[j-nsp] juniper mpls mtu

[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
>> https://puck.nether.net/mailman/listinfo/juniper-nsp
>
> _______________________________________________
> juniper-nsp mailing list juniper-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/juniper-nsp

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