AToM Graceful Restart

The AToM Graceful Restart feature assists neighboring devices that have nonstop forwarding (NSF), stateful switchover (SSO), and graceful restart (GR) for Any Transport over Multiprotocol Label Switching (AToM) to recover gracefully from an interruption in service. AToM GR functions strictly in helper mode, which means it helps other devices that are enabled with the NSF/SSO—Any Transport over MPLS and AToM Graceful Restart feature to recover. If the device 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.

  • For brevity, the NSF/SSO—Any Transport over MPLS and AToM Graceful Restart feature is called AToM SSO/NSF in this document.

Prerequisites for AToM Graceful Restart

Any Transport over Multiprotocol Label Switching (AToM) must be configured.

Restrictions for AToM Graceful Restart

  • Any Transport over Multiprotocol Label Switching (AToM) graceful restart (GR) is supported in strict helper mode.

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

  • On some hardware platforms, Tag Distribution Protocol (TDP) sessions are not supported. Only LDP sessions are supported.

Information About AToM Graceful Restart

How AToM Graceful Restart Works

Any Transport over Multiprotocol Label Switching Graceful Restart (AToM GR) works in strict helper mode, which means it helps a neighboring Route Processor (RP) that has AToM nonstop forwarding (NSF) and stateful switchover (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 SSO of an RP. AToM GR is based on the MPLS Label Distribution Protocol (LDP) Graceful Restart feature, which preserves forwarding information for AToM circuits during an LDP session interruption. When the neighboring device establishes a new session, the LDP bindings and MPLS forwarding state are recovered.

How to Configure AToM Graceful Restart

Configuring AToM Graceful Restart

There is no Any Transport over Multiprotocol Label Switching (AToM)-specific configuration for AToM Graceful Restart (GR). You enable the Label Distribution Protocol (LDP) GR to assist a neighboring device configured with AToM nonstop forwarding (NSF) and stateful switchover (SSO) to maintain its forwarding state while the LDP session is disrupted.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip cef distributed
  4. mpls ldp graceful-restart
  5. exit
  6. show mpls l2transport vc detail

DETAILED STEPS

  Command or Action Purpose

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

ip cef distributed

Example:


Device(config)# ip cef distributed

Enables distributed Cisco Express Forwarding.

Step 4

mpls ldp graceful-restart

Example:


Device(config)# mpls ldp graceful-restart

Enables the device 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.

Step 5

exit

Example:


Device(config)# exit

Exits to privileged EXEC mode.

Step 6

show mpls l2transport vc detail

Example:


Device# show mpls l2transport vc detail

Displays detailed information about AToM virtual circuits (VCs).

Configuration Examples for AToM Graceful Restart

Example: Configuring AToM Graceful Restart

The following example shows a Fast Ethernet VLAN over Multiprotocol Label Switching (MPLS) configuration. PE1 is configured with Any Transport over MPLS Graceful Restart (AToM GR). PE2 is configured with AToM nonstop forwarding (NSF) and stateful switchover (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 distributed
!
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 FastEthernet2/1/1
 no ip address
!
interface FastEthernet2/1/1.2
 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 distributed
!
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 FastEthernet0/3/2
 no ip address
!
interface FastEthernet0/3/2.2
 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 cisco 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

Examples: Verifying AToM Graceful Restart Recovery from an LDP Session Disruption

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

The following example shows the status of the virtual circuit (VC) on PE1 with Any Transport over Multiprotocol Label Switching Graceful Restart (AToM GR) during normal operation: 


Device# show mpls l2transport vc

Local intf     Local circuit        Dest address    VC ID      Status
-------------  -------------------- --------------- ---------- ----------
Fa2/1/1.2      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. 


Device# show mpls l2transport vc

Local intf     Local circuit        Dest address    VC ID      Status
-------------  -------------------- --------------- ---------- ----------
Fa2/1/1.2      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. 


Device# show mpls l2transport vc

Local intf     Local circuit        Dest address    VC ID      Status
-------------  -------------------- --------------- ---------- ----------
Fa2/1/1.2      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: 


Device# show mpls l2transport vc detail

Local interface: Fa2/1/1.2 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: Se2/0/2, 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. 


Device# show mpls l2transport vc detail

Local interface: Fa2/1/1.2 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: Se2/0/2, 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

Related Documents

Related Topic

Document Title

Cisco IOS commands

Cisco IOS Master Command List, All Releases

MPLS AToM and LDP commands

Cisco IOS Multiprotocol Label Switching Command Reference

MPLS LDP graceful restart

“MPLS LDP Graceful Restart” module in the MPLS: High Availability Configuration Guide (part of the Multiprotocol Label Switching Configuration Guide Library)

Configuring AToM

“Any Transport over MPLS” module in the MPLS: Layer 2 VPNs Configuration Guide (part of the Multiprotocol Label Switching Configuration Guide Library)

Nonstop forwarding and stateful switchover for AToM

“NSF SSO Any Transport over MPLS and AToM Graceful Restart” module in the MPLS: High Availability Configuration Guide (part of the Multiprotocol Label Switching Configuration Guide Library)

High availability commands

Cisco IOS High Availability Command Reference

MIBs

MIBs

MIBs Link

MPLS Label Distribution Protocol MIB Version 8 Upgrade

To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mib

RFCs

RFCs

Title

RFC 3036

LDP Specification

RFC 3478

Graceful Restart Mechanism for Label Distribution

Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

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

Feature Information for AToM Graceful Restart

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 1. Feature Information for AToM Graceful Restart

Feature Name

Releases

Feature Information

AToM Graceful Restart

12.0(29)S

12.2(33)SRA

12.2(33)SXH

12.4(11)T

Cisco IOS XE Release 2.3

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

In Cisco IOS Release 12.0(29)S, this feature was introduced.

In Cisco IOS Release 12.2(33)SRA, support was added for the Cisco 7600 series routers.

In Cisco IOS Release 12.2(33)SXH, this feature was integrated into the release.

In Cisco IOS Release 12.4(11)T, this feature was integrated into the release.

In Cisco IOS Release XE 2.3, this feature was implemented on the Cisco ASR 1000 Series Aggregation Services Routers.

This feature uses no new or modified commands.