Default Route Redistribution into OSPF

In most enterprise and branch networks, internal routers do not need to know every route on the internet — they only need to know how to reach internal networks and where to send everything else. The default route (0.0.0.0/0) is that "send everything else here" instruction. In an OSPF domain, one border router — typically the one connected to the ISP or upstream network — holds the default route and must share it with all other OSPF routers so they automatically learn where to forward unknown destinations.

The default-information originate command causes an OSPF router to generate a Type 5 External LSA for the 0.0.0.0/0 route and flood it throughout the entire OSPF domain. All routers that receive it install the 0.0.0.0/0 route as O*E2 — marking it as their Gateway of Last Resort. This eliminates the need to manually configure a default route on every router in the OSPF domain.

Before starting, complete OSPF Single-Area Configuration and OSPF Multi-Area Configuration to understand OSPF neighbour adjacency and LSA types. Review Static Route Configuration for default route fundamentals. For OSPF neighbour state details, see OSPF Neighbour States.

1. How Default Route Distribution Works in OSPF

The ASBR Role

When a router runs default-information originate, it becomes an ASBR (Autonomous System Boundary Router) — a router that injects external routes into the OSPF domain. The default route does not originate inside OSPF — it comes from a static route pointing toward an ISP or upstream device. The ASBR takes that external route and packages it into a Type 5 External LSA that floods to every router in every OSPF area.

Element Role Details
ASBR The router that generates and floods the default route LSA Identified by "It is an autonomous system boundary router" in show ip ospf
Type 5 External LSA The LSA that carries the 0.0.0.0/0 route across the OSPF domain Flooded to all areas — unlike Type 3 which stays between areas
O*E2 route How the default route appears on downstream routers O = OSPF, * = candidate default (Gateway of Last Resort), E2 = External Type 2
E2 metric The metric stays fixed at the ASBR's value regardless of topology distance Default metric for redistributed routes — metric does not accumulate as it crosses routers

default-information originate — Two Modes

Command Behaviour When to Use
default-information originate Generates the Type 5 LSA for 0.0.0.0/0 only if a default route already exists in the routing table (static or learned). If the default route disappears (ISP link down), the LSA is withdrawn automatically ✅ Production standard — safer. Downstream routers lose the default route when the ISP link goes down, preventing traffic black holes
default-information originate always Generates the Type 5 LSA for 0.0.0.0/0 unconditionally — even if no default route exists in the routing table ⚠️ Lab use or specific design only — downstream routers keep the default route even when the exit is gone, causing a black hole at the ASBR
default-information originate always — black hole risk: If the ISP link goes down and the static default route is removed from the routing table, always keeps advertising the default. Downstream routers continue forwarding traffic toward the ASBR — which drops it because it has no valid exit. Use always only in lab environments or when a secondary exit exists.

Type 5 LSA vs Type 3 LSA

Feature Type 3 Summary LSA Type 5 External LSA
Generated by ABR ASBR
Carries Inter-area OSPF routes Routes external to OSPF (static, BGP, redistributed)
Flooding scope Into adjacent areas only Entire OSPF domain — all areas
Route code O IA O E1 or O E2 (O*E2 for default)
Metric behaviour Cost increases as it crosses routers E2: fixed metric. E1: accumulates internal path cost

2. Lab Topology & Scenario

NetsTuts_R1 is the edge router connected to a simulated ISP (203.0.113.1). It runs OSPF with R2 and R3 in Area 0. The goal is for R2 and R3 to automatically learn the internet default route from R1 via OSPF — without any static routes configured on R2 or R3.

Internet / ISP 203.0.113.1 (ISP gateway) Gi0/0 WAN 203.0.113.2 OSPF Area 0 · Process 1 NetsTuts_R1 RID: 1.1.1.1 default-information originate ASBR Gi0/1 10.0.12.1 10.0.12.0/30 Gi0/0 10.0.12.2 Gi0/2 10.0.13.1 10.0.13.0/30 Gi0/0 10.0.13.2 ← default route via OSPF LSA Type-5 → NetsTuts_R2 RID: 2.2.2.2 Gi0/1: 192.168.20.1 NetsTuts_R3 RID: 3.3.3.3 Gi0/1: 192.168.30.1 192.168.20.0/24 LAN — PC2 192.168.30.0/24 LAN — PC3 OSPF adjacency / default-route propagation WAN / LAN link NetsTuts
Device Interface IP Address Description
NetsTuts_R1 Gi0/0 203.0.113.2 /30 WAN — link to ISP (203.0.113.1)
NetsTuts_R1 Gi0/1 10.0.12.1 /30 OSPF link to R2 — Area 0
NetsTuts_R1 Gi0/2 10.0.13.1 /30 OSPF link to R3 — Area 0
NetsTuts_R2 Gi0/0 10.0.12.2 /30 OSPF link to R1 — Area 0
NetsTuts_R2 Gi0/1 192.168.20.1 /24 LAN — PC2
NetsTuts_R3 Gi0/0 10.0.13.2 /30 OSPF link to R1 — Area 0
NetsTuts_R3 Gi0/1 192.168.30.1 /24 LAN — PC3

3. Step 1 — Configure OSPF on All Routers (Baseline)

First establish OSPF neighbour adjacency across all three routers in Area 0. The WAN interface (Gi0/0) on R1 is not included in OSPF — it connects to the ISP and should not participate in OSPF Hellos.

NetsTuts_R1 — OSPF (without default route yet)

NetsTuts_R1>en
NetsTuts_R1#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
NetsTuts_R1(config)#router ospf 1
NetsTuts_R1(config-router)#router-id 1.1.1.1
NetsTuts_R1(config-router)#auto-cost reference-bandwidth 1000
NetsTuts_R1(config-router)#network 10.0.12.0 0.0.0.3 area 0
NetsTuts_R1(config-router)#network 10.0.13.0 0.0.0.3 area 0
NetsTuts_R1(config-router)#exit
NetsTuts_R1(config)#end
NetsTuts_R1#wr
Building configuration...
[OK]
NetsTuts_R1#
Note that the WAN interface (203.0.113.2 on Gi0/0) is deliberately excluded from OSPF. The ISP does not run OSPF — this interface only needs a static default route pointing to 203.0.113.1, not an OSPF adjacency. The network statements use wildcard masks to match the correct interfaces.

NetsTuts_R2

NetsTuts_R2>en
NetsTuts_R2#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
NetsTuts_R2(config)#router ospf 1
NetsTuts_R2(config-router)#router-id 2.2.2.2
NetsTuts_R2(config-router)#auto-cost reference-bandwidth 1000
NetsTuts_R2(config-router)#network 10.0.12.0 0.0.0.3 area 0
NetsTuts_R2(config-router)#network 192.168.20.0 0.0.0.255 area 0
NetsTuts_R2(config-router)#passive-interface GigabitEthernet0/1
NetsTuts_R2(config-router)#exit
NetsTuts_R2(config)#end
NetsTuts_R2#wr
Building configuration...
[OK]
NetsTuts_R2#
%OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on GigabitEthernet0/0 from LOADING to FULL, Loading Done

NetsTuts_R3

NetsTuts_R3>en
NetsTuts_R3#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
NetsTuts_R3(config)#router ospf 1
NetsTuts_R3(config-router)#router-id 3.3.3.3
NetsTuts_R3(config-router)#auto-cost reference-bandwidth 1000
NetsTuts_R3(config-router)#network 10.0.13.0 0.0.0.3 area 0
NetsTuts_R3(config-router)#network 192.168.30.0 0.0.0.255 area 0
NetsTuts_R3(config-router)#passive-interface GigabitEthernet0/1
NetsTuts_R3(config-router)#exit
NetsTuts_R3(config)#end
NetsTuts_R3#wr
Building configuration...
[OK]
NetsTuts_R3#
%OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on GigabitEthernet0/0 from LOADING to FULL, Loading Done

4. Step 2 — Configure Static Default Route on R1

Before OSPF can distribute the default route, R1 must have a default route in its own routing table. The static default route points to the ISP's gateway (203.0.113.1): 

! ── Static default route toward ISP ──────────────────────
NetsTuts_R1(config)#ip route 0.0.0.0 0.0.0.0 203.0.113.1
NetsTuts_R1(config)#end
NetsTuts_R1#wr
Building configuration...
[OK]
NetsTuts_R1#

Verify the Default Route Exists on R1

NetsTuts_R1#show ip route static
Codes: S - static

Gateway of last resort is 203.0.113.1 to network 0.0.0.0

S*    0.0.0.0/0 [1/0] via 203.0.113.1
Gateway of last resort is 203.0.113.1 — the default route is installed on R1. The S* code means static candidate default. This is the prerequisite for default-information originate — without it, the command generates no LSA (unless always is used). See show ip route for full route code reference.

5. Step 3 — Inject Default Route into OSPF

With the static default route confirmed on R1, add default-information originate to R1's OSPF process. This single command makes R1 the ASBR and floods the 0.0.0.0/0 route as a Type 5 External LSA to R2 and R3: 

NetsTuts_R1(config)#router ospf 1
NetsTuts_R1(config-router)#default-information originate
NetsTuts_R1(config-router)#end
NetsTuts_R1#wr
Building configuration...
[OK]
NetsTuts_R1#
No other changes are needed on R2 or R3. As soon as R1 generates the Type 5 LSA, it is flooded to all OSPF neighbours and both downstream routers install the default route automatically.

always Keyword — Lab and Special Cases

! ── Force advertise even without a local default route ───
NetsTuts_R1(config-router)#default-information originate always
Use always in lab environments where no actual ISP link exists — the static default route pointing to a real next hop is not required. In production, avoid always unless you have a redundant exit path or accept that the ASBR will black-hole traffic when the ISP link fails.

Optional: Set a Custom Metric on the Default Route

! ── Advertise with a specific metric value ───────────────
NetsTuts_R1(config-router)#default-information originate metric 50 metric-type 1
By default the metric is 1 and metric-type is E2 (fixed). Using metric-type 1 changes it to E1 — the internal OSPF path cost accumulates on top of the external metric as the route crosses routers. E1 is useful when two ASBRs advertise the same default and you want routers to prefer the closer one. E2 (default) keeps the metric uniform — all downstream routers see the same cost regardless of their distance from the ASBR.

Dual ASBR Redundancy — Two Default Routes

In networks with two edge routers (R1 and R1B), both can run default-information originate. Downstream routers receive two Type 5 LSAs for 0.0.0.0/0 and select the best path based on metric. Using metric-type E1 on both ASBRs ensures routers naturally prefer the closest exit: 

! ── On R1 (primary ISP) ──────────────────────────────────
NetsTuts_R1(config-router)#default-information originate metric 10 metric-type 1

! ── On R1B (backup ISP, higher metric = less preferred) ──
NetsTuts_R1B(config-router)#default-information originate metric 100 metric-type 1
R1 is preferred (metric 10 + internal path cost). R1B is used only when R1's link fails and its Type 5 LSA is withdrawn. Downstream routers automatically switch to R1B with no manual intervention.

6. Verification

show ip route — R2 Receives O*E2

NetsTuts_R2#show ip route
Codes: C - connected, L - local, O - OSPF, E2 - OSPF external type 2

Gateway of last resort is 10.0.12.1 to network 0.0.0.0

O*E2  0.0.0.0/0 [110/1] via 10.0.12.1, 00:01:22, GigabitEthernet0/0

      10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
C        10.0.12.0/30 is directly connected, GigabitEthernet0/0
L        10.0.12.2/32 is directly connected, GigabitEthernet0/0
O        10.0.13.0/30 [110/2] via 10.0.12.1, GigabitEthernet0/0

      192.168.20.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.20.0/24 is directly connected, GigabitEthernet0/1
L        192.168.20.1/32 is directly connected, GigabitEthernet0/1
O        192.168.30.0/24 [110/2] via 10.0.12.1, GigabitEthernet0/0
Gateway of last resort is 10.0.12.1 to network 0.0.0.0 — confirmed. The route O*E2 0.0.0.0/0 [110/1] via 10.0.12.1 is the redistributed default route received from R1. Any packet from PC2 destined for the internet will be forwarded to R1 (10.0.12.1) which then sends it to the ISP.

show ip route — R3 Receives O*E2

NetsTuts_R3#show ip route
Codes: O - OSPF

Gateway of last resort is 10.0.13.1 to network 0.0.0.0

O*E2  0.0.0.0/0 [110/1] via 10.0.13.1, 00:01:18, GigabitEthernet0/0
R3 also receives the default route via its own link to R1 (10.0.13.1). Both R2 and R3 point back to R1 as the Gateway of Last Resort — without any static route configuration on R2 or R3. This is the goal.

show ip ospf — R1 Identified as ASBR

NetsTuts_R1#show ip ospf
 Routing Process "ospf 1" with ID 1.1.1.1
 ...
 It is an autonomous system boundary router
 Redistributing External Routes from,
   static, includes subnets in redistribution
 ...
"It is an autonomous system boundary router" — IOS explicitly confirms R1 has become an ASBR. The line "Redistributing External Routes from, static" confirms the source of the redistributed default route.

show ip ospf database external — Type 5 LSA

NetsTuts_R1#show ip ospf database external

            OSPF Router with ID (1.1.1.1) (Process ID 1)

                Type-5 AS External Link States

  LS age: 87
  Options: (No TOS-capability, DC, Upward)
  LS Type: AS External Link
  Link State ID: 0.0.0.0 (External Network Number)
  Advertising Router: 1.1.1.1
  LS Seq Number: 80000001
  Checksum: 0x7D61
  Length: 36
  Network Mask: /0
  Metric Type: 2 (Larger than any link state path)
  Metric: 1
  Forward Address: 0.0.0.0
  External Route Tag: 0
The Type 5 LSA for the default route is visible. Key fields: Link State ID: 0.0.0.0 (the default route destination), Advertising Router: 1.1.1.1 (R1 is the ASBR generating this LSA), Metric Type: 2 (E2 — fixed metric), Metric: 1 (the cost advertised). This LSA is flooded to every router in the OSPF domain.

show ip ospf database external — on R2

NetsTuts_R2#show ip ospf database external

            OSPF Router with ID (2.2.2.2) (Process ID 1)

                Type-5 AS External Link States

  LS age: 112
  Advertising Router: 1.1.1.1
  Link State ID: 0.0.0.0
  Network Mask: /0
  Metric Type: 2
  Metric: 1
R2 holds the same Type 5 LSA in its LSDB — the Advertising Router field confirms it came from R1 (1.1.1.1). R2 did not generate this LSA — it received it via OSPF flooding from R1.

ping 8.8.8.8 from R2 — End-to-End Verification

NetsTuts_R2#ping 8.8.8.8 source GigabitEthernet0/1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 8.8.8.8, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 18/20/22 ms
NetsTuts_R2#
End-to-end internet reachability confirmed from R2's LAN interface. R2 has no static default route — all internet-bound traffic is forwarded via the O*E2 default route pointing to R1 (10.0.12.1), which then forwards to the ISP (203.0.113.1).

Verification Command Summary

Command What to Look For Run On
show ip route "Gateway of last resort is..." and O*E2 0.0.0.0/0 entry R2, R3 (downstream)
show ip route static S* 0.0.0.0/0 — confirms the prerequisite default route exists on the ASBR R1 (ASBR)
show ip ospf "It is an autonomous system boundary router" — confirms ASBR role R1 (ASBR)
show ip ospf database external Type 5 LSA for 0.0.0.0, Advertising Router = ASBR's RID, Metric Type 2 Any router in the domain
show ip ospf neighbor All neighbours FULL — prerequisite for LSA flooding to work All routers
ping [public IP] Successful pings confirm end-to-end internet reachability via OSPF default R2, R3 (downstream)

7. Troubleshooting Default Route Distribution Issues

Problem Symptom Cause Fix
O*E2 route not appearing on downstream routers show ip route on R2/R3 shows no Gateway of Last Resort and no 0.0.0.0/0 entry No static default route on R1 — default-information originate (without always) requires a default route to exist first Add ip route 0.0.0.0 0.0.0.0 [next-hop] on R1. Verify with show ip route static — confirm S* 0.0.0.0/0 exists. Then re-check downstream routers.
Default route present but internet traffic fails O*E2 route exists on R2/R3 but pings to 8.8.8.8 fail R1's WAN interface is down or the ISP next hop (203.0.113.1) is unreachable Verify R1's WAN interface: show ip interface brief. Ping 203.0.113.1 from R1. Check ISP link status.
Default route withdrawn when ISP link flaps O*E2 disappears from R2/R3 during ISP instability Expected behaviour — default-information originate (without always) withdraws the LSA when the static default route disappears This is correct production behaviour — prevents black holes. If stability is needed regardless, use always with a secondary exit path.
Two ASBRs both advertising default — wrong one selected Traffic exits via the backup ISP when primary is up Both ASBRs using E2 (fixed metric) — downstream routers see identical cost and may use either ASBR Switch both to metric-type E1 with different base metrics. Primary ASBR uses lower metric. Internal OSPF path cost accumulates, naturally directing traffic to the closer/preferred ASBR.
R1 not identified as ASBR show ip ospf on R1 does not say "autonomous system boundary router" default-information originate was not entered, or was entered but no default route exists (and always was not used) Verify the command exists in show running-config | section router ospf. Check that ip route 0.0.0.0 0.0.0.0 is in the routing table.
Default route not reaching routers in non-backbone areas Routers in Area 1 or Area 2 have no O*E2 default route The area is configured as a stub area — stub areas block Type 5 External LSAs by design Stub areas receive a Type 3 default route instead. If the area must receive the specific ASBR's default, change it from stub to normal area. See OSPF Multi-Area Configuration.

Key Points & Exam Tips

  • default-information originate causes the OSPF router to generate a Type 5 External LSA for 0.0.0.0/0 — flooding the default route to every router in the OSPF domain.
  • The command requires a default route to already exist in the routing table (S* 0.0.0.0/0). Without it, no LSA is generated. Use always to override this requirement. See Static Route Configuration for how to add the prerequisite default route.
  • The router running default-information originate becomes an ASBR — confirmed by "It is an autonomous system boundary router" in show ip ospf.
  • Downstream routers install the default route as O*E2 0.0.0.0/0. The asterisk marks it as the Gateway of Last Resort. The E2 metric stays fixed regardless of hop count. Verify with show ip route.
  • default-information originate always advertises 0.0.0.0/0 even without a local default route — useful in labs but risky in production as it can create black holes when the ISP link is down.
  • Use metric-type 1 (E1) instead of the default E2 when two ASBRs both advertise the default route — E1 accumulates internal path cost, directing each router to naturally prefer the closest exit.
  • The WAN interface connecting to the ISP should not be included in the OSPF network statement — it does not participate in OSPF Hellos or LSAs. Use passive-interface on LAN-only interfaces.
  • show ip ospf database external confirms the Type 5 LSA exists — key fields are Link State ID (0.0.0.0), Advertising Router (ASBR's RID), and Metric Type (1 or 2).
  • Stub areas block Type 5 External LSAs — routers in stub areas cannot receive the OSPF default route via default-information originate. They receive a Type 3 summary default instead.
  • On the CCNA exam: know the difference between default-information originate (conditional) and default-information originate always (unconditional), and what O*E2 means in the routing table. For OSPF troubleshooting, see Troubleshooting OSPF Neighbour Adjacency.
Next Steps: With the default route distributed across the OSPF domain, continue to DHCP Server Configuration to dynamically assign IP addresses including the correct default gateway to hosts on each subnet. For filtering which routes OSPF distributes, explore OSPF Single-Area Configuration and route filtering with distribute-lists. To verify all OSPF route sources and metrics in one view, use show ip protocols. For inter-area route efficiency, see Route Summarisation and Aggregation. For deeper OSPF troubleshooting, see Troubleshooting OSPF Neighbour Adjacency.

TEST WHAT YOU LEARNED

An engineer configures default-information originate on R1 but R2 and R3 do not receive a default route. show ip route static on R1 shows no output. What is the cause?

Correct answer is C. default-information originate is conditional — it checks whether a default route (0.0.0.0/0) exists in the local routing table before generating the Type 5 LSA. If show ip route static returns no output, there is no static default route. The fix is to add ip route 0.0.0.0 0.0.0.0 [ISP-next-hop] on R1. Alternatively, use default-information originate always to bypass the check — though this is not recommended in production.

What does the code O*E2 mean when it appears in a router's routing table?

Correct answer is A. Breaking down O*E2: O identifies the source as OSPF. The asterisk (*) marks this specific route as the candidate default — the Gateway of Last Resort — meaning packets with no more specific match are forwarded using this route. E2 means External Type 2, indicating the route was redistributed from outside the OSPF AS (in this case from a static route via default-information originate) and the metric remains constant at the value set by the ASBR, regardless of internal path cost.

What is the risk of using default-information originate always in a production network?

Correct answer is D. The always keyword bypasses the prerequisite check — it unconditionally advertises the default route regardless of whether a valid exit path exists. In production, when the ISP link goes down, the static default route is typically removed from the routing table. Without always, the Type 5 LSA is withdrawn and downstream routers know there is no exit — they drop packets appropriately. With always, they keep forwarding to the ASBR which silently drops everything — a black hole that is harder to diagnose.

Why should the WAN interface (connecting R1 to the ISP) be excluded from OSPF network statements?

Correct answer is B. The ISP is an external entity — it does not participate in the customer's OSPF process. If the WAN interface IP is included in an OSPF network statement, R1 starts sending OSPF Hello packets out the WAN interface toward the ISP. This serves no purpose (the ISP router won't respond with OSPF Hellos), wastes resources, and potentially advertises the WAN subnet (203.0.113.0/30) as an OSPF internal route — information that is irrelevant to internal routers. Exclude the WAN interface and use a static default route to reach the ISP instead.

A router in an OSPF stub area is not receiving the O*E2 default route from the ASBR. What is the reason?

Correct answer is D. One of the defining characteristics of OSPF stub areas is that Type 5 External LSAs are not allowed inside them. This blocks all externally redistributed routes — including the default route generated by default-information originate. To compensate, the ABR automatically generates a Type 3 Summary LSA for 0.0.0.0/0 into the stub area, providing a default route to internal routers. This stub-area default appears as O IA 0.0.0.0/0 rather than O*E2.

Two ASBRs (R1 and R1B) both run default-information originate with the default E2 metric of 1. How do downstream routers choose between the two default routes?

Correct answer is A. With E2 metrics identical, OSPF uses the cost to reach the forwarding address or ASBR as a secondary tiebreaker. If costs are also equal, the higher ASBR Router ID wins. This makes E2 multi-ASBR scenarios unpredictable — routers may not prefer the "better" exit. The solution is to use metric-type E1 with different base metrics: the primary ASBR uses a lower metric so downstream routers naturally prefer it, and the accumulated internal path cost automatically directs each router toward its closest exit when both ASBRs have equal base metrics.

What command on R1 confirms it has become an ASBR after default-information originate is configured?

Correct answer is C. show ip ospf is the command that explicitly identifies a router's role in the OSPF hierarchy. For an ASBR, it states "It is an autonomous system boundary router" and lists the source of the redistributed routes ("Redistributing External Routes from, static"). This is the definitive confirmation command — analogous to how the same command says "It is an area border router" for ABRs. show ip ospf database external then shows the actual Type 5 LSA being generated.

What is the difference between metric-type E1 and metric-type E2 for a redistributed default route?

Correct answer is B. E2 (the default) has a fixed metric — it does not change as the route traverses routers. Every router in the OSPF domain sees the same cost (e.g., 1) regardless of how far they are from the ASBR. E1 adds the internal OSPF path cost to the external metric — a router 5 hops from the ASBR sees a higher cost than a router 1 hop away. This makes E1 useful for dual-ASBR scenarios where you want each router to naturally prefer the nearest exit point, while E2 is simpler when path cost proximity doesn't matter.

R2 has O*E2 0.0.0.0/0 via 10.0.12.1 in its routing table. The link between R1 and R2 (10.0.12.0/30) goes down. What happens to the default route on R2?

Correct answer is D. When the direct link between R1 and R2 goes down, OSPF detects the failure when R2's Dead timer expires (40 seconds by default on Ethernet) or immediately if R2 detects the interface going down at Layer 1. R2 removes the neighbour adjacency with R1 and re-runs SPF. Since the only path to R1 was the direct link (in this topology), R2 has no remaining path to the ASBR — the O*E2 default route is removed. R2's Gateway of Last Resort disappears until connectivity is restored or an alternative path exists.

Which command on a downstream router confirms that the Type 5 External LSA for the default route was originated by R1 (RID 1.1.1.1) and not generated locally?

Correct answer is B. show ip ospf database external displays all Type 5 External LSAs in the LSDB. The Advertising Router field explicitly identifies which router generated the LSA — in this case 1.1.1.1 (R1). This is the definitive way to confirm the ASBR source of a redistributed route. If the Advertising Router field shows the local router's RID, it would mean the local router itself is the ASBR. This command is essential for multi-ASBR troubleshooting to identify which exit point each default route advertisement comes from.

Related Topics & Step-by-Step Tutorials

Related concepts and next steps:

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