Nokia VPLS flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- VPLS definition
- A Layer 2 multipoint service that emulates an Ethernet bridge across an MPLS network, forwarding frames by MAC learning rather than IP lookup.
- VSI
- Virtual Switch Instance: the forwarding entity inside a VPLS service that holds the MAC table and performs bridging decisions.
- Split-horizon rule
- A frame received from a pseudowire is never forwarded back out another pseudowire, preventing loops in the full mesh.
- Full mesh requirement
- Classic VPLS requires a pseudowire between every pair of participating PEs for a given service ID to provide multipoint reachability.
- VPLS service creation
- Configure service vpls <service-id> customer <cust-id>; the same service ID must exist on every PE in the mesh.
- SAP binding command
- sap <port>:<encapsulation> attaches a customer port to the VPLS; encapsulation must match the customer handoff (null, dot1q, qinq).
- Spoke-SDP binding
- spoke-sdp <sdp-id>:<vc-id> create binds a pseudowire to the VPLS; the vc-id must match the far-end PE's local vc-id.
- Service MTU consistency
- Service MTU must match end to end; a mismatch causes large frames to drop silently while small frames pass.
- Pseudowire VC type
- VPLS pseudowires use VC type 19; the VC label identifies the VPLS instance at the egress PE.
- PW state machine
- A pseudowire moves to up when both the local SAP/SDP binding and the remote label mapping succeed; check with show service id sdp.
- PW status signaling
- LDP status TLV propagates remote failures so the local PE can react without waiting for MAC aging.
- PW MTU negotiation
- The negotiated pseudowire MTU is the minimum of local and remote values; mismatches cause silent drops for large frames.
- SAP definition
- Service Access Point: the local customer-facing attachment defined as port:encapsulation, such as 1/1/1:100.
- SDP definition
- Service Distribution Point: the tunnel toward a remote PE, defined by sdp-id and far-end IP address, carrying one or more pseudowires.
- SDP keepalives
- Hello messages that monitor tunnel liveness; without them a dead tunnel may not be detected until traffic fails.
- SAP encapsulation options
- Null (untagged), dot1q (single tag), qinq (double tag), and default; the choice must match the customer CPE.
- PW redundancy
- Primary and secondary spoke-SDPs to the same far-end PE; only one is active at a time, with failover on PW status or keepalive failure.
- MC-LAG
- Multi-chassis LAG lets two PEs share a customer attachment; only one is active per SAP at a time, providing access redundancy.
- MAC flush on topology change
- When a PW or SAP goes down, flush stale MAC entries to avoid blackholing traffic to a dead path.
- STP inside VPLS
- Customer STP BPDUs are tunneled transparently across the VPLS; the provider does not participate unless configured.
- show service id fdb
- Displays the MAC forwarding database, including MAC address, SAP or SDP interface, and aging state.
- show service sdp detail
- Confirms SDP far-end reachability, signaling state, keepalive status, and negotiated MTU.
- MAC flapping symptom
- Usually a Layer 2 loop or duplicate MAC; inspect FDB entries and STP state to localize the cause.
- PW down with LDP up
- Indicates a vc-id mismatch or label mapping failure; compare configuration on both ends of the pseudowire.
- Verification step order
- Verify underlay, then SDP, then PW, then SAP, then FDB, then flooding, then MTU end to end.
- Flooding verification
- Unknown unicast and broadcast should reach all other SAPs and PWs; split-horizon prevents forwarding back out the ingress PW.
- MTU mismatch symptom
- Small frames pass while large frames drop; test with large pings or frames to confirm end-to-end MTU.
- Baseline documentation
- Record known-good states and counters after commissioning so future faults can be compared against a snapshot.
- H-VPLS
- Hierarchical VPLS: spoke PEs connect to core PEs via a single spoke-SDP, reducing full-mesh requirements at the edge.
- Mesh scaling formula
- Pseudowire count grows as N*(N-1)/2 for N PEs in a full mesh, driving hardware and control-plane limits.
- IGMP snooping
- Prunes multicast to interested receivers, reducing unnecessary flooding and replication inside the VSI.
- SAP QoS policer
- Shapes and polices customer ingress at the SAP to protect the VSI and core from oversubscription and bursts.