[j-nsp] juniper mpls mtu

[Andreas Friedrich]

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
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> juniper-nsp mailing list juniper-nsp at puck.nether.net
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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
>
>
>
>
>
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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