[129585] in North American Network Operators' Group
Transporting QinQ across a Layer 2 link locked at 1518 octets AND
daemon@ATHENA.MIT.EDU (Francois Menard)
Sun Sep 12 22:07:04 2010
From: Francois Menard <francois@menards.ca>
Date: Sun, 12 Sep 2010 22:06:47 -0400
To: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
Folks,
Question #1:
Is it possible for me to put an MPLS router on both ends of a circuit =
leased from a transport service provider which does not support QinQ =
(i.e. packets of 1526 bytes), and which requires us to tag traffic onto =
a well specified set of VLANs (i.e. if we want two VLANs, the service =
provider tells us which two VLANs to use).
I was thinking of lowering the MTU size on my MPLS router such that I =
could do QinQ over VPLS, over MPLS, over Ethernet transport locked at @ =
1514 octets.
I would imagine that my effective IPv4 payload would be reduced to =
something like (not taking into account CRC removed in the Ethernet =
driver)
1514 minus 8 bytes for MPLS label minus 4 bytes for VPLS control word =
minus 4 bytes for VLAN tag #1 minus 4 bytes for VLAN tag #2 =3D=20
1514 -8 -4 -4 -4 -4 =3D 1490 octets
So if I set my MTU on my MPLS router at 1490 octets and send QinQ over =
VPLS over , wouldn't that allow for all of the above mentioned overhead =
to pile-up without exceeding the 1514 octets size allowed by my =
transport provider ?
Question #2:
I have another link, which is restricted by the transport service =
provider, which is an MPLS-VPN service, and which does not support QinQ, =
nor supports layer 2 bridging.
An option available to me is to use an EoIP tunnel on a Mikrotik =
RouterOS router, which maps Ethernet over GRE over IP, causing some 28 =
octets of overhead. This is proprietary to Mikrotik.
So in this case, assuming that I want to do something as dangerous as:
QinQ over VPLS over MPLS over Ethernet over EoIP (over GRE, over IP)
And accordingly set my MTU to:
1480 (from above) minus 28 octets (Ethernet over GRE over IP) =3D 1452 =
octets=20
So if I set my MTU on my MPLS router at 1452 octets, wouldn't that allow =
for all of the above mentioned overhead to be successfully transported =
across an IP layer 3 circuit, effectively ending up with
QinQ over MPLS over Ethernet over IP ?
What are the consequences of setting the MTU as low as 1452 octets? =
What applications end-up breaking ?
-=3DFrancois=3D-
