Re: IPV6 Duplicate Address Detection(DAD)

You rock man. Happy Friday and happy labbing!

On Fri, Sep 18, 2009 at 10:11 AM, Anantha Subramanian Natarajan <
anantha.natarajan_at_gravitant.com> wrote:

> Hi Andrew,
>
> Thank you very much .....Totally missed the concept that the link-local
> address doesn't have the /64 ...Thanks for highlighting the same
> ......Tested and found out that,when the link local address has duplicate
> address detection,the ipv6 interface would be stalled and that means no
> processing of ipv6 on the interface but if the global addresses are detected
> with duplicate address the interface will still process ipv6 .Please correct
> me if my understanding is wrong .
>
> R1#sh ipv6 interface
> FastEthernet0/0 is up, line protocol is up
> *IPv6 is stalled,* link-local address is *FE80::1 [DUP]*
>
> Once again thank you very much andrew
>
> Regards
> Anantha Subramanian Natarajan
>
>
>
>
> On Fri, Sep 18, 2009 at 8:46 AM, ALL From_NJ <all.from.nj_at_gmail.com>wrote:
>
>> Ok cool. I would suggest to start over and clear your configs. For this
>> testing, you do not need anything but a common segment between 2 routers.
>>
>> You might want to turn this on --> debug ipv6 nd (see a lot of output when
>> you no shut the interface, great for learning)
>>
>> For the link local address, type this instead on both routers:
>>
>> interface xyz
>> shut
>> ipv6 add fe80::1 link-local
>> no shut
>>
>> Once you add the same link local on both routers and type no shut, you
>> will see the problem manifest itself.
>>
>> Notice the link local address does not have the concept of a /64 bit masks
>> ... it is not global, but link local.
>>
>> HTH,
>>
>> Andrew
>>
>>
>>
>>
>>
>> On Fri, Sep 18, 2009 at 7:53 AM, Anantha Subramanian Natarajan <
>> anantha.natarajan_at_gravitant.com> wrote:
>>
>>> Hi Andrew,
>>>
>>> Thank you very much for the time and the explanation.So you mean if the
>>> link local address is been detected on a link having duplicate address will
>>> not causes the interface to be in stalled (ipv6 processing disabled).Very
>>> good info and thank you very much.
>>>
>>> I had chance to lab it with duplicate global address on the link and the
>>> output showed as below which clarified my earlier question oh how to
>>> differentiate DAD on link local or global ipv6 address.It seems if there is
>>> a DAD with global ipv6 address,it will just indicate DUP as below and the
>>> ipv6 interface will not have any issue as you mentioned which is logical as
>>> there can be many global ipv6 addresses per link.
>>>
>>> FastEthernet0/0 is up, line protocol is up
>>> IPv6 is enabled, link-local address is FE80::C001:16FF:FEC4:0
>>> Global unicast address(es):
>>> 2001::1, subnet is *2001::/64 [DUP]*
>>> **
>>> But I couldn't able to create Duplicate addresses for link-local ,I was
>>> under impression that I would be able to create link local by using the
>>> command ipv6 address FE80::1/64 link-local manually but while I type it ,it
>>> didn't give me an option for link-local,I am using dynamips,I am sure
>>> missing something.Kindly correct me .
>>>
>>> Andrew I am hoping that if the link-local has Duplicate address,the ipv6
>>> interface should go into stalled state and thus no ipv6 processing.I just
>>> want to reconfirm with you, that you created duplicate address for the link
>>> local address but still that interface was up and working fine.Kinly let me
>>> know
>>>
>>> Thank you very much for the help.
>>>
>>> Regards
>>> Anantha Subramanian Natarajan
>>>
>>> * *
>>>
>>>
>>> On Thu, Sep 17, 2009 at 11:01 PM, ALL From_NJ <all.from.nj_at_gmail.com>wrote:
>>>
>>>> Good evening team,
>>>>
>>>> Anantha, dup global addresses will not create any issues with the
>>>> interface coming up or with the control protocol traffic. Team, ... keep me
>>>> honest here. ;-)
>>>>
>>>> In a lab test I just did, I configured two routers on the same segment
>>>> to have dup global addresses and unique link local. I then added some loops
>>>> to one of these and configured OSPF on everything.
>>>>
>>>> I then configured IPv6 and OSPF on another router from another segment;
>>>> one hop away. Since everything is associated with link local, there was not
>>>> any problems with connectivity, routing updates and or pings. I could get
>>>> to the loops on the correct router, and at first it appeared that dups did
>>>> not matter much at all.
>>>>
>>>> Interesting to lab this out and understand where a routing loop can
>>>> occur. Since clients get their addresses from DHCP or autoconfig, having
>>>> dups in your network could cause two segments in different parts of the
>>>> network to have an identity crisis / overlapping address space.
>>>>
>>>> Apart from this, no worries. Have a great night,
>>>>
>>>> Andrew
>>>>
>>>>
>>>>
>>>> On Thu, Sep 17, 2009 at 11:00 PM, Anantha Subramanian Natarajan <
>>>> anantha.natarajan_at_gravitant.com> wrote:
>>>>
>>>>> Hi All,
>>>>>
>>>>> Would like to confirm about the IPV6 Duplicate Address Detection(DAD),
>>>>> DAD
>>>>> would detect duplicate addresses ,if exist for both link local address
>>>>> and
>>>>> global ipv6 unique address on a link.Is that right ?..If so,in the
>>>>> below
>>>>> show output,if it mentions ipv6 is stalled,I am understanding that a
>>>>> duplicate link local address is been detected on the link and ipv6
>>>>> processing on the interface is disabled.Please correct me if I am wrong
>>>>> on
>>>>> this.
>>>>>
>>>>> My question is ,if DAD detects duplicate address on the global ipv6
>>>>> address
>>>>> on the link,does that also will lead to stalled interface,if so,how we
>>>>> can
>>>>> distinguish between link local and global ipv6 duplicate address
>>>>> detection.
>>>>>
>>>>> Kindly help me to understand the above.
>>>>>
>>>>> Router# show ipv6 interface ethernet 0
>>>>> Ethernet0 is up, line protocol is up
>>>>> *IPv6 is stalled*, link-local address is FE80::1
>>>>>
>>>>> Thank you very much for the help
>>>>>
>>>>> Regards
>>>>> Anantha Subramanian Natarajan
>>>>>
>>>>>
>>>>> Blogs and organic groups at http://www.ccie.net
>>>>>
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> Andrew Lee Lissitz
>>>> all.from.nj_at_gmail.com
>>>>
>>>
>>>
>>
>>
>> --
>> Andrew Lee Lissitz
>> all.from.nj_at_gmail.com
>>
>
>

-- 
Andrew Lee Lissitz
all.from.nj_at_gmail.com
Blogs and organic groups at http://www.ccie.net