
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try RFC2547 for MPLS VPNs from a vendor neutral perspective.

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