Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Use the additional-paths receive command to allow add-path receive capability to be negotiated for a specified address family. When the additional-paths receive command is configured, the receive capability is automatically enabled for all internal BGP neighbors for a specified address family. When this command is either not configured or explicitly disabled, none of the neighbors are allowed to negotiate receive capability for the address family.

After enabling the receive capability, the session needs to be reset for the configuration to take into effect.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

To configure additional paths selection mode for some or all prefixes, use the additional-paths selection command by specifying a route-policy.

Use the additional-path selection command with an appropriate route-policy to calculate backup paths and to enable Prefix Independent Convergence (PIC) functionality. Refer BGP Prefix Independent Convergence Unipath Primary/Backup section in Routing Configuration Guide for Cisco ASR 9000 Series Routers for details on the PIC functionality.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Use the additional-paths send command to allow add-path send capability to be negotiated for a specified address family. When the additional-paths send command is configured, the send capability is automatically enabled for all internal BGP neighbors for the specified address family. When the command is either not configured or explicitly disabled, none of the neighbors are allowed to negotiate send capability for the address family.

After enabling the send capability, the session needs to be reset for the configuration to take into effect.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Use the address-family command to enter various address family configuration modes while configuring BGP routing sessions. When you enter the address-family command from router configuration mode, you enable the address family and enter global address family configuration mode.

The IPv4 unicast address family must be configured in router configuration mode before configuring the IPv4 labeled-unicast address family for a neighbor in neighbor configuration mode.

When you enter the address-family command from neighbor configuration mode, you activate the address family on the neighbor and enter neighbor address family configuration mode. IPv4 neighbor sessions support IPv4 unicast, , labeled-unicast, and VPNv4 unicast address families. IPv6 neighbor sessions support IPv6 unicast address families.

Outbound Route Filter (ORF) capability is not supported with address-family l2vpn vpls-vpws

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Unlabelled best-external is not supported as it may create routing loop.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

If this command configures a neighbor group or session group, all neighbors using the group inherit the configuration. Values of commands configured specifically for a neighbor override inherited values.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Use the af-group command to group address family-specific neighbor commands within an IPv4 or IPv6 address family. Neighbors that have address family configuration are able to use the address family group. Further, neighbors inherit the configuration parameters of the entire address family group.

You cannot define two address family groups with the same name in different address families.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

You can implement aggregate routing in BGP either by redistributing an aggregate route into BGP using the network command or the aggregate-address command.

Use the aggregate-address command without optional arguments to create an aggregate entry in the BGP routing table if any more-specific BGP routes are available that fall in the specified range. The aggregate route is advertised as coming from your autonomous system and has the atomic aggregate attribute set to show that information might be missing. (By default, the atomic aggregate attribute is set unless you specify the as-set keyword.)

Use of the as-set keyword creates an aggregate entry using the same rules that the command follows without this keyword. However, the advertised path for this route is an AS_SET, a set of all autonomous systems contained in all paths that are being summarized.

Do not use this form of the aggregate-address command when aggregating many paths because this route must be continually withdrawn and updated as autonomous system path reachability information for the summarized routes changes.

Use the as-confed-set keyword to create an AS_CONFED_SET in the autonomous system path of the aggregate from any confederation segments in the paths being summarized. This keyword takes effect only if the as-set keyword is also specified.

Use of the summary-only keyword creates an aggregate entry (for example, 10.0.0.0/8) but suppresses advertisements of more-specific routes to all neighbors. If you want to suppress only advertisements to certain neighbors, use the route-policy (BGP) command in neighbor address family configuration mode with caution. If a more-specific route leaks out, all BGP speakers (the local router) prefer that route over the less-specific aggregate you generate (using longest-match routing).

Use the route-policy keyword to specify a routing policy for the aggregate entry. The route-policy keyword is used to select which more-specific information to base the aggregate entry on and which more-specific information to suppress. You can also use the keyword to modify the attributes of the aggregate entry.

Aggregate contributor flag is set in the router where you configure it. This feature is applicable for the following Address Family Indicators (AFIs):

• IPv4 unicast

• IPv6 unicast

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Cost community point of insertion can be configured either to be pre-bestpath or after igp cost. The transitive keyword is not required for iBGP sessions. However, the transitive keyword is required for eBGP sessions to convert AiGP metric into cost-community and advertise to the eBGP neighbors.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Use the allocate-label command with a route policy to trigger BGP to allocate labels for all or a filtered set of global IPv4 routes (as dictated by the route policy). The command enables autonomous system border routers (ASBRs) that have labeled IPv4 unicast sessions to exchange Multiprotocol Label Switching (MPLS) labels with the IPv4 routes to the other autonomous system (AS) in Layer 3 Virtual Private Network (L3VPN) inter-AS deployments.

Note	The allocate-label all command is functionally equivalent to the allocate-label route-policy route-policy-name command when the route policy is a pass-all policy.

See MPLS Configuration Guide for Cisco ASR 9000 Series Routersfor information on using the allocate-label command for L3VPN inter-AS deployments and carrier-supporting-carrier IPv4 BGP label distribution.

Usage Guidelines

This command only enables the router to advertise itself as the next-hop router for a default route to its BGP VPN neighbors. To actually forward the default route to a BGP VPN neighbor, you need to run the default-originate command under the BGP neighbor Address-Family configuration mode.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Usage Guidelines

Additional paths send and receive capabilities are negotiated per neighbor per address family. Originally, Add-path capability was supported only for iBGP and confederation neighbors and not supported for eBGP neighbors. Use the as-league peers command to configure a subset of peer ASs so that the eBGP peers belonging to that league can participate in the add path send/receive. You can create a subset of peer ASs that are under a common administration, have a trusted relationship, or enable a select set of features among themselves.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Use the as-override command in conjunction with the site-of-origin (SoO) feature, identifying the site where a route originated, and preventing routing loops between routers within a VPN.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Configure the as-path-loopcheck out disable command to disable the default behavior of PE router not announcing BGP routes to the CE router if the routes contain an AS number matching the AS number of the receiving CE router.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Use the attribute-filter group command in neighbor configuration mode to configure a specific attribute filter group for a BGP neighbor.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

If the minimum interval is changed using the bfd minimum-interval command, the new parameter updates all affected BFD sessions under the command mode in which the minimum interval was changed.

If the multiplier is changed using the bfd multiplier command, the new parameter is used to update only the BFD sessions associated with the affected neighbor gets affected.

The assumption is that when BFD fast-detect is enabled under neighbor address family independent configuration, the values for the multiplier and minimum-interval values are always derived from the per-neighbor values if they are configured; otherwise, they are to be taken from the global BGP configuration mode. In the event that this has not been explicitly stated, then these values are taken to be the default values. Also, the bfd arguments can be configured under neighbor-group and session-group and the inheritance adheres to the standard way of BGP configuration inheritance.

Accordingly, there are four cases in which bfd-fast detect is enabled.

This is shown in table below where the BFD value is either multiplier or minimum-interval. Local indicates per NBR value, global is the BGP global value.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

When BGP attribute download is enabled using the bgp attribute-download command, BGP reinstalls all routes whose attributes are not currently in the RIB. Likewise, if the user disables BGP attribute download using the no form of the command, BGP reinstalls previously installed routes with a null key, and removes the attributes from the RIB.

Use the bgp attribute-download command to enable the Netflow BGP data export function. When attribute download is enabled, BGP downloads the attribute information for prefixes (community, extended community, and as-path) to the Routing Information Base (RIB) and Forwarding Information Base (FIB). This enables FIB to associate the prefixes with attributes and send the Netflow statistics along with the associated attributes.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Note

If the inbound policy changes, it is not always possible to perform a soft reset. This is the case if the neighbor does not support route refresh and soft-reconfiguration inbound is not configured for the neighbor. In such instances, a message is logged in the system log indicating that a manual hard reset is needed.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Use the bgp bestpath as-path ignore command to ignore the length of autonomous system paths when the software selects a preferred path. When the best path is selected, if this command is specified, all steps are performed as usual except comparison of the autonomous path length between candidate paths.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Use the bgp bestpath compare-routerid command to affect how the software selects the best path, in the case where there are two paths of equal cost according to the BGP selection algorithm. This command is used to force the software to select the path with the lower router ID as the best path. If this command is not used, the software continues to use whichever path is currently the best path, regardless of which has the lower router ID.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Use the bgp bestpath cost-community ignore command to disable the evaluation of the cost community attribute to help isolate problems and troubleshoot issues that relate to BGP path selection. This command can also be used to delay the activation of cost community attribute evaluation so that cost community filtering can be deployed in a large network at the same time.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

The MED is one of the parameters that is considered by the software when selecting the best path among many alternative paths. The software chooses the path with the lowest MED.

By default, during the best-path selection process, the software makes a MED comparison only among paths from the same autonomous system. This command changes the default behavior of the software by allowing comparison of MEDs among paths regardless of the autonomous system from which the paths are received.

When the bgp bestpath med always command is not enabled and distributed BGP is configured, speakers calculate partial best paths only (executes the best-path steps up to the MED comparison) and send them to BGP Routing Information Base (bRIB). bRIB calculates the final best path (executes all the steps in the best-path calculation). When the bgp bestpath med always command is enabled and distributed BGP is configured, speakers can compare the MED across all ASs, allowing the speaker to calculate a single best path to send it to bRIB. bRIB is the ultimate process that calculates the final best path, but when the bgp bestpath med always command is enabled, the speakers send a single best path instead of potentially sending multiple, partial best paths

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

By default, the MED of the following paths is not compared with the MED of any other path:

• Paths with an empty autonomous system path
• Paths beginning with an AS_SET
• Paths containing only confederation segments
• Paths containing confederation segments followed by an AS_SET

Use the bgp bestpath med confed command to affect how the following types of paths are treated in the BGP best-path algorithm:

• Paths containing only confederation segments
• Paths containing confederation segments followed by an AS_SET

The MED for paths that start with an AS_SEQUENCE or that start with confederation segments followed by an AS_SEQUENCE only is compared with the MED of other paths that share the same first autonomous system number in the autonomous system sequence (the neighbor autonomous system number). This behavior is not affected by the bgp bestpath med confed command.

As an example, suppose that autonomous systems 65000, 65001, 65002, and 65004 are part of a confederation, but autonomous system 1 is not. Suppose that for a particular route, the following paths exist:

• Path 1: 65000 65004, med = 2, IGP metric = 20
• Path 2: 65001 65004, med = 3, IGP metric = 10
• Path 3: 65002 1, med = 1, IGP metric = 30

If the bgp bestpath med confed command is enabled, the software selects path 1 as the best path because it:

• Has a lower MED than path 2
• Has a lower IGP metric than path 3

The MED is not compared with path 3 because it has an external autonomous system number (that is, an AS_SEQUENCE) in the path. If the bgp bestpath med confed command is not enabled, then MED is not compared between any of these paths. Consequently, the software selects path 2 as the best path because it has the lowest IGP metric.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Configuring the bgp bestpath origin-as allow invalid command allows paths marked with an 'invalid' origin-as to be considered for best path computation. This can be limited to an address family by configuring it at the address-family submode.

This configuration takes effect only when the bgp bestpath origin-as use validity configuration is enabled.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

There are three RPKI states - valid, invalid, and not found. When the bgp bestpath origin-as use validity command is configured, only paths marked with 'valid' or 'not found' are considered as best path candidates. When the bgp bestpath origin-as allow invalid command is configured, paths marked as 'invalid' are also considered but preference is given to routes marked 'valid' over those marked 'invalid'.

The bgp bestpath origin-as use validity command takes precedence over the configured weight and local preferences attributes.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

By default, BGP always prefers a path with the AIGP metric. When there are two paths, one with the AIGP metric and the other without, then executing the bgp bestpath aigp ignore command results in BGP performing best path computation as if neither paths has the AIGP metric.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

When BGP multi-pathing is enabled, BGP load-balances user traffic within a single autonomous system (AS). The criteria are that all attributes must match (weight, AS path, etc). However when a device is multi-homed to multiple autonomous systems, BGP cannot load balance traffic between them by default. In order to enable load-balancing of traffic among the multi-homed autonomous systems, the bgp bestpath as-path multipath-relax command needs to be enabled. The criteria required for this is that the AS-path length should be equal.

Before you use this command, ensure that BGP is enabled

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

By default, the clients of a route reflector are not required to be fully meshed and the routes from a client are reflected to other clients. However, if the clients are fully meshed, route reflection is not required.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Together, a route reflector and its clients form a cluster. A cluster of clients usually has a single route reflector. In such instances, the cluster is identified by the software as the router ID of the route reflector. To increase redundancy and avoid a single point of failure in the network, a cluster might have more than one route reflector. If it does, all route reflectors in the cluster must be configured with the same 4-byte cluster ID so that a route reflector can recognize updates from route reflectors in the same cluster.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

One way to reduce the internal BGP (iBGP) mesh is to divide an autonomous system into multiple autonomous systems and group them into a single confederation. Each autonomous system is fully meshed within itself, and has a few connections to another autonomous system in the same confederation. Although the peers in different autonomous systems have external BGP (eBGP) sessions, they exchange routing information as if they are iBGP peers. Specifically, the confederation maintains the next hop and local preference information, and that allows you to retain a single Interior Gateway Protocol (IGP) for all autonomous systems. To the outside world, the confederation looks like a single autonomous system.

Use the bgp confederation identifier command to specify the autonomous system number for the confederation. This autonomous system number is used when BGP sessions are established with external peers in autonomous systems that are not part of the confederation.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

The autonomous systems specified in this command are visible internally to a confederation. Each autonomous system is fully meshed within itself. The bgp confederation identifier command specifies the confederation to which the autonomous systems belong.

To specify multiple autonomous systems, enter BGP confederation peer configuration mode then enter one autonomous-system-number for each command line.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Use the bgp dampening command without arguments to enable BGP route dampening with the default parameters. The parameters can be changed by setting them on the command line or specifying them with a routing policy.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Generally, the default value of 100 allows you to easily define a particular path as less preferable than paths with no local preference attribute. The preference is sent to all networking devices in the local autonomous system.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

By default, the software ignores any update received from an eBGP neighbor that does not have the autonomous system configured for that neighbor at the beginning of the AS path. When configured, the command applies to all eBGP peers of the router.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

By default, BGP sessions of any directly adjacent external peers are immediately reset, which allows the network to recover faster when links go down between BGP peers.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Use the bgp graceful-restart command to enable graceful restart functionality on the router, and also to advertise graceful restart to neighboring routers.

Note	The bgp graceful-restart command with no options must be used to enable graceful restart before using the bgp graceful-restart purge-time , bgp graceful-restart restart-time , bgp graceful-restart stalepath-time , or bgp graceful-restart graceful-reset commands.

When graceful restart is enabled, the BGP graceful restart capability is negotiated with neighbors in the BGP OPEN message when the session is established. If the neighbor also advertises support for graceful restart, then graceful restart is activated for that neighbor session. If the neighbor does not advertise support for graceful restart, then graceful restart is not activated for that neighbor session even though it is enabled locally.

If you enter the bgp graceful-restart command after some BGP sessions are established, you must restart those sessions before graceful restart takes effect. Use the clear bgp command to restart sessions.

Unconfiguring a neighbor (no neighbor command) or BGP (no router bgp command) may trigger a graceful restart (GR) on the neighboring router. If you do not want the BGP to perform a graceful restart, disable the BGP neighbor by configuring an administrative shutdown under the neighbor settings before unconfiguring the neighbor or BGP.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

BGP graceful restart must be enabled using the bgp graceful-restart command before enabling graceful reset using the bgp graceful-restart graceful-reset command.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

BGP graceful restart must be enabled using the bgp graceful-restart command before setting the purge time using the bgp graceful-restart purge-time command.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

BGP graceful restart must be enabled using the bgp graceful-restart command before setting the restart timer using the bgp graceful-restart restart-time command.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

BGP graceful restart must be enabled using the bgp graceful-restart command before setting the stalepath time using the bgp graceful-restart stalepath-time command.

If the stalepath time is exceeded before an End-of-RIB message is received from a neighbor, paths learned from the neighbor are purged from the BGP routing table.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Usage Guidelines

To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. If the user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Logging of BGP neighbor status changes (up or down) and resets is used for troubleshooting network connectivity problems and measuring network stability. Unexpected neighbor resets might indicate high error rates or high packet loss in the network, and should be investigated.

Status change message logging does not substantially affect performance, unlike, for example, enabling per-BGP update debugging. If the UNIX syslog facility is enabled, messages are sent by the software to the UNIX host running the syslog daemon so that the messages can be stored and archived on disk. If the UNIX syslog facility is not enabled, the status change messages are kept in the internal buffer of the router, and are not stored to disk.

The neighbor status change messages are not tracked if the bgp log neighbor changes disable command is disabled, except for the last reset reason, which is always available as output of the show bgp neighbors command.

Up and down messages for BGP neighbors are logged by the software by default. Use the bgp log neighbor changes disable command to stop logging BGP neighbor changes.