Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and 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 table at the end of this module.

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• Your network must be configured to run BGP.

• Multiprotocol Layer Switching (MPLS) Layer 3 VPNs must be configured.

• You must be familiar with NSF and SSO concepts and tasks.

Prior to the introduction of Border Gateway Protocol (BGP) Nonstop Routing (NSR) with Stateful Switchover (SSO), BGP required that all neighboring devices participating in BGP Nonstop Forwarding (NSF) be configured to be either NSF-capable or NSF-aware (by configuring the devices to support the BGP graceful restart mechanism). BGP NSF, thus, required that all neighboring devices be upgraded to a version of Cisco IOS software that supports BGP graceful restart. However, in many Multiprotocol Layer Switching (MPLS) Virtual Private Networks (VPN) deployments, there are situations where provider edge (PE) devices engage in exterior BGP (eBGP) peering sessions with customer edge (CE) devices that do not support BGP graceful restart and cannot be upgraded to a software version that supports BGP graceful restart in the same time frame as the PE devices.

BGP NSR with SSO provides a high availability (HA) solution to service providers whose PE devices engage in eBGP peering relationships with CE devices that do not support BGP graceful restart. BGP NSR works with SSO to synchronize BGP state information between the active and standby route processor (RP). SSO minimizes the amount of time a network is unavailable to its users following a switchover. When the BGP Support for NSR with SSO feature is configured, in the event of an RP switchover, the PE device uses BGP NSR with SSO to maintain BGP state for eBGP peering sessions with CE devices that are not NSF-aware (see the illustration below).

Additionally, the BGP Support for NSR with SSO feature dynamically detects NSF-aware peers and runs graceful restart with those CE devices. For eBGP peering sessions with NSF-aware peers and for internal BGP (iBGP) sessions with BGP route reflectors (RRs) in the service provider core, the PE device uses NSF to maintain BGP state. BGP NSR with SSO, thus, enables service providers to provide the benefits of NSF with the additional benefits of NSR without requiring CE devices to be upgraded to support BGP graceful restart.

Figure 1. BGP NSR with SSO Operations During an RP Switchover

BGP NSR with SSO is supported in BGP peer, BGP peer group, and BGP session template configurations. To configure support for BGP NSR with SSO in BGP peer and BGP peer group configurations, use the neighbor ha-mode sso command in address family configuration mode for IPv4 VRF address family BGP peer sessions. To include support for Cisco BGP NSR with SSO in a peer session template, use the ha-mode sso command in session-template configuration mode.

When BGP NSR with graceful restart is configured, graceful restart takes precedence over BGP NSR for all BGP peers, if graceful restart capability is received from the BGP peer.

When you enable graceful restart globally, the graceful restart capability exchange takes effect after all current BGP sessions are reset. You must do a session renegotiation for all BGP peers manually. To reset all current BGP sessions, use the clear ip bgp * command in privileged EXEC mode. After the session reset, graceful restart takes precedence over BGP NSR for all peers.

To configure a particular BGP peer to choose NSR over graceful restart, you must disable graceful restart for that particular BGP peer on a per neighbor basis. To disable graceful restart, use the neighbor ip-address ha-mode graceful-restart disable command.

• Minimizes services disruptions--Border Gateway Protocol (BGP) Nonstop Routing (NSR) with Stateful Switchover (SSO) reduces impact on customer traffic during route processor (RP) switchovers (scheduled or unscheduled events), extending high availability (HA) deployments and benefits at the edge.

• Enhances high-availability Nonstop Forwarding (NSF) and SSO deployment at the edge--BGP NSR with SSO allows incremental deployment by upgrading the provider edge device with the NSR capability so that customer-facing edge devices are synchronized automatically and no coordination or NSF awareness is needed with the customer side Cisco or third-party customer edge devices. The BGP NSR feature dynamically detects NSF-aware peers and runs graceful restart with those CE devices.

• Provides transparent route convergence--BGP NSR with SSO eliminates route flaps by keeping BGP state on both active and standby RPs and ensures continuous packet forwarding with minimal packet loss during RP failovers.

Global support for Border Gateway Protocol (BGP) Nonstop Routing (NSR) enhancement enables or disables BGP NSR for all neighbors configured on the provider edge (PE) device, customer edge (CE) device, and core devices under router configuration mode.

When BGP NSR and graceful restart are configured on the same BGP device, graceful restart takes precedence over NSR configuration. The BGP peer advertises the graceful restart capability, becomes graceful restart-enabled by default, and does not support NSR. To configure support for BGP NSR globally and NSR preference over graceful restart, use the bgp ha-mode sso [prefer] command in router configuration mode. The optional keyword prefer enables NSR to take precedence over graceful restart configuration. In the current scenario, when BGP NSR with graceful restart is configured, graceful restart takes precedence over BGP NSR for all BGP peers, if graceful restart capability is received from the BGP peer.

Note	The prefer keyword is used to take precedence if BGP NSR with graceful restart is configured on the same device. If the device is configured with NSR only, you need not to use the prefer keyword.

1.    enable


2.    configure terminal


3.    router bgp as-number


4.    bgp ha-mode sso [prefer]


5.    end

Device> enable

Device# configure terminal

Device(config)# router bgp 65000

Device(config-router)# bgp ha-mode sso prefer

Device(config-router)# end

Perform this task to enable a provider edge (PE) device to maintain BGP state with customer edge (CE) devices and ensure continuous packet forwarding during a route processor (RP) switchover or during a planned ISSU. Border Gateway Protocol (BGP) Nonstop Routing (NSR) with Stateful Switchover (SSO) enables service providers to provide the benefits Nonstop Forwarding (NSF) with the additional benefits of NSR without requiring CE devices to be upgraded to support BGP graceful restart.

BGP NSR with SSO is supported in BGP peer, BGP peer group, and BGP session template configurations. Perform one of the following tasks in this section on a PE device, depending on whether you want to configure support for BGP NSR with SSO in a peer, a peer group, or a session template configuration:

1.    enable


2.    show ip bgp vpnv4 all sso summary


3.    show ip bgpl2vpnvpls all neighbors

Device> enable

Device# show ip bgp vpnv4 all sso summary
   Stateful switchover support enabled for 40 neighbors

Device# show ip bgp l2vpn vpls all neighbors 10.3.3.3
BGP neighbor is 10.3.3.3,  vrf vrf1,  remote AS 3, external link
  Inherits from template 10vrf-session for session parameters
   BGP version 4, remote router ID 10.1.105.12
   BGP state = Established, up for 04:21:39
   Last read 00:00:05, last write 00:00:09, hold time is 30, keepalive interval is 10 seconds
   Configured hold time is 30, keepalive interval is 10 seconds
   Minimum holdtime from neighbor is 0 seconds
   Neighbor capabilities:
     Route refresh: advertised and received(new)
     Address family IPv4 Unicast: advertised and received
     Stateful switchover support enabled
   Message statistics:
     InQ depth is 0
     OutQ depth is 0
                          Sent       Rcvd
     Opens:                  1          1
     Notifications:          0          0
     Updates:                1          4
     Keepalives:          1534       1532
     Route Refresh:          0          0
     Total:               1536       1537
   Default minimum time between advertisement runs is 30 seconds
  For address family: L2VPN VPLS
   BGP table version 25161, neighbor version 25161/0
   Output queue size : 0
   Index 7, Offset 0, Mask 0x80
   7 update-group member
   Inherits from template 10vrf-policy
   Overrides the neighbor AS with my AS before sending updates
   Outbound path policy configured
   Route map for outgoing advertisements is Deny-CE-prefixes
                                  Sent       Rcvd
   Prefix activity:               ----       ----
     Prefixes Current:              10         50 (Consumes 3400 bytes)
     Prefixes Total:                10         50
     Implicit Withdraw:              0          0
     Explicit Withdraw:              0          0
     Used as bestpath:             n/a          0
     Used as multipath:            n/a          0
                                    Outbound    Inbound
   Local Policy Denied Prefixes:    --------    -------
     route-map:                          150          0
     AS_PATH loop:                       n/a        760
     Total:                              150        760
   Number of NLRIs in the update sent: max 10, min 10
   Address tracking is enabled, the RIB does have a route to 10.3.3.3
   Address tracking requires at least a /24 route to the peer
   Connections established 1; dropped 0
   Last reset never
   Transport(tcp) path-mtu-discovery is enabled
   TCP session must be opened passively
Connection state is ESTAB, I/O status: 1, unread input bytes: 0 Connection is ECN Disabled Local host: 10.0.21.1, Local port: 179 Foreign host: 10.0.21.3, Foreign port: 51205 Connection tableid (VRF): 1
Enqueued packets for retransmit: 0, input: 0  mis-ordered: 0 (0 bytes)
Event Timers (current time is 0x1625488):
Timer          Starts    Wakeups            Next
Retrans          1746        210             0x0
TimeWait            0          0             0x0
AckHold          1535       1525             0x0
SendWnd             0          0             0x0
KeepAlive           0          0             0x0
GiveUp              0          0             0x0
PmtuAger            0          0             0x0
DeadWait            0          0             0x0
Linger              0          0             0x0
iss: 2241977291  snduna: 2242006573  sndnxt: 2242006573     sndwnd:  13097
irs:  821359845  rcvnxt:  821391670  rcvwnd:      14883  delrcvwnd:   1501
SRTT: 300 ms, RTTO: 303 ms, RTV: 3 ms, KRTT: 0 ms
minRTT: 0 ms, maxRTT: 300 ms, ACK hold: 200 ms Status Flags: passive open, retransmission timeout, gen tcbs
   0x1000
Option Flags: VRF id set, always push, md5
Datagrams (max data segment is 4330 bytes):
Rcvd: 3165 (out of order: 0), with data: 1535, total data bytes: 31824
Sent: 3162 (retransmit: 210 fastretransmit: 0),with data: 1537, total data
bytes: 29300
SSO Last Disable Reason: Application Disable (Active)

The illustration below illustrates a sample Border Gateway Protocol (BGP) Nonstop Routing (NSR) with Stateful Switchful (SSO) network topology using L2VPN VPLS technology, and the configuration examples that follow show configurations from two devices in the topology: the RR1 device and the provider edge (PE) device.

Note	The configuration examples omit some of the configuration required for Multiprotocol Label Switching (MPLS) VPNs because the purpose of these examples is to illustrate the configuration of BGP NSR with SSO.

Figure 2. BGP NSR with SSO Example Topology

!
router bgp 1
 no synchronization
 bgp log-neighbor-changes
 bgp graceful-restart restart-time 120
 bgp graceful-restart stalepath-time 360
 bgp graceful-restart
 neighbor 10.2.2.2 remote-as 1
 neighbor 10.2.2.2 update-source Loopback0
 no auto-summary
 !        
 address-family l2vpn vpls
 neighbor 10.2.2.2 activate
 neighbor 10.2.2.2 send-community both
 neighbor 10.2.2.2 route-reflector-client
 exit-address-family
 !

!
router bgp 2
 no synchronization
 bgp log-neighbor-changes
 bgp graceful-restart restart-time 120
 bgp graceful-restart stalepath-time 360
 bgp graceful-restart
 neighbor 10.1.1.1 remote-as 1
 neighbor 10.1.1.1 update-source Loopback0
	neighbor 10.3.3.3 remote-as 3
 neighbor 10.3.3.3 ha-mode sso
 neighbor 10.3.3.3 activate
 neighbor 10.3.3.3 as-override
 no auto-summary
 !        
 address-family l2vpn vpls
 neighbor 10.1.1.1 activate
 neighbor 10.1.1.1 send-community both
 exit-address-family
 !
 no auto-summary
 no synchronization
 exit-address-family
!