LAB 16 / 20

MPLS Traffic Engineering — TE Tunnels and RSVP

MPLS TERSVPExplicit PathAuto-Bandwidth

Active Nodes

16 MPLS TRAFFIC ENG MPLS TE — Active: CORE-1,CORE-2,CORE-3,CORE-4 See master topology for full 20-router diagram Active Nodes: CORE-1,CORE-2,CORE-3,CORE-4 MPLS TE CORE-1,CORE-2,CORE-3,CORE-4 Refer to lab.html for complete step-by-step configuration and verification commands for each active router Active Zone Inactive (dimmed) Ioannis (John) Alexander Konstas

Active routers: CORE-1, CORE-2, CORE-3, CORE-4, EDGE-1, EDGE-4

Key Concepts

MPLS TE Fundamentals

MPLS Traffic Engineering creates explicit LSPs (TE tunnels) that can be steered through specific paths, bypassing the shortest-path IGP. TE uses RSVP to signal and reserve bandwidth along the path. OSPF-TE extensions (opaque LSAs Type-10) flood link attributes (bandwidth, TE metric, admin groups) throughout the TE domain. CSPF (Constrained Shortest Path First) runs on the tunnel head-end, computing the path that satisfies constraints from the TE database.

RSVP Bandwidth Reservation

When a TE tunnel is signaled, the head-end sends an RSVP PATH message down the computed path. Each intermediate router sends a RESV message upstream, reserving the requested bandwidth. If any link cannot accommodate the reservation, RSVP rejects it and CSPF must find an alternative path. Bandwidth is pre-reserved even when no traffic flows through the tunnel — this guarantees the path is available but wastes capacity. Auto-bandwidth (auto-bw) measures actual tunnel traffic and adjusts the reservation periodically.

Explicit Path vs Dynamic Path

An explicit path specifies each hop the TE tunnel must traverse, either strictly (no deviation) or loosely (CSPF fills in intermediate hops). Explicit paths provide deterministic traffic engineering but break if a hop fails. Dynamic paths let CSPF compute the entire path using TE constraints — more resilient but less predictable. For the CCIE, understand both options and how fast-reroute (FRR) provides sub-50ms protection for TE tunnels.

TE Configuration

CORE-1TE tunnel head-end toward CORE-4
mpls traffic-eng tunnels
ip rsvp bandwidth 1000000

interface GigabitEthernet0/0
 mpls traffic-eng tunnels
 ip rsvp bandwidth 1000000

router ospf 1
 mpls traffic-eng router-id Loopback0
 mpls traffic-eng area 0

interface Tunnel10
 description TE-CORE1-TO-CORE4-EXPLICIT
 ip unnumbered Loopback0
 tunnel destination 10.255.1.4
 tunnel mode mpls traffic-eng
 tunnel mpls traffic-eng bandwidth 500000
 tunnel mpls traffic-eng path-option 10 explicit name CORE1-CORE4
 tunnel mpls traffic-eng path-option 20 dynamic
 tunnel mpls traffic-eng priority 4 4
 tunnel mpls traffic-eng auto-bw max-bw 1000000 frequency 3600

ip explicit-path name CORE1-CORE4 enable
 next-address 10.0.12.1
 next-address 10.0.24.1
 next-address 10.255.1.4

Verification

show mpls traffic-eng tunnels brief
Expected: Tunnel10 in "up/up" state. Shows signaled bandwidth, path-option used (explicit or dynamic), LSP ID.
show mpls traffic-eng link-management bandwidth-allocation
Expected: Each link shows current bandwidth allocation, unreserved bandwidth at each priority level (0-7).
show ip rsvp installed
Expected: Active RSVP reservations with source (CORE-1 tunnel IP), destination (CORE-4 loopback), bandwidth, and path.
show mpls traffic-eng autoroute
Expected: Routes steered through TE tunnel via autoroute. Shows destination prefixes using the tunnel.

Research and direction by Ioannis (John) Konstas; compiled and finalized with AI assistance.

Initial Configs — Load These First
⬇ CORE-1-initial.cfg ⬇ CORE-2-initial.cfg ⬇ CORE-3-initial.cfg ⬇ CORE-4-initial.cfg