Table Of Contents

Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs

Finding Feature Information

Contents

Prerequisites for Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs

Restrictions for Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs

Information About Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs

Overview on Bridged 1483 Encapsulated Traffic over ATM SVCs

ATM RBE Subinterface Grouping by PVC Range

DHCP Option 82 Support for RBE

DHCP Lease Limit per ATM RBE Unnumbered Interface

Benefits of Providing Connectivity Using ATM Routed Bridge Encapsulation

How to Configure ATM Routed Bridge Encapsulation over PVCs

Configuring ATM Routed Bridge Encapsulation Using PVCs

Examples

Configuring DHCP Option 82 for RBE

Prerequisites for Configuring DHCP Option 82 for RBE

Configuring the DHCP Lease Limit

Troubleshooting the DHCP Lease Limit

Configuration Examples for Providing Connectivity Using ATM Routed Bridge Encapsulation

Configuring ATM RBE on PVCs: Example

Configuring ATM RBE on an Unnumbered Interface: Example

Concurrent Bridging and ATM RBE: Example

DHCP Option 82 for RBE Configuration: Example

DHCP Lease Limit: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for Providing Connectivity Using ATM Routed Bridge Encapsulation

Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs

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First Published: May 2, 2005

Last Updated: November 20, 2009

The Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs feature provides the functionality of bridged ATM interface support to ATM switched virtual circuits (SVCs). Unlike permanent virtual circuits (PVCs), SVCs need to be triggered by ongoing traffic and can be brought down when idle for some time. The SVCs are triggered, if down, and the traffic is passed on to the SVCs belonging to bridged ATM interface.

ATM routed bridge encapsulation (RBE) is used to route IP over bridged RFC 1483 Ethernet traffic from a stub-bridged LAN.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Providing Connectivity Using ATM Routed Bridge Encapsulation" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs

•Restrictions for Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs

•Information About Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs

•How to Configure ATM Routed Bridge Encapsulation over PVCs

•Configuration Examples for Providing Connectivity Using ATM Routed Bridge Encapsulation

•Additional References

•Feature Information for Providing Connectivity Using ATM Routed Bridge Encapsulation

Prerequisites for Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs

•When ATM SVCs are used, support for a form of bridging, such as integrated routing and bridging, is required.

•Before configuring connectivity from a remote bridged Ethernet network to a routed network using ATM routed bridge encapsulation, you must understand the concepts in the Understanding Broadband Access Aggregation module.

Restrictions for Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs

•Unlike PVCs, SVCs must be triggered by ongoing traffic and might be brought down after they have been idle for some time. The Bridged 1483 Encapsulated Traffic over ATM SVCs feature allows for the SVC to be triggered if down, and to pass the traffic on to the SVCs belonging to the bridged ATM interface.

•ATM RBE does not support MAC-layer access lists; only IP access lists are supported.

Information About Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs

To provide connectivity using ATM routed bridge encapsulation over PVCs, you should understand the following concepts:

•Overview on Bridged 1483 Encapsulated Traffic over ATM SVCs

•ATM RBE Subinterface Grouping by PVC Range

•ATM RBE Subinterface Grouping by PVC Range

•DHCP Option 82 Support for RBE

•DHCP Lease Limit per ATM RBE Unnumbered Interface

•Benefits of Providing Connectivity Using ATM Routed Bridge Encapsulation

Overview on Bridged 1483 Encapsulated Traffic over ATM SVCs

ATM RBE is used to route IP over bridged RFC 1483 Ethernet traffic from a stub-bridged LAN.

Figure 1 shows an ATM subinterface on a headend router that is configured to function in ATM routed-bridge encapsulation mode. This configuration is useful when a remote bridged Ethernet network device needs connectivity to a routed network via a device bridging from an Ethernet LAN to an ATM RFC 1483 bridged encapsulation.

Figure 1 ATM Routed Bridge Encapsulation

Because PVCs are statically configured along the entire path between the end systems, it would not be suitable to route bridged encapsulated traffic over them when the user wants to configure the virtual circuits (VCs) dynamically and tear down the VCs when there is no traffic.

ATM RBE Subinterface Grouping by PVC Range

You can configure ATM routed bridge encapsulation using an ATM PVC range rather than individual PVCs. When you configure a PVC range for routed bridge encapsulation, a point-to-point subinterface is created for each PVC in the range. The number of PVCs in a range can be calculated using the following formula:

number of PVCs = (end-vpi - start-vpi + 1) x (end-vci - start-vci +1)

Subinterface numbering begins with the subinterface on which the PVC range is configured and increases sequentially through the range.

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Note You cannot explicitly configure the individual point-to-point subinterfaces created by the PVC range on a point-to-point subinterface. All the point-to-point subinterfaces in the range share the same configuration as the subinterface on which the PVC range is configured.

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DHCP Option 82 Support for RBE

The DHCP relay agent information option (option 82) enables a Dynamic Host Configuration Protocol (DHCP) relay agent to include information about itself when forwarding client-originated DHCP packets to a DHCP server. The DHCP server can use this information to implement IP address or other parameter-assignment policies.

The DHCP Option 82 Support for RBE feature provides support for the DHCP relay agent information option when ATM RBE is used. Figure 2 shows a typical network topology in which ATM RBE and DHCP are used. The aggregation router that is using ATM RBE is also serving as the DHCP relay agent.

Figure 2 Network Topology Using ATM RBE and DHCP

This feature communicates information to the DHCP server using a suboption of the DHCP relay agent information option called agent remote ID. The information sent in the agent remote ID includes an IP address identifying the relay agent and information about the ATM interface and the PVC over which the DHCP request came in. The DHCP server can use this information to make IP address assignments and security policy decisions.

Figure 3 shows the format of the agent remote ID suboption.

Figure 3 Format of the Agent Remote ID Suboption

Table 1 describes the agent remote ID suboption fields displayed in Figure 3.

Table 1 Agent Remote ID Suboption Field Description s

Field	Description
Port Type	Port type. The value 0x01 indicates RBE. (1 byte)
Version	Option 82 version. The value 0x01 specifies the RBE version of Option 82 (1 byte).
Reserved	RBE reserved (2 bytes).
NAS IP Address	One of the interfaces on the DHCP relay agent. The rbe nasip command can be used to specify which IP address will be used. (4 bytes)
NAS Port	RBE-enabled virtual circuit on which the DHCP request has come in. See Figure 4 for the format of this field. (4 bytes)

Figure 4 shows the format of the network access server (NAS) port field in the agent remote ID suboption.

Figure 4 Format of the NAS Port Field

Figure 5 shows the format of the interface field. If there is no module, the value of the module bit is 0.

Figure 5 Format of the Interface Field

DHCP Lease Limit per ATM RBE Unnumbered Interface

The DHCP lease limit per ATM RBE Unnumbered Interface feature is enabled on a Cisco IOS DHCP relay agent connected to clients through unnumbered interfaces. The relay agent keeps information about the DHCP leases offered to the clients per subinterface. When a DHCPACK message is forwarded to the client, the relay agent increments the number of leases offered to clients on that subinterface. If a new DHCP client tries to obtain an IP address and the number of leases has already reached the configured lease limit, DHCP messages from the client will be dropped and will not be forwarded to the DHCP server.

If this feature is enabled on the Cisco IOS DHCP server directly connected to clients through unnumbered interfaces, the server allocates addresses and increments the number of leases per subinterface. If a new client tries to obtain an IP address, the server will not offer an IP address if the number of leases on the subinterface has already reached the configured lease limit.

Benefits of Providing Connectivity Using ATM Routed Bridge Encapsulation

Bridged IP packets received on an ATM interface configured in routed-bridge mode are routed via the IP header. Such interfaces take advantage of the characteristics of a stub LAN topology commonly used for digital subscriber line (DSL) access and offer increased performance and flexibility over integrated routing and bridging (IRB).

Another benefit of ATM RBE is that it reduces the security risk associated with normal bridging or IRB by reducing the size of the nonsecured network. By using a single VC allocated to a subnet (which could be as small as a single IP address), ATM RBE uses an IP address in the subnet to limit the "trust environment" to the premises of a single customer.

ATM RBE supports Cisco Express Forwarding (CEF), fast switching, and process switching.

The DHCP Option 82 Support for RBE feature enables those service providers to use DHCP to assign IP addresses and DHCP option 82 to implement security and IP address assignment policies.

The DHCP Lease Limit per ATM RBE Unnumbered Interface feature allows an Internet service provider (ISP) to globally limit the number of leases available to clients per household or connection.

How to Configure ATM Routed Bridge Encapsulation over PVCs

This section contains the following procedures:

•Configuring ATM Routed Bridge Encapsulation Using PVCs (required)

•Configuring DHCP Option 82 for RBE (required)

•Configuring the DHCP Lease Limit (required)

•Troubleshooting the DHCP Lease Limit (optional)

Configuring ATM Routed Bridge Encapsulation Using PVCs

Perform the following task to configure ATM RBE using PVCs. Only the specified network layer (IP) is routed. Any remaining protocols can be passed on to bridging or other protocols. In this manner, ATM RBE can be used to route IP, while other protocols (such as IPX) are bridged normally.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface atm slot/0.subinterface-number point-to-point

4. pvc vpi/vci

or

range [range-name] pvc start-vpi/start-vci end-vpi/end-vci

5. exit

6. ip address ip-address mask [secondary]

7. end

8. show arp

or

show ip cache verbose

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	interface atm slot/0.subinterface-number point-to-point Example: Router(config)# interface atm 5/0.5 point-to-point	Specifies an ATM point-to-point subinterface and enters the subinterface mode.
Step 4	pvc vpi/vci or range [range-name] pvc start-vpi/start-vci end-vpi/end-vci Example: Router(config-subif)# pvc 0/32 or Router(config-subif)# range range1 pvc 1/200 1/299	Configures a PVC to carry the routed bridge traffic and enters ATM VC class configuration mode. Configures a range of PVCs to carry the routed bridge traffic and enters ATM PVC range configuration mode.
Step 5	exit Example: Router(config-if-atm-vc)# exit	Exits to subinterface configuration mode.
Step 6	ip address ip-address mask [secondary] Example: Router(config-subif)# ip address 209.165.200.224 255.255.255.0	Provides an IP address on the same subnetwork as the remote network.
Step 7	end Example: Router(config-subif)# end	Exits to privileged EXEC mode.
Step 8	show arp or show ip cache verbose Example: Router# show arp or Router# show ip cache verbose	(Optional) Displays ATM RBE configuration information.

Examples

To confirm that ATM RBE is enabled, use the show arp command and the show ip cache verbose command in privileged EXEC mode:

Router# show arp 

Protocol  Address          Age (min)  Hardware Addr   Type   Interface

Internet 	209.165.201.51          6   0001.c9f2.a81d  ARPA   Ethernet3/1

Internet 	209.165.201.49          -   0060.0939.bb55  ARPA   Ethernet3/1

Internet 209.165.202.128         30   0010.0ba6.2020  ARPA   Ethernet3/0

Internet 209.165.201.52           6   00e0.1e8d.3f90  ARPA   ATM1/0.4

Internet 209.165.201.53           5   0007.144f.5d20  ARPA   ATM1/0.2

Internet 209.165.202.129          -   0060.0939.bb54  ARPA   Ethernet3/0

Internet 209.165.201.125         30   00b0.c2e9.bc55  ARPA   Ethernet3/1#

Router# show ip cache verbose

IP routing cache 3 entries, 572 bytes

   9 adds, 6 invalidates, 0 refcounts

Minimum invalidation interval 2 seconds, maximum interval 5 seconds,

   quiet interval 3 seconds, threshold 0 requests

Invalidation rate 0 in last second, 0 in last 3 seconds

Last full cache invalidation occurred 00:30:34 ago

Prefix/Length       Age       Interface       Next Hop

209.165.201.51/32-24         00:30:10  Ethernet3/1     10.1.0.51

                   14  0001C9F2A81D00600939BB550800

209.165.202.129/32-24       00:00:04  ATM1/0.2        10.8.100.50

                   28  00010000AAAA030080C2000700000007144F5D2000600939

                       BB1C0800

209.165.201.125/32-24       00:06:09  ATM1/0.4        10.8.101.35

                   28  00020000AAAA030080C20007000000E01E8D3F9000600939

                       BB1C0800

Configuring DHCP Option 82 for RBE

Perform this task to configure the DHCP Option 82 Support for RBE feature.

Prerequisites for Configuring DHCP Option 82 for RBE

DHCP option 82 support must be configured on the DHCP relay agent using the ip dhcp relay information option command before you can use the DHCP Option 82 Support for RBE feature.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip dhcp relay information option

4. rbe nasip source-interface

5. end

DETAILED STEPS

	Command	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip dhcp relay information option Example: Router(config)# ip dhcp relay information option	Enables the DHCP option 82 support on relay agent. •Enabling the DHCP option 82 support allows the system to insert the DHCP relay agent information option in forwarded BOOT REQUEST messages to a Cisco IOS DHCP server.
Step 4	rbe nasip source-interface Example: Router(config)# rbe nasip loopback0	Specifies the IP address of an interface on the DHCP relay agent that will be sent to the DHCP server via the Agent Remote ID suboption.
Step 5	end Example: Router(config)# end	Exits global configuration mode and enters privileged configuration mode.

Configuring the DHCP Lease Limit

Perform this task to limit the number of DHCP leases allowed on ATM RBE unnumbered or serial unnumbered interfaces.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip dhcp limit lease per interface lease-limit

4. end

DETAILED STEPS

	Command	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip dhcp limit lease per interface lease-limit Example: Router(config)# ip dhcp limit lease per interface 2	Limits the number of leases offered to DHCP clients behind an ATM RBE unnumbered or serial unnumbered interface.
Step 4	end Example: Router(config)# end	Exits global configuration mode and returns to privileged EXEC mode.

Troubleshooting the DHCP Lease Limit

Perform this task to troubleshoot the DHCP lease limit.

SUMMARY STEPS

1. enable

2. debug ip dhcp server packet

3. debug ip dhcp server events

DETAILED STEPS

	Command	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	debug ip dhcp server packet Example: Router# debug ip dhcp server packet	(Optional) Decodes DHCP receptions and transmissions.
Step 3	debug ip dhcp server events Example: Router(config)# debug ip dhcp server events	(Optional) Displays server events.

Configuration Examples for Providing Connectivity Using ATM Routed Bridge Encapsulation

The following examples show various ways to provide connectivity from a remote bridged network to a routed network using ATM RBE.

•Configuring ATM RBE on PVCs: Example

•Configuring ATM RBE on an Unnumbered Interface: Example

•Concurrent Bridging and ATM RBE: Example

•DHCP Option 82 for RBE Configuration: Example

•DHCP Lease Limit: Example

Configuring ATM RBE on PVCs: Example

The following example shows a typical ATM routed bridge encapsulation configuration:

enable

 configure terminal

 interface atm 4/0.100 point-to-point

  ip address 209.165.200.225 255.255.255.224

   pvc 0/32

    end

Configuring ATM RBE on an Unnumbered Interface: Example

The following example uses a static route to point to an unnumbered interface:

 enable

  configure terminal

  interface loopback 0

  ip address 209.165.200.226 255.255.255.224

  interface atm 4/0.100 point-to-point

   ip unnumbered loopback 0

   pvc 0/32

    atm route-bridge ip

    exit

  ip route 209.165.200.228 255.255.255.224 atm 4/0.100

  end

Concurrent Bridging and ATM RBE: Example

The following example shows concurrent use of ATM RBE with normal bridging. IP datagrams are route-bridged, and other protocols (such as IPX or AppleTalk) are bridged.

bridge 1 protocol ieee

interface atm 4/0.100 point-to-point

 ip address 209.165.200.225 255.255.255.224

 pvc 0/32

 bridge-group 1

 atm route-bridge ip

DHCP Option 82 for RBE Configuration: Example

In the following example, DHCP option 82 support is enabled on the DHCP relay agent using the ip dhcp relay information option command. The rbe nasip command configures the router to forward the IP address for Loopback0 to the DHCP server.

ip dhcp-server 209.165.200.225

!

ip dhcp relay information option

!

interface Loopback0

 ip address 209.165.201.0 255.255.255.248

!

interface atm 4/0

 no ip address

!

interface atm 4/0.1 point-to-point

 ip unnumbered Loopback0

 ip helper-address 209.165.201.3

 atm route-bridged ip

 pvc 88/800

  encapsulation aal5snap

!

!

interface Ethernet5/1

 ip address 209.165.201.4 255.255.255.248

!

router eigrp 100

 network 209.165.201.0

 network 209.165.200.0

!

rbe nasip Loopback0

For the configuration example, the value (in hexadecimal) of the agent remote ID suboption would be 010100000B01018140580320. Table 2 shows the value of each field within the agent remote ID suboption.

Table 2 Agent Remote ID Suboption Field Values

Agent Remote ID Suboption Field	Value
Port Type	0x01
Version	0x01
Reserved	undefined
NAS IP Address	0x0B010181 (hexadecimal value of 11.1.1.129)
NAS Port •Interface (slot/module/port) •VPI •VCI	•0x40 (The slot/module/port values are 01 00/0/000.) •0x58 (hexadecimal value of 88) •0x320 (hexadecimal value of 800)

DHCP Lease Limit: Example

In the following example, if more than three clients try to obtain an IP address from interface ATM4/0.1, the DHCPDISCOVER packets will not be forwarded to the DHCP server. If the DHCP server resides on the same router, DHCP will not reply to more than three clients.

ip dhcp limit lease per interface 3

!

interface loopback0

 ip address 209.165.201.3 255.255.255.248

!

interface atm 4/0.1

 no ip address

!

interface atm 4/0.1 point-to-point

 ip helper-address 172.16.1.2

 ip unnumbered loopback0

 atm route-bridged ip

  pvc 88/800

  encapsulation aal5snap

Additional References

The following sections provide references related to using ATM RBE:

Related Documents

Related Topic	Document Title
Broadband access aggregation concepts	Understanding Broadband Access Aggregation
Preparing for broadband access aggregation task	Preparing for Broadband Access Aggregation
DHCP commands	Cisco IOS IP Addressing Services Command Reference
Broadband access aggregation and DSL commands: complete command syntax, command mode, defaults, usage guidelines, and examples	Cisco IOS Broadband Access Aggregation and DSL Command Reference
DHCP configuration tasks	"Configuring the Cisco IOS DHCP Server" module of the Cisco IOS IP Addressing Services Configuration document
Cisco IOS commands	Cisco IOS Master Commands List, All Releases

Standards

Standards	Title
None	—

MIBs

MIBs	MIBs Link
None	To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: http://www.cisco.com/go/mibs

RFCs

RFCs	Title
None	—

Technical Assistance

Description

Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies. To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds. Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html

Feature Information for Providing Connectivity Using ATM Routed Bridge Encapsulation

Table 3 lists the features in this module and provides links to specific configuration information. Only features that were introduced or modified in Cisco IOS Release 12.2(15)T, Cisco IOS Release 12.2(33)SRE, or later releases appear in the table.

Not all commands may be available in your Cisco IOS software release. For details on when support for specific commands was introduced, see the command reference documents.

For information on a feature in this technology that is not documented here, see the "Configuring Broadband Access Aggregation Features Roadmap."

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

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Note Table 3 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.

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Table 3 Feature Information for Providing Connectivity Using ATM Routed Bridge Encapsulation 

Feature Name	Releases	Feature Information
Bridged 1483 Encapsulated Traffic over ATM SVCs	12.4(15)T 12.2(33)SRE	The Bridged 1483 Encapsulated Traffic over ATM SVCs feature provides support for bridged 1483 encapsulated packets to trigger ATM SVC and also support for sending this traffic on triggered ATM SVCs. The following section provides information about this feature: •"Information About Providing Connectivity Using ATM Routed Bridge Encapsulation over PVCs" section
DHCP Option 82 Support for Routed Bridge Encapsulation	12.2(2)T	This feature provides support for the DHCP relay agent information option when ATM RBE is used. The following sections provide information about this feature: •"DHCP Option 82 Support for RBE" section •"Configuring DHCP Option 82 for RBE" section The following command was introduced: rbe nasip
DHCP Lease Limit per ATM RBE Unnumbered Interface	12.3(2)T	This feature limits the number of DHCP leases per subinterface offered to DHCP clients connected from an ATM RBE unnumbered interface or serial unnumbered interface of the DHCP server or DHCP relay agent. The following sections provide information about this feature: •"DHCP Lease Limit per ATM RBE Unnumbered Interface" section •"Configuring the DHCP Lease Limit" section The following command was introduced: ip dhcp limit lease per interface

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