Lab Objective
Configure Area 1 as a standard OSPF stub area, verify external routes disappear while inter-area routes remain, then upgrade it to a totally stubby area and verify inter-area routes disappear too, leaving only a default route.
Lab Purpose
This lab builds directly on the multi-area topology from the previous lab, adding a redistributed external route to demonstrate exactly how stub and totally stubby areas filter LSA types, discussed earlier in this series regarding OSPF area types.
Lab Topology
R1 (Area 1, leaf) ---- R2 (ABR) ---- R3 (Area 0, backbone)
Same topology as the previous summarization
lab, with one addition: R3 redistributes a
static route representing an external network
(203.0.113.0/24) into OSPF as a Type 5 LSATask 1: Configure the External Route on R3
Configure a static route to a dummy network on R3, then redistribute it into OSPF.
Task 2: Verify R1 Receives the External Route
Confirm R1's routing table initially shows the external route as an O E2 entry.
Task 3: Configure Area 1 as a Stub Area
Configure area 1 as a stub area on both R1 and R2.
Task 4: Verify the External Route Is Gone, Inter-Area Routes Remain
Confirm R1 no longer sees the external route, but still sees R3's directly connected networks as O IA entries, plus a new default route.
Task 5: Upgrade to a Totally Stubby Area
Add the no-summary keyword on R2 (the ABR) only.
Task 6: Verify Only the Default Route Remains
Confirm R1's routing table now shows only a default route and its own local networks.
Solution and Verification
R3(config)# ip route 203.0.113.0 255.255.255.0 null0
R3(config)# router ospf 1
R3(config-router)# redistribute static subnetsR1# show ip route ospf
O E2 203.0.113.0/24 [110/20] via 10.1.1.2
O IA 10.2.2.0/30 [110/128] via 10.1.1.2
-- The external route (O E2) is present,
-- confirming normal flooding before any
-- stub restriction is appliedR1(config)# router ospf 1
R1(config-router)# area 1 stub
R2(config)# router ospf 1
R2(config-router)# area 1 stub
-- Configuration must match on every router
-- in the area, discussed earlier in this
-- series regarding OSPF area typesR1# show ip route ospf
O*IA 0.0.0.0/0 [110/65] via 10.1.1.2
O IA 10.2.2.0/30 [110/128] via 10.1.1.2
-- The external route is gone entirely, and
-- a default route has appeared -- but the
-- inter-area route to R2-R3's link remains,
-- since stub only blocks Type 5, not Type 3R2(config)# router ospf 1
R2(config-router)# area 1 stub no-summary
-- Only the ABR needs this keyword --
-- R1 keeps its plain "area 1 stub" configurationR1# show ip route ospf
O*IA 0.0.0.0/0 [110/65] via 10.1.1.2
R1# show ip route
C 192.168.4.0/24 is directly connected, Loopback1
C 192.168.5.0/24 is directly connected, Loopback2
C 192.168.6.0/24 is directly connected, Loopback3
C 192.168.7.0/24 is directly connected, Loopback4
C 10.1.1.0/30 is directly connected, Serial0/0/0
O*IA 0.0.0.0/0 [110/65] via 10.1.1.2
-- Now even the 10.2.2.0/30 inter-area route
-- is gone -- R1's routing table contains
-- only its own directly connected networks
-- plus the single default route, the smallest
-- possible routing table for this topologyKey Takeaway
Progressing from a standard stub area to a totally stubby area removes one additional LSA type at each stage — first Type 5 external routes disappear, then Type 3 inter-area routes disappear too — with the no-summary keyword applied only at the ABR being the single configuration difference between the two, exactly as described in the underlying theory covered earlier in this series.