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You cannot rewrite or remove existing tags.
•
VLAN—Packets transmitted over a PW must carry a P-tag.
For a packet from a CE:
− If the peer PE does not require the ingress to rewrite the P-tag, the PE keeps the P-tag
− If the peer PE requires the ingress to rewrite the P-tag, the PE changes the P-tag to the
For a packet to a CE:
− If the access mode is configured as VLAN by using the ac interface command, the PE
− If the access mode is configured as Ethernet by using the ac interface command, the
Ethernet over MPLS supports the following modes:
•
Port mode—A Layer 3 Ethernet interface is bound to a PW. Packets received from the Layer 3
Ethernet interface are forwarded through the bound PW. The default PW type for port mode is
Ethernet.
Figure 102 Packet encapsulation in port mode
•
VLAN mode—A Layer 3 Ethernet subinterface or VLAN interface is bound to a PW. Packets
received from the VLAN are forwarded through the bound PW. The peer PE can modify the
VLAN tag as needed. The default PW type for VLAN mode is VLAN.
PPP/HDLC over MPLS
PPP/HDLC over MPLS uses MPLS L2VPN to connect PPPs or HDLC networks, and delivers PPP or
HDLC packets through a PW over the MPLS backbone.
If the link type of the AC is PPP, the PW type is PPP. If the link type of the AC is HDLC, the PW type
is HDLC.
PPP/HDLC over MPLS supports only the port mode. You can associate a Layer 3 interface whose
encapsulation type is PPP or HDLC with a PW.
In a PPP/HDLC over MPLS network, a PE processes a PPP or HDLC packet as follows:
1.
After receiving a packet from a Layer 3 interface, the PE searches for the PW bound to the
interface.
2.
The PE encapsulates the packet and sends the packet to the peer PE through the PW.
unchanged for the packet, and then encapsulates the packet. If the packet contains no
P-tag, the PE adds a null label (the label value is 0) into the packet, and then
encapsulates the packet.
expected VLAN tag (the tag value might be 0), and then adds a PW label and an outer
tag into the packet. If the packet contains no P-tag, the PE adds a VLAN tag expected by
the peer PE (the tag value might be 0), and then adds a PW label and an outer tag into
the packet.
rewrites or retains the P-tag before forwarding the packet.
PE removes the P-tag before forwarding the packet.
408
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