MPLS case studies
MPLS · Put your knowledge to work in context.
The MPLS exam validates practical knowledge of Multiprotocol Label Switching as it is deployed in service provider and large enterprise networks. It suits network engineers, design and operations staff, and candidates moving from pure IP routing into label-switched transport, L3VPN and L2VPN services, traffic engineering, and modern Segment Routing evolution. Expect the exam to test why labels exist and how they are pushed, swapped, and popped; how LDP and RSVP-TE distribute and signal label bindings; how VRF tables, MP-BGP, and route targets build L3VPNs; how pseudowires and VPLS carry Layer 2; how TE tunnels and QoS classes shape traffic; how fast reroute and protection restore forwarding; how to verify and troubleshoot a label path with show and trace commands; and how Segment Routing changes the control plane. Preparation should combine a solid IP routing base (OSPF or IS-IS, BGP) with hands-on lab work on a router or virtual platform: build an LDP core, add a VRF and MP-BGP VPN, then a TE tunnel with FRR, and read the label stack at each hop. The MPLS case studies are 5 cases and about 2,707 words.
1Implicit Null Erases EXP Before the Congested Egress
A carrier core runs LDP. PE1 classifies voice at ingress: DSCP EF is mapped to MPLS EXP 5, and core queuing trusts EXP.
572 words, about 3 min2VPNv4 Route Arrives Without Its Route Target
A route reflector (RR) serves PE1 and PE2 in AS 65000. PE2 exports VRF BLUE prefix 10.20.20.0/24 with RD 65000:2 and route target 65000:100.
521 words, about 3 min3Pseudowire Up but 1500-Byte Frames Disappear
A carrier provides an LDP-signalled VPWS between PE1 and PE2. Both PEs show VC ID 200 up with local and remote labels assigned.
560 words, about 3 min4Bypass Tunnel Is Ready but Node Failure Still Drops Traffic
A TE tunnel from PE1 to PE2 traverses P1-P2-P3. P1 is the point of local repair.
519 words, about 3 min5New SRGB Turns a Prefix-SID into a Black Hole
A network is migrating from LDP to SR-MPLS. P1 and P2 use SRGB 16000-23999.
535 words, about 3 min