Table of Contents

Configuring ATM Uplinks

This chapter describes basic configuration tasks for the ATM Uplink interface, and includes the following sections:

About ATM Uplinks and the ATM Uplink Interface

ATM uses cell-switching and multiplexing technology that combines the benefits of circuit switching (constant transmission delay and guaranteed capacity) with those of packet switching (flexibility and efficiency for intermittent traffic). ATM is a common network technology for enterprise backbones, MANs, and WANs. By using an ATM uplink, Layer 3 traffic can be routed over an ATM network. The ATM uplink facilitates this by segmenting packet data into fixed-size cells at the transmitting end and reassembling them into packets at the receiving end. This conversion process is defined by the ATM adaptation layer (AAL).

For further information about ATM and its implementation on the Catalyst 8540 MSR and Catalyst 8510 MSR, refer to the Guide to ATM Technology.

The ATM uplink interface allows the Catalyst 8540 switch router to be deployed as part of an existing network where a router with an ATM interface would otherwise have been used. Additionally, the ATM uplink interface allows a Catalyst 8540 deployed as a Layer 3 switch (CSR) to be connected to a Catalyst 8540 deployed as an ATM switch (MSR).

Figure 7-1 shows an example application of the ATM uplink in which traffic from a LAN switch is aggregated at the Catalyst 8540 CSR and passed to the ATM network over the ATM uplink. The Layer 3 enabled ATM uplink supports RFC 1483 (Multiprotocol Encapsulation over ATM), which provides traffic shaping and provides for the mapping of Layer 3 addresses to ATM virtual circuits. Refer to the Guide to ATM Technology for additional information on RFC 1483.

Note   The ATM uplink interface module does not work in a Catalyst 8540 MSR when the ATM router module is present.

Configuring the ATM Uplink Interface

This section describes the default configuration of the ATM uplink interface, initial configurations you should set for a newly installed interface, and optional configurations to customize the interfaces to the requirements of your network.

Note   The ATM uplink interface module consists of one OC-12c or OC-3c port and one enhanced Gigabit Ethernet port. For instructions on configuring the enhanced Gigabit Ethernet interface, see the "About the Enhanced Gigabit Ethernet Interfaces (Catalyst 8540)" section.

Configuration Overview

The following steps provide an overview for configuring an ATM uplink from the switch router to the ATM network:

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Note    You must configure at least one PVC or SVC. The VC options you configure must match in three places: on the switch router, on the ATM switch, and at the remote end of the PVC or SVC connection.

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Step 2   Configure the ATM switch to which the ATM uplink connects.

Default Configuration

On power up, the ATM uplink interface is shut down. When you enter the no shutdown command, the interface is enabled with the default configuration values shown in Table 7-1.

In addition, the ATM uplink interface uses the non-configurable values shown in Table 7-2.

Initially Configuring the Layer 3 Enabled ATM Uplink Interface

Configure the following properties for a newly installed ATM uplink interface:

To initially configure the ATM uplink interface, perform the following steps, beginning in global configuration mode:

Example

The following example shows how to initially configure the ATM uplink interface:

Configuring the Clock Source

The ATM uplink interfaces support internal and line clock sources. The default mode for the clock is no internal, which is the same as the line clock. If your system clock source is set to the line clock, it uses the recovered received clock to transmit.

When two ATM uplink interfaces are connected and set to line clock, the interfaces at each end of the link cannot both accurately synchronize the clock. This configuration causes corruption of the data being transferred, which might cause the line protocol on both interfaces to go down. To prevent this, make sure you configure one end of the connection with internal clock and the other end with no internal clock.

When your system is configured to use the line clock, the following conditions cause the clock to automatically revert to the internal clock source:

When these conditions clear, the clock automatically reverts back to the line clock.

Customizing the Configuration

This section describes how to configure your ATM uplink interface to match your network configuration.

Setting the MTU Size

To set the maximum transmission unit (MTU) size, perform the following steps, beginning in global configuration mode:

Note   The ATM uplink supports IP unicast and IP multicast fragmentation. For IP unicast fragmentation, the packet must ingress on a ATM interface and can egress on any interface. For IP multicast fragmentation, IP multicast data packets greater than 1500 bytes in size are segmented into 1500-byte fragments on the ingress ATM interface, before being switched to other members in the multicast group. The size of the MTU of all members of the multicast group must be equal to or greater than 1500 bytes.

Configuring SONET Framing

In STM-1 mode or STM-4 mode, the ATM uplink interface sends idle cells for cell-rate decoupling. In STS-3c mode or STS-12c mode, the interface sends unassigned cells for cell-rate decoupling. STS-3c is the default SONET framing mode for the ATM OC-3c uplink interface; STS-12c is the default SONET framing mode for the ATM OC-12c uplink interface.

To configure the SONET framing mode, perform the following steps, beginning in global configuration mode:

To return the SONET framing mode to the default, use the no form of the atm sonet command.

Configuring SONET Overhead

You can use the sonet overhead command to set the SONET overhead bytes in the frame header to meet the requirements of a particular standard or to ensure interoperability of the ATM uplink interface with the equipment of another vendor. Use the no form of this command to restore default values.

To configure the SONET overhead, perform the following steps, beginning in global configuration mode:

Note   On the ATM OC-3c interface, you can configure the c2 byte and the s1s0 bits. On the ATM OC-12c interface, you can configure the c2 byte, j0 byte, and j1 byte, and the s1s0 bits.

SONET Overhead Values

The value of the c2 byte is determined as follows:

The value of the s1s0 byte is determined as follows:

The value of the j0 and j1 bytes are determined as follows:

Configuring SONET Alarms

The ATM OC-12c and the ATM OC-3c uplink interfaces support SONET alarm monitoring. To configure alarm monitoring, perform the following steps, beginning in global configuration mode:

To determine which alarms are reported on the ATM interface, and to display the BER thresholds, use the show controllers atm command, as described in the "Verifying the ATM Uplink Configuration" section. For a detailed description of the sonet report and sonet threshold commands, refer to the ATM Switch Router Command Reference.

Configuring Loopback

The default ATM uplink interface configuration is no loopback. To enable loopback, use the loopback command in interface configuration mode.

Configuring CDP

The ATM uplink interface is configured by default with Cisco Discovery Protocol (CDP) disabled. To enable CDP, use the cdp enable command in interface configuration mode.

Configuring the Maximum VCs per VP

The ATM uplink interface is configured by default to allow a maximum of 1024 VCs per VP. To change this value, perform the following steps, beginning in global configuration mode:

Configuring Virtual Circuits

A virtual circuit is a point-to-point connection between the switch router and a remote system. A virtual circuit is established for each ATM end node with which the switch router communicates. The virtual circuit characteristics are established when the virtual circuit is created and include the following:

To configure a PVC, you must complete the following tasks:

Creating a PVC

When you create a PVC, you specify a virtual circuit descriptor (VCD) and associate it with the VPI/VCI pair. The number chosen from the VCD is independent of the VPI/VCI used. When you create a PVC, you also specify the AAL, the encapsulation type, and traffic parameters. Traffic parameters include peak and average rate (specified in kilobits per second) and burst rate (specified in cells). Omitting a peak and average value causes the PVC to be connected at the highest bandwidth rate available. In this case, the peak and average values are the same.

To create a PVC, perform the following steps, beginning in global configuration mode:

The atm pvc command allows you to specify additional optional parameters for the connection, including peak, average, and burst transmission rate, and the rate at which OAM cells are generated.

Mapping a Protocol Address to a PVC

Cisco IOS supports a mapping scheme that allows you to associate a protocol address with a VCD (for PVCs) or with an ATM NSAP address (for SVCs). To create a mapping scheme, first create a map list, then associate the map list to an interface.

For more information about mapping protocol addresses, refer to the Cisco IOS Configuration Guide .

To map a protocol address to a PVC, perform the following steps, beginning in global configuration mode:

You can create multiple map lists. An interface can have only one map list associated with it, but a map list can be associated with multiple interfaces.

PVC Example

In the following example, PVC 5 is created on ATM interface 1/0/0 by means of LLC/sNAP encapsulation over AAL5. ATM interface 1/0/0 (IP address 1.1.1.1) connects to the ATM interface (IP address 1.1.1.5) at the other end, over VC 5.

SVC Example

In the following example, two switch routers with Layer 3 enabled ATM interfaces are connected by means of SVCs. For SVCs, the map-list associates each of the IP addresses with an ATM NSAP-format address, rather than with a specific VC. This configuration could also be used to connect two switch routers with ATM interfaces, through an ATM cloud of other switches:

Switch Router A

Switch Router B

Note the following about this configuration:

Configuring VC Bundles

ATM VC bundle management allows you to configure multiple VCs that have different QoS characteristics between any pair of ATM-enabled switches or routers. As shown in Figure 7-2, these VCs are grouped in a bundle and are referred to as bundle members.

Figure 7-2   ATM VC Bundle

Using VC bundles, you can create differentiated service by flexibly distributing IP Precedence levels among the VC bundle members. You can map a single precedence level or a range of levels to each discrete VC within a bundle. Mapping a range of precedence levels enables individual VCs within the bundle to carry packets marked with different precedence levels. To further differentiate service across traffic that has different IP Precedence levels but that uses the same VC in a bundle, you can use the Weighted Random Early Detection (WRED) network queuing mechanism.

To determine which of the VCs in the bundle to use to forward a packet to its destination, the ATM VC bundle management software matches precedence levels between packets and vCs. IP traffic is sent to the next-hop address for the bundle (because all VCs in a bundle share the same destination), but the selection of the VC to be used to carry a packet depends on the value that is set for that packet in the "IP Precedence bits" section of the type of service (ToS) byte of its header. The ATM VC bundle management software matches the IP Precedence of the packet to the IP Precedence value or range of values assigned to a VC, and sends the packet out on the appropriate VC. Moreover, the ATM VC bundle management feature allows you to configure how traffic will be redirected in the event the VC to which the packet was matched goes down.

Features Supported

The following VC bundling features are supported on the Catalyst 8540 CSR:

Restrictions

VC bundling on the Catalyst 8540 has the following restrictions:

Creating a Bundle

To create a bundle and enter the bundle configuration mode, in which you can assign attributes and parameters to the bundle and all of its member VCs, use the following command in subinterface configuration mode:

Applying Bundle-level Parameters

Bundle-level parameters can be applied either by assigning VC classes or by directly applying them to the bundle. Parameters applied through a VC class assigned to the bundle are superseded by those applied at the bundle level. Bundle-level parameters are superseded by parameters applied to an individual VC.

Configuring the Bundle-Level Parameters

Configuring the bundle-level parameters is optional if a VC class is assigned to the bundle and provides the configuration you want.

To configure parameters that apply to the bundle and all of its members, use the following commands in bundle configuration mode:

Configuring VC Class Parameters to Apply to a Bundle

To configure a VC class to contain commands that configure all VC members of a bundle when the class is applied to that bundle, use the following command in vc-class configuration mode. To enter vc-class configuration mode, use the vc-class atm command.

Attaching a Class to a Bundle

To attach a preconfigured VC class containing bundle-level configuration commands to a bundle, use the following command in bundle configuration mode:

Committing a VC to a Bundle

To add a VC to an existing bundle and enter bundle-vc configuration mode, use the following command in bundle configuration mode:

Applying Parameters to Individual VCs

Parameters applied to individual VCs supersede bundle-level parameters. Parameters applied directly to a VC take precedence over the same parameters applied within a class to the VC at the bundle-vc configuration level.

To configure an individual VC bundle member directly, use the following command in bundle-vc configuration mode:

For more detailed information on configuring VC bundles, refer to the Cisco IOS Quality of Service Solutions Configuration Guide.

Verifying the ATM Uplink Configuration

To verify the configuration on the ATM uplink interface, use the following commands:

Displaying ATM Uplink Interfaces

The following example shows sample output of the show interfaces atm command.

Displaying ATM Information

The following example shows sample output of the show controllers atm command.

Displaying Bundle Attributes

The following example shows sample output for the show atm bundle bundle-name command: