Document ID: 10392
Updated: Jun 05, 2005
Contents
Introduction
This document illustrates a sample configuration between three routers and an ATM switch, using Logical Link Control (LLC) encapsulation. Router A routes on the Ethernet and performs bridging between Router B and Router C. Router B and Router C bridge between the ATM and Ethernet. No mapping is done on the PVC for bridging, because all VCs on a bridged subinterface are automatically used for bridging.
In the sample configuration, Router B and Router C are only used as Layer 2 devices, with end stations attached to their Ethernets. Therefore, you need to turn off ip routing on Router B and C.
Note: This document focuses on permanent virtual circuit (PVC) configurations on Cisco routers that run Cisco IOS® software. For PVC configuration examples on Cisco WAN switches, click here.
Prerequisites
Requirements
There are no specific requirements for this document.
Components Used
The information in this document is based on these software and hardware versions:
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Cisco IOS Software Release 11.2 or later is needed for integrated routing and bridging (IRB). Commands were enhanced in Cisco IOS Software Release 11.3T, and the enhanced commands are used in the configurations that immediately follow the network diagram.
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.
Conventions
For more information on document conventions, refer to Cisco Technical Tips Conventions.
Bridged RFC 1483
When PVCs are used, a user has two ways to carry multiple protocols over Asynchronous Transfer Mode (ATM).
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virtual circuit (VC) multiplexing—The user defines one PVC per protocol. This method uses more VCs than LLC encapsulation, but reduces overhead. This is because a header is not necessary.
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LLC/SNAP Encapsulation—The user multiplexes multiple protocols over a single ATM VC. The protocol of a carried protocol data unit (PDU) is identified by prefixing the PDU with a Logical Link Control (LLC)/Subnetwork Access Protocol (SNAP) header.
LLC/SNAP headers use a routed format or a bridged format. The format of the ATM Adaptation Layer 5 (AAL5) common part convergence sublayer (CPCS)-PDU Payload field for bridged Ethernet/802.3 PDUs is seen here:
A bridged format does not necessarily mean that the encapsulated protocol is not routable. Rather, it typically is used when one side of the link supports only the bridged-format PDUs. For example, in a connection between a router and a Catalyst switch in a corporate campus ATM network. In this application, the router interface typically serves as the default gateway for the remote users. Then, integrated routing and bridging (IRB), routed bridge encapsulation (RBE) or bridged-style PVCs (BPVCs) provide the mechanism to route traffic off-network.
These protocols allow the ATM interface to receive bridged-format PDUs. However, they have important differences in performance. Cisco recommends that you consider RBE when the configuration supports it.
Configure
In this section, you are presented with the information to configure the features described in this document.
Note: To find additional information on the commands used in this document, use the Command Lookup Tool (registered customers only) .
Network Diagram
This document uses this network setup:
Network Diagram Notes:
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In the example, 1/116 is switched to 1/116 by the ATM switch and 1/118 is switched to 1/118.
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The topology is a hub-and-spoke topology where Router A is the hub. Each PVC uses a different subinterface to ensure that PDUs received from Router B can be forwarded back out to Router C. Otherwise, flooded traffic that comes on one PVC on a subinterface is not flooded back on another PVC on the same subinterface.
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All ATM subinterfaces are configured as multipoint. A multipoint subinterface supports multiple VCs. A point-to-point subinterface supports only one VC.
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This example uses IRB for routing off-network. Refer to Configuring Integrated Routing and Bridging in the Cisco IOS Bridging and IBM Networking Configuration Guide for guidance on the use of IRB commands. See the Related Information
Configurations
This document uses these configurations:
| Router A: IRB Configuration |
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bridge irb ! interface ATM1/0 no ip address ! interface ATM1/0.116 point-to-point pvc 1/116 encapsulation aal5snap ! bridge-group 1 ! interface ATM1/0.118 point-to-point pvc 1/118 encapsulation aal5snap ! bridge-group 1 ! interface BVI1 ip address 10.1.1.1 255.255.255.0 ! bridge 1 protocol ieee bridge 1 route ip |
| Router B |
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no ip routing ! interface Ethernet0/0 no ip address bridge-group 1 ! interface ATM1/0 no ip address ! interface ATM1/0.116 point-to-point pvc 1/116 encapsulation aal5snap ! bridge-group 1 ! bridge 1 protocol ieee |
| Router C |
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no ip routing ! interface Ethernet0/0 no ip address bridge-group 1 ! interface ATM1/0 no ip address ! interface ATM1/0.118 point-to-point pvc 1/118 encapsulation aal5snap ! bridge-group 1 ! bridge 1 protocol ieee |
Configurations for Cisco IOS Software Release 11.3T and Earlier
With Cisco IOS Software Releases earlier than 11.3T, the configurations appear similar to these:
| Router B |
|---|
no ip routing ! interface Ethernet0/0 no ip address bridge-group 1 ! interface ATM1/0 no ip address ! interface ATM1/0.116 point-to-point atm pvc 6 1 116 aal5snap bridge bridge-group 1 ! bridge 1 protocol ieee |
| Router C |
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no ip routing ! interface Ethernet0/0 no ip address bridge-group 1 ! interface ATM1/0 no ip address ! interface ATM1/0.118 point-to-point atm pvc 8 1 118 aal5snap bridge bridge-group 1 ! bridge-group 1 protocol ieee |
Verify
This section provides information you can use to confirm your configuration is working properly.
Certain show commands are supported by the Output Interpreter Tool (registered customers only) , which allows you to view an analysis of show command output.
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show atm pvc <vpi/vci> (for Cisco IOS Software Release 11.3T and later )—Displays all ATM PVCs and traffic information. This includes the ATM VPI and VCI numbers.
Router_A#show atm pvc 1/116 ATM1/0.116: VCD: 6, VPI: 1, VCI: 116 UBR, PeakRate: 155000 AAL5-LLC/SNAP, etype:0x0, Flags: 0xC20, VCmode: 0x0 OAM frequency: 0 second(s), OAM retry frequency: 1 second(s) OAM up retry count: 3, OAM down retry count: 5 OAM Loopback status: OAM Disabled OAM Managed VC Status: Not Managed ILMI Managed VC status: Not Managed InARP frequency: 15 minutes(s) InPkts: 258, OutPkts: 258, InBytes: 0, OutBytes: 0 InPRoc: 0, OutPRoc: 0 InFast: 0, OutFast: 0, InAS: 0, OutAS: 0 OAM cells received: 0 F5 InEndloop: 0, F5 InSegloop: 0, F5 InAIS: 0, F5 InRDI: 0 F4 InEndloop: 0, F4 InSegloop: 0, F4 InAIS: 0, F4 InRDI: 0 OAM cells sent: 0 F5 OutEndloop: 0, F5 OutSegloop: 0, F5 OutRDI: 0 F4 OutEndloop: 0, F4 OutSegloop: 0, F4 OutRDI: 0 OAM cell drops: 0 Status: UP Router_A#
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show atm pvc interface atm <slot/port> —Displays all ATM PVCs and traffic information. This includes the interface number or subinterface number of the PVC. Displays all PVCs on the specified interface or subinterface.
Router_A#show atm pvc interface atm1/0 VCD / Peak Avg/Min Burst Interface Name VPI VCI Type Encaps SC Kbps Kbps Cells Sts 1/0.116 6 1 116 PVC SNAP UBR 155000 UP 1/0.118 8 1 118 PVC SNAP UBR 155000 UP Router_A# -
show atm map—Displays the list of all configured ATM static maps to remote hosts on an ATM network.
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show atm traffic—Display current, global ATM traffic information to and from all ATM networks connected to the router.
Router_A#show atm traffic Input OAM Queue: 0/1063 (size/max) 1772 Input packets 1772 Output packets 0 Broadcast packets 0 Packets received on non-existent VC 0 Packets attempted to send on non-existent VC 0 OAM cells received F5 InEndloop: 0, F5 InSegloop: 0, F5 InAIS: 0, F5 InRDI: 0 F5 InEndcc: 0, F5 InSegcc: 0, F4 InEndloop: 0, F4 InSegloop: 0, F4 InAIS: 0, F4 InRDI: 0 0 OAM cells sent F5 OutEndloop: 0, F5 OutSegloop: 0, F5 OutRDI: 0 F5 OutEndcc: 0, F5 OutSegcc: 0, F4 OutEndloop: 0, F4 OutSegloop: 0, F4 OutRDI: 0 0 OAM cell drops Router_A#
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show atm interface atm <slot/port> —Displays ATM-specific information about an ATM interface.
Router_A#show atm interface atm 1/0 Interface ATM1/0: AAL enabled: AAL5 , Maximum VCs: 4095, Current VCCs: 2 Maximum Transmit Channels: 0 Max. Datagram Size: 4528 PLIM Type: SONET - 155000Kbps, TX clocking: LINE Cell-payload scrambling: ON sts-stream scrambling: ON 4407 input, 5386 output, 774 IN fast, 387 OUT fast, 0 out drop Avail bw = 155000 Config. is ACTIVE Router_A#
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show spanning-tree—Displays the spanning-tree topology known to the router.
Router_A#show spanning-tree Bridge group 1 is executing the ieee compatible Spanning Tree protocol Bridge Identifier has priority 32768, address 0000.0c7b.bf70 Configured hello time 2, max age 20, forward delay 15 We are the root of the spanning tree Topology change flag not set, detected flag not set Number of topology changes 1 last change occurred 00:42:00 ago from ATM1/0.116 Times: hold 1, topology change 35, notification 2 hello 2, max age 20, forward delay 15 Timers: hello 1, topology change 0, notification 0, aging 300 Port 6 (ATM1/0.116) of Bridge group 1 is forwarding Port path cost 14, Port priority 128, Port Identifier 128.6. Designated root has priority 32768, address 0000.0c7b.bf70 Designated bridge has priority 32768, address 0000.0c7b.bf70 Designated port id is 128.6, designated path cost 0 Timers: message age 0, forward delay 0, hold 0 Number of transitions to forwarding state: 1 BPDU: sent 1266, received 0 Port 7 (ATM1/0.118) of Bridge group 1 is forwarding Port path cost 14, Port priority 128, Port Identifier 128.7. Designated root has priority 32768, address 0000.0c7b.bf70 Designated bridge has priority 32768, address 0000.0c7b.bf70 Designated port id is 128.7, designated path cost 0 Timers: message age 0, forward delay 0, hold 0 Number of transitions to forwarding state: 1 BPDU: sent 1266, received 0 Router_A# -
show bridge—Displays classes of entries in the bridge forwarding database.
Router_A#show bridge Total of 300 station blocks, 298 free Codes: P - permanent, S - self Bridge Group 1: Address Action Interface Age RX count TX count 0010.7bb9.bd20 forward ATM1/0.116 0 5571 4544 0010.7bb9.bd14 forward ATM1/0.118 0 5245 4214 Router_A#
Troubleshoot
Refer to Troubleshooting Bridging and IRB over ATM PVCs for detailed troubleshooting tips.
Related Information
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Refer to Cisco Technical Tips Conventions for information on conventions used in this document.