CCNP SP MPLS FAQ: MPLS Traffic Engineering
Q1. Name the advantages of MPLS traffic engineering
Answer: The advantages of MPLS traffic engineering include the following:
- Steering traffic so that all links in the network are used optimally
- Routing traffic around hotspots in the network
- Fast rerouting traffic around link and node failures
Q2. What are the components of MPLS traffic engineering?
Answer: Following are the components of MPLS traffic engineering:
- OSPF or IS-IS with TE extensions enabled
- Link attributes
- CSPF on the head end router
- TE Tunnel (Trunk) attributes
- Link manager
Q3. What are the attributes of the links enabled for traffic engineering?
Answer: The attributes of the links that are enabled for traffic engineering include these:
- Maximum reservable bandwidth
- Maximum reservable sub-pool bandwidth
- Attribute flags
- Traffic engineering metric
Q4. Name the six ways how you can forward IP traffic onto a TE tunnel.
Answer: You can forward IP traffic onto a TE tunnel by using the following:
- A static route
- Policy-based routing
- Forwarding adjacency
- Autoroute announce
- Direct mapping of AToM traffic onto TE tunnels
Q5. Name four kind of path options you can specify.
Answer: You can specify the following path options:
- Explicit with exclude address
- Explicit with loose next address
Q6. When you have an MPLS VPN network and TE tunnels that do not always have the PE routers as head/tail end routers, what do you need to have?
Answer: When you have an MPLS VPN network and TE tunnels that do not always have the PE routers as head/tail end routers, you need the following:
- LDP enabled on the links
- LDP targeted session on the TE tunnel if the tail end router is a P router
Q7. What is the LSR that is the head end router of a backup tunnel called?
Q8. Why do you need a link-state routing protocol for MPLS TE?
Q9. What is the feature called that has the IGP advertise TE tunnels as links?
Q10. How does the head end LSR of a TE tunnel know that the tunnel is fast rerouted over a backup tunnel?
Q11. Is it possible to restrict which prefixes have labels assigned to them so that label switching occurs to only certain destination prefixes?
Q12. What is the maximum frame size permissible across an Ethernet segment, and how can introducing MPLS affect forwarding across this type of media?
Q13. Which mechanism can you deploy to help determine the maximum allowable Path MTU for a packet? Path MTU discovery as described in RFC 1191.
Q14. What is the maximum size datagram, which does not support Path MTU discovery, that hosts can send?
Q15. What is the purpose of the DF bit?
Q16.In a frame-mode MPLS implementation, how are loops detected in the forwarding plane?
Q17. Is it possible to detect loops in the forwarding plane by using the TTL field in a cell-mode implementation of MPLS?
Q18. Using the hop-count TLV, an ATM-LSR can detect a loop in the control plane. What is the maximum number of permissible hops within a Cisco implementation, and can you change this maximum?
Q19. When using traceroute across an MPLS network, how can ICMP messages be forwarded back to the source of the traceroute?
Q20. What action does an aggregation LSR take if no label exists on an incoming packet?