MPLS basic interview questions and Answers

MPLS basic interview questions and Answers

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1. Networking Study Guide MPLS basic Questions and Answers Presented By - SIDDHARTH

2. Question - What is MPLS? MPLS is a forwarding mechanism which allows the router to forwarding packets based upon labels instead of IP Address. Answer Networking Study Guide

3. Question - Why MPLS is called as Multi Protocol Label Switching? MPLS is called as Multi Protocol because it supports all the protocols like Ethernet, Frame-Relay , X.25 and forwards packets based upon Labels. Answer Networking Study Guide

4. Question - Why MPLS is called as Layer 2.5 Technology ? MPLS is called as Layer 2.5 Technology because the router inserts MPLS Header in between Layer 2 and Layer 3 Header. Answer Networking Study Guide

5. Question - What are the applications of MPLS? MPLS supports following applications, – Unicast and multicast IP routing – VPN – TE – QoS – AToM Answer Networking Study Guide

6. Question - What are the advantages of MPLS? MPLS provides following advantages- MPLS decreases the forwarding overhead on the core routers.   MPLS supports multiple useful applications such as VPN,TE,QOS.  MPLS supports the forwarding of non-IP protocols, because MPLS technologies are applicable to any network layer protocol.  BGP Free Core Answer Networking Study Guide

7. Question - What is the protocol used by MPLS? MPLS uses TDP or LDP. Answer Networking Study Guide

8. Question - What is the port number used by LDP? LDP runs on port number 646 ( UDP port number for discovery of LDP neighbors and TCP port for exchanging the label  information. Answer Networking Study Guide

9. Question - What is LDP? LDP is a Labelling Protocol used to share label information with other routers and create label forwarding table. Answer Networking Study Guide

10. Question - What are the prerequisites to run MPLS? IP CEF IGP Protocol LDP router-id must be reachable Answer Networking Study Guide

11. Question - What is the default range of MPLS labels in Cisco routers ? 16 – 100000 is default range Answer Networking Study Guide

12. Question - What is the difference between P and PE router? P router doesn’t have Customer network routes where in PE router is having customer network routes. Another reason is P router doesn’t require MP- iBGP but for PE it is must. Answer Networking Study Guide

13. Question - What are the functions done by MPLS? PUSH ( Adding the Label) POP ( Removing the Label) SWAP ( Changing the Label) Answer Networking Study Guide

14. Question - Can I make my PE router as P? To make your PE router as P, you need to remove the BGP configurations and after that it will not participate with customer network. Answer Networking Study Guide

15. Question - What is Penultimate Hop Popping? Penultimate hop popping is a method of reducing label lookups on egress router. It is basically done by the one hop before the egress router. Answer Networking Study Guide

16. Question - What is TTL Propagation in MPLS? TTL Propagation is a method of copying the TTL value from IP Header to MPLS header. Answer Networking Study Guide

17. Question - What is the difference between Per Platform Label Space and Per Interface Label Space? Per Platform label space indicates the labels assigned based upon the destination network and Per Interface label space indicates the labels assigned based upon the destination network and interface. Answer Networking Study Guide

18. Question - What is LDP IGP Synchronization? LDP IGP Synchronization allows the router not to forward the packets on the link where ldp is down but IGP is enabled. Answer Networking Study Guide

19. Question - Is summarization is recommended in MPLS? No Answer Networking Study Guide

20. Question - What is the difference between Implicit Null and Explicit Null? Implicit Null ( Label 3) is used to indicate the other router to remove label before sending the packets ( PHP). Explicit Null ( Label 0) is used for QOS and disables PHP behavior. Answer Networking Study Guide

21. Question - What is the difference between VPN and MPLS? VPN is generally Virtual Private Network which could be configured by using GRE tunnels. In that if you want a full mesh than administrator need to setup n*n-1 tunnels. But in case of MPLS VPN, by default CPE works in full mesh form because of route target. Answer Networking Study Guide

22. Question - Two routers are having 4 equal cost links, how many ldp sessions will be established? One session Answer Networking Study Guide

23. Question - What are the different types of labels? Implicit Null, Explicit Null, Aggregate Label etc., Answer Networking Study Guide

24. Question - My LDP router id, OSPF router id and BGP router id is different, will it work to forward the traffic of customers or not? LDP router id and BGP router-id should be same if SP is using labels only for loopbacks. If labels are generated for each and every route then no problem at all. Answer Networking Study Guide

25. Question - Without route reflector can I implement MPLS? Yes, need to develop full mesh BGP Answer Networking Study Guide

26. Question - Does LDP require OSPF, IS-IS or BGP? Yes, IGP is required for IP Reachability Answer Networking Study Guide

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