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debug mpls packet

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andy.saykao at staff

Nov 16, 2009, 11:03 PM

Post #1 of 10 (943 views)
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debug mpls packet

Hi All,

Does anyone know what the middle number represents in a "debug mpls
packet" ( eg: {7963 6 254} )?
I can't find this information anywhere.

router#debug mpls packet gigabitEthernet 0/2
Packet debugging is on on idb GigabitEthernet0/2
router#
Nov 17 16:26:07.670 AEDT: MPLS turbo: Gi0/2: rx: Len 97 Stack {7963 6
254} - ipv4 data
Nov 17 16:26:08.442 AEDT: MPLS turbo: Gi0/2: rx: Len 78 Stack {7963 6
254} - ipv4 data
Nov 17 16:26:11.882 AEDT: MPLS turbo: Gi0/2: rx: Len 82 Stack {18 0 254}
{2750 0 255} - ipv4 data
Nov 17 16:26:11.882 AEDT: MPLS turbo: Gi0/1: tx: Len 82 Stack {8878 0
253} {2750 0 255} - ipv4 data

{7963 6 254}

7693 = Label
6 = ???
254 = I presume is the TTL

What does the 6 represent??

In the other label, it's a ZERO instead {18 0 254} .

Thanks.

Andy

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oboehmer at cisco

Nov 16, 2009, 11:25 PM

Post #2 of 10 (917 views)
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Re: debug mpls packet [In reply to]

>
> Does anyone know what the middle number represents in a "debug mpls
> packet" ( eg: {7963 6 254} )?
> I can't find this information anywhere.
>
> 7693 = Label
> 6 = ???
> 254 = I presume is the TTL
>
> What does the 6 represent??

it's the EXP value. you're right about the last being the TTL.

oli
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bandwidth.user at gmail

Nov 16, 2009, 11:43 PM

Post #3 of 10 (916 views)
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Re: debug mpls packet [In reply to]

Oliver Boehmer (oboehmer) wrote:
>> Does anyone know what the middle number represents in a "debug mpls
>> packet" ( eg: {7963 6 254} )?
>> I can't find this information anywhere.
>>
>> 7693 = Label
>> 6 = ???
>> 254 = I presume is the TTL
>>
>> What does the 6 represent??
>
> it's the EXP value. you're right about the last being the TTL.
>
> oli

Could it be the 3-bit EXP and 1-bit Bottom of Stack Flag combined?

Roy
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oboehmer at cisco

Nov 16, 2009, 11:49 PM

Post #4 of 10 (915 views)
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Re: debug mpls packet [In reply to]

> >> Does anyone know what the middle number represents in a "debug mpls
> >> packet" ( eg: {7963 6 254} )?
> >> I can't find this information anywhere.
> >>
> >> 7693 = Label
> >> 6 = ???
> >> 254 = I presume is the TTL
> >>
> >> What does the 6 represent??
> >
> > it's the EXP value. you're right about the last being the TTL.
> >
> > oli
>
> Could it be the 3-bit EXP and 1-bit Bottom of Stack Flag combined?

Hmm, why do you think so? Looking at the code, it only prints the 3 exp.
bits.

oli
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bandwidth.user at gmail

Nov 17, 2009, 12:05 AM

Post #5 of 10 (916 views)
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Re: debug mpls packet [In reply to]

Oliver Boehmer (oboehmer) wrote:
>>>> Does anyone know what the middle number represents in a "debug mpls
>>>> packet" ( eg: {7963 6 254} )?
>>>> I can't find this information anywhere.
>>>>
>>>> 7693 = Label
>>>> 6 = ???
>>>> 254 = I presume is the TTL
>>>>
>>>> What does the 6 represent??
>>> it's the EXP value. you're right about the last being the TTL.
>>>
>>> oli
>> Could it be the 3-bit EXP and 1-bit Bottom of Stack Flag combined?
>
> Hmm, why do you think so? Looking at the code, it only prints the 3 exp.
> bits.

Cisco must have combined RFC3032 [2.1. Encoding the Label Stack] into
one value.

Roy
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bandwidth.user at gmail

Nov 17, 2009, 12:19 AM

Post #6 of 10 (913 views)
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Re: debug mpls packet [In reply to]

roy wrote:
> Oliver Boehmer (oboehmer) wrote:
>>>>> Does anyone know what the middle number represents in a "debug mpls
>>>>> packet" ( eg: {7963 6 254} )?
>>>>> I can't find this information anywhere.
>>>>>
>>>>> 7693 = Label
>>>>> 6 = ???
>>>>> 254 = I presume is the TTL
>>>>>
>>>>> What does the 6 represent??
>>>> it's the EXP value. you're right about the last being the TTL.
>>>>
>>>> oli
>>> Could it be the 3-bit EXP and 1-bit Bottom of Stack Flag combined?
>>
>> Hmm, why do you think so? Looking at the code, it only prints the 3 exp.
>> bits.
>
> Cisco must have combined RFC3032 [2.1. Encoding the Label Stack] into
> one value.

Referring to EXP/CoS + S, that is.

Roy
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oboehmer at cisco

Nov 17, 2009, 4:19 AM

Post #7 of 10 (903 views)
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Re: debug mpls packet [In reply to]

> >>>> Does anyone know what the middle number represents in a "debug
mpls
> >>>> packet" ( eg: {7963 6 254} )?
> >>>> I can't find this information anywhere.
> >>>>
> >>>> 7693 = Label
> >>>> 6 = ???
> >>>> 254 = I presume is the TTL
> >>>>
> >>>> What does the 6 represent??
> >>> it's the EXP value. you're right about the last being the TTL.
> >>>
> >>> oli
> >> Could it be the 3-bit EXP and 1-bit Bottom of Stack Flag combined?
> >
> > Hmm, why do you think so? Looking at the code, it only prints the 3
exp.
> > bits.
>
> Cisco must have combined RFC3032 [2.1. Encoding the Label Stack] into
> one value.

still not sure what you refer to, and why you think the debug discussed
shows the 4-bit Exp+S value rather than the 3-bit Exp only?

oli
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bandwidth.user at gmail

Nov 17, 2009, 7:38 PM

Post #8 of 10 (904 views)
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Re: debug mpls packet [In reply to]

Oliver Boehmer (oboehmer) wrote:
>
>>>>>> Does anyone know what the middle number represents in a "debug
> mpls
>>>>>> packet" ( eg: {7963 6 254} )?
>>>>>> I can't find this information anywhere.
>>>>>>
>>>>>> 7693 = Label
>>>>>> 6 = ???
>>>>>> 254 = I presume is the TTL
>>>>>>
>>>>>> What does the 6 represent??
>>>>> it's the EXP value. you're right about the last being the TTL.
>>>>>
>>>>> oli
>>>> Could it be the 3-bit EXP and 1-bit Bottom of Stack Flag combined?
>>> Hmm, why do you think so? Looking at the code, it only prints the 3
> exp.
>>> bits.
>> Cisco must have combined RFC3032 [2.1. Encoding the Label Stack] into
>> one value.
>
> still not sure what you refer to, and why you think the debug discussed
> shows the 4-bit Exp+S value rather than the 3-bit Exp only?

If I may, MPLS Fundamentals refers to the stack on Fig 2-1 as
Label/EXP/BoS/TTL. It then breaks this on Example 3-8 with {label EXP
TTL}. All things held constant; label at 20, TTL at 8, then EXP must be 3+1.

Roy
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deadheadblues at gmail

Nov 17, 2009, 8:09 PM

Post #9 of 10 (902 views)
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Re: debug mpls packet [In reply to]

On Tue, Nov 17, 2009 at 8:38 PM, roy <bandwidth.user [at] gmail> wrote:

> Oliver Boehmer (oboehmer) wrote:
>
>>
>>
>>> Does anyone know what the middle number represents in a "debug
>>>>>>>
>>>>>> mpls
>>
>>> packet" ( eg: {7963 6 254} )?
>>>>>>> I can't find this information anywhere.
>>>>>>>
>>>>>>> 7693 = Label
>>>>>>> 6 = ???
>>>>>>> 254 = I presume is the TTL
>>>>>>>
>>>>>>> What does the 6 represent??
>>>>>>>
>>>>>> it's the EXP value. you're right about the last being the TTL.
>>>>>>
>>>>>> oli
>>>>>>
>>>>> Could it be the 3-bit EXP and 1-bit Bottom of Stack Flag combined?
>>>>>
>>>> Hmm, why do you think so? Looking at the code, it only prints the 3
>>>>
>>> exp.
>>
>>> bits.
>>>>
>>> Cisco must have combined RFC3032 [2.1. Encoding the Label Stack] into
>>> one value.
>>>
>>
>> still not sure what you refer to, and why you think the debug discussed
>> shows the 4-bit Exp+S value rather than the 3-bit Exp only?
>>
>
> If I may, MPLS Fundamentals refers to the stack on Fig 2-1 as
> Label/EXP/BoS/TTL. It then breaks this on Example 3-8 with {label EXP TTL}.
> All things held constant; label at 20, TTL at 8, then EXP must be 3+1.
>
> Roy
>
> _______________________________________________
> cisco-nsp mailing list cisco-nsp [at] puck
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/
>

Reading too much into it. It's just not showing the stack bit. The output is
for information. You don't need to know the stack bit, its the only label.
And if there were more than one, then it would show all labels.
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bandwidth.user at gmail

Nov 17, 2009, 9:25 PM

Post #10 of 10 (893 views)
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Re: debug mpls packet [In reply to]

Hobbs wrote:
>
>
> On Tue, Nov 17, 2009 at 8:38 PM, roy <bandwidth.user [at] gmail
> <mailto:bandwidth.user [at] gmail>> wrote:
>
> Oliver Boehmer (oboehmer) wrote:
>
>
>
> Does anyone know what the middle number
> represents in a "debug
>
> mpls
>
> packet" ( eg: {7963 6 254} )?
> I can't find this information anywhere.
>
> 7693 = Label
> 6 = ???
> 254 = I presume is the TTL
>
> What does the 6 represent??
>
> it's the EXP value. you're right about the last
> being the TTL.
>
> oli
>
> Could it be the 3-bit EXP and 1-bit Bottom of Stack
> Flag combined?
>
> Hmm, why do you think so? Looking at the code, it only
> prints the 3
>
> exp.
>
> bits.
>
> Cisco must have combined RFC3032 [2.1. Encoding the Label
> Stack] into
> one value.
>
>
> still not sure what you refer to, and why you think the debug
> discussed
> shows the 4-bit Exp+S value rather than the 3-bit Exp only?
>
>
> If I may, MPLS Fundamentals refers to the stack on Fig 2-1 as
> Label/EXP/BoS/TTL. It then breaks this on Example 3-8 with {label
> EXP TTL}. All things held constant; label at 20, TTL at 8, then EXP
> must be 3+1.
>
> Roy
>
> _______________________________________________
> cisco-nsp mailing list cisco-nsp [at] puck
> <mailto:cisco-nsp [at] puck>
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/
>
>
> Reading too much into it. It's just not showing the stack bit. The
> output is for information. You don't need to know the stack bit, its the
> only label. And if there were more than one, then it would show all labels.

Right on, too much reading. I didn't take the text as it is. Oli was on
spot. Cheers!

Roy
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