I have seen that but it does not make clear if the 12 byte are used by
Juniper or if it describe my 3 possible label.
But I see that we maybe did the mistake by setting the IP MTU to 1500.
Sound that IP MTU has a higher priority to the MPLS calculation as the
phys. interface MTU:
MPLS MTU = physical interface MTU - L2 encapsulation overhead - 12
if IP MTU is already set, so MPLS MTU = IP MTU + 20 bytes
Thanks,
Andreas
Am 02.12.2008 um 21:20 schrieb 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
<[EMAIL PROTECTED]> 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" <[EMAIL PROTECTED]
>
To: "Phil Bedard" <[EMAIL PROTECTED]>
Cc: <juniper-nsp@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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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: [EMAIL PROTECTED]
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 •
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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: [EMAIL PROTECTED]
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
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