Configuring the ECN330-switch
316 1553-KDU 137 365 Uen D 2006-06-16
Packet Flow for L2MPLS Tunnel
1. The ingress Provider Equipment (PE) switch receives an Ethernet frame
and encapsulates the packet by removing the preamble, the start of frame
delimiter (SFD), and the frame check sequence (FCS). The rest of the
packet header is not changed.
2. If a port based VC label is configured, it will be added to all incoming
packets.
3. If a packet has multiple VLAN tags, the access port uses the outer VLAN ID
as an index to search its VC table. If a valid VC entry is found and the
destination port is an uplink port, the ingress Provider Equipment (PE)
switch adds the VC label and an optional tunnel label to the packet for
normal MPLS routing through the MPLS backbone. If the packet already has
a port-based VC label, it will be replaced with the new VC label.
One VLAN can only be mapped to one input VC and one output VC.
However, one VC can be mapped to multiple VLANs. The input VC and
output VC should normally be configured to the same value. Also, note that
a maximum 8 input VCs and 8 output VCs are supported on the ECN330-
switch.
4. The network core routers use the tunnel label to move the packet through
the MPLS backbone and do not distinguish Ethernet traffic from any other
types of packets in the MPLS backbone.
5. At the other end of the MPLS backbone, the egress PE switch receives the
packet and de-encapsulates the packet by removing the tunnel label if one
is present. The PE switch also removes the VC label from the packet. Any
inbound traffic is not an MPLS packet is dropped.
6. The PE switch updates the header, if necessary, and sends the packet out
the appropriate interface to the destination switch.
Configuration Limitations for L2MPLS
The following configuration limitations apply to L2MPLS:
• Only one Gigabit Ethernet (GE) port can be configured to L2MPLS
uplink mode.
• L2MPLS 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
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