30-14
Catalyst 3750 Metro Switch Software Configuration Guide
78-15870-01
Chapter 30 Configuring MPLS and EoMPLS
Understanding EoMPLS
By entering the mpls l2transport route or the xconnect interface configuration command on either a
VLAN for VLAN-based EoMPLS or an Ethernet port for port-based EoMPLS, you can configure an
EoMPLS tunnel to forward traffic based on either the customer VLAN or the Ethernet port.
• To forward 802.1Q tunnel-encapsulated traffic through the MPLS core to a specific recipient on the
other side of the MPLS network, configure port-based EoMPLS.
• To forward 802.1Q tunnel-encapsulated traffic from an access device to a PE router, configure
VLAN-based EoMPLS.
EoMPLS and Layer 2 Tunneling
Layer 2 protocol tunneling over an EoMPLS link allows CDP, STP, and VTP protocol data units (PDUs)
to be tunneled through an MPLS network. To support Layer 2 protocol tunneling when the Layer 2
device connects to an MPLS network through a switch functioning as a PE, you configure the ingress
port on the PE that receives the Layer 2 protocol traffic as a tunnel port. The Layer 2 protocol traffic is
encapsulated before it is forwarded over the MPLS network. For more information about Layer 2
protocol tunneling, see Chapter 13, “Configuring IEEE 802.1Q and Layer 2 Protocol Tunneling.”
EoMPLS and QoS
EoMPLS supports QoS by using three experimental bits in a label to determine the priority of packets.
To support QoS between label edge routers (LERs), you set the experimental bits in both the VC and
tunnel labels. EoMPLS QoS classification occurs on ingress, and you can only match on Layer 3
parameters (such as IP or DSCP), not Layer 2 parameters (CoS). See the “Configuring MPLS and
EoMPLS QoS” section on page 30-18 for more information about EoMPLS and QoS.
EoMPLS Limitations
These restrictions apply to EoMPLS:
• EoMPLS requires that at least one of the two ES ports be configured for MPLS. Therefore, if you
want to run EoMPLS on an ES port, you can only configure it on the ES port that is not configured
for MPLS.
• MTU—EoMPLS does not support packet fragmentation and reassembly. Therefore, the maximum
transmission unit (MTU) of all intermediate links between endpoints must be sufficient to carry the
largest Layer 2 VLAN received. The ingress and egress PE routers must have the same MTU value.
• Address Format—All loopback addresses on PE routers must be configured with 32-bit masks to
ensure proper operation of MPLS forwarding. OSPF requires the use of loopback addresses.
• Packet Format—EoMPLS supports VLAN packets that conform to the IEEE 802.1Q standard. ISL
encapsulation is not supported between PE and CE routers.
• The maximum number of VLANs using EoMPLS on a switch is 1005.
• Layer 2 connection restrictions:
–
You cannot have a direct Layer 2 connection between PEs with EoMPLS.
–
You cannot have more than one Layer 2 connection between routers if those routers are
configured to transport Ethernet VLANs over the MPLS backbone. Adding a second Layer 2
connection causes the spanning-tree state to constantly toggle if you disable spanning tree on
the peer router.
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