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 (50) Comments
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  1. 戦艦
    November 15th, 2017

    R3:show ipv6 ospf neighbor

  2. Greg
    December 6th, 2017

    Still valid but not able to ping 2026::1:2 from R1

  3. Fattah RazzaqghanimughnI
    January 5th, 2018

    on packet tracer lab:
    Ans1) R4
    Ans2) IPv4 and IPv6 interoperability
    Ans3) under “interface tunnel 34”, execute command “no tunnel mode”

  4. Frankie96
    January 9th, 2018

    There is no s0/0/0.34 sub interface on R4.. is the topology diag incorrect? Can networktut advise?

  5. CCNP
    January 10th, 2018

    Per JJ link:

    Since : ‘tunnel mode ipv6’ is mandatory
    The tunnel will function without the tunnel mode command, but not as an IPv6 tunnel.
    Ticket is IPv6 ticket in this case.
    can network tut or any one explain if it ‘tunnel mode ipv6’ is mandatory why “remove tunnel mode” or “no tunnel mode”

  6. CCNP
    January 10th, 2018

    Will it also fix issue if add “tunnel mode ipv6” to R4? Both sites have the same configurations

  7. emk
    January 11th, 2018

    no, there is no ipv6 config on r3/4 s0/0/0/34 interfaces. so you want to use v4 to transport v6

  8. CCNP
    January 13th, 2018

    Thank you emk for the explaination!!!!

  9. Test
    February 2nd, 2018

    Ticket 15 – IPv6 GRE Tunnel

    Can somebody please let me know how to identify the above TICKET ?

  10. Test
    February 3rd, 2018

    Question 1
    Gre Tunnel Header Mandatory and Optional ??
    Mandatory: Reserved0, Version, Protocol Type
    Optional: Checksum, Reserved1, Key, and Sequence Number

    Question 2
    Gre tunnel Header,which one is standard,witch one Extended? (4 Standard,2 Extended)

    Standard Header :Reserved0 , Version , Protocol Type , Checksum , Reserved1
    Extended Header : Key , Sequence Number

    For the above two DnD is there like a sequence in which we have to drop them ?

  11. Hunter
    February 9th, 2018


    No particular sequence needed to drop. Just Drop em into the correct boxes.

  12. Hunter
    February 9th, 2018

    IPv6 tickets are on R2, R3, R4. Narrow down pinging loss and figure which two routers are not having routes..
    IPv6 Ping Plan
    R1#ping ipv6 2026::1:2 (Can you reach the R3 Area 0 interface)
    No –> IPv6 OSPF
    Yes R1# ping ipv6 2026::34:2 (Can you reach the R4 GRE tunnel interface)
    No –> IPv6 GRE Tunnel
    Yes –> IPv6 RIPng OSPFv3
    You can also determine the answer using sh ipv6 ospf nei on DSW1.
    No routes for ospf area 12 (2026::12) –> R2: IPv6 OSPF Routing
    No routes for ospf areas 12, 0, or 34 –> R3: IPv6 GRE Tunnel
    All ospf routes for areas 12, 0, & 34 –> R4: IPv6 RIPng OSPFv3 redistribution

    ipv6 ospf 6 area 0 – R2
    R1 and R2 are not ospf6 neighbors with each other, after runing sh ipv6 ospf nei. R2 has no
    interfaces in area 0. As a result, R1 will have no OI routes for area 0 (2026::1) nor 2026::34 (area 34) that connects to area 0. But DSW will have routes for area 0 (2026::1) and 2026::34 (area 34), but not area 12 (2026::12)
    IPV6 Tunnel problem – R3
    R4 has no ospf6 neighbors because the tunnel mode on R3 is not compatible. As a result
    R3 will have no redistributed routes (OE2) from the DSW Ripzone (2026::3), (2026::102), and DSW will not have any routes to the OSPF6 network area 0 (2026::1), 2026::34 (area 34), or area 12 (2026::12)
    Redistribute Ripzone into OSPF -R4
    No missing ospf neighbors but R3 has no redistributed routes (OE2) from the DSW Ripzone (2026::3), (2026::102). DSW1 will however have routes to ALL OSPF6 area 0 (2026::1), 2026::34 (area 34) and area 12 (2026::12)

    February 23rd, 2018

    When show ipv6 route is done on R4, tunnel 34 is built although it is built but if it is confirmed by int tunnel 34, there is an error in the tunnel protocol and it can not be constructed. Is sh ipv6 route output error?

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  15. Rollodus
    March 15th, 2018

    Of course, again the simulator it is useless, allow me to demonstrate:
    interface Tunnel34
    no ip address
    mtu 1476
    ipv6 address 2026::34:1/122
    ipv6 ospf 6 area 34
    tunnel source Loopback3
    tunnel destination
    tunnel mode ipv6ip

    interface Tunnel34
    no ip address
    mtu 1476
    ipv6 address 2026::34:2/122
    ipv6 ospf 6 area 34
    tunnel source Loopback4
    tunnel destination
    tunnel mode ipv6ip

    I has nothing to do -again- with the answer– the client can ping the web server, without any fixes, it defeats the purpose from the very beginning…so what other options are there, learn by hear as a parrot???

    Sorry to say this: the guy that put together it is an IDIOT!!!!You either to a thing insanely good, or better don’t do anything that other can’t use!!!!

  16. Teddyme
    April 4th, 2018

    Thanks Networktut. I did it T_shoot ,940 scored.
    you guys almost all questions are similar to Networktu
    t but there is one new ticket in R1 . Networktut should find this and
    clear for members.

  17. Anonymous
    April 5th, 2018

    @teddyme do you remember what was the issue on R1 with the new ticket? Maybe it was old BGP issue ?

  18. Bala
    April 8th, 2018

    @Teddyme I am doing my exam tomorrow. do u remember what was the new ticket?

  19. Confuse guy
    April 17th, 2018


    calm down man. you are posting working configuration

    if you want to simulate the error exactly as the ticket pls remove this line in one of the router

    “tunnel mode ipv6ip”

    they guy that put together is NOT an idiot. he is definitely good and selfess guy LOL.

  20. CCNP2BE
    April 25th, 2018

    @Hunter, can you state whether Tipu Pasha’s strategy is effective in solving the tickets. i.e. for ticket 1, ospf issue, ping if NO then ping if YES then ticket one.

    May 14th, 2018


    IN R3 – R4

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  23. dhcp ticket
    June 6th, 2018

    guys this ticket is dhcp ticket not gre tunnel ticket.

  24. X
    June 8th, 2018

    Team, the correct answer is remove ‘tunnel mode ipv6’ under the R3’s tunnel34 configuration (R3 is the issue).

    CCNP-1000, ccnp-mx, Peter They got 1000 and they removed that command (Thank you guys). You may look for their comment in this ticket.

    Also we may identify IPv6 tickets using the following method mentioned by ‘Hopeful June 7th, 2017’

    “IPv6 Ping Plan
    R1#ping ipv6 2026::1:2 (Can you reach the R3 Area 0 interface)
    No –> IPv6 OSPF
    Yes R1# ping ipv6 2026::34:2 (Can you reach the R4 GRE tunnel interface)
    No –> IPv6 GRE Tunnel
    Yes –> IPv6 RIPng OSPFv3

    You can also determine the answer using sh ipv6 ospf nei on DSW1.
    No routes for ospf area 12 (2026::12) –> R2: IPv6 OSPF Routing
    No routes for ospf areas 12, 0, or 34 –> R3: IPv6 GRE Tunnel
    All ospf routes for areas 12, 0, & 34 –> R4: IPv6 RIPng OSPFv3 redistribution”

    *Probably he wanted to say ‘show ipv6 route’ on DSW1.

    Thank you.

  25. Neemo143
    June 30th, 2018

    I am not able to use ping command for ipv6. Is this experienced by every one?

  26. Martin P
    July 3rd, 2018

    Regarding discussion about correct tunnel mode I have tried the tunnel configuration at Cisco ASR920 and the tunnel works with default „tunnel mode gre ip“. This mode is described as GRE and it can tunnel more protocols and one of them is IPV6. The „tunnel mode ipv6“ uses IPV6 as a transport protocol so it cannot work if the src/dst are IPV4 addresses as in this case.

    ASR920#sh run all | b 111
    interface Tunnel111
    no ip address
    ipv6 address 2A00:ABCD:1:2::1/64
    ipv6 enable
    tunnel source Loopback0
    tunnel mode gre ip ! default command
    tunnel destination

    ASR920#sh interface tunnel111
    Tunnel111 is up, line protocol is up
    Hardware is Tunnel
    Tunnel source (Loopback0), destination
    Tunnel protocol/transport GRE/IP

    ASR920#ping 2A00:ABCD:1:2::2
    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 2A00:ABCD:1:2::2, timeout is 2 seconds:
    Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms

  27. RF
    July 18th, 2018

    How do you know if it’s ipv6 and not an ipv4 ticket? Does the test state to look at the ipv6 topology when it’s ipv6?

  28. Nickname
    July 26th, 2018

    Is this typo? In r4 it says tunnel source int se0/0/0.
    Shouldnt it be se0/0/0.34?
    Or it will still work with se0/0/0?

  29. Anonymous
    August 15th, 2018


    clear this question, why are you not answering?

  30. Anonymous
    August 15th, 2018

    The answers is wrong can some one make it clear please. thank you

  31. someone in London
    September 17th, 2018


    The big clue that is an ipv6 issue is in the question, last paragraph.

    ‘Recently the implementation group has been using the test bed to do an IPv6 ‘proof-of-concept’. After several changes to the network addressing and routing schemes, a trouble ticket has been opened indicating that the loopback address on R1 (2026::111:1) is not able to ping the loopback address on DSW2 (2026::102:1).
    Use the supported commands to isolated the cause of this fault and answer the questions.’

  32. Anonymous
    October 4th, 2018

    Packet tracer labs for ticket 15 is ip helper-address issue from a few tickets before. Less than two mins to find because I know its from another lab. Client can ping webserver.

  33. Freeman
    October 10th, 2018

    Networktut. this TT15 has wrong ip helper address.
    please fix this.

  34. Dany1
    January 31st, 2019

    You can statically configure IPv6 tunneling over IPv4 in two ways:
    manually – > tunnel mode ipv6ip
    gre -> tunnel mode gre ip ( default; for that reason is not appear at show run int tu34)

    When you run in interface tu34. you practically revert to tunnel mode gre ip. Warning!! Only acceptable way is tunnel mode gre ip, because from CCNA we know GRE tunnel accept multicast (OSPFv3 multicast in our case).So NOT select some option
    How find quickly? show int tu 34 and for tunnel mode ipv6 line protocol is down.
    Related to various minors problems on each ticket on networktut simulator are quite few, BUT is important there are not errors on focused specific equipment correlated with Ticket number.

  35. Dany1
    January 31st, 2019

    running command no tunnel mode ivp6 in tunnel34

  36. @martin P n them
    March 30th, 2019

    Great explanation man if u cant understand Martin P’s explain on this then u dont know the concept u will fail in active interview if asked.

  37. bobbyboberton
    April 1st, 2019

    This was messed up on my exam today. The tunnel config was not on R3 like in the sim (it was on R4) but the answer from the sim was correct. Def a weird one.

  38. ss2
    April 7th, 2019

    I used show int tun34 on R3 and R4, could see the different tunnel protocol/transport which made the problem clear.
    I simulated this in gns3, the moment you add ‘tunnel mode ipv6’ on the tun34 int on R4, its line protocol goes down.
    as someone suggested earlier, in the networktut lab, R3 doesn’t have an ipv6 add although R4 does, so transport has to be ipv4-GRE.
    so the right answer is to remove tunnel mode ipv6 on R3 in the networtut lab.

  39. how to gre
    April 27th, 2019

    Hi guys, user SS2 explained correctly.

    In the TSHOOT exam the transport protocol is IPv4, the delivered protocol is Ipv6.
    If your Tunnel Source and Destination IPs are IPv4 you need GRE/IP default encapsulation.
    If you Tunnel Source and Destination IPs are IPv6 you need IPv6 encapsulation.

    If you are sourcing the tunnel from IPv4 address and have specified “tunnel mode Ipv6” it will fail, because it cannot be done on IOS level.

    What you can do to narrow down what type of IPv6 problem it is..
    On DSW1 do #show ipv6 route and examine what IP networks you see based on the topology.
    Can you see the transfer networks from R1,R2,R3?
    Next step is to go on R1 and do #show ipv6 route and check the reverse routes, remember for PING to work you have to have reachability in both directions.

    If all routes are good. This could imply IPv6 ACL blocking icmp in either directions or both.

    Hope that helps.

  40. Snow
    May 19th, 2019

    what is the final anserws?? Somebody can tell me.have we delete tunnel mode Ipv6 or not?

  41. Ipv6
    June 18th, 2019

    This ticket is stil present or no ?

  42. Jimi Page
    June 19th, 2019

    Hey @networktut there is a problem with this ticket when you try ping the interfase serial0/0/0.23 of R3 2026::1:2 this not respond and following the SAM’s diagram for troubleshooting this should to respond, to then go to R3 and check the tunnel configuration.

  43. I failed
    July 6th, 2019

    I look this exam today and failed 629 score

    There was 4 new lickets that I had never seen before and all new MCQs I even had premium and this didnt help

    pls help i need to pass this exam

  44. ebiebi
    July 8th, 2019

    I failed

    I also took the exam on July 1 and fell. MCQ has never been seen on networktut. The questions on ACL and NAT caused by R1 failure also changed. OSPF and BGP are the same. I have never seen any issues with IPV6. T6 can not choose an option. T8, 9 and 11 are as usual. T13 and T14 were not found.

    July 19th, 2019

    Troubleshooting is troubleshooting there’s nothing to memorise just know YOUR SHOW COMMANDS AND THE CONCEPTS. stop blaming networtut premium. lol.

  46. Consula
    July 23rd, 2019

    @NetworkTut, pls can I use the “source interface command” during pings from the routers???

  47. Sami
    July 24th, 2019

    show ip interface tunnel 34 …

  48. Raspasoti
    August 7th, 2019

    The “show interface tunnel 34” command will tell you the tunnel mode or tunnel protocol.

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