[c-nsp] MPLS Label stack depth and MTU

[Christopher Hunt]

I should have specified that links b,c and d are provided by local fiber 
providers (PUDs, telcos, etc.) and are not under our direct control.  
They are adding the VLAN tags.

Christopher Hunt
ReachONE Internet, Inc.
(888)820-7559



Gert Doering wrote:
> Hi,
>
> On Tue, Apr 29, 2008 at 09:01:05AM -0700, Christopher Hunt wrote:
>   
>>     My understanding is there is one 4 byte label for the MPLS VPN 
>> (MP-BGP label) plus one for MPLS transport (which is switched out by 
>> each P, then popped by PE2. If I want to deliver an edge MTU (at points 
>> a and e) of 1500 i expect to need a core MTU (at points b,c,e) of 1526 
>> bytes (edge MTU 1500 + transport header (18 bytes for 802.1Q Vlan 
>> tagging) + 8 bytes for the 2 MPLS labels.  
>>     
>
> I don't see why you would need 18 bytes 802.1Q Ethernet framing here.
>
> If this is a *L3* VPN, there are no Ethernet frames.
>
> (If you do EoMPLS, then there is 18 bytes Ethernet, of course, plus
> two labels - but that's L2 VPN)
>
> gert
>