Lab 08 — DMVPN EIGRP — Summarization, Stub, and Leak-Map

Active Nodes

Active routers: HUB-WC-1, SPK-WC-1, SPK-WC-2, SPK-WC-3

Key Concepts

EIGRP Stub and Leak-Map

EIGRP stub routing prevents spokes from being used as transit paths. A stub spoke advertises only connected and summary routes, never acting as a relay for other spokes. The stub connected summary configuration is standard for DMVPN spokes. The leak-map feature selectively allows specific prefixes to "leak" past the stub restriction — useful when a spoke has a secondary connection that should be advertised despite stub mode.

Summary Routes on DMVPN Hub

The hub summarizes all spoke prefixes into a single aggregate before advertising to the MPLS core. This reduces the routing table size on core routers and PE routers. The hub uses summary-address under the af-interface to inject the summary. Important: the hub must have at least one component route in the topology table for the summary to be advertised — if all spokes disconnect, the summary disappears automatically (unlike manual static routes).

Split-Horizon Impact

EIGRP split-horizon is disabled on the hub (no split-horizon) to allow the hub to re-advertise spoke routes back out the same tunnel interface to other spokes. Without disabling split-horizon, a spoke receiving a route via Tunnel0 would not see routes from other spokes learned via the same interface — breaking full-mesh spoke-to-spoke routing even with Phase 3 shortcuts.

Summarization Config

HUB-WC-1Summary injection toward MPLS core

router eigrp DMVPN-FABRIC
 address-family ipv4 unicast autonomous-system 100
  af-interface GigabitEthernet0/0
   summary-address 10.10.0.0 255.255.0.0
  af-interface Tunnel0
   no split-horizon

SPK-WC-1Stub with leak-map

router eigrp DMVPN-FABRIC
 address-family ipv4 unicast autonomous-system 100
  af-interface Tunnel0
   summary-address 10.10.11.0 255.255.255.0
  topology base
   stub connected summary
   leak-map ALLOWED-LEAKS
  network 10.10.11.0 0.0.0.255

ip prefix-list LEAK-LIST permit 10.10.11.128/25
route-map ALLOWED-LEAKS permit 10
 match ip address prefix-list LEAK-LIST

Verification

show ip eigrp topology summary

Expected: Summary routes shown with component count. Summary 10.10.0.0/16 on hub shows multiple component prefixes from spokes.

show ip eigrp neighbors detail

Expected: Spoke neighbors show "Stub Peer" flag on hub. Hub knows not to query stubs during DUAL computation.

show ip eigrp topology 10.10.11.128/25

Expected: Leaked prefix visible on hub despite spoke being in stub mode — leak-map worked.

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