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Inheritance of Configuration Values

Peer groups inherit all configuration values that are globally configured. However, attributes configured for a peer group override inherited global configuration values. Individual peers that are members of peer groups inherit all configuration values from the peer group. However, attributes configured on a peer override values inherited from the peer group of which it is a member.

The neighbor commands enable you to control features or set parameters for individual peers or for peer groups. These commands can be classified into the four categories shown in Table 11, based on whether the command enables a feature or sets parameters, the levels at which it behaves, and how the no version of the command compares with the default version.

Table 11: Behavior of Neighbor Commands

Category A: Enable or disable a feature that can be configured for a peer or for a peer group	Category B: Enable or disable a feature that can be configured for a peer, for a peer group, or globally	Category C: Set parameters for a peer or for a peer group	Category D: Set parameters for a peer, for a peer group, or globally
		Category C: Set parameters for a peer or for a peer group
neighbor activate neighbor advertise-map neighbor as-override neighbor bfd-liveness-detection neighbor capability neighbor ebgp-multihop neighbor ibgp-singlehop neighbor lenient neighbor next-hop-self neighbor next-hop-unchanged neighbor passive neighbor remove-private-as neighbor route-reflector-client neighbor send-community neighbor soft-reconfiguration inbound	neighbor default-originate neighbor graceful-restart neighbor rib-out disable neighbor shutdown	neighbor advertisement-interval neighbor allow neighbor allowas-in neighbor description neighbor distribute-list neighbor filter-list neighbor graceful-restart restart-time neighbor graceful-restart stalepaths-time neighbor local-as neighbor maximum-orf-entries neighbor maximum-prefix neighbor maximum-update-size neighbor password neighbor peer-group neighbor peer-type neighbor prefix-list neighbor prefix-tree neighbor remote-as neighbor route-map neighbor send-label neighbor site-of-origin neighbor unsuppress-map neighbor update-source neighbor weight	neighbor timers

Some of the commands in Table 11 inherit global values set by other commands. Table 12 describes the relationship between these commands.

Table 12: Inheritance from Other Commands

Category B Command	Inherits Global Values Set By
neighbor default-originate	default-information originate
neighbor graceful-restart	bgp graceful-restart
neighbor rib-out disable	rib-out disable
neighbor shutdown	bgp shutdown
neighbor graceful-restart restart-time	bgp graceful-restart restart-time
neighbor graceful-restart stalepaths-time	bgp graceful-restart stalepaths-time

Example 1

For category A and B commands, the behavior of the no version of the command is different from the behavior of the default version of the command. The no version explicitly disables the feature:

Applied to a peer, the no version disables the feature regardless of whether the feature is enabled for any peer group to which it belongs.
Applied to a peer group, the no version disables the feature regardless of whether the feature is enabled for BGP globally or by default.

The default version simply unconfigures the feature for the peer or peer group.

Applied to a peer, the default version causes the peer to inherit the state of the feature (enabled or disabled) from any peer group to which it belongs.
Applied to a peer group, the default version causes the peer group to inherit the state of the feature (enabled or disabled) from the BGP global configuration.

The following example illustrates this difference and the inheritance concept with the neighbor soft-reconfiguration inbound command.



host1(config-router)#neighbor lisbon peer-group 

host1(config-router)#neighbor 10.19.7.8 peer-group
lisbon

Inbound soft-reconfiguration is disabled by default, hence it is currently disabled for both the lisbon peer group and peer 10.19.7.8.



host1(config-router)#neighbor lisbon soft-reconfiguration
inbound

Inbound soft-reconfiguration is now enabled for the lisbon peer group. Because the peer inherits values from the peer group, inbound soft-reconfiguration is now also enabled for peer 10.19.7.8.



host1(config-router)#no neighbor 10.19.7.8
soft-reconfiguration inbound

The no command disables inbound soft-reconfiguration for peer 10.19.7.8, overriding the configuration of the peer group to which the peer 10.19.7.8 belongs. The configuration of an individual peer takes precedence over the configuration of the peer group to which the peer belongs.



host1(config-router)#default neighbor 10.19.7.8
soft-reconfiguration inbound

The default version returns the peer to inheriting the peer group configuration. Because inbound soft-reconfiguration is still enabled for lisbon, it is now also enabled for peer 10.19.7.8.



host1(config-router)#default neighbor lisbon
soft-reconfiguration inbound

Finally, this last command returns the peer group configuration to the default value, disabling inbound soft-reconfiguration. The peer 10.19.7.8 inherits this value.

Example 2

For category C and D commands, the behavior of the no version of the command is the same as the behavior of the default version of the command. The following example illustrates this behavior and the inheritance concept for the neighbor timers command.

By default, the BGP global keepalive timer is 30 seconds and the global hold-time timer is 90 seconds.



host1(config-router)#neighbor eastcoast peer-group 

host1(config-router)#neighbor 10.10.21.23
peer-group eastcoast

Peer group eastcoast and peer 10.10.21.23 both have the default timer values. The peer group inherits the global timer values; the peer is a member of eastcoast and inherits the timer values from the peer group.



host1(config-router)#neighbor eastcoast timers
15 40

Now peer group eastcoast has a keepalive timer of 15 seconds and a hold-time timer of 40 seconds. Peer 10.10.21.23 inherits these values from the peer group.



host1(config-router)#no neighbor 10.10.21.23
timers

Now peer 10.10.21.23 has its timers reset to the global values of 30 and 90 seconds. The configuration of an individual peer takes precedence over the configuration of the peer group to which the peer belongs, which in turn takes precedence over the global configuration.



host1(config-router)#default neighbor 10.10.21.23
timers

Nothing changes. For commands in categories C and D, the behavior of the default version is the same as the no version. Peer 10.10.21.23 still has the global timer values.



host1(config-router)#neighbor eastcoast timers
20 20

The eastcoast peer group now has timer values of 20 seconds. Peer 10.10.21.23 still has the global timer values.

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