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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Andreas Friedrich
Network Engineer
COLT Telecom GmbH
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Email: [EMAIL PROTECTED]
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