[nsp] Réf. : cisco-nsp Digest, Vol 13, Issue 54

[m.rapoport at completel.fr]

I don't think that the Control Word is used for Ethernet encapsulation.
draft-ietf-pwe3-ethernet-encap states that CW is optional for Ethernet
encapsulation and
implementations must support sending no CW.

Did someone check if the CW is used between Cisco gear for EoMPLS ?
Rgs,






Message: 12
Date: Tue, 23 Dec 2003 12:10:02 +0100
From: sthaug at nethelp.no
Subject: Re: [nsp] AToM
To: skiv at caravan.ru
Cc: cisco-nsp at puck.nether.net
Message-ID: <24052.1072177802 at verdi.nethelp.no>
Content-Type: Text/Plain; charset=us-ascii

> > Keep in mind that MPLS normally requires at least 8 bytes extra, and
> > EoMPLS has further encapsulation overhead.
>
> I know about additional bytes because of VLAN and MPLS tags.
> Let's count the maximum size of the packet.
> One PC sending 1500 bytes to other PC.
> When the packet arrives at the switch, switch adds 4 bytes VLAN tag.
> When packet arrives at the PE router (6509/7401) it adds 8 bytes (2x4
bytes)
> MPLS label tags. So total packet size is 1500 + 4 + 8 = 1512 bytes.
> Right?

No, there is more. If you're using EoMPLS, you have a normal Ethernet
frame minus the CRC (1514 bytes without VLAN tag, 1518 bytes with VLAN
tag), then add 2x4 bytes MPLS label and 4 bytes EoMPLS control word, for
a total of 1530 bytes.

> All input/output ports of the switches was configured with MTU=1540
bytes.
> But big packets didn't reach remote PE.

With 1540 bytes your configuration *should* have worked. I'm afraid I
have no idea why it didn't.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no


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