Cisco IOS Software Releases 12.0 S

Table Of Contents

AToM Graceful Restart

Contents

Information About AToM Graceful Restart

How AToM Graceful Restart Works

How to Configure AToM Graceful Restart

Configuring AToM Graceful Restart

Prerequisites

Restrictions

Configuration Examples for AToM Graceful Restart

AToM Graceful Restart: Configuration Example

AToM Graceful Restart: Recovering from an LDP Session Disruption Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Command Reference

Feature Information for AToM Graceful Restart

AToM Graceful Restart

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First Published: August 9, 2004

Last Updated: August 21, 2007

The AToM Graceful Restart feature assists neighboring routers that have nonstop forwarding (NSF), stateful switchover (SSO) and graceful restart (GR) for Any Transport over MPLS (AToM) to recover gracefully from an interruption in service. AToM GR functions strictly in helper mode, which means it helps other routers that are enabled with the NSF/SSO: Any Transport over MPLS and AToM Graceful Restart feature to recover. If the router with AToM GR fails, its peers cannot help it recover. AToM GR is based on the MPLS Label Distribution Protocol (LDP) Graceful Restart feature.

Keep the following points in mind when reading this document:

•The AToM GR feature described in this document refers to helper mode.

•The NSF/SSO: Any Transport over MPLS and AToM Graceful Restart feature is supported in Cisco IOS Releases 12.2(25)S and 12.2(33)SRA. For brevity, the NSF/SSO: Any Transport over MPLS and AToM Graceful Restart feature is called AToM SSO/NSF in this document.

Finding Feature Information in This Module

Your Cisco IOS software release may not support all of the features documented in this module. To reach links to specific feature documentation in this module and to see a list of the releases in which each feature is supported, use the "Feature Information for AToM Graceful Restart" section.

Finding Support Information for Platforms and Cisco IOS and Catalyst OS Software Images

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

•Information About AToM Graceful Restart

•How to Configure AToM Graceful Restart

•Configuration Examples for AToM Graceful Restart

•Additional References

•Command Reference

•Feature Information for AToM Graceful Restart

Information About AToM Graceful Restart

To configure AToM GR, you should understand the following concepts:

•How AToM Graceful Restart Works

How AToM Graceful Restart Works

AToM GR works in strict helper mode, which means it helps a neighboring route processor that has AToM NSF/SSO to recover from a disruption in service without losing its MPLS forwarding state. The disruption in service could result from a TCP or User Datagram Protocol (UDP) event or the stateful switchover of a route processor. AToM GR is based on the MPLS LDP Graceful Restart feature, which preserves forwarding information for AToM circuits during an LDP session interruption. When the neighboring router establishes a new session, the LDP bindings and MPLS forwarding state are recovered. For more information related to how the LDP Graceful Restart feature works, see the MPLS LDP Graceful Restart feature module.

How to Configure AToM Graceful Restart

This section contains the following procedures:

•Configuring AToM Graceful Restart (required)

Configuring AToM Graceful Restart

There is no AToM-specific configuration for AToM GR. You enable LDP GR to assist a neighboring router configured with AToM NSF/SSO to maintain its forwarding state while the LDP session is disrupted.

Prerequisites

•See the LDP Graceful Restart document for information about how LDP GR works and how you can customize it for your network.

•Configure AToM. For information about setting up or configuring AToM, see the Any Transport over MPLS document.

Restrictions

•AToM GR is supported in strict helper mode.

•AToM NSF/SSO is supported in Cisco IOS Release 12.2(25)S and 12.2(33)SRA.

•Tag Distribution Protocol (TDP) sessions are not supported. Only LDP sessions are supported.

•MPLS LDP GR cannot be configured on label-controlled ATM (LC-ATM) interfaces.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip cef [distributed]

4. mpls ldp graceful-restart

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	ip cef [distributed] Example: Router(config)# ip cef distributed	Enables Cisco Express Forwarding.
Step 4	mpls ldp graceful-restart Example: Router(config)# mpls ldp graceful-restart	Enables the router to protect the LDP bindings and MPLS forwarding state during a disruption in service. AToM GR is enabled globally. When you enable AToM GR, it has no effect on existing LDP sessions. New LDP sessions that are established can perform AToM GR.

Configuration Examples for AToM Graceful Restart

This section provides the following configuration examples:

•AToM Graceful Restart: Configuration Example

•AToM Graceful Restart: Recovering from an LDP Session Disruption Example

AToM Graceful Restart: Configuration Example

The following example shows an Ethernet VLAN over MPLS configuration. PE1 is configured with AToM Graceful Restart. PE2 is configured with AToM NSF/SSO. The commands for configuring AToM GR and NSF/SSO are shown in bold.

PE1 with AToM GR

PE2 with AToM NSF/SSO

ip cef ! mpls label protocol ldp mpls ldp graceful-restart mpls ldp router-id Loopback0 ! pseudowire-class atom encapsulation mpls ! interface Loopback0  ip address 10.1.1.2 255.255.255.255 ! interface FastEthernet5/1/1  no ip address ! interface FastEthernet5/1/1.2  description "xconnect to PE2"  encapsulation dot1Q 2 native  xconnect 10.2.2.2 1002 pw-class mpls ! ! IGP for MPLS router ospf 10 log-adjacency-changes auto-cost reference-bandwidth 1000 network 10.1.1.2 10.0.0.0 area 0 network 10.1.1.0 10.0.0.255 area 0

redundancy   mode sso ip cef ! mpls label protocol ldp mpls ldp graceful-restart mpls ldp router-id Loopback0 ! pseudowire-class atom encapsulation mpls ! interface Loopback0  ip address 10.2.2.2 255.255.255.255 ! interface Ethernet3/3  no ip address ! interface Ethernet3/3.2  description "xconnect to PE1"  encapsulation dot1Q 2  xconnect 10.1.1.2 1002 pw-class mpls ! ! IGP for MPLS router ospf 10 log-adjacency-changes nsf enforce global auto-cost reference-bandwidth 1000 network 10.2.2.2 10.0.0.0 area 0 network 10.1.1.0 10.0.0.255 area 0

AToM Graceful Restart: Recovering from an LDP Session Disruption Example

The following examples show the output of the show mpls l2transport vc command during normal operation and when an LDP session is recovering from a disruption.

The following example shows the status of the VC on PE1 with AToM GR during normal operation:

Router# show mpls l2transport vc

Local intf     Local circuit        Dest address    VC ID      Status

-------------  -------------------- --------------- ---------- ----------

Fa5/1/1.2      Eth VLAN 2           10.2.2.2         1002       UP

The following example shows the status of the VC on PE1 with AToM GR while the VC is recovering from an LDP session disruption. The forwarding state for the circuit remains as it was before the disruption.

Router# show mpls l2transport vc

Local intf     Local circuit        Dest address    VC ID      Status

-------------  -------------------- --------------- ---------- ----------

Fa5/1/1.2      Eth VLAN 2           10.2.2.2         1002       RECOVERING

The following example shows the status of the VC on PE1 with AToM GR after the LDP session disruption was cleared. The AToM label bindings were advertised within the allotted time and the status returned to UP.

Router# show mpls l2transport vc

Local intf     Local circuit        Dest address    VC ID      Status

-------------  -------------------- --------------- ---------- ----------

Fa5/1/1.2      Eth VLAN 2           10.2.2.2         1002       UP

The following example shows the detailed status of the VC on PE1 with AToM GR during normal operation:

Router# show mpls l2transport vc detail

Local interface: Fa5/1/1.2 up, line protocol up, Eth VLAN 2 up

  Destination address: 10.2.2.2, VC ID: 1002, VC status: up

    Preferred path: not configured

    Default path: active

    Tunnel label: imp-null, next hop point2point

    Output interface: Se4/0/3, imposed label stack {16}

  Create time: 1d00h, last status change time: 1d00h

  Signaling protocol: LDP, peer 10.2.2.2:0 up

    MPLS VC labels: local 21, remote 16

    Group ID: local 0, remote 0

    MTU: local 1500, remote 1500

    Remote interface description: "xconnect to PE2"

  Sequencing: receive disabled, send disabled

  VC statistics:

    packet totals: receive 3466, send 12286

    byte totals:   receive 4322368, send 5040220

    packet drops:  receive 0, send 0

The following example shows the detailed status of the VC on PE1 with AToM GR while the VC is recovering.

Router# show mpls l2transport vc detail

Local interface: Fa5/1/1.2 up, line protocol up, Eth VLAN 2 up

  Destination address: 10.2.2.2, VC ID: 1002, VC status: recovering

    Preferred path: not configured

    Default path: active

    Tunnel label: imp-null, next hop point2point

    Output interface: Se4/0/3, imposed label stack {16}

  Create time: 1d00h, last status change time: 00:00:03

  Signaling protocol: LDP, peer 10.2.2.2:0 down

    MPLS VC labels: local 21, remote 16

    Group ID: local 0, remote 0

    MTU: local 1500, remote 1500

    Remote interface description: "xconnect to PE2"

  Sequencing: receive disabled, send disabled

  VC statistics:

    packet totals: receive 20040, send 28879

    byte totals:   receive 25073016, send 25992388

    packet drops:  receive 0, send 0

Additional References

The following sections provide references related to AToM GR.

Related Documents

Related Topic	Document Title
MPLS LDP graceful restart	MPLS LDP Graceful Restart
Configuring AToM	Any Transport over MPLS
Nonstop forwarding and stateful switchover for AToM	NSF/SSO—Any Transport over MPLS and AToM Graceful Restart

Standards

Standards	Title
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.	—

MIBs

MIBs	MIBs Link
MPLS Label Distribution Protocol MIB Version 8 Upgrade	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
RFC 3036	LDP Specification
RFC 3478	Graceful Restart Mechanism for Label Distribution

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. Access to most tools on the Cisco Support website requires a Cisco.com user ID and password. If you have a valid service contract but do not have a user ID or password, you can register on Cisco.com.	http://www.cisco.com/techsupport

Command Reference

This feature uses no new or modified commands.

Feature Information for AToM Graceful Restart

Table 1 lists the release history for this feature.

Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.

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 1 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 1 Feature Information for AToM Graceful Restart 

Feature Name	Releases	Feature Information
AToM Graceful Restart	12.0(29)S 12.2(33)SRA 12.4(11)T 12.2(33)SXH	In 12.0(29)S, this feature was introduced. In 12.2(33)SRA, support was added for the Cisco 7600 series routers. In 12.4(11)T, this feature was integrated into the release. In 12.2(33)SXH, this feature was integrated into the release.

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All other trademarks mentioned in this document or Website are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (0612R)

Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.

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