The default-information originate Command
Format:
Router(config-router)# default-information originate [always] [metric value] [metric-type {1 | 2}]
What it does:
- Advertises
0.0.0.0/0into OSPF as a Type 5 External LSA - Marks the router as an ASBR (Autonomous System Boundary Router)
Basic Configuration
Scenario:
Edge router (R1) has Internet connectivity via 0.0.0.0/0 static route. Advertise it to internal routers.
R1 Configuration:
interface gi0/0
description Internet link
ip address dhcp
ip route 0.0.0.0 0.0.0.0 gi0/0
router ospf 1
default-information originate
Result:
- R1 advertises
0.0.0.0/0into OSPF - Other OSPF routers install the default route pointing to R1
Verification
Check Default Route on Internal Routers
R2 (internal router):
R2# show ip route
Gateway of last resort is 10.1.1.1 to network 0.0.0.0
O*E2 0.0.0.0/0 [110/1] via 10.1.1.1, 00:05:23, GigabitEthernet0/0
Key indicators:
- O* — OSPF default route
- E2 — External Type 2 (default metric type)
- via 10.1.1.1 — Points to R1
Check OSPF Database
R2:
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: 123
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: 0xABCD
Length: 36
Network Mask: /0
Metric Type: 2 (Larger than any link state path)
MTID: 0
Metric: 1
Forward Address: 0.0.0.0
External Route Tag: 0
Key fields:
- Link State ID: 0.0.0.0 — Default route
- Advertising Router: 1.1.1.1 — R1 is advertising it
- Metric Type: 2 — E2 route
The always Keyword
Problem:
By default, default-information originate only works if the router already has a default route in its routing table.
Scenario:
R1's Internet link goes down. Static default route is removed from routing table. OSPF stops advertising 0.0.0.0/0.
Result:
Internal routers lose their default route and can't reach the Internet.
Solution: Use always
Router(config-router)# default-information originate always
What always does:
- Advertises
0.0.0.0/0into OSPF even if the router doesn't have a default route - Useful when:
- You want to force a default route for traffic engineering
- You're using route tracking (advanced)
⚠️ Warning: Use carefully. If R1 advertises 0.0.0.0/0 but has no Internet connectivity, traffic black-holes.
Setting the Metric
Default metric: 1
To change it:
Router(config-router)# default-information originate metric 100
Use case:
You have two edge routers. One is primary (metric 10), one is backup (metric 100). Routers prefer the primary.
Example:
R1 (primary):
router ospf 1
default-information originate metric 10
R2 (backup):
router ospf 1
default-information originate metric 100
Result:
Internal routers prefer R1 (lower cost). If R1 fails, they fail over to R2.
Metric Type: E1 vs E2
OSPF external routes can be Type 1 (E1) or Type 2 (E2).
E2 (Default)
- Cost calculation: Fixed external cost (doesn't add internal OSPF cost)
- Example: If external metric is 10, cost is 10 everywhere
E1
- Cost calculation: External cost + internal OSPF cost
- Example: If external metric is 10 and internal cost to ASBR is 5, total cost is 15
Configuration:
Router(config-router)# default-information originate metric-type 1
When to use E1:
- Multiple exit points
- You want routers to pick the closest exit point
When to use E2 (default):
- Single exit point
- Simpler metric calculation
Dual Default Route (Redundancy)
Scenario:
Two edge routers for redundancy.
R1 (primary):
router ospf 1
default-information originate metric 10
R2 (backup):
router ospf 1
default-information originate metric 100
Internal router view:
R3# show ip route
O*E2 0.0.0.0/0 [110/10] via 10.1.1.1, GigabitEthernet0/0
[110/100] via 10.1.2.1, GigabitEthernet0/1
Result:
- Primary path via R1 (cost 10)
- Backup path via R2 (cost 100)
- If R1 fails, R3 uses R2
Conditional Default Route Advertisement (Advanced)
Scenario:
Only advertise default route if Internet is reachable.
Uses IP SLA tracking:
Step 1: Create IP SLA probe
ip sla 1
icmp-echo 8.8.8.8 source-interface gi0/0
frequency 30
ip sla schedule 1 life forever start-time now
Step 2: Track the probe
track 1 ip sla 1 reachability
Step 3: Conditional default route
ip route 0.0.0.0 0.0.0.0 gi0/0 track 1
router ospf 1
default-information originate
Result:
- If 8.8.8.8 is reachable, static default route exists
- OSPF advertises it
- If 8.8.8.8 is unreachable, static route removed, OSPF stops advertising
Common Mistakes
Mistake 1: Using always Without Understanding
Problem:
router ospf 1
default-information originate always
(Router has no Internet connectivity)
Impact:
Router advertises 0.0.0.0/0, but traffic black-holes.
Fix:
Only use always if you understand the implications. Otherwise, rely on static default route existence.
Mistake 2: Multiple ASBRs with Same Metric
Problem:
Both R1 and R2 advertise default route with metric 1.
Impact:
ECMP load-balancing. If one path is slower, traffic suffers.
Fix:
Set different metrics to prefer one router.
Mistake 3: Advertising Default into Stub Areas
Problem:
You manually configure default-information originate on an ABR in a stub area.
Impact:
Stub areas already get a default route automatically from the ABR. Manual config is redundant.
Fix:
Let stub area ABR auto-generate the default route.
Best Practices
1. Use Conditional Advertisement (IP SLA)
Prevent black-holing by only advertising when Internet is up.
2. Set Metrics for Redundancy
Primary: low metric
Backup: high metric
3. Document in Config
router ospf 1
! Advertise default route for Internet access
default-information originate metric 10
4. Monitor Default Route
Set up alerts if default route disappears from internal routers.
Summary
Now you know:
✅ Why default routes matter — Internet connectivity for internal routers
✅ default-information originate — Injects 0.0.0.0/0 into OSPF
✅ always keyword — Advertises even without default route in table
✅ Metric control — Prefer primary over backup
✅ E1 vs E2 — Metric calculation differences
✅ Conditional advertisement — IP SLA tracking for reliability
Next Step:
You've mastered single-area OSPF and default routes. Ready to scale? Learn How to Configure Multi-Area OSPF next.
Screenshot Suggestions:
- Topology: Edge router advertising default route to internal routers
show ip routeon internal router showing O*E2 routeshow ip ospf database externaloutput for 0.0.0.0- Dual edge router topology with primary/backup metrics
Internal Links:
- ← OSPF Passive Interfaces (Article 9)
- → Configuring Multi-Area OSPF (Article 12)
- → OSPF Redistribution (Article 29)
