First, the essential ideas
- OSPFv3
- OSPF version 3 retains link-state routing, areas and SPF while changing protocol structures for IPv6. This lesson uses its IPv6 function; later address-family extensions are outside the lab.
- 32-bit router ID
- A dotted-decimal OSPF identity that remains 32 bits even when all carried routes and interfaces are IPv6. It does not assign an IPv4 address.
- Link-local next hop
- An adjacent IPv6 router address associated with an output interface. OSPFv3 normally uses link-local sources for link communication and learns scoped next-hop information.
- Point-to-point and broadcast
- Two OSPF network types. Point-to-point forms direct full adjacency without DR/BDR; broadcast elects those roles on a shared segment.
- Link LSA and prefix LSA
- A Link LSA describes link-specific information including a link-local address. Intra-Area-Prefix LSAs carry IPv6 prefixes associated with the topology.
- Process and instance IDs
- The Cisco process number is local configuration bookkeeping. The on-link OSPFv3 Instance ID separates protocol conversations and must be compatible; this lab leaves it at its default.
- Area mismatch
- Neighbor-facing interfaces assigned to different OSPF areas reject each other's intended adjacency. Correct IP addressing alone does not correct the mismatch.
- Full and learned route
- Full indicates completed adjacency synchronization. A learned OSPF route and a successful fixed-source probe provide separate evidence for the desired destination.
Transfer the reasoning from OSPFv2, not every command verbatim. Area, cost, neighbor and router-ID concepts remain useful, but this lab uses the classic IOS ipv6 router ospf and ipv6 ospf command family consistently. Do not mix it with the newer router ospfv3 address-family configuration style.
See the idea
One area with two OSPFv3 network types
Verify the direct Gi0/1 adjacency before the shared VLAN adds another R1-R2 relationship.
Direct Gi0/1 link
First verify R1 and R2's point-to-point adjacency and complete loopback exchange.
What this model leaves out: Four actual cables only. Loopback endpoints reside inside their routers. Direct-link and broadcast verification are separate stages; no unnamed gateway or measured convergence is implied.
Full visual explanation and references
R1 and R2 have a direct Gi0/1 link. R1, R2 and R3 also attach through Gi0/0 to SW1 VLAN 36. Each router owns its explicitly named loopback endpoint.
Four actual cables only. Loopback endpoints reside inside their routers. Direct-link and broadcast verification are separate stages; no unnamed gateway or measured convergence is implied.
- Direct Gi0/1 link
First verify R1 and R2's point-to-point adjacency and complete loopback exchange.
www.cisco.com - Shared Gi0/0 LAN
Then establish R1 DR, R2 BDR and R3 DROTHER on the separate VLAN 36 broadcast segment.
www.rfc-editor.org - R3 endpoint verification
R3's source loopback reaches R1's loopback through the shared LAN; restore area 0 after the fault.
www.cisco.com
One idea at a time
Start with something familiar.
Label R1's identity 1.1.1.1, loopback 2001:db8:1::1 and LAN neighbor address fe80::1 in separate columns. None is interchangeable with the others.
Why learn this?
An IPv4-looking router ID in an IPv6-only lab is not a mistake. Confusing identity with reachability can send troubleshooting toward an unassigned address instead of the actual remote prefix.
An everyday comparison
An employee can retain a short staff number after the office changes to a new mailing-address format. The identity and the delivery address serve different purposes.
What happens in a network
The staff number resembles OSPF's router ID. The IPv6 endpoint is the delivery destination, while a link-local neighbor identifies the immediate local handoff.
Where the comparison stopsOSPF identities are protocol fields, not human account credentials. The analogy does not reproduce link scope, database exchange or routing decisions.
Follow one worked example
- Build the direct cable first.
R1 and R2 form point-to-point adjacency on Gi0/1 and learn each other's loopback.
Why: Verification occurs before the broadcast link can provide an alternative path.
- Add the shared VLAN in order.
R1 becomes DR, R2 joins as BDR and R3 joins with priority 0.
Why: Both required network types are now actually configured, not inferred from a comparison.
- Move only R3's LAN into the wrong area.
R3 loses its only OSPFv3 path while the local IPv6 LAN remains present.
Why: This isolates the routing-protocol mismatch from basic addressing.
Your first small task
Explain why R1 can have router ID 1.1.1.1 without any configured IPv4 interface and still learn 2001:db8:2::1/128.
Show a hint
Look at the type of field, not just whether its text contains dots or colons.
Check the expected result
The router ID is a 32-bit protocol identity, not an IPv4 forwarding dependency. The learned destination and adjacency transport are IPv6.
Pause and explain it in your own words
Does a Full OSPFv3 neighbor prove a particular IPv6 prefix was advertised?
Show a hint
Adjacency synchronization and interface prefix membership are different evidence.
Show the explanation
No. Verify the specific remote /128 in show ipv6 route and test the actual endpoint with an explicit source. A missing loopback OSPF command can leave the adjacency healthy but the intended route absent.
Short answer
What should you understand today?
OSPFv3 for IPv6 still uses areas, unique 32-bit router IDs and SPF calculations. Its adjacent link communication uses IPv6 link-local addresses, and IPv6 prefixes are carried separately from basic topology descriptions. Configure each interface explicitly, verify both point-to-point and broadcast behavior, and check remote routes as well as neighbor state.
Before you begin
Learning targets
- Complete IPv6 address scope and OSPFv2 neighbor and broadcast lessons.
- Use three fresh CML 2.10 IOSv 15.9M routers and a bundled IOSvL2 15.2 switch with entitlement.
- Do not reuse static routes or defaults from earlier projects; they would mask the intended OSPFv3 failure.
- Separate a 32-bit router ID from IPv6 interface addresses.
- Build a point-to-point OSPFv3 adjacency and verify its remote endpoint.
- Build a broadcast OSPFv3 segment with deliberate election roles.
- Interpret a link-local next hop together with its interface.
- Repair one area mismatch and repeat the original IPv6 test.
Words you will meet
Open a word when you need its meaning. You do not need to memorize the whole list before reading.
OSPFv3
OSPF version 3 retains link-state routing, areas and SPF while changing protocol structures for IPv6. This lesson uses its IPv6 function; later address-family extensions are outside the lab.
32-bit router ID
A dotted-decimal OSPF identity that remains 32 bits even when all carried routes and interfaces are IPv6. It does not assign an IPv4 address.
Link-local next hop
An adjacent IPv6 router address associated with an output interface. OSPFv3 normally uses link-local sources for link communication and learns scoped next-hop information.
Point-to-point and broadcast
Two OSPF network types. Point-to-point forms direct full adjacency without DR/BDR; broadcast elects those roles on a shared segment.
Link LSA and prefix LSA
A Link LSA describes link-specific information including a link-local address. Intra-Area-Prefix LSAs carry IPv6 prefixes associated with the topology.
Process and instance IDs
The Cisco process number is local configuration bookkeeping. The on-link OSPFv3 Instance ID separates protocol conversations and must be compatible; this lab leaves it at its default.
Area mismatch
Neighbor-facing interfaces assigned to different OSPF areas reject each other's intended adjacency. Correct IP addressing alone does not correct the mismatch.
Full and learned route
Full indicates completed adjacency synchronization. A learned OSPF route and a successful fixed-source probe provide separate evidence for the desired destination.
Know which exam window this chapter serves
The current CCNA v1.1 blueprint names single-area OSPFv2, while announced v2.0 explicitly includes OSPFv2 for IPv4 and OSPFv3 for IPv6. v1.1 remains current through February 2, 2027; v2.0 begins February 3. This chapter is therefore a labeled v1.1 extension and a direct v2.0 bridge, not a retroactive claim that the old objective named OSPFv3.
- Keep current and announced mappings distinct.
- An authoring checklist does not prove that a learner executed the configurations.
Keep identities while changing address semantics
Router IDs and area IDs remain 32 bits. Neighbor identities are distinct from interface IPv6 addresses. OSPFv3 separates basic topology from prefix information, with Link and Intra-Area-Prefix LSAs serving different roles. You do not need to memorize every LSA encoding to understand why a neighbor identity is not itself the route being learned.
- Do not configure an unnecessary IPv4 address just to obtain a router ID.
- A link-local address and an advertised global-prefix endpoint have different scopes.
Use one documented command family consistently
IOS supports the classic IPv6-specific OSPFv3 commands used here, and some platforms support newer address-family syntax. The command families must not be pasted together indiscriminately. This lab enables IPv6 forwarding, creates ipv6 router ospf 10, sets a router ID and enables interfaces with ipv6 ospf 10 area 0. Check the exact command family supported by the selected image.
- Record the full image build and parser behavior.
- The local process number is not the on-wire OSPFv3 Instance ID.
Verify both network types before comparing them
On the direct link, R1 and R2 should reach Full without DR/BDR roles. On the broadcast VLAN, R1 and R2 also establish a separate adjacency on Gi0/0, with election roles scoped to that segment. Seeing the same router ID on two interfaces can therefore be legitimate. Always include the interface column when counting neighbors.
- One physical router can have multiple adjacency relationships on separate links.
- An observed role is scoped to its interface, not globally to every connection.
An area fault can coexist with working IPv6
R3's planned fault replaces area 0 with area 1 on its only neighbor-facing interface. The local subnet and link-local addresses remain assigned, so a connected IPv6 ping can still work. OSPFv3 adjacency and learned remote loopbacks should disappear after processing and expiry. Restore the original area membership and repeat the same neighbor, route and fixed-source test; no broad protocol clear is needed.
- Check area, timers, instance, type and unique IDs before applying disruptive resets.
- Do not describe a predicted recovery as measured convergence or a completed independent review.
Real-world walkthrough
IPv6 neighbors were reachable, but OSPFv3 was not
In a hypothetical lab, R3's LAN interface is moved to area 1 while its peers remain in area 0. The learner sees working IPv6 addresses and assumes routing must work. The connected test succeeds, but the learned loopback route is absent.
- Identify the exact source and destination used in the failed remote test.
- Compare connected LAN reachability with the remote loopback route.
- Inspect OSPFv3 area membership on the same interface as the connected neighbor.
- Restore area 0 without altering IPv6 addresses or router IDs.
- Wait for Full and repeat the original source-qualified exchange.
Guided GNS3 lab
OSPFv3 point-to-point plus broadcast in area 0
Configure and verify both link types in distinct stages, then restore an isolated R3 area mismatch. The procedure contains expected outcomes only; no virtual router execution occurred during authoring.
Addressing plan
| Device | Interface | Address | Purpose |
|---|---|---|---|
| R1 | Gi0/1 | 2001:db8:12::1/64; fe80::11 | Direct point-to-point link |
| R2 | Gi0/1 | 2001:db8:12::2/64; fe80::12 | Direct point-to-point peer |
| R1 | Gi0/0 | 2001:db8:36::1/64; fe80::1 | Broadcast LAN, priority 200 |
| R2 | Gi0/0 | 2001:db8:36::2/64; fe80::2 | Broadcast LAN, priority 100 |
| R3 | Gi0/0 | 2001:db8:36::3/64; fe80::3 | Broadcast LAN, priority 0 |
| R1 | Loopback0 | 2001:db8:1::1/128 | Endpoint, router ID 1.1.1.1 |
| R2 | Loopback0 | 2001:db8:2::1/128 | Endpoint, router ID 2.2.2.2 |
| R3 | Loopback0 | 2001:db8:3::1/128 | Endpoint, router ID 3.3.3.3 |
Set up the lab
- Use Cisco Modeling Labs 2.10 with its legally entitled bundled IOSv 15.9M reference image. Record the complete show version release; do not export that image to GNS3. No paid API is involved.
- Create fresh nodes and only the listed links. No External Connector, NAT node, bridge, public uplink or production network is permitted. Leave console access independent of the test data links.
- IOSv examples use GigabitEthernet0/0 and GigabitEthernet0/1. Confirm those exact ports in the workbench and show ip interface brief before configuring; if your image differs, document an explicit port substitution first.
- Decline the initial configuration dialog on a new authorized node, press Enter to reach the prompt, then use enable. Do not bypass unknown credentials. All displayed expected results are predictions, not author runtime.
- Without an entitled compatible image, complete the address and route-selection worksheet only. Mark command execution, packet forwarding and recovery unmeasured.
- Use bundled IOSvL2 for SW1 and verify its exact build. Create only the four cables listed above and leave SW1 without an SVI or management IP.
- Read show version on every router and switch. Build the direct-link stage before the shared LAN; leave the OSPFv3 Instance ID at its default.
Initialize R1 identity and endpoint
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Create the IPv6 process and explicit router ID before enabling any neighbor-facing interface.
enable
configure terminal
ipv6 unicast-routing
ipv6 router ospf 10
router-id 1.1.1.1
exit
interface Loopback0
ipv6 address 2001:db8:1::1/128
ipv6 ospf 10 area 0
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
ipv6 unicast-routing- Enable IPv6 forwarding on this isolated router.
ipv6 router ospf 10- Create the classic IOS IPv6 OSPFv3 process.
router-id 1.1.1.1- Set the unique 32-bit identity without requiring an IPv4 interface.
exit- Return to global configuration.
interface Loopback0- Create the actual IPv6 traffic endpoint.
ipv6 address 2001:db8:1::1/128- Assign this router's unique endpoint address.
ipv6 ospf 10 area 0- Advertise the endpoint in the single backbone area.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- R1 has IPv6 forwarding and its advertised /128 endpoint.
- Why this step matters
- The dotted router ID does not require an IPv4 interface address.
Initialize R2 identity and endpoint
In the isolated CML workbench, select R2, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Use the matching command family with a distinct identity and endpoint.
enable
configure terminal
ipv6 unicast-routing
ipv6 router ospf 10
router-id 2.2.2.2
exit
interface Loopback0
ipv6 address 2001:db8:2::1/128
ipv6 ospf 10 area 0
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
ipv6 unicast-routing- Enable IPv6 forwarding on this isolated router.
ipv6 router ospf 10- Create the classic IOS IPv6 OSPFv3 process.
router-id 2.2.2.2- Set the unique 32-bit identity without requiring an IPv4 interface.
exit- Return to global configuration.
interface Loopback0- Create the actual IPv6 traffic endpoint.
ipv6 address 2001:db8:2::1/128- Assign this router's unique endpoint address.
ipv6 ospf 10 area 0- Advertise the endpoint in the single backbone area.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- R2 has its own /128 and unique 32-bit identity.
- Why this step matters
- A duplicate router ID would undermine the topology even with different IPv6 addresses.
Enable R1's direct-link interface
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Configure Gi0/1 only; leave the shared-LAN interface untouched for now.
enable
configure terminal
interface GigabitEthernet0/1
ipv6 address 2001:db8:12::1/64
ipv6 address fe80::11 link-local
ipv6 ospf network point-to-point
ipv6 ospf 10 area 0
no shutdown
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface GigabitEthernet0/1- Select the direct R1-R2 cable, not the shared VLAN port.
ipv6 address 2001:db8:12::1/64- Assign the direct transit address.
ipv6 address fe80::11 link-local- Set this interface's explicit link-local identity.
ipv6 ospf network point-to-point- Use OSPF point-to-point behavior with no DR election.
ipv6 ospf 10 area 0- Enable OSPFv3 on this direct link in area 0.
no shutdown- Enable the direct Ethernet interface.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- R1 is ready for point-to-point OSPFv3 on the direct cable.
- Why this step matters
- This keeps initial verification independent of any alternate shared-LAN path.
Enable R2's direct-link interface
In the isolated CML workbench, select R2, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Use the opposite IPv6 endpoint and matching point-to-point area 0 configuration.
enable
configure terminal
interface GigabitEthernet0/1
ipv6 address 2001:db8:12::2/64
ipv6 address fe80::12 link-local
ipv6 ospf network point-to-point
ipv6 ospf 10 area 0
no shutdown
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface GigabitEthernet0/1- Select the direct R1-R2 cable, not the shared VLAN port.
ipv6 address 2001:db8:12::2/64- Assign the direct transit address.
ipv6 address fe80::12 link-local- Set this interface's explicit link-local identity.
ipv6 ospf network point-to-point- Use OSPF point-to-point behavior with no DR election.
ipv6 ospf 10 area 0- Enable OSPFv3 on this direct link in area 0.
no shutdown- Enable the direct Ethernet interface.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- The direct adjacency should reach Full without DR/BDR election.
- Why this step matters
- Both routers must use compatible link parameters and the intended area.
Verify point-to-point before adding LAN
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Preserve the direct-link results now; do not postpone them until a second path exists.
enable
show ipv6 ospf interface GigabitEthernet0/1
show ipv6 ospf neighbor
show ipv6 route 2001:db8:2::1
ping ipv6 2001:db8:2::1 source 2001:db8:1::1What each command means
enable- Enter authorized privileged EXEC mode to inspect this named router.
show ipv6 ospf interface GigabitEthernet0/1- Confirm point-to-point type and area 0.
show ipv6 ospf neighbor- Identify R2's Full adjacency on Gi0/1 without DR role.
show ipv6 route 2001:db8:2::1- Check the learned /128 and scoped next hop.
ping ipv6 2001:db8:2::1 source 2001:db8:1::1- Test the two actual loopback endpoints across the direct link.
- What you should see
- Expect a remote OSPF route and replies before proceeding.
- Why this step matters
- The staged test proves which declared link was available for the initial exchange.
Create the shared broadcast VLAN
In the isolated CML workbench, select SW1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Configure only the three router-facing access ports in VLAN 36.
enable
configure terminal
vlan 36
exit
interface range GigabitEthernet0/0 - 2
switchport mode access
switchport access vlan 36
no shutdown
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
vlan 36- Create the isolated shared broadcast VLAN.
exit- Return to global switch configuration.
interface range GigabitEthernet0/0 - 2- Select exactly the three declared router-facing ports.
switchport mode access- Make each selected port an untagged access port.
switchport access vlan 36- Put all three ports into the same isolated VLAN.
no shutdown- Enable the three mapped ports.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- SW1 connects all three Gi0/0 interfaces at Layer 2.
- Why this step matters
- The switch is not an OSPF participant and needs no IP address.
Initialize the third router
In the isolated CML workbench, select R3, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Create R3's own identity and endpoint before enabling its only transit.
enable
configure terminal
ipv6 unicast-routing
ipv6 router ospf 10
router-id 3.3.3.3
exit
interface Loopback0
ipv6 address 2001:db8:3::1/128
ipv6 ospf 10 area 0
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
ipv6 unicast-routing- Enable IPv6 forwarding on this isolated router.
ipv6 router ospf 10- Create the classic IOS IPv6 OSPFv3 process.
router-id 3.3.3.3- Set the unique 32-bit identity without requiring an IPv4 interface.
exit- Return to global configuration.
interface Loopback0- Create the actual IPv6 traffic endpoint.
ipv6 address 2001:db8:3::1/128- Assign this router's unique endpoint address.
ipv6 ospf 10 area 0- Advertise the endpoint in the single backbone area.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- R3 owns 2001:db8:3::1 and uses router ID 3.3.3.3.
- Why this step matters
- The later fault cannot be bypassed through an undeclared second R3 interface.
Start the LAN's DR candidate
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Enable the broadcast LAN first. After end, wait for show output to report DR before starting R2's LAN.
enable
configure terminal
interface GigabitEthernet0/0
ipv6 address 2001:db8:36::1/64
ipv6 address fe80::1 link-local
ipv6 ospf network broadcast
ipv6 ospf priority 200
ipv6 ospf 10 area 0
no shutdown
end
show ipv6 ospf interface GigabitEthernet0/0What each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface GigabitEthernet0/0- Select the cable to SW1's shared VLAN.
ipv6 address 2001:db8:36::1/64- Assign this router's address on the shared LAN.
ipv6 address fe80::1 link-local- Set this LAN interface's explicit neighbor address.
ipv6 ospf network broadcast- Use broadcast OSPFv3 with DR/BDR election.
ipv6 ospf priority 200- Set election preference or ineligibility, not path cost.
ipv6 ospf 10 area 0- Enable this LAN interface in the same area 0.
no shutdown- Enable the LAN connection.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
show ipv6 ospf interface GigabitEthernet0/0- Inspect broadcast mode and wait for R1's DR role.
- What you should see
- Expect R1 to become DR on VLAN 36, independently of Gi0/1.
- Why this step matters
- Election roles belong to the shared interface, not to the point-to-point adjacency.
Join the LAN's backup candidate
In the isolated CML workbench, select R2, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. After R1 is DR, enable R2's LAN and wait for BDR before enabling R3.
enable
configure terminal
interface GigabitEthernet0/0
ipv6 address 2001:db8:36::2/64
ipv6 address fe80::2 link-local
ipv6 ospf network broadcast
ipv6 ospf priority 100
ipv6 ospf 10 area 0
no shutdown
end
show ipv6 ospf interface GigabitEthernet0/0What each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface GigabitEthernet0/0- Select the cable to SW1's shared VLAN.
ipv6 address 2001:db8:36::2/64- Assign this router's address on the shared LAN.
ipv6 address fe80::2 link-local- Set this LAN interface's explicit neighbor address.
ipv6 ospf network broadcast- Use broadcast OSPFv3 with DR/BDR election.
ipv6 ospf priority 100- Set election preference or ineligibility, not path cost.
ipv6 ospf 10 area 0- Enable this LAN interface in the same area 0.
no shutdown- Enable the LAN connection.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
show ipv6 ospf interface GigabitEthernet0/0- Confirm R1 DR and R2 BDR on the broadcast interface.
- What you should see
- Expect a second R1-R2 relationship on Gi0/0 with broadcast roles.
- Why this step matters
- The same peer router can legitimately appear on two different interfaces.
Join R3 as a DROTHER
In the isolated CML workbench, select R3, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Use priority 0 so R3 does not compete for either elected role.
enable
configure terminal
interface GigabitEthernet0/0
ipv6 address 2001:db8:36::3/64
ipv6 address fe80::3 link-local
ipv6 ospf network broadcast
ipv6 ospf priority 0
ipv6 ospf 10 area 0
no shutdown
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface GigabitEthernet0/0- Select the cable to SW1's shared VLAN.
ipv6 address 2001:db8:36::3/64- Assign this router's address on the shared LAN.
ipv6 address fe80::3 link-local- Set this LAN interface's explicit neighbor address.
ipv6 ospf network broadcast- Use broadcast OSPFv3 with DR/BDR election.
ipv6 ospf priority 0- Set election preference or ineligibility, not path cost.
ipv6 ospf 10 area 0- Enable this LAN interface in the same area 0.
no shutdown- Enable the LAN connection.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- R3 should form Full adjacencies to the LAN's DR and BDR.
- Why this step matters
- Priority 0 prevents election, not prefix learning or packet forwarding.
Record R3's broadcast baseline
In the isolated CML workbench, select R3, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Wait for Full and verify the actual source-to-R1-loopback exchange.
enable
show ipv6 ospf neighbor
show ipv6 route 2001:db8:1::1
ping ipv6 2001:db8:1::1 source 2001:db8:3::1What each command means
enable- Enter authorized privileged EXEC mode to inspect this named router.
show ipv6 ospf neighbor- Expect R1 DR and R2 BDR on Gi0/0.
show ipv6 route 2001:db8:1::1- Inspect the learned /128 and link-local next hop with its interface.
ping ipv6 2001:db8:1::1 source 2001:db8:3::1- Test the complete broadcast-stage endpoint exchange.
- What you should see
- Expect learned R1 endpoint and replies before the area fault.
- Why this step matters
- Neighbor role, route selection and final delivery are separate evidence.
Inject and observe one area mismatch
In the isolated CML workbench, select R3, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Replace only the LAN's area. After end, wait beyond the displayed dead interval before the show and ping checks.
enable
configure terminal
interface GigabitEthernet0/0
no ipv6 ospf 10 area 0
ipv6 ospf 10 area 1
end
show ipv6 ospf neighbor
ping ipv6 2001:db8:36::1
show ipv6 route 2001:db8:1::1
ping ipv6 2001:db8:1::1 source 2001:db8:3::1What each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface GigabitEthernet0/0- Select R3's only neighbor-facing link.
no ipv6 ospf 10 area 0- Remove its original area 0 membership.
ipv6 ospf 10 area 1- Deliberately attach it to the wrong area 1.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
show ipv6 ospf neighbor- Check loss of the former area 0 adjacencies.
ping ipv6 2001:db8:36::1- Check that local LAN IPv6 reachability can remain.
show ipv6 route 2001:db8:1::1- Inspect withdrawal of the remote /128.
ping ipv6 2001:db8:1::1 source 2001:db8:3::1- Repeat the now-failed remote exchange.
- What you should see
- Expect local reachability but no intended area 0 neighbor or remote route.
- Why this step matters
- The single changed variable is protocol area membership, not cabling or IPv6 addressing.
Restore the original area
In the isolated CML workbench, select R3, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Reverse the deliberate membership change without resetting the process.
enable
configure terminal
interface GigabitEthernet0/0
no ipv6 ospf 10 area 1
ipv6 ospf 10 area 0
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface GigabitEthernet0/0- Select the same LAN interface.
no ipv6 ospf 10 area 1- Remove the deliberately wrong area membership.
ipv6 ospf 10 area 0- Restore the correct shared area 0 membership.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- The original broadcast adjacencies should reform.
- Why this step matters
- The exact inverse preserves identities, addresses and the direct-link stage.
Retest the original broadcast exchange
In the isolated CML workbench, select R3, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Wait for synchronization, then repeat the same route and endpoint checks.
enable
show ipv6 ospf neighbor
show ipv6 route 2001:db8:1::1
ping ipv6 2001:db8:1::1 source 2001:db8:3::1What each command means
enable- Enter authorized privileged EXEC mode to inspect this named router.
show ipv6 ospf neighbor- Verify restored Full adjacencies with the expected roles.
show ipv6 route 2001:db8:1::1- Verify the remote /128 returns.
ping ipv6 2001:db8:1::1 source 2001:db8:3::1- Repeat the original source-qualified broadcast-stage test.
- What you should see
- Expect recovery; record real observations rather than predicted success characters.
- Why this step matters
- Matching the original source and target closes the fault experiment.
Verify
- Preserve point-to-point evidence before the broadcast link is enabled.
- Record each neighbor's router ID, interface and role, not just the total count.
- Show both the remote IPv6 prefix and its scoped link-local next hop.
- Retain connected success, remote failure and restoration evidence for the area mismatch.
Troubleshoot
- If the process cannot choose an ID, confirm the explicit router-id command rather than adding an unnecessary IPv4 address.
- If two entries share a neighbor ID, compare interfaces before declaring a duplicate identity fault.
- If neighbors fail, compare area, default Instance ID, timers, type, IPv6 enablement and packet delivery; do not blindly clear all processes.
GNS3 does not provide Cisco images. Use software only when the applicable license or entitlement permits that environment. Do not share or redistribute image files. Cisco Modeling Labs is the official alternative; its reference images are licensed for use within CML unless separately licensed. A paper exercise needs no image, but does not establish hands-on competence. Virtual routers do not reproduce physical radios, PoE delivery, hardware forwarding rates or failover timing.
- Restore R3 Gi0/0 to area 0 and leave all original addresses and IDs unchanged.
- Retain stage-specific outputs privately and stop the isolated project; no authentication or timing test is claimed.
Practice set
Answer before you reveal
01Why does OSPFv3 still show 1.1.1.1?
The identity field is not an IPv4 address assignment. An IPv6-only router can use an explicit ID without IPv4 forwarding.
02What accompanies a link-local route next hop?
Link-local addresses are scoped to one link. The interface distinguishes the immediate neighbor from the globally described destination.
03Why verify Gi0/1 before enabling Gi0/0?
Once both links exist, another route may be available. Staged verification avoids attributing later success to an unverified link.
04Are two neighbor entries with one peer ID always wrong?
This topology deliberately connects R1 and R2 through a direct cable and the shared LAN. Compare the interface and network-type fields.
05Why can R3's connected ping survive the area fault?
Area membership controls the OSPF conversation. The remote loopback requires a learned route that the broken adjacency no longer supplies.
06Is authentication required by the announced neighbor objective?
This isolated lesson follows that named scope. Production authentication design is a separate security concern, not silently added exam coverage.
Knowledge check
Quiz: prove the reasoning
Keep these
Technical takeaways
- OSPFv3 retains 32-bit router IDs without requiring IPv4 interfaces.
- Link-local communication and prefix advertisements have distinct roles.
- Use one platform-appropriate command family consistently.
- Verify point-to-point and broadcast interfaces separately.
- An area mismatch can break routing while local IPv6 still works.
- Map this lesson as v1.1 extension and direct announced v2.0 preparation.