1. What is MPLS?
MPLS stands for Multiprotocol Label Switching. It is a protocol used in telecommunications and computer networking to speed up and shape network traffic flows.
2. What is the main purpose of MPLS?
The main purpose of MPLS is to improve the speed and efficiency of network traffic routing by using labels to make forwarding decisions rather than complex IP route lookups.
3. How does MPLS differ from traditional IP routing?
MPLS uses labels to make forwarding decisions, while traditional IP routing relies on IP address lookups in routing tables.
4. What are the benefits of using MPLS?
MPLS provides benefits like traffic engineering, improved quality of service (QoS), faster packet forwarding, and simplified network management.
5. Explain the concept of an MPLS label.
An MPLS label is a short, fixed-length identifier that is used to determine how packets should be forwarded through an MPLS network.
6. What is an MPLS label stack?
An MPLS label stack is a series of MPLS labels that are stacked together to represent a path for a packet to follow through the MPLS network.
7. What are the three labels used in an MPLS label stack?
The three labels are the top label, the outer label, and the inner label.
8. What is the purpose of the top label in an MPLS label stack?
The top label is used for forwarding decisions within the MPLS network.
9. What is the purpose of the outer label in an MPLS label stack?
The outer label is used for routing the packet from the ingress router to the egress router.
10. What is the purpose of the inner label in an MPLS label stack?
- The inner label is used for switching the packet within the egress router to its final destination.
11. What is the MPLS header structure?
- The MPLS header consists of a 20-bit label, a 3-bit Experimental (EXP) field, a 1-bit Bottom of Stack (S) flag, a 8-bit Time-to-Live (TTL) field, and a 3-bit Traffic Class field.
12. What is a Forwarding Equivalence Class (FEC) in MPLS?
- A Forwarding Equivalence Class (FEC) is a group of packets that are forwarded in the same way through an MPLS network. Packets belonging to the same FEC are assigned the same MPLS label.
13. What is an MPLS label distribution protocol?
- MPLS label distribution protocols are used to distribute MPLS labels and forwarding information throughout an MPLS network. Examples include LDP (Label Distribution Protocol) and RSVP-TE (Resource Reservation Protocol - Traffic Engineering).
14. Explain the operation of LDP (Label Distribution Protocol).
- LDP distributes labels between routers based on their IP routing tables. It uses a TCP connection between neighbors to exchange label mappings.
15. What is MPLS tunneling?
- MPLS tunneling involves encapsulating packets in MPLS labels to create virtual paths or tunnels through an MPLS network.
16. What is MPLS VPN (Virtual Private Network)?
- MPLS VPN is a technology that allows multiple virtual private networks to be overlaid on top of a shared MPLS network, providing secure communication between different customer sites.
17. What is the difference between MPLS Layer 2 VPN and MPLS Layer 3 VPN?
- MPLS Layer 2 VPN is used for point-to-point and multipoint Layer 2 connectivity, while MPLS Layer 3 VPN provides routed, Layer 3 connectivity between customer sites.
18. What is the purpose of the MPLS label "Implicit Null"?
- The Implicit Null label is used to indicate that the label should be popped (removed) when forwarding a packet. It's often used in MPLS networks to optimize label stack depth.
19. What is MPLS traffic engineering (MPLS TE)?
- MPLS traffic engineering is a mechanism to optimize traffic distribution in an MPLS network by specifying explicit paths for traffic flows.
20. What is the purpose of the MPLS RSVP-TE protocol?
- RSVP-TE is used for MPLS traffic engineering to establish explicit paths for labeled traffic flows and allocate network resources accordingly.
21. What is Penultimate Hop Popping (PHP) in MPLS?
- Penultimate Hop Popping is a technique where the MPLS label is removed at the penultimate router (second-to-last) before reaching the egress router. This reduces label stack depth.
22. Explain the difference between MPLS PHP and Explicit Null label.
- MPLS PHP removes the label at the penultimate hop, while the Explicit Null label is a label that explicitly indicates that the label should be popped.
23. What is MPLS Fast Reroute (FRR)?
- MPLS Fast Reroute is a mechanism used to quickly reroute traffic in case of link or node failures in an MPLS network to minimize downtime.
24. What is MPLS LSR (Label Switch Router)?
- An MPLS LSR is a router that is capable of performing label switching within an MPLS network.
25. What is MPLS LSP (Label Switched Path)?
- An MPLS LSP is a path through an MPLS network that is defined by a series of labels and routing decisions.
26. Explain the MPLS Control Plane vs. Data Plane.
- The Control Plane is responsible for label distribution and signaling, while the Data Plane is responsible for forwarding packets based on the labels.
27. What is MPLS TTL propagation behavior?
- In MPLS, the TTL (Time-to-Live) value in the MPLS header is decremented at each hop, just like in traditional IP routing.
28. What is MPLS PHP TTL propagation?
- In MPLS PHP (Penultimate Hop Popping), the TTL value is propagated from the incoming label to the outgoing label.
29. What is the role of the MPLS Penultimate Hop?
- The Penultimate Hop is the router just before the egress router in an MPLS network. Its role is to perform actions such as Penultimate Hop Popping (PHP) and TTL propagation.
30. Explain the concept of MPLS DiffServ-aware traffic engineering.
- MPLS DiffServ-aware traffic engineering is a technique that takes into account Differentiated Services (DiffServ) markings in IP packets to optimize traffic engineering decisions.
31. What is MPLS Push and Swap operation?
- In MPLS Push and Swap, a new label is pushed onto the label stack, and the old label is swapped out, effectively changing the label used for forwarding.
32. What is MPLS Explicit Routing?
- MPLS Explicit Routing allows for the specification of a precise path for MPLS traffic through the network, bypassing the usual dynamic routing.
