Course contents

Module 5: PracticeLesson 5.2 (2 of 5 in this module)18 of 29 in the OSPF course

Beyond CCNA (optional). This topic is not on the CCNA 200-301 exam. It is useful at work and in later study; skip it if you are preparing for the exam. (The v1.1 exam covers single-area OSPFv2 only (3.4); OSPFv3 is not listed.)

Lab: single-area OSPFv3 for IPv6

Can the PC on LAN 1 reach the IPv6 server behind R3? Build the routes, read the evidence, then break one neighbour setting at a time and recover it.

Intermediate · 20 min read

What must work before we add OSPFv3?

OSPFv3 is the version of Open Shortest Path First used here to learn IPv6 routes. A dual-stack router runs IPv4 and IPv6 side by side. Its working IPv4 routes do not replace the IPv6 routes this lab needs.

We want a PC on LAN 1, 2001:db8:acad:1::10/64, to reach the LAN 3 server, 2001:db8:acad:3::10/64. The PC uses R1 as its IPv6 gateway; the server uses R3. Give those hosts gateway fe80::1 and fe80::3 respectively on their local interfaces, or use the router's LAN IPv6 address if your simulator requires that form.

Check the neighbour, learned route and end-to-end test separately: success at one step does not prove the others.

Three dual-stack routers and no learned IPv6 routes yet

These are the routers from the single-area OSPF lab, with OSPFv2 already running for IPv4. Every interface now also has the IPv6 address and link-local address below, and all interfaces are up. IPv6 forwarding is not enabled and there are no learned remote IPv6 routes. An addressed interface can still have local or connected information; that differs from forwarding between LANs. Use Cisco Packet Tracer, a lab emulator or paper. The OSPFv3 lesson explains every command used here.

RouterInterfaceIPv6 addressLink-localConnects to
R1Gi0/02001:db8:acad:1::1/64fe80::1LAN 1
Gi0/12001:db8:acad:12::1/64R2
Gi0/22001:db8:ffff::2/64ISP (2001:db8:ffff::1)
R2Gi0/02001:db8:acad:12::2/64fe80::2R1
Gi0/12001:db8:acad:23::1/64R3
Gi0/22001:db8:acad:2::1/64LAN 2
R3Gi0/02001:db8:acad:23::2/64fe80::3R2
Gi0/12001:db8:acad:3::1/64LAN 3 (server 2001:db8:acad:3::10)

Gi means Gigabit Ethernet. Link-local addresses such as fe80::2 identify a neighbour on one link; they are not forwarded to another link. Reusing FE80::2 on R2's different links is possible because each has a separate scope. A route needs both the next-hop address and the exit interface.

The addresses beginning 2001:db8: are documentation addresses. The /64 is the prefix length: 64 bits identify each subnet. R2's router ID, 2.2.2.2, is a separate 32-bit OSPF name, not an IPv6 address the PC tries to reach.

Task 1: plan the OSPFv3 settings

Decide which interfaces run OSPFv3 and which are passive, the router IDs, the network type on the router links, and how R2 and R3 will reach the internet over IPv6.

What to plan
What to planDecide addresses and OSPFv3 settings first.Plan the labAddressesglobal and link-localRouter IDs32-bit, set manuallyAreaarea 0 everywhere

On small screens, swipe sideways or focus the diagram and use the arrow keys.

Planning avoids mistakes.
Show the plan
Task 1: plan the OSPFv3 settings
Task 1: plan the OSPFv3 settingsItem; Decision; Why. LAN interfaces: OSPFv3, passive Advertise the /64, but no routers live there. Router links: OSPFv3, point-to-point Two routers per link: no DR election needed. R1 Gi0/2 (ISP): No OSPFv3 R1 advertises a default route instead. Router IDs: 1.1.1.1, 2.2.2.2, 3.3.3.3 Set by hand, the same as OSPFv2, so output is easy to read. Default route: Static ::/0 on R1, then default-information originate The same pattern as the IPv4 default route.ItemDecisionWhyLAN interfacesOSPFv3, passiveAdvertise the /64, but no routerslive there.Router linksOSPFv3, point-to-pointTwo routers per link: no DR electionneeded.R1 Gi0/2 (ISP)No OSPFv3R1 advertises a default routeinstead.Router IDs1.1.1.1, 2.2.2.2, 3.3.3.3Set by hand, the same as OSPFv2, sooutput is easy to read.Default routeStatic ::/0 on R1, thendefault-information originateThe same pattern as the IPv4 defaultroute.

On small screens, swipe sideways or focus the diagram and use the arrow keys.

Read each row across: the left box names the item, the others describe it.

Task 2: configure the three routers

Start from global configuration mode, reached with configure terminal from each router's privileged prompt. The table's IPv6 addresses must already be applied and the interfaces must be up. The solution adds forwarding and OSPF settings; it does not configure those prerequisite addresses.

Configure in order
Configure in orderEnable IPv6 routing, then the process, then the interfaces.Routingipv6 unicast-routingProcessipv6 router ospf 1Interfacesipv6 ospf 1 area 0Savecopy run start

On small screens, swipe sideways or focus the diagram and use the arrow keys.

Same steps on each router.

ipv6 unicast-routing enables IPv6 forwarding. ipv6 router ospf 1 creates local process 1; ipv6 ospf 1 area 0 selects an interface. Process numbers need not match across routers; the area on a shared link must match. Reference bandwidth 10000 Mb/s makes each 1-Gb/s interface cost 10 without an explicit cost override.

Show the configuration
ipv6 unicast-routing ipv6 route ::/0 2001:db8:ffff::1 ! ipv6 router ospf 1 router-id 1.1.1.1 auto-cost reference-bandwidth 10000 passive-interface GigabitEthernet0/0 default-information originate ! interface GigabitEthernet0/0 ipv6 ospf 1 area 0 interface GigabitEthernet0/1 ipv6 ospf 1 area 0 ipv6 ospf network point-to-point

R1. No ipv6 ospf command on Gi0/2, so OSPFv3 stays off the ISP link.

ipv6 unicast-routing ! ipv6 router ospf 1 router-id 2.2.2.2 auto-cost reference-bandwidth 10000 passive-interface GigabitEthernet0/2 ! interface GigabitEthernet0/0 ipv6 ospf 1 area 0 ipv6 ospf network point-to-point interface GigabitEthernet0/1 ipv6 ospf 1 area 0 ipv6 ospf network point-to-point interface GigabitEthernet0/2 ipv6 ospf 1 area 0

R2: two router links and one passive LAN.

ipv6 unicast-routing ! ipv6 router ospf 1 router-id 3.3.3.3 auto-cost reference-bandwidth 10000 passive-interface default no passive-interface GigabitEthernet0/0 ! interface GigabitEthernet0/0 ipv6 ospf 1 area 0 ipv6 ospf network point-to-point interface GigabitEthernet0/1 ipv6 ospf 1 area 0

R3: passive by default, hellos switched back on towards R2.

Task 3: verify neighbours, then routes

Example output written for this lab, based on Cisco IOS documentation
R2#show ipv6 ospf neighbor
            OSPFv3 Router with ID (2.2.2.2) (Process ID 1)

Neighbor ID     Pri   State           Dead Time   Interface ID    Interface
3.3.3.3           0   FULL/  -        00:00:36    3               GigabitEthernet0/1
1.1.1.1           0   FULL/  -        00:00:31    4               GigabitEthernet0/0
R2 has two Full neighbours, so the relevant OSPF database exchange has completed. Neighbor ID names the other router; Interface is R2's local interface. FULL/- has no DR role on these point-to-point links. OSPFv2 is still running separately: show ip ospf neighbor shows its own two neighbours.
Example output written for this lab, based on Cisco IOS documentation
R3#show ipv6 route ospf
OE2 ::/0 [110/1], tag 1
     via FE80::2, GigabitEthernet0/0
O   2001:DB8:ACAD:1::/64 [110/30]
     via FE80::2, GigabitEthernet0/0
O   2001:DB8:ACAD:2::/64 [110/20]
     via FE80::2, GigabitEthernet0/0
O   2001:DB8:ACAD:12::/64 [110/20]
     via FE80::2, GigabitEthernet0/0
O marks an internal route. In [110/30], 110 is administrative distance, used to compare route sources, and 30 is OSPF path cost. OE2 marks an external type 2 default, with metric 1 here. FE80::2 is R2 on R3's Gi0/0 link, not R3 itself. Connected LAN 3 does not appear in an OSPF-only route listing.
Puzzle: why is 2001:db8:ffff::/64 missing from R3's table?

R1 Gi0/2 is not in OSPFv3, so its prefix is never advertised. R3 doesn't need it: anything outside the company, including the ISP link, matches the default route ::/0.

Verify neighbours, then routes
Verify neighbours, then routesCheck in order.show ipv6 ospf neighborFULL on each linkshow ipv6 ospf interface briefInterfaces in the right areashow ipv6 route ospfRoutes to every LAN

On small screens, swipe sideways or focus the diagram and use the arrow keys.

A missing route usually means a missing neighbour.

Task 4: test from end to end

First check the LAN 1 PC and LAN 3 server addresses and gateways given above. This test stays inside the lab, so the ISP default route is not needed to reach LAN 3.

End to end test
End to end testPing the IPv6 address across the network.PingPC to serverTracerouteeach hopCompareexpected path

On small screens, swipe sideways or focus the diagram and use the arrow keys.

Use the global address, not the link-local one.
Example output from a PC on LAN 1, written for this lab
C:\> tracert -d 2001:db8:acad:3::10
Tracing route to 2001:db8:acad:3::10 over a maximum of 30 hops

  1    1 ms    1 ms    1 ms  2001:db8:acad:1::1
  2    1 ms    1 ms    1 ms  2001:db8:acad:12::2
  3    2 ms    1 ms    1 ms  2001:db8:acad:23::2
  4    2 ms    2 ms    2 ms  2001:db8:acad:3::10

Trace complete.
The first three responding hops are R1, R2 and R3; the fourth is the server. Times and responding source addresses can vary by platform and return path. A timeout alone does not prove a router is down: ICMPv6 replies may be filtered or rate-limited.

Task 5: three faults on the R2–R3 link

Begin each fault from the healthy state above. Apply one fault, collect evidence, then undo it before trying the next. There is only one path here, so losing R2–R3 removes R3's learned routes after detection. OSPF cannot create a missing backup cable.

Common faults on a link
Common faults on a linkMismatches stop a neighbour.R2-R3 link problemsTimershello or dead differsAreaarea differsNetwork typepoint-to-point vsbroadcast

On small screens, swipe sideways or focus the diagram and use the arrow keys.

Compare both ends.

Pick a fault and watch what happens between R2 and R3. Before you press play, say which show command would reveal it.

Fault on the R2–R3 link:
Gi0/2Gi0/1Gi0/0:12::/64Gi0/1Gi0/0:23::/64Gi0/0Gi0/2Gi0/1ISPIPv6 2001:db8:ffff::1R1IPv6 fe80::1R2IPv6 fe80::2R3IPv6 fe80::3LAN 1IPv6 :1::/64LAN 2IPv6 :2::/64LAN 3IPv6 :3::/64

Device key: ISP (network / service) · R1, R2, R3 (router) · LAN 1, LAN 2 (computer) · LAN 3 (server)

Lines show the example’s network connections. Thick links: uplinks/WAN, as labelled. The coloured path and envelope follow the current step; its text identifies the sender, receiver and traffic type.

Reading the addresses

IP labels identify interfaces or destinations. Subnet labels identify networks; /n is the prefix length. A router ID (RID) identifies a routing process and need not be a reachable interface.

An IP address alone is not a URL. A web URL includes a scheme such as https://; an address on a router or printer does not imply a website.

  • ISP: IPv6 2001:db8:ffff::1
  • R1: IPv6 fe80::1
  • R2: IPv6 fe80::2
  • R3: IPv6 fe80::3
  • LAN 1: IPv6 :1::/64
  • LAN 2: IPv6 :2::/64
  • LAN 3: IPv6 :3::/64
  1. 1. Hellos both ways: from fe80::2 and fe80::3, each listing the other's router ID, so both reach 2-Way.
  2. 2. Databases synchronised: the routers exchange their LSAs and reach Full.
  3. 3. Routes installed: R3 learns 2001:db8:acad:1::/64 at cost 30.
Hello mismatches stop OSPFv3 neighbours exactly as they stop OSPFv2 ones.
Which command would you run first for each fault?
  • Area mismatch: show ipv6 ospf interface brief on both routers: compare the Area column.
  • Passive link: show ipv6 protocols or show running-config | section ipv6 router ospf.
  • Timer mismatch: compare show ipv6 ospf interface GigabitEthernet0/1 on R2 with show ipv6 ospf interface GigabitEthernet0/0 on R3. Read the Hello and Dead intervals.
Recover each fault before trying another

For the area fault, confirm that R3 Gi0/0 is incorrectly attached to area 1. Remove that attachment and restore area 0:

interface GigabitEthernet0/0 no ipv6 ospf 1 area 1 ipv6 ospf 1 area 0

R3, global configuration mode. Repair only the deliberately wrong area-1 attachment.

For the passive fault, add passive-interface GigabitEthernet0/1 under R2's IPv6 OSPF process. Restore Hellos towards R3 with the following command. R2's user LAN, Gi0/2, stays passive.

ipv6 router ospf 1 no passive-interface GigabitEthernet0/1

R2, global configuration mode. Restore only the router-facing link.

For the timer fault, explicitly set ipv6 ospf hello-interval 5 and ipv6 ospf dead-interval 20 on R3 Gi0/0. To recover, remove both overrides, then verify the intended 10/40-second baseline on both routers:

interface GigabitEthernet0/0 no ipv6 ospf hello-interval no ipv6 ospf dead-interval

R3, global configuration mode. Read both ends' actual timers after removing the overrides.

After each repair, check R2's neighbour list for 3.3.3.3 reaching Full. Check R3's LAN 1 route via FE80::2 on Gi0/0, then repeat the host test. A neighbour entry alone is not the final acceptance check.

Bonus: two IPv6-only faults

A new router, R4, has only IPv6 addresses. Its engineer typed ipv6 router ospf 1 and ipv6 ospf 1 area 0 on its link to R3, and nothing else. Name the two things that stop it working.

Show answer
  1. ipv6 unicast-routing is missing, so IOS does not route IPv6 or accept the OSPFv3 process.
  2. There is no router-id, and with no IPv4 address OSPFv3 cannot choose one, so the process does not start.

Then a trap that is not a fault: R4's global address on the R3 link is in a different /64 from R3's. OSPFv3 still forms the neighbourship over link-local addresses, so this alone would not stop it.

Three checks before you finish

Predict · scenario 1

R3 learns LAN 1 via FE80::2 on Gi0/0. Which router is the next hop?

Predict · scenario 2

R2 has two Full neighbours, but the server cannot reply to the LAN 1 PC. What should you also inspect?

Predict · scenario 3

You made R2 Gi0/1 passive to create a fault. Which recovery keeps the user LAN free of OSPF Hellos?

Technical references

The protocol model follows RFC 5340. Classic configuration follows Cisco's OSPFv3 example. Timer commands follow the Cisco IPv6 command reference. Outputs are written examples; this page does not run an IOS router or verify your simulator.