Cisco 10000-2P2-2DC Software Guide - Page 459

Chapter 21 Configuring L2VPN Interworking Ethernet/VLAN to ATM AAL5 Interworking The interworking function is performed in the same way as for the ATM to Ethernet Port case, implemented on the PE connected to the ATM attachment VC. The implementation is based on Multiprotocol Encapsulation over ATM Adaptation Layer 5 (see Figure 21-4). For the PE connected to the Ethernet side, one major difference exists due the existence of the VLAN header in the incoming packet. The PE discards the VLAN header of the incoming frames from the VLAN CE, and the PE inserts a VLAN header into the Ethernet frames traveling from the MPLS cloud. The frames sent on the pseudowire (with VC type 5) are Ethernet frames without the VLAN header. Encapsulation over ATM Adaptation Layer 5, as shown in Figure 21-6. Figure 21-6 Protocol Stack for ATM to VLAN AToM Bridged Interworking ATM CE ATM ATM Header LLC (AA-AA) LLC(03) OUI (00) OUI (80-C2) PID (00-07) PAD (00-00) MAC Header DA SA Type/Length ATM PE MPLS Emulated VC of Eth PE Tunnel Label VC Label Control Word MAC Header DA SA Type/Length Tunnel Label VC Label Control Word MAC Header DA SA Type/Length Ethernet MAC Header DA SA Type/Length VLAN Remainder of MAC Frame Remainder of MAC Frame Remainder of MAC Frame Remainder of MAC Frame CPCS - UU CPI Length CRC LAN FCS ATM to Ethernet-Routed Interworking To perform routed interworking, both the ATM PE and Ethernet PE routers must be configured. Figure 21-7 shows the routed interworking between ATM to Ethernet. The IP encapsulation over the pseudowire is performed on the ATM packets arriving from the ATM CE router. The address resolution is done at the ATM PE router; it is required when the ATM CE router does an inverse ARP. It is not required when the ATM CE router is configured using P2P subinterfaces or static maps. When packets arrive from the Ethernet CE router, the Ethernet PE router removes the L2 frame tag, and then 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, the VLAN ID, or port ID, of the incoming L2 frame. At the ATM PE router, after label disposition, the IP packets are encapsulated over the AAL5 using routed encapsulation based on RFC 2684. The address resolution at the Ethernet PE router can be done when the Ethernet CE router configures the static ARP, or by the proxy ARP on the Ethernet PE. If the proxy ARP is used, the IP address of the remote CE can be learned dynamically. Cisco IOS Release 12.2(33)XNE supports static and proxy ARP. Routing protocols need to be configured to operate in the P2P mode on the Ethernet CE. 270314 OL-2226-23 Cisco 10000 Series Router Software Configuration Guide 21-11