Lab Objective
Configure a branch router as an EIGRP stub advertising only connected networks, verify the hub router correctly identifies it as a stub and excludes it from EIGRP queries triggered elsewhere in the topology, and confirm the stub router itself never attempts to act as a transit path for other routers' traffic.
Lab Purpose
In a hub-and-spoke EIGRP topology with many branch routers, a single topology change at the hub can trigger EIGRP queries fanning out to every spoke, each of which must respond before the hub's DUAL computation can complete — a slow process at scale. EIGRP stub routing tells the hub explicitly not to query specific branch routers, since they have no alternate paths to offer, dramatically reducing query scope.
Lab Topology
Hub ---- R1 (branch, to be configured as stub)
Hub ---- R2 (another branch, not a stub,
will trigger a query)
R1's LAN: 192.168.50.0/24
Hub also connects to a third router R3
whose link failure will trigger the test
query in this labTask 1: Configure R1 as an EIGRP Stub
Configure R1 as an EIGRP stub advertising only connected routes.
Task 2: Verify the Hub Recognizes R1 as a Stub
Confirm the hub's neighbor table shows R1 flagged as a stub router.
Task 3: Verify R1's Advertised Routes Are Restricted
Confirm R1 only advertises its own connected LAN, not any routes it may have learned from elsewhere.
Task 4: Trigger a Topology Change Elsewhere in the Network
Simulate a link failure on R3's connection to the hub, an event that would normally trigger EIGRP queries.
Task 5: Verify R1 Is Excluded from the Query Process
Confirm debug output on the hub shows R1 was never queried as part of recomputing the affected route.
Solution and Verification
R1(config)# router eigrp 100
R1(config-router)# eigrp stub connected
-- "connected" restricts R1 to advertising
-- only its own directly connected
-- networks -- other stub variants exist
-- (static, summary, receive-only) for
-- different advertisement restrictions,
-- but connected is the most common for a
-- simple branch office scenarioHub# show ip eigrp neighbors detail
EIGRP-IPv4 Neighbors for AS(100)
H Address Interface Hold Uptime
0 10.1.1.2 Se0/0/0 12 00:02:15
Version 20.0/3.0, Retrans: 0, Retries: 0
Stub Peer Advertising ( CONNECTED )Routes
-- The hub explicitly recognizes R1 as
-- advertising only connected routes,
-- information learned during the initial
-- neighbor handshake itselfHub# show ip route eigrp | include 192.168.50
D 192.168.50.0/24 [90/2681856] via 10.1.1.2, Serial0/0/0
-- R1's connected LAN is still advertised
-- and learned normally -- stub restricts
-- WHICH routes R1 forwards onward from
-- other sources, not its own directly
-- connected networksHub# debug eigrp fsm
R3(config)# interface serial0/0/1
R3(config-if)# shutdown
-- (simulating R3's link failure, which
-- would normally cause the hub to query
-- neighbors for an alternate path to
-- whatever R3 was advertising)Hub# show ip eigrp topology active
-- (checking whether any routes entered
-- active/query state)
*Jun 25 14:22:01.204: DUAL: Find FS for
dest 192.168.60.0/24. FD is 2681856, RD
is 2681856
*Jun 25 14:22:01.208: DUAL: Peer 10.2.2.2:
metric 4294967295 not FS. Old FD: 2681856
*Jun 25 14:22:01.210: DUAL: New topology
entry for 192.168.60.0/24
*Jun 25 14:22:01.212: DUAL: RT installed
192.168.60.0/24 via 10.3.3.2
-- Notice the query process, and its
-- associated debug messages, involve only
-- R2's address (10.2.2.2) and R3's --
-- 10.1.1.2 (R1, the stub) never appears
-- anywhere in this exchange, confirming
-- it was correctly excluded from the
-- query fan-out entirelyKey Takeaway
Configuring a branch router as an EIGRP stub is a query-scope optimization built on an honest declaration: the branch is telling the hub "I have no alternate paths to offer, so never bother asking me during a query" — this is precisely why stub routers should only ever be configured on legitimate dead-end branches with no transit role, since applying it to a router that genuinely does have alternate paths would cause the hub to silently miss viable routing information during convergence.