[j-nsp] juniper mpls mtu

[Ricardo Tavares]

Hi!

Old topic:

http://puck.nether.net/pipermail/juniper-nsp/2007-June/008349.html


On Tue, Dec 2, 2008 at 6:05 PM, Andreas Friedrich <andreasf at colt.net> wrote:

> That sounds as we have interpreted it. But it does not seam to work for us.
> We have following setup
> CPE - PE (E-Series) - P (Cisco CRS-1)
> We send from the CPE ipv4 ping with 1500 byte DF set
> We get at the PE 2 labels on top. Only difference for E-Series is 18 bytes
> for Ethernet.
> PE int to P config:
> mtu 1534
> ip mtu 1500
>
> Calculation: 1534 - Ethernet header 18 byte - 4 byte .1q - 12 byte labels =
> 1500
>
> We use only 2 labels.
>
> If we configure mtu 1542 it works. If I calculate back I get
>
> 1500    IP packet
> 4               .1q
> 8               2 MPLS labels
> 18              Ethernet
> ------
> 1530 byte used
>
> So I need to configure 12 byte more. And that sounds for the 12 byte (3
> labels).
>
> What do you think?
>
> Thanks,
> Andreas
>
>
> Am 02.12.2008 um 20:47 schrieb Cyn D.:
>
>  Juniper default physical layer MTU 1514, family inet (IP) MTU 1500, family
>> MPLS 1488 (=1514-14-3X4) counted most tags possible (3).
>>
>> To pass big IP packet (1460+20+20), make MPLS MTU 1500, therefore
>> interface physical MTU is set to 1500+3x4+14=1526. this also makes family
>> inet mtu=1526-14=1512.
>>
>>
>>
>> C.
>>
>> ----- Original Message ----- From: "Andreas Friedrich" <andreasf at colt.net
>> >
>> To: "Phil Bedard" <philxor at gmail.com>
>> Cc: <juniper-nsp at puck.nether.net>
>> Sent: Tuesday, December 02, 2008 2:04 PM
>> Subject: Re: [j-nsp] juniper mpls mtu
>>
>>
>>
>> One more question regarding this MPLS MTU.
>> Are the 12 byte (3 labels) reserved by Juniper for there purpose and I
>> have to calculate my labels additional? So is MPLS MTU  than 1512 if I
>> want to use also 3 labels?
>>
>> Thanks,
>> Andreas
>>
>> Am 04.06.2008 um 01:54 schrieb Phil Bedard:
>>
>>  I think with most of the forwarding engines, the maximum number of
>>>  labels that can be pushed at one time is 3, hence the 12 bytes.
>>>
>>> Phil
>>>
>>> On Jun 3, 2008, at 9:15 AM, cp wrote:
>>>
>>>  I hoping someone can provide insight into why by default juniper
>>>> calculates mpls mtu at 12 bytes less than the ip mtu?  I've been
>>>>  testing
>>>> using l3vpn and it seems that mpls mtu pads 8 bytes to its mpls mtu
>>>> reducing the ip mtu the inside packet by 8 bytes. Quick example. So  if
>>>> mpls mtu is 1508 the ip mtu of the packet inside is 1500. That  means
>>>> the
>>>> ip mtu of the mpls interface is 1520. The only reason I can see
>>>> additional bytes needed on top of the l3vpn two is for fast reroute
>>>> bypass.  I assume it's for the safety factor although I am probably
>>>> missing something. Any information is appreciated.
>>>>
>>>>
>>>>
>>>> -Chip
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
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>>>
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>>
>> Andreas Friedrich
>> Network Engineer
>>
>> COLT Telecom GmbH
>> Herriotstr. 4
>> 60528 Frankfurt
>>
>>
>> Tel: + 49 (0)69 56606 6005    Internal: 8 491 6005
>> Fax: + 49 (0)69 56606 6350
>> Email: andreasf at colt.net
>>
>>
>>
>> www.colt.net
>>
>>
>>
>>
>>
>> Data | Voice | Managed Services
>>
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>>
>> *****************************************
>> COLT Telecom GmbH, Herriotstraße 4, 60528 Frankfurt/Main, Deutschland
>> • Tel +49 (0)69 56606 0 • Fax +49 (0)69 56606 2222 •
>>
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>>
>>
>> _______________________________________________
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>
> Andreas Friedrich
> Network Engineer
>
> COLT Telecom GmbH
> Herriotstr. 4
> 60528 Frankfurt
>
>
> Tel: + 49 (0)69 56606 6005    Internal: 8 491 6005
> Fax: + 49 (0)69 56606 6350
> Email: andreasf at colt.net
>
>
>
> www.colt.net
>
>
>
>
>
> Data | Voice | Managed Services
>
> Schütze Deine Umwelt | Erst denken, dann drucken
>
> *****************************************
> COLT Telecom GmbH, Herriotstraße 4, 60528 Frankfurt/Main, Deutschland • Tel
> +49 (0)69 56606 0 • Fax +49 (0)69 56606 2222 •
>
> Geschäftsführer: Albertus Marinus Oosterom (Vors.), Rita Thies •
> Amtsgericht Frankfurt/Main HRB 46123 • USt.-IdNr. DE 197 498 400
>
>
> _______________________________________________
> juniper-nsp mailing list juniper-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/juniper-nsp
>



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