[j-nsp] Juniper Ethernet MTU question

[Ihsan Junaidi Ibrahim]

The interface will be used for a P-facing temporarily until a better PIC can
be POed. In what situation does an MPLS application warrant up to 3 labels
or an additional of 8 bytes over stock header of 4 bytes? How many labels
does a VPLS transport require?

On 9/29/06, Harry Reynolds <harry at juniper.net> wrote:
>
> Ah, dfe mtus. A subject near to my heart theses days.
>
> A few things.
>
> 1. The device mtu includes 14 bytes of ethernet header, the real mtu is
> 1500 bytes.
>
> 2. The inet mtu is automatically set to 1500, which matches real
> ethernet mtu.
>
> 3. The mpls mtu is automatically computed to be 12 bytes less than real
> mtu to accommodate up to 3 labels.
>
> In you case it does not sound that inet will be configured. The vlan tag
> does add an extra 4 bytes to the ethernet payload, resulting in need for
> 1504 byes of information and total device mtu of 1518. JUNOS software
> automatically adjust the device mtu when you enable vlan tagging.
>
> As for support of mpls, I assume this is a ce facing interface. As such
> packets to and from this interface will not be labeled. Labels are
> pushed as the packet enters the core. In a typical l2 vpn there would be
> two labels added; vrf and outer transport. The core interfaces will need
> an mtu of ethernet (1500) + vlan (4) + martini encap (0 | 4) + labels
> (8) + what ever link encap is needed based on core interface type. If
> the core interfaces are also ethernet then this is another 14 for total
> of 1526-1530 (the latter is with optional martini control word). Pos
> only add 4 bytes for link encap so mtu for core would be at least
> 1516-1520 for pos.
>
> As you seem aware the max mtu on the dfe cards is only 1532. In order to
> get this level of jumbo support you need to make sure you have the
> latest fpga. See below for tips on that. I believe that you will be OK
> with these cards as ce facing with the 1518 device mtu that results from
> simply enabling vlan tagging, but should be safe to enable a larger mtu
> as well. Technically the mtu of the CE devices should be used to
> dimension your ce and core facing interfaces, as best I can tell you
> will not need over 1518 device mtu if ce uses default ethernet mtu.
>
> To determine if you have the needed rev "c" 12x dfe firmware, do this
> (note hidden commands should only be used with Jtac guidance, and I'm
> not in jtac):
>
>
> Determine fpc/pic location. In this example its 0/2.
>
> Go to a shell, become root and vty to the fpc (0 in this case). Or use
> hidden command:
>
> start shell pfe network fpc0
>
> [edit interfaces fe-0/2/0]
> regress at boing# run start shell pfe network fpc0
>
>
> FPC platform (PPC 603e processor, 32MB memory, 256KB flash)
>
> FPC0(vty)#
>
> Now display the dfpga rev:
>
> FPC0(vty)# show dfe-pic 2 defpga
>
> PIC 2 DFE information:
>
> Dense FE PIC, 12 port(s) 1 GE links 1 cards
> Periodics are enabled
> Normal interrupts are enabled, total count is 406872
> IFD count is 12
> Main Card DE FPGA:
> Channel 0
>    Transmit Packets :  4397, Transmit Bytes : 0
>    Receive Packets :  11090, Receive Bytes : 0
>    (0x850e1080)                  DFE CPU cntl  : 0x8004
>    (0x850e1082)                    DFE Version : 0x000c <<<<< Rev c is
> needed to get over 1500 mtu
>    (0x850e1086)           DFE interrupt enable : 0x0010
> Transmit Tagged Status:
>
>
> HTHs
>
>
>
>
> > -----Original Message-----
> > From: juniper-nsp-bounces at puck.nether.net
> > [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of
> > Ihsan Junaidi Ibrahim
> > Sent: Friday, September 29, 2006 7:02 AM
> > To: Juniper-NSP
> > Subject: [j-nsp] Juniper Ethernet MTU question
> >
> > Hi all,
> >
> > 2 questions:
> >
> > 1) On a 12-port FE PIC, for vlan-cc encapsulation, should the
> > interface MTU be configured as 1518, 1522 or 1504? The
> > documentation below indicates that for vlan-ccc
> > encapsulation, it's a 4-byte field but I need to be certain.
> > http://www.junipernetworks.nl/techpubs/software/junos/junos76/
> > swconfig76-network-interfaces/html/interfaces-physical-config5
> .html#1085070
> >
> > 2) For a 12-port FE PIC, if I were to configure the maximum
> > physical MTU of 1532, will the PIC be able to accommodate MPLS MTU?
> >
> > --
> > Thank you for your time,
> > Ihsan Junaidi Ibrahim
> > _______________________________________________
> > juniper-nsp mailing list juniper-nsp at puck.nether.net
> > https://puck.nether.net/mailman/listinfo/juniper-nsp
> >
>



-- 
Thank you for your time,
Ihsan Junaidi Ibrahim