RFC 1483 bridging on ATM interfaces supports the point-to-point bridging of Layer 2 packet data units (PDUs) over Ethernet networks. RFC 1490 Frame Relay bridging on Packet over SONET (POS) or serial interfaces that are configured for Frame Relay encapsulation provides bridging of Frame Relay packets over Ethernet networks.
The Cisco 7600 router can transmit BPDUs with a PID of either 0x00-0E or 0x00-07. When the router connects to a device that is fully compliant with RFC 1483 Appendix B, in which the IEEE BPDUs are sent and received by the other device using a PID of 0x00-0E, you must not use the ignore-bpdu-pidkeyword.
If you do not enter the ignore-bpdu-pid keyword, the PVC between the devices operates in compliance with RFC 1483 Appendix B. This is referred to as strict mode
. Entering the ignore-bpdu-pid keyword creates loose mode
. Both modes are described as follows:
Without the ignore-bpdu-pidkeyword, in strict mode, IEEE BPDUs are sent out using a PID of 0x00-0E, which complies with RFC 1483.
With the ignore-bpdu-pidkeyword, in loose mode, IEEE BPDUs are sent out using a PID of 0x00-07, which is normally reserved for RFC 1483 data.
Cisco-proprietary PVST+ BPDUs are always sent out on data frames using a PID of 0x00-07, regardless of whether you enter the ignore-bpdu-pid keyword.
Use the ignore-bpdu-pid keyword when connecting to devices such as ATM digital subscriber line (DSL) modems that send PVST (or 802.1D) BPDUs with a PID of 0x00-07.
The pvst-tlv keyword enables BPDU translation when the router interoperates with devices that understand only PVST or IEEE Spanning Tree Protocol. Because the Catalyst 6500 series switch ATM modules support PVST+ only, you must use the pvst-tlv keyword when connecting to a Catalyst 5000 family switch that understands only PVST on its ATM modules, or when connecting with other Cisco IOS routers that understand IEEE format only.
When the router or switch is transmitting, the pvst-tlv keyword translates PVST+ BPDUs into IEEE BPDUs.
When the router or switch is receiving, the pvst-tlv keyword translates IEEE BPDUs into PVST+ BPDUs.
The bridge-domainand bre-connect commands are mutually exclusive. You cannot use both commands on the same PVC for concurrent RFC 1483 and BRE bridging.
To preserve class of service (CoS) information across the ATM network, use the dot1q option. This configuration uses IEEE 802.1Q tagging to preserve the VLAN ID and packet headers as they are transported across the ATM network.
To enable service providers to use a single VLAN to support customers that have multiple VLANs, while preserving customer VLAN IDs and segregating traffic in different customer VLANs, use the dot1q-tunnel option on the service provider router. Then use the dot1q option on the customer routers.
The access, dot1q, and dot1q-tunnel options are mutually exclusive. If you do not specify any of these options, the connection operates in “raw” bridging access mode, which is similar to access, except that the connection does act on and transmit BPDU packets.
RFC 1483 bridging is supported on AAL5-MUX and AAL5-LLC Subnetwork Access Protocol (SNAP) encapsulated PVCs. RFC-1483 bridged PVCs must terminate on the ATM interface, and the bridged traffic must be forwarded over an Ethernet interface, unless the split-horizon option is used, which allows bridging of traffic across bridged PVCs.
RFC 1483 bridging is not supported for switched virtual circuits (SVCs). It also cannot be configured for PVCs on the main interface.
In interface configuration mode, only the dot1q and dot1q-tunnel keyword options are supported.
The following example shows a PVC being configured for IEEE 802.1Q VLAN bridging using a VLAN ID of 99:
Router# configure terminal
Router(config)# interface ATM6/2
Router(config-if)# pvc 2/101
Router(config-if-atm-vc)# bridge-domain 99 dot1q
The following example shows how to enable BPDU translation when a Catalyst 6500 series switch is connected to a device that understands only IEEE BPDUs in an RFC 1483-compliant topology:
100 pvst-tlv 150
The ignore-bpdu-pid keyword is not used because the device operates in an RFC 1483-compliant topology for IEEE BPDUs.
The following example shows how to enable BPDU translation when a Catalyst 5500 ATM module is a device that understands only PVST BPDUs in a non-RFC1483-compliant topology. When a Catalyst 6500 series switch is connected to a Catalyst 5500 ATM module, you must enter both keywords.
100 ignore-bpdu-pid pvst-tlv 150
To enable BPDU translation for the Layer 2 Protocol Tunneling (
L2PT) topologies, use the following command:
100 dot1q-tunnel ignore-bpdu-pid pvst-tlv 150
The following example shows a range of PVCs being configured, with the bridge domain number being incremented for each PVC in the range:
Router(config)# interface atm 8/0.100
Router(config-if)# range pvc 102/100 102/199
Router(config-if-atm-range)# bridge-domain 102 increment