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CCNP SP MPLS FAQ: Any Transport over MPLS

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CCNP SP MPLS FAQ: Any Transport over MPLS

Q1. Name the advantages of AToM for the service provider.

Answer: Following are the advantages of AToM for the service provider:

  • You can apply AToM over the existing MPLS infrastructure and protect existing investments.
  • You can provision AToM easily, because you do not need to deploy IP routing with the customer routers.
  • You decouple edge and core technologies in the MPLS network. No changes are needed for the P routers, and only the PE routers need to have the intelligence to run AToM.

Q2. Name the advantages of AToM for the customers of the service provider.

Answer: AToM has several advantages for the customers of the service provider:

  • The customer can keep the virtual leased line-like service between his routers.
  • The customer needs to make no configuration changes when migrating from the legacy network to the MPLS network.
  • The customer does not have to interact with the service provider at Layer 3 (IP routing). As such, the Layer 3 protocol of the customer can be anything; it is not limited to IP.

Q3. How many labels are used to forward AToM traffic, and what is the use of each of those labels?

Answer: Two labels forward AToM traffic. The top label, or tunnel label, identifies the PSN Tunnel (LSP) of the frame. In other words, it forwards the frame from the ingress PE to the egress PE. The bottom label, the VC label, identifies the pseudowire. In other words, the egress PE looks at the VC label; it uses the VC label to determine to which AC the frame should be forwarded.

Q4. Name three of the five functions of the control word.

Answer: The control word has five functions:

  • Padding small packets
  • Carrying control bits of the Layer 2 header of the transported protocol
  • Preserving the sequence of the transported frames
  • Facilitating the correct load balancing of AToM packets in the MPLS backbone network
  • Facilitating fragmentation and reassembly

Q5. Ethernet over MPLS can be done in two modes. What are they called?

Answer: The two modes of Ethernet over MPLS are Ethernet Port mode and Ethernet VLAN mode.

Q6. Which two modes exist to carry Frame Relay over MPLS?

Answer: DLCI-to-DLCI mode and Port-to-Port mode carry Frame Relay over MPLS.

Q7. What is the command to limit the number of ATM cells going into one frame in Packed Cell Relay mode?

Answer: cell-packing cells mcpt-timer timer limits the number of ATM cells going into one frame in Packed Cell Relay mode.

Q8. Which VC types (PW types) can EoMPLS use?

Answer: EoMPLS can use VC types 4 and 5.

Q9. What is the AToM signaling protocol between PE routers?

Answer: (Targeted) LDP is the AToM signaling protocol between PE routers.

Q10. What does the C-bit in the PW ID FEC TLV indicate?

Answer: If the C-bit is set, it indicates the use of the control word.
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