Routing protocol for MPLS

Discussion in 'Cisco' started by bluetooth995, Oct 23, 2005.

  1. bluetooth995

    bluetooth995 Guest


    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)?

    bluetooth995, Oct 23, 2005
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  2. 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

, Oct 23, 2005
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  3. bluetooth995

    stephen Guest

    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
    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
    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

    a bunch of cisco info

    try RFC2547 for MPLS VPNs from a vendor neutral perspective.
    stephen, Oct 23, 2005
  4. bluetooth995

    Guest Guest

    Guest, Oct 24, 2005
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