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Routing & Switching · Intermediate

Label Switch Router (LSR)

Any router that forwards MPLS packets based on labels; core LSRs are called P routers.

Definition

An LSR swaps the incoming top label for an outgoing label based on its LFIB. Edge LSRs (LERs) push labels on ingress and pop on egress.

Example

show mpls forwarding-table on an IOS XE P router.

Exam tip

P routers do not need customer or BGP routes in an MPLS L3VPN; they only know IGP and labels.

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