This section lists general restrictions that apply to L2VPN Interworking. Other restrictions that are platform-specific or device-specific are listed in the following sections.

• The interworking type on one provider edge (PE) router must match the interworking type on the peer PE router.

• The following quality of service (QoS) features are supported with L2VPN Interworking:

  • Static IP type of service (ToS) or Multiprotocol Label Switching (MPLS) experimental bit (EXP) setting in tunnel header
  • IP ToS reflection in tunnel header (Layer 2 Tunnel Protocol Version 3 (L2TPv3) only)
  • Frame Relay policing
  • Frame Relay data-link connection identifier (DLCI)-based congestion management (Cisco 7500/Versatile Interface Processor (VIP))
  • One-to-one mapping of VLAN priority bits to MPLS EXP bits

• Only ATM AAL5 VC mode is supported; ATM VP and port mode are not supported.

• In Cisco IOS Release 12.2(52)SE and Cisco IOS Release 12.2(33)SRE, the encapsulation command supports only the mpls keyword. The l2tpv3 keyword is not supported. The interworking command supports only the ethernet and vlan keywords. The ip keyword is not supported.

The following line cards are supported on the Cisco 7600 series router. The first table below shows the line cards that are supported on the WAN (ATM, Frame Relay, or PPP) side of the interworking link. The second table below shows the line cards that are supported on the Ethernet side of the interworking link. For more details on the Cisco 7600 routers supported shared port adapters and line cards, see the following document:

• Release Notes for Cisco IOS Release 12.2SR for the Cisco 7600 Series Routers

The following restrictions apply to the Cisco 7600 series routers and L2VPN Interworking:

• OAM Emulation is not required with L2VPN Interworking on the SIP-200, SIP-400, and Flexwan2 line cards.

• Cisco 7600 series routers support the L2VPN Interworking: VLAN Enable/Disable Option for AToM feature starting in Cisco IOS Release 12.2(33)SRE. This feature has the following restrictions:

  • PFC-based EoMPLS is not supported.
  • Scalable and SVI-based EoMPLS are supported with the SIP-400 line card.

• The Cisco 7600 series routers do not support L2VPN Interworking over L2TPv3.

• Cisco 7600 series routers support only the following interworking types:

  • Ethernet/VLAN to Frame Relay (IP and Ethernet modes)
  • Ethernet/VLAN to ATM AAL5SNAP (IP and Ethernet modes)
  • Ethernet/VLAN to PPP (IP only)
  • Ethernet to VLAN Interworking
• Cisco 7600 series routers do not support the following interworking types:

  • Ethernet/VLAN to ATM AAL5MUX
  • Frame Relay to PPP Interworking
  • Frame Relay to ATM AAL5 Interworking
• Both ends of the interworking link must be configured with the same encapsulation and interworking type:

  • If you use Ethernet encapsulation, you must use the Ethernet (bridged) interworking type. If you are not using Ethernet encapsulation, you can use a bridging mechanism, such as routed bridge encapsulation (RBE).
  • If you use an IP encapsulation (such as ATM or Frame Relay), you must use the IP (routed) interworking type. The PE routers negotiate the process for learning and resolving addresses.
  • You must use the same MTU size on the attachment circuits at each end of the pseudowire.

• PFC-based EoMPLS is not supported on ES40 line cards. SVI and EVC/scalable EoMPLS are the alternative options.

• PFC-based EoMPLS is not supported for Routed/IP interworking in Cisco IOS Release 12.2(33)SRD and later releases. The alternative Routed/IP interworking options are SVI and EVC or scalable EoMPLS. However, PFC-based EoMPLS is supported for Ethernet/Bridged interworking and for like-to-like over AToM.

For more information about hardware requirements on the Cisco12000 series routers, see the Cross-Platform Release Notes for Cisco IOS Release 12.0S.

For QOS support on the Cisco 12000 series routers, see Any Transport over MPLS (AToM): Layer 2 QoS (Quality of Service) for the Cisco 12000 Series Router

The following restrictions apply to ATM AAL5 Interworking:

• Switched virtual circuits (SVCs) are not supported.

• Inverse Address Resolution Protocol (ARP) is not supported with IP interworking.

• Customer edge (CE) routers must use point-to-point subinterfaces or static maps.

• Both AAL5MUX and AAL5SNAP encapsulation are supported. In the case of AAL5MUX, no translation is needed.

• In the Ethernet end-to-end over ATM scenario, the following translations are supported:

  • Ethernet without LAN frame check sequence (FCS) (AAAA030080C200070000)
  • Spanning tree (AAAA030080c2000E)

Everything else is dropped.

• In the IP over ATM scenario, the IPv4 (AAAA030000000800) translation is supported. Everything else is dropped.

• Operation, Administration, and Management (OAM) emulation for L2VPN Interworking is the same as like-to-like. The end-to-end F5 loopback cells are looped back on the PE router. When the pseudowire is down, an F5 end-to-end segment Alarm Indication Signal (AIS)/Remote Defect Identification (RDI) is sent from the PE router to the CE router.

• Interim Local Management Interface (ILMI) can manage virtual circuits (VCs) and permanent virtual circuits (PVCs).

• To enable ILMI management, configure ILMI PVC 0/16 on the PE router’s ATM interface. If a PVC is provisioned or deleted, an ilmiVCCChange trap is sent to the CE router.

• Only the user side of the User-Network Interface (UNI) is supported; the network side of the UNI is not supported.

The following restrictions apply to Ethernet/VLAN interworking:

• When you configure VLAN to Ethernet interworking, VLAN to Frame Relay (routed), or ATM using Ethernet (bridged) interworking, the PE router on the Ethernet side that receives a VLAN tagged frame from the CE router removes the VLAN tag. In the reverse direction, the PE router adds the VLAN tag to the frame before sending the frame to the CE router.

(If you enable the L2VPN Interworking: VLAN Enable/Disable Option for AToM feature with the interworking vlan command, VLAN ID is included as part of the Ethernet frame. See the VLAN Interworking for more information. )

• In bridged interworking from VLAN to Frame Relay, the Frame Relay PE router does not strip off VLAN tags from the Ethernet traffic it receives.

• The Cisco 10720 Internet router supports Ethernet to VLAN Interworking Ethernet only over L2TPv3.

• Ethernet interworking for a raw Ethernet port or a VLAN trunk is not supported. Traffic streams are not kept separate when traffic is sent between transport types.

• In routed mode, only one CE router can be attached to an Ethernet PE router.

• There must be a one-to-one relationship between an attachment circuit and the pseudowire. Point-to-multipoint or multipoint-to-point configurations are not supported.

• Configure routing protocols for point-to-point operation on the CE routers when configuring an Ethernet to non-Ethernet setup.

• In the IP interworking mode, the IPv4 (0800) translation is supported. The PE router captures ARP (0806) packets and responds with its own MAC address (proxy ARP). Everything else is dropped.

• The Ethernet or VLAN must contain only two IP devices: PE router and CE router. The PE router performs proxy ARP and responds to all ARP requests it receives. Therefore, only one CE and one PE router should be on the Ethernet or VLAN segment.

• If the CE routers are doing static routing, you can perform the following tasks:

  • The PE router needs to learn the MAC address of the CE router to correctly forward traffic to it. The Ethernet PE router sends an Internet Control Message Protocol (ICMP) Router discovery protocol (RDP) solicitation message with the source IP address as zero. The Ethernet CE router responds to this solicitation message. To configure the Cisco CE router’s Ethernet or VLAN interface to respond to the ICMP RDP solicitation message, issue the ip irdpcommand in interface configuration mode. If you do not configure the CE router, traffic is dropped until the CE router sends traffic toward the PE router.
  • To disable the CE routers from running the router discovery protocol, issue the ip irdp maxadvertinterval 0 command in interface mode.

• This restriction applies if you configure interworking between Ethernet and VLAN with Catalyst switches as the CE routers. The spanning tree protocol is supported for Ethernet interworking. Ethernet interworking between an Ethernet port and a VLAN supports spanning tree protocol only on VLAN 1. Configure VLAN 1 as a nonnative VLAN.

• When you change the interworking configuration on an Ethernet PE router, clear the ARP entry on the adjacent CE router so that it can learn the new MAC address. Otherwise, you might experience traffic drops.

The following restrictions apply to the L2VPN Interworking: VLAN Enable/Disable Option for AToM feature, which allows the VLAN ID to be included as part of the Ethernet frame:

• The L2VPN Interworking: VLAN Enable/Disable Option for AToM feature is supported on the following releases:

  • Cisco IOS release 12.2(52)SE for the Cisco Catalyst 3750 Metro switches
  • Cisco IOS Release 12.2(33)SRE for the Cisco 7600 series routers

• L2VPN Interworking: VLAN Enable/Disable Option for AToM is not supported with L2TPv3. You can configure the featue only with AToM.

• If the interface on the PE router is a VLAN interface, it is not necessary to specify the interworking vlan command on that PE router.

• The L2VPN Interworking: VLAN Enable/Disable Option for AToM feature works only with the following attachment circuit combinations:

  • Ethernet to Ethernet
  • Ethernet to VLAN
  • VLAN to VLAN

• If you specify an interworking type on a PE router, that interworking type must be enforced. The interworking type must match on both PE routers. Otherwise, the VC may be in an incompatible state and remain in the down state. If the attachment circuit (AC) is VLAN, the PE router can negotiate (autosense) the VC type using Label Distribution Protocol (LDP).

For example, both PE1 and PE2 use Ethernet interfaces, and VLAN interworking is specified on PE1 only. PE2 is not configured with an interworking type and cannot autosense the interworking type. The result is an incompatible state where the VC remains in the down state.

On the other hand, if PE1 uses an Ethernet interface and VLAN interworking is enabled (which will enforce VLAN as the VC type), and PE2 uses a VLAN interface and interworking is not enabled (which causes PE2 to use Ethernet as its default VC type), PE2 can autosense and negotiate the interworking type and select VLAN as the VC type.

The table below summarizes shows the AC types, interworking options, and VC types after negotiation.

The following restrictions apply to Frame Relay interworking:

• The attachment circuit maximum transmission unit (MTU) sizes must match when you connect them over MPLS. By default, the MTU size associated with a Frame Relay DLCI is the interface MTU. This may cause problems, for example, when connecting some DLCIs on a PoS interface (with a default MTU of 4470 bytes) to Ethernet or VLAN (with a default MTU of 1500 bytes) and other DLCIs on the same PoS interface to ATM (with a default MTU of 4470 bytes). To avoid reducing all the interface MTUs to the lowest common denominator (1500 bytes in this case), you can specify the MTU for individual DLCIs using the mtu command.

• Only DLCI mode is supported. Port mode is not supported.

• Configure Frame Relay switching to use DCE or Network-to-Network Interface (NNI). DTE mode does not report status in the Local Management Interface (LMI) process. If a Frame Relay over MPLS circuit goes down and the PE router is in DTE mode, the CE router is never informed of the disabled circuit. You must configure the frame-relay switching command in global configuration mode in order to configure DCE or NNI.

• Frame Relay policing is non-distributed on the Cisco 7500 series routers. If you enable Frame Relay policing, traffic is sent to the route switch processor for processing.

• Inverse ARP is not supported with IP interworking. CE routers must use point-to-point subinterfaces or static maps.

• The PE router automatically supports translation of both the Cisco encapsulations and the Internet Engineering Task Force (IETF) encapsulations that come from the CE, but translates only to IETF when sending to the CE router. This is not a problem for the Cisco CE router, because it can handle IETF encapsulation on receipt even if it is configured to send Cisco encapsulation.

• With Ethernet interworking, the following translations are supported:

  • Ethernet without LAN FCS (0300800080C20007 or 6558)
  • Spanning tree (0300800080C2000E or 4242)

All other translations are dropped.

• With IP interworking, the IPv4 (03CC or 0800) translation is supported. All other translations are dropped.

• PVC status signaling works the same way as in like-to-like case. The PE router reports the PVC status to the CE router, based on the availability of the pseudowire. PVC status detected by the PE router will also be reflected into the pseudowire. LMI to OAM interworking is supported when you connect Frame Relay to ATM.

The following restrictions apply to PPP interworking:

• There must be a one-to-one relationship between a PPP session and the pseudowire. Multiplexing of multiple PPP sessions over the pseudowire is not supported.

• There must be a one-to-one relationship between a PPP session and a Frame Relay DLCI. Each Frame Relay PVC must have only one PPP session.

• Only IP (IPv4 (0021) interworking is supported. Link Control Protocol (LCP) packets and Internet Protocol Control Protocol (IPCP) packets are terminated at the PE router. Everything else is dropped.

• Proxy IPCP is automatically enabled on the PE router when IP interworking is configured on the pseudowire.

• By default, the PE router assumes that the CE router knows the remote CE router’s IP address.

• Password Authentication Protocol (PAP) and Challenge-Handshake Authentication Protocol (CHAP) authentication are supported.