MPLS: High Availability Configuration Guide, Cisco IOS XE Release 3S

AToM Graceful Restart

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.

•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

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 AToM Graceful Restart" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE 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 AToM Graceful Restart

•Restrictions for AToM Graceful Restart

•Information About AToM Graceful Restart

•How to Configure AToM Graceful Restart

•Configuration Examples for AToM Graceful Restart

•Additional References

•Feature Information for AToM Graceful Restart

Prerequisites for AToM Graceful Restart

AToM must be configured. For information about setting up or configuring AToM, see the Any Transport over MPLS document.

Restrictions for AToM Graceful Restart

•AToM GR is supported in strict helper mode.

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

Information About AToM Graceful Restart

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

•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 (RP) 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 procedure:

•Configuring AToM Graceful Restart (required)

Configuring AToM Graceful Restart

To configure AToM Graceful Restart, perform the following task.

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

SUMMARY STEPS

1. enable

2. configure terminal

3. ip cef distributed

4. mpls ldp graceful-restart

5. exit

DETAILED STEPS

Router(config)# mpls ldp graceful-restart

Configuration Examples for AToM Graceful Restart

This section provides the following configuration examples:

•Configuring AToM Graceful Restart: Example

•AToM Graceful Restart—Recovering from an LDP Session Disruption: Examples

Configuring AToM Graceful Restart: Example

The following example shows a Fast 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.

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

AToM Graceful Restart—Recovering from an LDP Session Disruption: Examples

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

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

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.

Router# 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.

Router# 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:

Router# 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.

Router# 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

The following sections provide references related to the AToM GR feature.

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for AToM Graceful Restart

Table 1 lists the features in this module and provides links to specific configuration information.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE 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.

Note Table 1 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.

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