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BGP Session and Route Flaps

Understanding BGP Session Resets

Certain configuration actions and events cause BGP sessions to be reset (dropped and then reestablished).

If you configure both route reflection and VPNs on the same routing device, the following modifications to the route reflection configuration cause current BGP sessions to be reset:

  • Adding a cluster ID—If a BGP session shares the same autonomous system (AS) number with the group where you add the cluster ID, all BGP sessions are reset regardless of whether the BGP sessions are contained in the same group.

  • Creating a new route reflector—If you have an internal BGP (IBGP) group with an AS number and create a new route reflector group with the same AS number, all BGP sessions in the IBGP group and the new route reflector group are reset.

  • Changing configuration statements that affect BGP peers, such as renaming a BGP group, resets the BGP sessions.

  • If you change the address family specified in the [edit protocols bgp family] hierarchy level, all current BGP sessions on the routing device are dropped and then reestablished.

Example: Preventing BGP Session Flaps When VPN Families Are Configured

This example shows a workaround for a known issue in which BGP sessions sometimes go down and then come back up (in other words, flap) when virtual private network (VPN) families are configured. If any VPN family (for example, inet-vpn, inet6-vpn, inet-mpvn, inet-mdt, inet6-mpvn, l2vpn, iso-vpn, and so on) is configured on a BGP master instance, a flap of either a route reflector (RR) internal BGP (IBGP) session or an external BGP (EBGP) session causes flaps of other BGP sessions configured with the same VPN family.

Requirements

Before you begin:

  • Configure router interfaces.

  • Configure an interior gateway protocol (IGP).

  • Configure BGP.

  • Configure VPNs.

Overview

When a router or switch is configured as either a route reflector (RR) or an AS boundary router (an external BGP peer) and a VPN family (for example, the family inet-vpn unicast statement) is configured, a flap of either the RR IBGP session or the EBGP session causes flaps of all other BGP sessions that are configured with the family inet-vpn unicast statement. This example shows how to prevent these unnecessary session flaps.

The reason for the flapping behavior is related to BGP operation in Junos OS when originating VPN routes.

BGP has the following two modes of operation with respect to originating VPN routes:

  • If BGP does not need to propagate VPN routes because the session has no EBGP peer and no RR clients, BGP exports VPN routes directly from the instance.inet.0 routing table to other PE routers. This behavior is efficient in that it avoids the creation of two copies of many routes (one in the instance.inet.0 table and one in the bgp.l3vpn.0 table).

  • If BGP does need to propagate VPN routes because the session has an EBGP peer or RR clients, BGP first exports the VPN routes from the instance.inet.0 table to the bgp.l3vpn.0 table. Then BGP exports the routes to other PE routers. In this scenario, two copies of the route are needed to enable best-route selection. A PE router might receive the same VPN route from a CE device and also from an RR client or EBGP peer.

Note:

The route export is not performed if the route in instance.inet.0 is a secondary route. In Junos OS, a route is only exported one time from one routing table as a primary route to another routing table as a secondary route. Because the route in instance.inet.0 is already a secondary route, it is not allowed to be moved again to the bgp.l3vpn.0 table, as needed to be advertised. The route does not reach the bgp.l3vpn.0 table and thus is not advertised. One workaround is to send the routes that should be advertised to inet.0 so that they are advertised.

When, because of a configuration change, BGP transitions from needing two copies of a route to not needing two copies of a route (or the reverse), all sessions over which VPN routes are exchanged go down and then come back up. Although this example focuses on the family inet-vpn unicast statement, the concept applies to all VPN network layer reachability information (NLRI) families. This issue impacts logical systems as well. All BGP sessions in the master instance related to the VPN NLRI family are brought down to implement the table advertisement change for the VPN NLRI family. Changing an RR to a non-RR or the reverse (by adding or removing the cluster statement) causes the table advertisement change. Also, configuring the first EBGP session or removing the EBGP session from the configuration in the master instance for a VPN NLRI family causes the table advertisement change.

The way to prevent these unnecessary session flaps is to configure an extra RR client or EBGP session as a passive session with a neighbor address that does not exist. This example focuses on the EBGP case, but the same workaround works for the RR case.

When a session is passive, the routing device does not send Open requests to a peer. Once you configure the routing device to be passive, the routing device does not originate the TCP connection. However, when the routing device receives a connection from the peer and an Open message, it replies with another BGP Open message. Each routing device declares its own capabilities.

Topology

Figure 1 shows the topology for the EBGP case. Router R1 has an IBGP session with Routers R2 and R3 and an EBGP session with Router R4. All sessions have the family inet-vpn unicast statement configured. If the R1-R4 EBGP session flaps, the R1-R2 and R1-R3 BGP sessions flap also.

Figure 1: Topology for the EBGP CaseTopology for the EBGP Case

Figure 2 shows the topology for the RR case. Router R1 is the RR, and Router R3 is the client. Router R1 has IBGP sessions with Routers R2 and R3. All sessions have the family inet-vpn unicast statement configured. If the R1-R3 session flaps, the R1-R2 and R1-R4 sessions flap also.

Figure 2: Topology for the RR CaseTopology for the RR Case

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Procedure

Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide.

To configure the EBGP scenario:

  1. Configure one or more VPN families.

  2. Configure the EBGP session.

  3. Configure the IBGP sessions.

  4. (Optional) Configure BGP so that it generates a syslog message whenever a BGP peer makes a state transition.

    Enabling the log-updown statement causes BGP state transitions to be logged at warning level.

Procedure

Step-by-Step Procedure

To verify that unnecessary session flaps are occurring:

  1. Run the show bgp summary command to verify that the sessions have been established.

  2. Deactivate the EBGP session.

  3. Run the show bgp summary command to view the session flaps.

Procedure

Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide.

To prevent unnecessary BGP session flaps:

  1. Add a passive EBGP session with a neighbor address that does not exist in the peer autonomous system (AS).

  2. Run the show bgp summary command to verify that the real sessions have been established and the passive session is idle.

Verification

Confirm that the configuration is working properly.

Bringing Down the EBGP Session

Purpose

Try to cause the flap issue after the workaround is configured.

Action

Verifying That the IBGP Sessions Remain Up

Purpose

Make sure that the IBGP sessions do not flap after the EBGP session is deactivated.

Action

Understanding Damping Parameters

BGP route flapping describes the situation in which BGP systems send an excessive number of update messages to advertise network reachability information. BGP flap damping is a method of reducing the number of update messages sent between BGP peers, thereby reducing the load on these peers, without adversely affecting the route convergence time for stable routes.

Flap damping reduces the number of update messages by marking routes as ineligible for selection as the active or preferable route. Marking routes in this way leads to some delay, or suppression, in the propagation of route information, but the result is increased network stability. You typically apply flap damping to external BGP (EBGP) routes (routes in different ASs). You can also apply flap damping within a confederation, between confederation member ASs. Because routing consistency within an AS is important, do not apply flap damping to internal BGP (IBGP) routes. (If you do, it is ignored.)

There is an exception that rule. Starting in Junos OS Release 12.2, you can apply flap damping at the address family level. In a Junos OS Release 12.2 or later installation, when you apply flap damping at the address family level, it works for both IBGP and EBGP.

By default, route flap damping is not enabled. Damping is applied to external peers and to peers at confederation boundaries.

When you enable damping, default parameters are applied, as summarized in Table 1.

Table 1: Damping Parameters

Damping Parameter

Description

Default Value

Possible Values

half-life minutes

Decay half-life—Number of minutes after which an arbitrary value is halved if a route stays stable.

15 (minutes)

1 through 45

max-suppress minutes

Maximum hold-down time for a route, in minutes.

60 (minutes)

1 through 720

reuse

Reuse threshold—Arbitrary value below which a suppressed route can be used again.

750

1 through 20,000

suppress

Cutoff (suppression) threshold—Arbitrary value above which a route can no longer be used or included in advertisements.

3000

1 through 20,000

To change the default BGP flap damping values, you define actions by creating a named set of damping parameters and including it in a routing policy with the damping action. For the damping routing policy to work, you also must enable BGP route flap damping.

Example: Configuring BGP Route Flap Damping Parameters

This example shows how to configure damping parameters.

Requirements

Before you begin, configure router interfaces and configure routing protocols.

Overview

This example has three routing devices. Device R2 has external BGP (EBGP) connections with Device R1 and Device R3.

Device R1 and Device R3 have some static routes configured for testing purposes, and these static routes are advertised through BGP to Device R2.

Device R2 damps routes received from Device R1 and Device R3 according to these criteria:

  • Damp all prefixes with a mask length equal to or greater than 17 more aggressively than routes with a mask length between 9 and 16.

  • Damp routes with a mask length between 0 and 8, inclusive, less than routes with a mask length greater than 8.

  • Do not damp the 10.128.0.0/9 prefix at all.

The routing policy is evaluated when routes are being exported from the routing table into the forwarding table. Only the active routes are exported from the routing table.

Figure 3 shows the sample network.

Figure 3: BGP Flap Damping TopologyBGP Flap Damping Topology

CLI Quick Configuration shows the configuration for all of the devices in Figure 3.

The section #d479e76__d479e263 describes the steps on Device R2.

Configuration

Procedure

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Device R1

Device R2

Device R3

Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide.

To configure damping parameters:

  1. Configure the interfaces.

  2. Configure the BGP neighbors.

  3. Create and configure the damping parameter groups.

  4. Configure the damping policy.

  5. Enable damping for BGP.

  6. Apply the policy as an import policy for the BGP neighbor.

    Note:

    You can refer to the same routing policy one or more times in the same or different import statements.

  7. Configure an export policy.

  8. Apply the export policy.

  9. Configure the autonomous system (AS) number.

Results

From configuration mode, confirm your configuration by issuing the show interfaces, show protocols, show policy-options, and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

If you are done configuring the device, enter commit from configuration mode.

Verification

Confirm that the configuration is working properly.

Causing Some Routes to Flap

Purpose

To verify your route flap damping policy, some routes must flap. Having a live Internet feed almost guarantees that a certain number of route flaps will be present. If you have control over a remote system that is advertising the routes, you can modify the advertising router's policy to effect the advertisement and withdrawal of all routes or of a given prefix. In a test environment, you can cause routes to flap by clearing the BGP neighbors or by restarting the routing process on the BGP neighbors, as shown here.

Action

From operational mode on Device R1 and Device R3, enter the restart routing command.

CAUTION:

Use this command cautiously in a production network.

Meaning

On Device R2, all of the routes from the neighbors are withdrawn and re-advertised.

Checking the Route Flaps

Purpose

View the number of neighbor flaps.

Action

From operational mode, enter the show bgp summary command.

Meaning

This output was captured after the routing process was restarted on Device R2’s neighbors four times.

Verifying Route Flap Damping

Purpose

Verify that routes are being hidden due to damping.

Action

From operational mode, enter the show route damping suppressed command.

Meaning

The output shows some routing instability. Eleven routes are hidden due to damping.

Displaying the Details of a Damped Route

Purpose

Display the details of damped routes.

Action

From operational mode, enter the show route damping suppressed 172.16.192.0/20 detail command.

Meaning

This output indicates that the displayed route has a mask length that is equal to or greater than /17, and confirms that it has been correctly mapped to the aggressive damping profile. You can also see the route’s current (and last) figure of merit value, and when the route is expected to become active if it remains stable.

Verifying That Default Damping Parameters Are in Effect

Purpose

Locating a damped route with a /16 mask confirms that the default parameters are in effect.

Action

From operational mode, enter the show route damping suppressed detail | match 0/16 command.

Meaning

Routes with a /16 mask are not impacted by the custom damping rules. Therefore, the default damping rules are in effect.

To repeat, the custom rules are as follows:

  • Damp all prefixes with a mask length equal to or greater than 17 more aggressively than routes with a mask length between 9 and 16.

  • Damp routes with a mask length between 0 and 8, inclusive, less than routes with a mask length greater than 8.

  • Do not damp the 10.128.0.0/9 prefix at all.

Filtering the Damping Information

Purpose

Use OR groupings or cascaded piping to simplify the determination of what damping profile is being used for routes with a given mask length.

Action

From operational mode, enter the show route damping suppressed command.

Meaning

When you are satisfied that your EBGP routes are correctly associated with a damping profile, you can issue the clear bgp damping operational mode command to restore an active status to your damped routes, which will return your connectivity to normal operation.

Example: Configuring BGP Route Flap Damping Based on the MBGP MVPN Address Family

This example shows how to configure an multiprotocol BGP multicast VPN (also called Next-Generation MVPN) with BGP route flap damping.

Requirements

This example uses Junos OS Release 12.2. BGP route flap damping support for MBGP MVPN, specifically, and on an address family basis, in general, is introduced in Junos OS Release 12.2.

Overview

BGP route flap damping helps to diminish route instability caused by routes being repeatedly withdrawn and readvertised when a link is intermittently failing.

This example uses the default damping parameters and demonstrates an MBGP MVPN scenario with three provider edge (PE) routing devices, three customer edge (CE) routing devices, and one provider (P) routing device.

Topology

Figure 4 shows the topology used in this example.

Figure 4: MBGP MVPN with BGP Route Flap DampingMBGP MVPN with BGP Route Flap Damping

On PE Device R4, BGP route flap damping is configured for address family inet-mvpn. A routing policy called dampPolicy uses the nlri-route-type match condition to damp only MVPN route types 3, 4, and 5. All other MVPN route types are not damped.

This example shows the full configuration on all devices in the CLI Quick Configuration section. The Configuring Device R4 section shows the step-by-step configuration for PE Device R4.

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, and then copy and paste the commands into the CLI at the [edit] hierarchy level.

Device R1

Device R2

Device R3

Device R4

Device R5

Device R6

Device R7

Configuring Device R4

Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide.

To configure Device R4:

  1. Configure the interfaces.

  2. Configure MPLS and the signaling protocols on the interfaces.

  3. Configure BGP.

    The BGP configuration enables BGP route flap damping for the inet-mvpn address family. The BGP configuration also imports into the routing table the routing policy called dampPolicy. This policy is applied to neighbor PE Device R2.

  4. Configure an interior gateway protocol.

  5. Configure a damping policy that uses the nlri-route-type match condition to damp only MVPN route types 3, 4, and 5.

  6. Configure the damping policy to disable BGP route flap damping.

    The no-damp policy (damping no-damp disable) causes any damping state that is present in the routing table to be deleted. The then damping no-damp statement applies the no-damp policy as an action and has no from match conditions. Therefore, all routes that are not matched by term1 are matched by this term, with the result that all other MVPN route types are not damped.

  7. Configure the parent_vpn_routes to accept all other BGP routes that are not from the inet-mvpn address family.

    This policy is applied as an OSPF export policy in the routing instance.

  8. Configure the VPN routing and forwarding (VRF) instance.

  9. Configure the router ID and the autonomous system (AS) number.

  10. If you are done configuring the device, commit the configuration.

Results

From configuration mode, confirm your configuration by entering the show interfaces, show protocols, show policy-options, show routing-instances, and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

Verification

Confirm that the configuration is working properly.

Verifying That Route Flap Damping Is Disabled

Purpose

Verify the presence of the no-damp policy, which disables damping for MVPN route types other than 3, 4, and 5.

Action

From operational mode, enter the show policy damping command.

Meaning

The output shows that the default damping parameters are in effect and that the no-damp policy is also in effect for the specified route types.

Verifying Route Flap Damping

Purpose

Check whether BGP routes have been damped.

Action

From operational mode, enter the show bgp summary command.

Meaning

The Damp State field shows that zero routes in the bgp.mvpn.0 routing table have been damped. Further down, the last number in the State field shows that zero routes have been damped for BGP peer 172.16.1.2.

Understanding BGP-Static Routes for Preventing Route Flaps

BGP-static routes can be configured to ensure that a prefix does not flap. BGP-static routes do not flap unless they are deleted manually. If the BGP-static routes are configured globally, then each neighbor, group, or all neighbors must be explicitly configured to receive them. Peer routers receive advertisements for these routes regardless of dynamic routing information learned by the advertising router for those prefixes. Despite being the active route, BGP-static routes are never advertised to a BGP neighbor for which they are not configured. You can specify any number of BGP-static routes in the configuration. You can also define a policy to specify which BGP-static routes need to be advertised and included in a BGP advertisement.

BGP-static routes are placed in the routing table. If the BGP-static routes are active routes (if there are no other routes for that prefix), they are placed in the forwarding table. These routes are advertised only to those BGP hosts that are configured to receive them. The configured BGP-static routes are not advertised by any other protocol besides BGP. Service providers who have one or more single-homed customers can configure BGP-static routes on a BGP network to advertise static paths for these customers.

Note:

Configuring the advertisement of BGP-static routes at the neighbor level causes an internal group split. Configure the advertisement of BGP-static routes only at the global and group levels to keep the configuration simple. The configured BGP-static routes do not affect the VPN routes that are advertised.

If a BGP-static route is advertised to a neighbor, it is the only route advertised for the prefix. BGP-static routes are not considered as candidate routes for BGP multipath or protocol-independent multipath. They do not cause an aggregate or generated route to be added to the routing table.

CAUTION:

Configuring BGP-static routes on networks that are accessible by multiple paths and are not the only point of access to all of the paths might cause traffic to be silently dropped or discarded. In a multihomed network, BGP-static routes can be configured on devices that are the only point of access to other paths. By default, all BGP-static routes that are advertised to the internal peers include a local-pref value of 0 to mitigate the risk of a null route for multihomed networks. You can override this default value by setting an explicit preference2 value on the BGP-static routes.

Configuring BGP-Static Routes for Preventing Route Flaps

BGP-static routes are configured to ensure that routes to a customer network do not flap. The configured BGP-static routes are not advertised by any other protocol besides BGP. BGP-static routes are configured globally, but each neighbor, group, or all neighbors must be explicitly configured to receive them. Peer routers will receive advertisements for these routes regardless of dynamic routing information learned by the advertising router for those prefixes. You can specify any number of BGP-static routes in the configuration. You can also define a policy to specify which BGP-static routes need to be advertised.

Before you configure BGP-static routes:

  1. Ensure that the IGP and BGP protocols are configured and working.

  2. Ensure that BGP-static route that you configure is behind a customer router.

    Do not use BGP-static routes for prefixes that BGP uses to reach BGP neighbors.

To configure BGP-static routes:

  1. Configure a BGP-static route for a customer router on a BGP network to advertise static paths for these customers.

    You can also configure other configuration options such as as-path, color, community, tag, and preference as needed.

  2. Configure the BGP groups or the BGP neighbors that are to receive the BGP-static route advertisements.

    You can also configure this statement at a global level if you want every host on the BGP network to receive the BGP-static advertisements.

  3. (Optional) Specify an additional export policy to control whether or not a given BGP-static route needs to be advertised.

    The policy is applied to the BGP-static route and not the active route.

  4. Apply the defined policy to a BGP group or neighbor.

Example: Configuring BGP-Static Routes to Prevent Route Flaps

This example shows how to configure BGP-static routes. BGP hosts advertise these BGP-static routes only to those neighbors who are configured to receive these routes. A BGP-static route is configured to ensure that a prefix does not flap. However, If the BGP-static routes are configured globally, then each neighbor, group, or all neighbors must be explicitly configured to receive them.

Requirements

This example uses the following hardware and software components:

  • Seven MX Series routers with BGP enabled on the connected interfaces

  • Junos OS Release 14.2 or later running on all devices

Overview

Beginning with Junos OS Release 14.2, you can configure and advertise BGP-static routes in a BGP network. You can advertise a BGP-static route in a BGP network even if it is not the active route for the prefix. BGP-static routes do not flap unless they are deleted manually. You can define a policy that determines which BGP-static routes need to be advertised and included in the advertisements. Peer routers receive advertisements for these BGP-static routes regardless of dynamic routing information learned by the advertising router.

In the sample BGP network, Devices CE1, CE2, and CE3 are directly connected to Routers PE1, PE2, and PE3. Both PE1 and PE2 are connected to Router P. Router P is directly connected to Router PE3. EBGP is configured on the provider edge and customer edge routers. IBGP is configured on directly connected provider edge routers. The IGP protocol IS-IS is configured on all provider routers. Configure a BGP-static route on Router PE1 to ensure that customer route 10.0.0.28 behind CE1 does not flap. Provider Router PE2 is configured to receive the BGP-static route. The objective is to advertise a BGP-static route only to CE2 and not to CE3, and to demonstrate that the configured BGP-static route does not flap.

Topology

Figure 5 shows the sample topology.

Figure 5: Configuring BGP-Static RouteConfiguring BGP-Static Route

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, copy and paste the commands into the CLI at the [edit] hierarchy level, and then enter commit from configuration mode.

Router P

Router PE1

Router PE2

Router PE3

Router CE1

Router CE2

Router CE3

Procedure

Step-by-Step Procedure

The following example requires that you navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the CLI User Guide.

To configure Router PE1:

  1. Configure the interfaces with IPv4 addresses.

  2. Enable the IS-IS protocol on interfaces connected to provider routers for learning and exchanging routes learned.

  3. Configure loopback addresses for inet and IS-IS.

  4. Configure the IS-IS interfaces.

  5. Configure EBGP.

  6. Configure an IBGP neighbor on internal routers connected to the provider network.

  7. Configure the BGP static route.

  8. Configure the BGP neighbor PE2 to receive BGP-static advertisements.

  9. Define a policy to export routes to the BGP network.

  10. Apply the policy to the IBGP group.

  11. Configure the router id and the autonomous system (AS) number.

Results

From configuration mode, confirm your configuration by entering the show interfaces, show policy-options, show protocols, and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

If you are done configuring the device, enter commit from configuration mode.

Verification

Confirm that the configuration is working properly.

Verifying the BGP Neighbors

Purpose

Verify that BGP is running on the configured interfaces and that the BGP session is active for each neighbor address.

Action

From operational mode, run the show bgp neighbor command on Router PE1.

Meaning

The output displays the BGP neighbors of Router PE1 and the configured BGP options such as whether the neighbor is configured to receive BGP-static routes. Router PE2 is configured to receive BGP-static route advertisements.

Verifying BGP Groups

Purpose

Verify that the intended BGP groups or neighbors are configured to receive the BGP-static routes.

Action

From operational mode, run the show bgp group command.

Meaning

The output shows the BGP neighbor that is configured to receive BGP-static advertisements.

Verifying the Routes

Purpose

Verify that the configured BGP-static route is saved in the routing table of the configured BGP neighbors.

Action

From operational mode, run the show route protocol bgp-static command to display the routing table.

Meaning

The output shows the BGP-static route configured on the device. The active path is learned from CE1, and the BGP-static route is inactive.

Verifying That the Configured Hosts Receive the BGP-Static Routes

Purpose

Verify that the BGP-static route is being advertised to the host configured to receive it.

Action

On Devices CE2 and CE3, from operational mode, run the show route protocol bgp command to display the learned routes in the routing table.

Meaning

Both Devices CE2 and CE3 have a route to 10.0.0.28/32. CE2 has received the BGP-static route and CE3 has received a dynamically-learned route, but you cannot tell the difference.

Verifying That the Configured BGP-Static Route Does Not Flap

Purpose

Verify that the BGP-static route does not flap even when the BGP peering session between Router PE1 and Device CE1 goes down.

Action

Deactivate the BGP peering session between Router PE1 and Device CE1. PE1 does not have a dynamically learned route to 10.0.0.28/32, but still has the configured BGP-static route.

Meaning

Router PE1 and Device CE2 still have the configured BGP-static route. However, Device CE3 does not have the route to 10.0.0.28/32 because this prefix has flapped. BGP-static routes do not flap unless deleted manually.

Release History Table
Release
Description
12.2
Starting in Junos OS Release 12.2, you can apply flap damping at the address family level.