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Cisco 10000 Series Router Software Configuration Guide
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Chapter 21 Configuring L2VPN Interworking
Ethernet/VLAN to Frame Relay Interworking
FR DLCI to VLAN 802.1Q Local Switching—Bridged Interworking
This interworking type provides interoperability between Frame Relay Attachment VC and Ethernet
VLAN Attachment VC connected to the same PE router. For this interworking type the Bridged
Encapsulation is used, corresponding to Bridged (Ethernet) Interworking mechanism.
In the case of an Ethernet VLAN attachment, the VLAN ID is a service delimiter, so the VLAN header
is not included in the frame to or from the FR CE.
• In the VLAN to FR direction, the PE router discards the VLAN header from the Layer 2 packet. The
PE
router sends the frame to the FR egress interface after encapsulating the L2 packet over FR using
Bridged encapsulation.
• In the FR to VLAN direction, the FR header and bridged encapsulation are discarded and the
L2
packet is sent out with a VLAN header inserted, followed by the destination/source MAC
addresses.
The protocol stack for FR to Ethernet local switching (bridged interworking) is shown in Figure 21-12.
FR DLCI to Ethernet Port AToM—Bridged Interworking
This interworking type provides interoperability between FR attachment VC and Ethernet attachment
VC connected to different PE routers. Bridged encapsulation is used, corresponding to the Bridged
(Ethernet) Interworking mechanism.
For an FR to Ethernet Port case, the interworking function is performed at the PE connected to the
FR
attachment VC based on multiprotocol interconnect over Frame Relay (Figure 21-13). The
Interworking is implemented similar to an ATM-to-Ethernet case.
Figure 21-13 Network Topology for FR to Ethernet AToM Bridged Interworking
The advantage of this architecture is that the Ethernet PE (connected to the Ethernet segment) operates
similarly to Ethernet like-to-like services: a pseudowire label is assigned to the Ethernet port and then
the remote Label Distribution Protocol (LDP) session distributes the labels to its peer PE. Ethernet
frames are carried through the MPLS network using Ethernet over MPLS (EoMPLS).
On the PE with Interworking function, in the direction from the FR segment to MPLS cloud, the bridged
encapsulation (FR/SNAP header) is discarded and the Ethernet frame is encapsulated with the labels
required to go through the pseudowire using the VC type 5 (Ethernet) (
Figure 21-14).
In the opposite direction, after the label disposition from the MPLS cloud, Ethernet frames are
encapsulated over FR using bridged encapsulation.
The Figure 21-14 shows the protocol stack for FR to Ethernet Bridged Interworking.
270321
Ethernet
DLCI
FR Link
Ethernet Link
Tunnel LSP
Pseudowire using EoMPLS
P Router
P Router PE
PE with
interworking
function
FR CE
MPLS Network
Ethernet
CE