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Ethernet/VLAN to Frame Relay Interworking
Frame Relay to Ethernet—Routed Interworking
To perform routed interworking, both the FR PE and Ethernet PE routers must be configured. When FR
packets arrive from the FR CE router, the FR PE router removes the frame relay header. The FR PE router
forwards the IP packet to the egress PE router using IPoMPLS encapsulation over the pseudowire. At
the Ethernet PE router, after label disposition, the IP packets are encapsulated with an MAC rewrite.
The address resolution is done at the FR PE router and is required when the FR CE router does an inverse
ARP. It is not required when the the FR CE router is configured using P2P subinterfaces or static maps.
For packets arriving from the Ethernet CE router, the Ethernet PE router removes the L2 framing. The
Ethernet PE router forwards the IP packet to the egress PE router, using IPoMPLS encapsulation over
the pseudowire. The Ethernet PE router makes the forwarding decision based on the L2 circuit ID
(VLAN ID or port ID) of the incoming L2 frame. At the FR PE router, after label disposition, the IP
packets are encapsulated over FR, using routed encapsulation based on RFC 2427.
The address resolution is also done at the Ethernet PE router by configuring static ARP on the Ethernet
CE router, or by implementing proxy ARP on the Ethernet PE router. If a proxy ARP is used, the IP
address of the remote CE router can be learned dynamically, or can be statically configured in the PE
router. Cisco IOS Release 12.2(33)XNE supports static and proxy ARP. Routing protocols need to be
configured to operate in a point-to-point mode on the Ethernet CE router.
Packets that arrive either from the FR CE or the Ethernet CE router with unsupported translations are
dropped.
Cisco IOS Release 12.2(33)XNE supports both Cisco and IETF Frame Relay.
Figure 21-16
routed interworking. Other than IPv4, the Prot_Type field is used while carrying L3 packets.
Figure 21-16
FR
CE
Cisco 10000 Series Router Software Configuration Guide
21-22
shows an example of the protocol stacks at the PEs when IPv4 PDUs are exchanged using
Protocol Stacks for FR to Ethernet Routed Interworking
Frame Relay
FR
PE
Q.922 Address
Control(03) NLPID(00)
Prot. Type
IPv4 Header
Data
FCS
Bridge Ethernet 802.3
MPLS Emulated VC of type TBD
Tunnel Label
VC Label
Control Word
(00-00)
(08-00)
Prot. Type
IPv4 Header
Data
MPoMPLS Encap
Chapter 21
Configuring L2VPN Interworking
Ethernet
Eth
PE
MAC Header
Tunnel Label
DA
VC Label
SA
Control Word
VLAN Tag
(00-00)
(08-00)
Type/Length
IPv4 Header
IPv4 Header
Data
Data
LAN FCS
802.1Q Encap
Eth
CE
OL-2226-23
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Troubleshooting
