Re: Weird MPLS Label Switching Problem

Hi,

On the same issue, that I was not seeing hops while tracing from CE1 to CE2
and vice versa, I realized something that for the same following
connectivity

The connectivity is CE1 - PE1 - P1 - P2 - PE2 - CE2

PE1(.1) - CE1 (.2) with subnet 172.16.1.0/24 with VRF A (RD=RT=1:1)
PE2(.1) - CE2 (.2) with subnet 172.16.2.0/24 with VRF A (RD=RT=1:1)

if I enable MPLS (using "mpls ip") on CE router on CE-PE interface, CE start
seeing the labels in the hops. I did not enable MPLS on the PE side on the
PE-CE interface and there was no LDP neighborship between PE and CE, but it
seems like after enabling MPLS on CE interface, it started understanding
MPLS label

   1. Is it a normal behavior?
   2. Are we required to do that in real life on CE routers?
   3. What about real lab? Should I enable MPLS on CE routers? Should PE-CE
   be LDP neighbors?

Please clarify this point as I have lab next week and I want to be sure
about the questions to solve the lab properly

Thanks,
Malik

On Sun, Feb 27, 2011 at 5:29 PM, Malik Nouman Ahmad <djmalik_at_gmail.com>wrote:

> Hi,
>
> Thanks for all the responses
>
> I am not using propagate-ttl thing anymore and I am getting 4-5 hops
> between the CE-CE trace but without any label as if SP core is not running
> MPLS
>
> I will try with another IOS and will get back to you
>
> Regards,
> Malik
>
> On Sun, Feb 27, 2011 at 2:39 PM, eseosa <eseosa.ehiwe_at_gmail.com> wrote:
>
>> Hi Malik
>>
>> did you use the no mpls ip propagate-ttl command with the forwarded
>> keyword ?? ,
>>
>> if you did then the behaviour you are experiencing is normal as
>> traceroutes from CE1 to CE2 will not show the hops in the SP core so
>> it appears to the customer as if they are having a single hop or
>> better perfromance :) , BUT traceroutes from the PE will shows the
>> transit P devices as the command with the forwarded keyword only
>> affects forwarded packets(CE TO CE) not locally generated ones.
>>
>> Else the next step is to consider the IOS version are you using as
>> Marko pointed out
>>
>> On 2/27/11, Marko Milivojevic <markom_at_ipexpert.com> wrote:
>> > Which IOS are you using?
>> >
>> > --
>> > Marko Milivojevic - CCIE #18427
>> > Senior Technical Instructor - IPexpert
>> >
>> > FREE CCIE training: http://bit.ly/vLecture
>> >
>> > Mailto: markom_at_ipexpert.com
>> > Telephone: +1.810.326.1444
>> > Web: http://www.ipexpert.com/
>> >
>> > On Sat, Feb 26, 2011 at 22:10, Malik Nouman Ahmad <djmalik_at_gmail.com>
>> wrote:
>> >
>> >> What I was trying to tell that the labels are not shown at all with or
>> >> without "no mpls ip propagate-ttl" command. I know this command is to
>> hide
>> >> all the hops between PE1 and PE2.
>> >>
>> >> When I was not using that command it was showing the hops from
>> >> CE1->PE1->P1->P2->PE1->CE2 BUT without labels like normal IPv4
>> traceroute.
>> >> I
>> >> used that command just to check if MPLS was working or not, just to be
>> >> sure
>> >>
>> >> The problem is that I cannot see the labels for CE1 to CE2 traceroute
>> at
>> >> any hop but when I use the same source/destination subnet for tracing
>> from
>> >> PE1 to PE2 I am able to see label swapping at each hop
>> >>
>> >> I hope I am able to describe the problem that I am facing
>> >>
>> >> Thanks,
>> >> Malik
>> >>
>> >>
>> >> On Sun, Feb 27, 2011 at 12:29 AM, Marko Milivojevic
>> >> <markom_at_ipexpert.com>wrote:
>> >>
>> >>>
>> >>> Which shows you that your "no mpls ip propagate-ttl" did its job and
>> MPLS
>> >>> backbone is "hidden" from CE devices. Remove this command from PE1,
>> run a
>> >>> traceroute from CE1 and see the labels re-appear.
>> >>>
>> >>> --
>> >>> Marko Milivojevic - CCIE #18427
>> >>> Senior Technical Instructor - IPexpert
>> >>>
>> >>> FREE CCIE training: http://bit.ly/vLecture
>> >>>
>> >>> Mailto: markom_at_ipexpert.com
>> >>> Telephone: +1.810.326.1444
>> >>> Web: http://www.ipexpert.com/
>> >>>
>> >>> On Sat, Feb 26, 2011 at 21:10, Malik Nouman Ahmad
>> >>> <djmalik_at_gmail.com>wrote:
>> >>>
>> >>>> One thing I forgot to mention. For CE-CE trace there is no label seen
>> in
>> >>>> the
>> >>>> traceroute but trace completes properly and I can ping between the
>> CEs
>> >>>> normally
>> >>>>
>> >>>> Thanks
>> >>>>
>> >>>> On Sun, Feb 27, 2011 at 12:07 AM, Malik Nouman Ahmad <
>> djmalik_at_gmail.com
>> >>>> >wrote:
>> >>>>
>> >>>> > Hi,
>> >>>> >
>> >>>> > I was studying MPLS VPN and while working on an example I am facing
>> >>>> some
>> >>>> > strange issue
>> >>>> >
>> >>>> > The connectivity is CE1 - PE1 - P1 - P2 - PE2 - CE2
>> >>>> >
>> >>>> > PE1(.1) - CE1 (.2) with subnet 172.16.1.0/24 with VRF A
>> (RD=RT=1:1)
>> >>>> > PE2(.1) - CE2 (.2) with subnet 172.16.2.0/24 with VRF A
>> (RD=RT=1:1)
>> >>>> >
>> >>>> > PE1 & PE2 have MPLS VPN set up and I can see labels for everything
>> >>>> > when
>> >>>> I
>> >>>> > check "show mpls forwarding" on the PEs
>> >>>> >
>> >>>> > when I trace from PE1 to CE2 I can see labels being switches
>> properly
>> >>>> using
>> >>>> > the following command
>> >>>> > trace vrf A 172.16.2.2 source 172.16.1.1
>> >>>> >
>> >>>> > but when trace from CE1 to CE2, there are no labels whatsoever
>> >>>> > trace 172.16.2.2 source 172.16.1.2
>> >>>> >
>> >>>> > Same thing is happening in the reverse direction (i.e. trace from
>> CE2
>> >>>> to
>> >>>> > CE1). I have done several examples previously and never faced such
>> >>>> issue.
>> >>>> > Instead of doing it all over again I want to troubleshoot the
>> problem
>> >>>> for
>> >>>> > learning purpose
>> >>>> >
>> >>>> > Can anybody suggest how to troubleshoot this problem? I have
>> applied
>> >>>> "no
>> >>>> > mpls ip propagate-ttl" just to see if it was working and it worked
>> >>>> >
>> >>>> > Please advise what should I do?
>> >>>> >
>> >>>> > Thanks,
>> >>>> > Malik
>> >>>>
>> >>>>
>> >>>> Blogs and organic groups at http://www.ccie.net
>> >>>>
>> >>>>
>> _______________________________________________________________________
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>> >
>> >
>> >
>> >
>> >
>> >
>>
>>
>> --
>> Warm Regards,
>>
>> Eseosa
>> CCIE #23782
>> You can learn anything just develop the right quantity of interest.

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Received on Sat Mar 05 2011 - 01:42:58 ART