7.6. IPv6 BGP Commands

Command Purpose

Use this command to enter the IPv6 address-family command mode.

Prerequisites

Command Syntax

address-family ipv6 (unicast| )

Command Mode

Router Configuration

Default

None

Usage

Use the address family command to enter the address family mode allowing configuration of address-family specific parameters.

To leave the address family mode and return to the Configure mode use the exit-address-family command.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)#address-family ipv6

Related Commands

exit-address-family

Command Purpose

Use this command to configure BGP aggregate entries.

Use the no parameter with this command to disable this function.

Prerequisites

Command Syntax

(no) aggregate-address IPADDRESS {summary-only|as-set}

Command Mode

Address Family Configuration

Default

Disabled

Usage

Aggregates are used to minimize the size of routing tables. Aggregation combines the characteristics of several different routes and advertises a single route.The aggregate-address command creates an aggregate entry in the BGP routing table if any more-specific BGP routes are available in the specified range. Using the summary-only parameter advertises the prefix only, suppressing the more-specific routes to all neighbors.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# aggregate-address 2018::1/64 as-set summary-only

Related Commands

N/A

Command Purpose

Use this command to compare the Multi Exit Discriminator (MED) for paths from neighbors in different autonomous systems.

Use the no parameter with this command to disallow the comparison.

Prerequisites

Command Syntax

(no) bgp always-compare-med

Command Mode

Router Configuration

Default

Disabled

Usage

Multi Exit Discriminator (MED) is used in best path selection by BGP. MED is compared after BGP attributes weight, local preference, AS-path and origin have been compared and are equal.

MED comparison is done only among paths from the same autonomous system (AS). Use bgp always-comparemed command to allow comparison of MEDs from different ASs. The MED parameter is used to select the best path. A path with lower MED is preferred.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp always-compare-med

Related Commands

bgp bestpath med

bgp bestpath as-path ignore

Command Purpose

Use this command to prevent the router from considering as-path as a factor in the algorithm for choosing a route.

Use the no parameter with this command to allow the router to consider as-path in choosing a route.

Prerequisites

Command Syntax

(no) bgp bestpath as-path ignore

Command Mode

Router Configuration

Default

Disabled

Usage

None

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp bestpath as-path ignore

Related Commands

bgp always-compare-med

bgp bestpath med

bgp bestpath compare-routerid

Command Purpose

Use this command to allow comparing of the confederation AS path length.

Use the no parameter with this command to revert the selection and ignore AS confederation path length in the BGP best path selection.

Prerequisites

Command Syntax

(no) bgp bestpath compare-confed-aspath

Command Mode

Router Configuration

Default

BGP receives routes with identical eBGP paths from eBGP peers and selects the first route received as the best path.

Usage

This command specifies that the AS confederation path length must be used, when available, in the BGP best path decision process. It is effective only when BGP bestpath as-path ignore command has not been specified.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp bestpath compare-confed-aspath

Related Commands

bgp bestpath as-path ignore

Command Purpose

Use this command to compare router-id for identical eBGP paths.

Use the no parameter with this command to disable this function.

Prerequisites

Command Syntax

(no) bgp bestpath compare-routerid

Command Mode

Router Configuration

Default

BGP receives routes with identical eBGP paths from eBGP peers and selects the first route received as the best path.

Usage

When comparing similar routes from peers the BGP router does not consider router ID of the routes. By default, it selects the first received route. Use this command to include router ID in the selection process; similar routes are compared and the route with lowest router ID is selected. The router-id is the highest IP address on the router, with preference given to loopback addresses. Router-id can be manually set by using the bgp router-id command.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp bestpath compare-routerid

Related Commands

show bgp ipv6

show ip bgp neighbors

Command Purpose

Use this command to specify Multi Exit Discriminator (MED) attribute comparison.

Use the no parameter with this command to prevent BGP from considering the MED attribute in comparing paths.

Prerequisites

Command Syntax

bgp bestpath med confed [missing-as-worst]

bgp bestpath med missing-as-worst [confed]

no bgp bestpath med confed [missing-as-worst]

no bgp bestpath med missing-as-worst [confed]

Command Mode

Router Configuration

Default

MED value is zero.

Usage

Use this command to specify two MED attributes–confed and missing-as-worst. The confed attribute enables MED comparison among paths learned from confederation peers. The MEDs are compared only if there is no external autonomous system (an AS not within the confederation) in the path. If there is an external autonomous system in the path, the MED comparison is not made.

The missing-as-worst attribute to consider a missing MED attribute in a path as having a value of infinity, making the path without a MED value the least desirable path. If missing-as-worst is disabled, the missing MED is assigned the value of 0, making the path with the missing MED attribute the best path.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp bestpath med missing-as-worst

Related Commands

bgp-always-compare-med

bgp bestpath as-path ignore

bgp deterministic-med

Command Purpose

Use this command to restore route reflection from a BGP route reflector to clients.

Use the no parameter with this command to turn off client-to-client reflection.

Prerequisites

Command Syntax

bgp client-to-client reflection

no bgp client-to-client reflection

Command Mode

Router Configuration

Default

When a router is configured as a route reflector, client-to-client reflection is enabled by default.

Usage

The BGP client-to-client reflection command is used to configure routers as route reflectors. Route reflectors are used when all Interior Border Gateway Protocol (iBGP) speakers are not fully meshed. If the clients are fully meshed the route reflector is not required, use no BGP client-to-client reflection command to disable the client-to-client route reflection.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# no bgp client-to-client reflection

Related Commands

bgp cluster-id

neighbor route-reflector-client

show bgp ipv6

Command Purpose

Use this command to configure the cluster ID if the BGP cluster has more than one route reflector.

Use the no parameter with this command to remove the cluster ID.

Prerequisites

Command Syntax

bgp cluster-id CLUSTERID

no bgp cluster-id

Command Mode

Router Configuration

Default

N/A

Usage

A cluster includes route reflectors and its clients. Usually, each cluster is identified by the router ID of its single route reflector but to increase redundancy sometimes a cluster may have more than one route reflector. All router reflectors in such a cluster are then identified by a cluster ID. The BGP cluster-id command is used to configure the 4 byte cluster ID for clusters with more than one route reflectors.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp cluster-id 1.1.1.1

Related Commands

bgp client-to-client reflection

neighbor route-reflector-client

show bgp ipv6

Command Purpose

Use this command to specify a BGP confederation identifier.

Use the no parameter with this command to remove the BGP confederation identifier.

Prerequisites

Command Syntax

bgp confederation identifier ID

no bgp confederation identifier

Command Mode

Router Configuration

Default

N/A

Usage

N/A

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp confederation identifier 1

Related Commands

bgp confederation peer

Command Purpose

Use this command to configure the Autonomous Systems (AS) that belong to the confederation.

Use the no parameter with this command to remove an autonomous system from the confederation.

Prerequisites

Command Syntax

bgp confederation peers ASN

no bgp confederation peers (ASN| )

Command Mode

Router Configuration

Default

N/A

Usage

A confederation allows an AS to be divided into several ASs. The AS is given a confederation identifier. External routers view only the whole confederation as one AS. Each AS is fully meshed within itself and is visible internally to the confederation. Use the bgp confederation peer command to define the list of confederation peers.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp confederation peers 1234 21345

Related Commands

bgp confederation identifier

Command Purpose

Use this command to set BGP dampening parameters.

Use the no parameter with this command to unset the BGP dampening parameters.

Prerequisites

Command Syntax

bgp dampening REACHTIME

bgp dampening REACHTIME REUSE

bgp dampening REACHTIME REUSE SUPPRESS MAXSUPPRESS (UNREACHTIME| )

bgp dampening route-map ROUTEMAP

no bgp dampening REACHTIME

no bgp dampening REACHTIME REUSE

no bgp dampening REACHTIME REUSE SUPPRESS MAXSUPPRESS (UNREACHTIME| )

no bgp dampening route-map ROUTEMAP

Command Mode

Router Configuration

Address Family Configuration

Default

N/A

Usage

Route dampening minimizes the instability caused by route flapping. A penalty is added for every flap in a flapping route. As soon as the total penalty reaches the suppress limit the advertisement of the route is suppressed. This penalty is decayed according to the configured half time value. Once the penalty is lower than the reuse limit, the route advertisement is un-suppressed.

The dampening information is purged from the router once the penalty becomes less than half of the reuse limit.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp dampening 20 800 2500 80 25

Related Commands

N/A

Command Purpose

Use this command to change the default local preference value.

Use the no parameter with this command to revert to the default setting.

Prerequisites

Command Syntax

bgp default local-preference PREF_VALUE

no default local-preference (PREF_VALUE| )

Command Mode

Router Configuration

Default

The default local preference value is 100.

Usage

Local preference indicates the preferred path when there are multiple paths to the same destination. The path having a higher preference is preferred. Use BGP default local-preference command to define preference of a particular path. The preference is sent to all routers and access servers in the local autonomous system.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp default local-preference 2345555

Related Commands

N/A

Command Purpose

Use this command to compare the Multi Exit Discriminator (MED) variable when choosing among routes advertised by different peers in the same autonomous system.

Use the no parameter with this command to disallow this setting.

Prerequisites

Command Syntax

bgp deterministic-med

no bgp deterministic-med

Command Mode

Router Configuration

Default

Disabled

Usage

Multi Exit Discriminator (MED) is used in best path selection by BGP. MED is compared after BGP attributes weight, local preference, AS-path and origin have been compared and are equal. Enable bgp deterministic med command on all routers in the local AS, for a correct comparison result. After enabling this command, all paths for the same prefix are grouped together and arranged according to their MED value.

Based on this comparison, the best path is then chosen.

This command compares MED variable when choosing routes advertised by different peers in the same AS, to compare MED, when choosing routes from neighbors in different ASs use the bgp always-compare-med command.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp deterministic-med

Related Commands

show bgp ipv6

show bgp ipv6 neighbors

Command Purpose

Use this command to specifies that any updates received from an external neighbor that do not have the neighbor’s configured Autonomous System (AS) at the beginning of the AS_PATH in the received update must be denied.

Use the no parameter with this command to disable this feature.

Prerequisites

Command Syntax

bgp enforce-first-as

no bgp enforce-first-as

Command Mode

Router Configuration

Default

Disabled

Usage

Enabling this feature adds to the security of the BGP network by not allowing traffic from unauthorized systems.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp enforce-first-as

Related Commands

N/A

Command Purpose

Use this command to reset a BGP session immediately, if the interface used for BGP connection goes down.

Use the no parameter with this command to disable this feature.

Prerequisites

Command Syntax

bgp fast-external-failover

no bgp fast-external-failover

Command Mode

Router Configuration

Default

Enabled

Usage

None

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp fast-external-failover

Related Commands

N/A

Command Purpose

Use this command to enable logging of status change messages without turning on debug BGP commands.

Use the no parameter with this command to disable this feature.

Prerequisites

Command Syntax

bgp log-neighbor-changes

no bgp log-neighbor-changes

Command Mode

Router Configuration

Default

Disabled

Usage

System implementation provides other kinds of logging services for neighbor status, for example, debug BGP FSM, debug BGP events, etc. However, these commands create a significant hit in the logging performance.

The BGP log-neighbor-changes command, logs the following events:

• BGP Notification Received

• Erroneous BGP Update Received

• User reset request

• Peer time-out

• Peer Closing down the session

• Interface flap

• Router ID changed

• Neighbor deleted

• Member added to peer group

• Administrative shutdown

• Remote AS changed

• RR client configuration modification

• Soft reconfiguration modification

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp log-neighbor-changes

Related Commands

N/A

Command Purpose

Use this command to configure the router identifier.

Use the no parameter with this command to disable this function

Prerequisites

Command Syntax

bgp router-id ROUTERID

no bgp router-id (ROUTERID| )

Command Mode

Router Configuration

Address Family Configuration

Default

In case the loopback interface is configured the router-ID is set to the IP address of a loopback interface. If not, the highest IP address is the router-ID.

Usage

Use BGP router-ID command to manually configure a fixed router ID as a BGP router identifier.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp router-id 1.1.2.3

Related Commands

N/A

Command Purpose

Use this command to set the interval for BGP route next-hop scanning.

Use the no parameter with this command to disable this function.

Prerequisites

Command Syntax

bgp scan-time TIME

no bgp scan-time (TIME| )

Command Mode

Router Configuration

Default

N/A

Usage

Use this command to configure scanning intervals of BGP routers. This interval is the period after which router checks the validity of the routes in its database.

To disable BGP scanning, set the scan time interval to 0 seconds.

Examples

Switch# configure terminal
Switch(config)# router bgp 1
Switch(config-router)# bgp scan-time 10

Related Commands

N/A

Command Purpose

Use this command to reset a BGP connection for all peers.

Prerequisites

Command Syntax

clear bgp ipv6 (in|out|soft| )

clear bgp ipv6 vrf NAME

Command Mode

Privileged EXEC

Default

N/A

Usage

There are two kinds BGP reset, hard reset will clear BGP peers and establish again. Soft reset only refresh routing table.

Examples

Switch# clear bgp ipv6 *
Switch# clear bgp ipv6 * soft
Switch# clear bgp ipv6 * vrf aa

Related Commands

N/A

Command Purpose

Use this command to reset a IPv6 BGP connection for a specific IPv6 address.

Prerequisites

Command Syntax

clear bgp ipv6 X:X::X:X (in|out|soft)

clear ipv6 bgp X:X::X:X vrf NAME

Command Mode

Privileged EXEC

Default

N/A

Usage

N/A

Examples

Switch# clear bgp ipv6 2018::1
Switch# clear bgp ipv6 2018::1 soft

Related Commands

N/A

Command Purpose

Use this command to reset all dampened BGP routes under the specified address family.

Prerequisites

Command Syntax

clear bgp ipv6 dampening (X:X::X:X|X:X::X:X/M| )

Command Mode

Privileged EXEC

Default

N/A

Usage

N/A

Examples

Switch# clear bgp ipv6 unicast dampening
Switch# clear bgp ipv6 unicast dampening 2018::1

Related Commands

N/A

Command Purpose

Use this command to clear the flap count and history duration for all the prefixes under the specified address family.

Prerequisites

Command Syntax

clear bgp ipv6 unicast flap-statistics (X:X::X:X|X:X::X:X/M| )