Home > Ticket 15 – IPv6 GRE Tunnel

Ticket 15 – IPv6 GRE Tunnel

April 22nd, 2018 in TSHOOT v2 Go to comments

Problem: Loopback address on R1 (2026::111:1) is not able to ping the loopback address on DSW2 (2026::102:1).

Configuration of R3:
interface Tunnel34
 no ip address
 ipv6 address 2026::34:1/122
 ipv6 enable
 ipv6 ospf 6 area 34
 tunnel source Serial0/0/0.34
 tunnel destination
 tunnel mode ipv6

Configuration of R4:
interface Tunnel34
 no ip address
 ipv6 address 2026::34:2/122
 ipv6 enable
 ipv6 ospf 6 area 34
 tunnel source Serial0/0/0
 tunnel destination

Ans1) R3
Ans2) Ipv4 and Ipv6 Interoperability
Ans3) Under the interface Tunnel34, remove ‘tunnel mode ipv6’ command

Comments (12) Comments
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  1. Sol
    December 2nd, 2019

    Both ipv6ip(6in4) and GRE can work in this case, but according to the IPv6 Topology diagram it has to use GRE tunnel.

  2. abdullah
    December 10th, 2019

    failed today, there were three ipv6 tickets. one r2 ,one r3, the third one was everything ok .no problem in the tunnel interface r3, ipv6 enable r2 or redist on r4. I couldn’t find any logical reason.

    other ticket was interfaces of sw1 down down administratively shutdown. in the show run , the both interfaces in access mod and access vlan 10, no port security mentioned, there was command shutdown at the end of each interface. I couldn’t find answer to it where the answer should be ” no should down command”

  3. MrBeachbum
    December 11th, 2019

    Good strategy to remember for ipv6 tickets:

    on R2/R3: show ipv6 ospf neigh

    If there is only 1 neighbor listed for R2 and R3: 1+1 = 2 : R2 is your culprit
    If there is only 1 neighbor listed for R2 and 2 for R3: 1+2 = 3: R3 is your culprit
    If 2 neighbors are listed for R2/R3: 2+2=4: R4 is your culprit

    Good luck!

  4. Neo
    December 13th, 2019

    Ticket 15 – IPv6 GRE Tunnel – (Follow SAM’s method).
    You can’t ping from R3. However, R4 works and redistribution is OK. Also, R2 has “ospf area 0″ in the right answer. What is the problem?
    R3 – Tunnel34 ” tunnel mode ipv6″. You should remove the command, however, it doesn’t appear the line when I introduced a “show run”. Please, follow SAM’s method.


  5. Neo
    December 13th, 2019

    I think my last comment is a bug in the Ticket 15

  6. question for MrBeachbum
    December 15th, 2019


    Your Ipv6 strategy is great but I’m seeing one issue.

    I don’t know how the IPv6 tickets are exactly in the real test but your strategy seems to be incorrect for R3/ticket #15:

    The practice test here: sh ipv6 ospf neighbor output is showing 2 neighbors for R2 and 1 neighbor for R3.

    Please clarify.

  7. abdullah
    December 15th, 2019

    in packettracer tik15 there is a problem. r1 can ping r4 int but r4 cant ping dsw1. r4 dsw1 ipv6 neighbour and they can see each other. routes are distributed full. what is the problem, I dont know where every thing is ok.

  8. wave06
    December 30th, 2019

    On R1 & R2
    sh ipv6 ospf nei
    sh ip ospf nei

  9. wave06
    December 30th, 2019

    Correction R2 & R3

  10. ccnp-acquirer
    January 8th, 2020

    my method-of-resolution:
    A) show running-config | b Loopback for R1, R2, R3, R4, DSW1, DSW2.
    DSW1 not needed for this problem but wanted to be thorough.
    B) write down the Loopback addresses for each of the above, specifically noting the IPv6 addresses.
    C) ping R1->R2, R1->R3, R1->R4 Loopback6 addresses.
    i) If you are diligent in your studies you will see Loopback6 addresses are IPv6, while Loopback0 and Loopback1 addresses are IPv4.
    ii) All Loopback6 addresses are in the 2026 network.
    iii)> R1->R4 ping fails; thus indicating an issue between R3 and R4.
    D) ping DSW2->R4, DSW2->R3.
    Note that DSW2->R3 fails,; again indicating something wrong between R3 & R4.
    E) Looking at IPv6 Topology Diagram we see there is an IPv6 GRE Tunnel in Area 34 that is Totally NSSA.
    i) show running-config on R3 & R4.
    ii) Note there is an interface Tunnel 34 on R3 & R4.
    iii) Comparing the two configs (R3 & R4), observe there is “tunnel mode ipv6” on R3 but not on R4
    iv) Hardest part is realizing that Fault Condition is not just IPv6.
    a) tunnel destination addresses are IPv4.
    b) GRE Tunnel (Tunnel 34) are IPv6 addresses under IPv6 OSPF process 6 in Area 34
    —–> Fault condition: IPv4 and IPv6 interoperability

  11. Majid
    January 18th, 2020

    My method to solve this:

    1. Start ping from R1 to R2, R3 and R4.
    2. R1 –> R4 ping fails… means problem should be between R3 and R4.
    3. Check configs of IPv6 on R3 and R4.
    4. Easiest method is to check the “show ipv6 ospf neighbor” command on R3. It will show only one neighborship with R2 but not with R4.
    5. Issue should be on R3-R4 ospf’s ipv6 process and interfaces.
    6. There is Tunnel interface between R3 and R4.. So the ambigious command “tunnel mode ipv6” can easily be identified from running config.

  12. el_recepo
    January 22nd, 2020

    im confused.. the “show ipv6 interface” command shows me that tun34 ipv6 is up/up on both sides… is that right? and why?

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