[j-nsp] juniper mpls mtu

[Andreas Friedrich]

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

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