IP Routing: BGP Configuration Guide, Cisco IOS XE Gibraltar 16.12.x
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The BGP graceful restart feature is already available on a global basis. The BGP Graceful Restart per Neighbor feature allows
BGP graceful restart to be enabled or disable for an individual neighbor, providing greater network flexibility and service.
Finding Feature Information
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see
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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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Information About BGP Graceful Restart per Neighbor
BGP Graceful Restart per Neighbor
The ability to enable or disable BGP graceful restart for every individual BGP neighbor was introduced. Three new methods
of configuring BGP graceful restart for BGP peers, in addition to the existing global BGP graceful restart configuration,
are now available. Graceful restart can be enabled or disabled for a BGP peer or a BGP peer group using the
neighborha-modegraceful-restart command, or a BGP peer can inherit a graceful restart configuration from a BGP peer-session template using the
ha-modegraceful-restart command.
Although BGP graceful restart is disabled by default, the existing global command enables graceful restart for all BGP neighbors
regardless of their capabilities. The ability to enable or disable BGP graceful restart for individual BGP neighbors provides
a greater level of control for a network administrator.
When the BGP graceful restart capability is configured for an individual neighbor, each method of configuring graceful restart
has the same priority, and the last configuration instance is applied to the neighbor. For example, if global graceful restart
is enabled for all BGP neighbors but an individual neighbor is subsequently configured as a member of a peer group for which
the graceful restart is disabled, graceful restart is disabled for that neighbor.
The configuration of the restart and stale-path timers is available only with the global
bgpgraceful-restart command, but the default values are set when the
neighborha-modegraceful-restart or
ha-modegraceful-restart commands are configured. The default values are optimal for most network deployments, and these values should be adjusted
only by an experienced network operator.
BGP Peer Session Templates
Peer session templates are used to group and apply the configuration of general BGP session commands to groups of neighbors
that share session configuration elements. General session commands that are common for neighbors that are configured in different
address families can be configured within the same peer session template. Peer session templates are created and configured
in peer session configuration mode. Only general session commands can be configured in a peer session template.
General session commands can be configured once in a peer session template and then applied to many neighbors through the
direct application of a peer session template or through indirect inheritance from a peer session template. The configuration
of peer session templates simplifies the configuration of general session commands that are commonly applied to all neighbors
within an autonomous system.
Peer session templates support direct and indirect inheritance. A BGP neighbor can be configured with only one peer session
template at a time, and that peer session template can contain only one indirectly inherited peer session template. A BGP
neighbor can directly inherit only one session template and can indirectly inherit up to seven additional peer session templates.
Peer session templates support inheritance. A directly applied peer session template can directly or indirectly inherit configurations
from up to seven peer session templates. So, a total of eight peer session templates can be applied to a neighbor or neighbor
group.
Peer session templates support only general session commands. BGP policy configuration commands that are configured only
for a specific address family or NLRI configuration mode are configured with peer policy templates.
To use a BGP peer session template to enable or disable BGP graceful restart, see the “Enabling and Disabling BGP Graceful
Restart Using BGP Peer Session Templates” section.
How to Configure BGP Graceful Restart per Neighbor
Enabling BGP Graceful Restart for an Individual BGP Neighbor
Perform this task on Router B in the figure above to enable BGP graceful restart on the internal BGP peer at Router C in
the figure above. Under the IPv4 address family, the neighbor at Router C is identified, and BGP graceful restart is enabled
for the neighbor at Router C with the IP address 172.21.1.2. To verify that BGP graceful restart is enabled, the optional
showipbgpneighbors command is used.
Specifies the IPv4 address family and enters address family configuration mode.
The
unicast keyword specifies the IPv4 unicast address family. By default, the router is placed in address family configuration mode
for the IPv4 unicast address family if the
unicast keyword is not specified.
The
multicast keyword specifies IPv4 multicast address prefixes.
The
vrf keyword and
vrf-name argument specify the name of the VRF instance to associate with subsequent IPv4 address family configuration mode commands.
Configures peering with a BGP neighbor in the specified autonomous system.
In this example, the BGP peer at 172.21.1.2 is an internal BGP peer because it has the same autonomous system number as the
router where the BGP configuration is being entered (see Step 3).
Enables the BGP graceful restart capability for a BGP neighbor.
Use the
disable keyword to disable BGP graceful restart capability.
If you enter this command after the BGP session has been established, you must restart the session in order for the capability
to be exchanged with the BGP neighbor.
In this example, the BGP graceful restart capability is enabled for the neighbor at 172.21.1.2.
Step 8
end
Example:
Device(config-router-af)# end
Exits address family configuration mode and returns to privileged EXEC mode.
(Optional) Displays information about TCP and BGP connections to neighbors.
“Graceful Restart Capability: advertised” will be displayed for each neighbor that has exchanged graceful restart capabilities
with this router.
In this example, the output is filtered to display information about the BGP peer at 172.21.1.2.
Examples
The following example shows partial output from the
showipbgpneighbors command for the BGP peer at 172.21.1.2. Graceful restart is shown as enabled. Note the default values for the restart and
stale-path timers. These timers can be set using only the global
bgpgraceful-restart command.
Device# show ip bgp neighbors 172.21.1.2
BGP neighbor is 172.21.1.2, remote AS 45000, internal link
BGP version 4, remote router ID 172.22.1.1
BGP state = Established, up for 00:01:01
Last read 00:00:02, last write 00:00:07, hold time is 180, keepalive intervals
Neighbor sessions:
1 active, is multisession capable
Neighbor capabilities:
Route refresh: advertised and received(new)
Address family IPv4 Unicast: advertised and received
Graceful Restart Capability: advertised
Multisession Capability: advertised and received
!
Address tracking is enabled, the RIB does have a route to 172.21.1.2
Connections established 1; dropped 0
Last reset never
Transport(tcp) path-mtu-discovery is enabled
Graceful-Restart is enabled, restart-time 120 seconds, stalepath-time 360 secs
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Enabling and Disabling BGP Graceful Restart Using BGP Peer Session Templates
Perform this task to enable and disable BGP graceful restart for BGP neighbors using peer session templates. In this task,
a BGP peer session template is created, and BGP graceful restart is enabled. A second peer session template is created, and
this template is configured to disable BGP graceful restart.
In this example, the configuration is performed at Router B in the figure below, and two external BGP neighbors—Router A
and Router E—are identified. The first BGP peer at Router A is configured to inherit the first peer session template, which
enables BGP graceful restart, whereas the second BGP peer at Router E inherits the second template, which disables BGP graceful
restart. Using the optional
showipbgpneighbors command, the status of the BGP graceful restart capability is verified for each BGP neighbor configured in this task.
Figure 1. Network Topology Showing BGP Neighbors
The restart and stale-path timers can be modified only using the global
bgpgraceful-restart command. The restart and stale-path timers are set to the default values when BGP graceful restart is enabled for BGP neighbors
using peer session templates.
Note
A BGP peer cannot inherit from a peer policy or session template and be configured as a peer group member at the same. BGP
templates and BGP peer groups are mutually exclusive.
Enables the BGP graceful restart capability and BGP NSF awareness.
Use the
disable keyword to disable BGP graceful restart capability.
If you enter this command after the BGP session has been established, you must restart the session in order for the capability
to be exchanged with the BGP neighbor.
In this example, the BGP graceful restart capability is enabled for the peer session template named S1.
Step 6
exit-peer-session
Example:
Device(config-router-stmp)# exit-peer-session
Exits session-template configuration mode and returns to router configuration mode.
Step 7
templatepeer-sessionsession-template-name
Example:
Device(config-router)# template peer-session S2
Enters session-template configuration mode and creates a peer session template.
In this example, a peer session template named S2 is created.
Enables the BGP graceful restart capability and BGP NSF awareness.
Use the
disable keyword to disable BGP graceful restart capability.
If you enter this command after the BGP session has been established, you must restart the session in order for the capability
to be exchanged with the BGP neighbor.
In this example, the BGP graceful restart capability is disabled for the peer session template named S2.
Step 9
exit-peer-session
Example:
Device(config-router-stmp)# exit-peer-session
Exits session-template configuration mode and returns to router configuration mode.
Step 10
bgplog-neighbor-changes
Example:
Device(config-router)# bgp log-neighbor-changes
Enables logging of BGP neighbor status changes (up or down) and neighbor resets.
Use this command 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.
Configures peering with a BGP neighbor in the specified autonomous system.
In this example, the BGP peer at 192.168.1.2 is an external BGP peer because it has a different autonomous system number
from the router where the BGP configuration is being entered (see Step 3).
Configures peering with a BGP neighbor in the specified autonomous system.
In this example, the BGP peer at 192.168.3.2 is an external BGP peer because it has a different autonomous system number
from the router where the BGP configuration is being entered (see Step 3).
The output can be filtered to display a single peer policy template by using the
session-template-name argument. This command also supports all standard output modifiers.
(Optional) Displays information about TCP and BGP connections to neighbors.
“Graceful Restart Capability: advertised” will be displayed for each neighbor that has exchanged graceful restart capabilities
with this router.
In this example, the output is filtered to display information about the BGP peer at 192.168.1.2.
Examples
The following example shows partial output from the
showipbgpneighbors command for the BGP peer at 192.168.1.2 (Router A in the figure above). Graceful restart is shown as enabled. Note the default
values for the restart and stale-path timers. These timers can be set only by using the
bgpgraceful-restart command.
Device# show ip bgp neighbors 192.168.1.2
BGP neighbor is 192.168.1.2, remote AS 40000, external link
Inherits from template S1 for session parameters
BGP version 4, remote router ID 192.168.1.2
BGP state = Established, up for 00:02:11
Last read 00:00:23, last write 00:00:27, hold time is 180, keepalive intervals
Neighbor sessions:
1 active, is multisession capable
Neighbor capabilities:
Route refresh: advertised and received(new)
Address family IPv4 Unicast: advertised and received
Graceful Restart Capability: advertised
Multisession Capability: advertised and received
!
Address tracking is enabled, the RIB does have a route to 192.168.1.2
Connections established 1; dropped 0
Last reset never
Transport(tcp) path-mtu-discovery is enabled
Graceful-Restart is enabled, restart-time 120 seconds, stalepath-time 360 secs
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
The following example shows partial output from the
showipbgpneighbors command for the BGP peer at 192.168.3.2 (Router E in the figure above). Graceful restart is shown as disabled.
Device# show ip bgp neighbors 192.168.3.2
BGP neighbor is 192.168.3.2, remote AS 50000, external link
Inherits from template S2 for session parameters
BGP version 4, remote router ID 192.168.3.2
BGP state = Established, up for 00:01:41
Last read 00:00:45, last write 00:00:45, hold time is 180, keepalive intervals
Neighbor sessions:
1 active, is multisession capable
Neighbor capabilities:
Route refresh: advertised and received(new)
Address family IPv4 Unicast: advertised and received
!
Address tracking is enabled, the RIB does have a route to 192.168.3.2
Connections established 1; dropped 0
Last reset never
Transport(tcp) path-mtu-discovery is enabled
Graceful-Restart is disabled
Connection state is ESTAB, I/O status: 1, unread input bytes: 0
Disabling BGP Graceful Restart for a BGP Peer Group
Perform this task to disable BGP graceful restart for a BGP peer group. In this task, a BGP peer group is created and graceful
restart is disabled for the peer group. A BGP neighbor, Router D at 172.16.1.2 in the figure above, is then identified and
added as a peer group member. It inherits the configuration associated with the peer group, which, in this example, disables
BGP graceful restart.
Specifies the IPv4 address family and enters address family configuration mode.
The
unicast keyword specifies the IPv4 unicast address family. By default, the router is placed in address family configuration mode
for the IPv4 unicast address family if the
unicast keyword is not specified.
The
multicast keyword specifies IPv4 multicast address prefixes.
The
vrf keyword and
vrf-name argument specify the name of the VRF instance to associate with subsequent IPv4 address family configuration mode commands.
Step 5
neighborpeer-group-namepeer-group
Example:
Device(config-router-af)# neighbor PG1 peer-group
Creates a BGP peer group.
In this example, the peer group named PG1 is created.
Enables the BGP graceful restart capability for a BGP neighbor.
Use the
disable keyword to disable BGP graceful restart capability.
If you enter this command after the BGP session has been established, you must restart the session for the capability to
be exchanged with the BGP neighbor.
In this example, the BGP graceful restart capability is disabled for the BGP peer group named PG1.
(Optional) Displays information about TCP and BGP connections to neighbors.
In this example, the output is filtered to display information about the BGP peer at 172.16.1.2 and the “Graceful-Restart
is disabled” line shows that the graceful restart capability is disabled for this neighbor.
Examples
The following example shows partial output from the
showipbgpneighbors command for the BGP peer at 172.16.1.2. Graceful restart is shown as disabled. Note the default values for the restart and
stale-path timers. These timers can be set using only the global
bgpgraceful-restart command.
Device# show ip bgp neighbors 172.16.1.2
BGP neighbor is 172.16.1.2, remote AS 45000, internal link
Member of peer-group PG1 for session parameters
BGP version 4, remote router ID 0.0.0.0
BGP state = Idle
Neighbor sessions:
0 active, is multisession capable
!
Address tracking is enabled, the RIB does have a route to 172.16.1.2
Connections established 0; dropped 0
Last reset never
Transport(tcp) path-mtu-discovery is enabled
Graceful-Restart is disabled
Configuration Examples for BGP Graceful Restart per Neighbor
Examples: Enabling and Disabling BGP Graceful Restart per Neighbor
The ability to enable or disable the BGP graceful restart capability for an individual BGP neighbor, peer group, or peer
session template was introduced. The following example is configured on Router B in the figure below and enables the BGP graceful
restart capability for the BGP peer session template named S1 and disables the BGP graceful restart capability for the BGP
peer session template named S2. The external BGP neighbor at Router A (192.168.1.2) inherits peer session template S1, and
the BGP graceful restart capability is enabled for this neighbor. Another external BGP neighbor at Router E (192.168.3.2)
is configured with the BGP graceful restart capability disabled after inheriting peer session template S2.
The BGP graceful restart capability is enabled for an individual internal BGP neighbor, Router C at 172.21.1.2, whereas the
BGP graceful restart is disabled for the BGP neighbor at Router D, 172.16.1.2, because it is a member of the peer group PG1.
The disabling of BGP graceful restart is configured for all members of the peer group, PG1. The restart and stale-path timers
are modified, and the BGP sessions are reset.
To demonstrate how the last configuration instance of the BGP graceful restart capability is applied, the following example
initially enables the BGP graceful restart capability globally for all BGP neighbors. A BGP peer group, PG2, is configured
with the BGP graceful restart capability disabled. An individual external BGP neighbor, Router A at 192.168.1.2 in the figure
above, is then configured to be a member of the peer group, PG2. The last graceful restart configuration instance is applied,
and, in this case, the neighbor, 192.168.1.2, inherits the configuration instance from the peer group PG2, and the BGP graceful
restart capability is disabled for this neighbor.
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Feature Information for BGP
Graceful Restart per Neighbor
The following table provides release information about the feature or features described in this module. This table lists
only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise,
subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature
Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 1. Feature Information for BGP
Graceful Restart per Neighbor
Feature Name
Releases
Feature
Information
BGP Graceful
Restart per Neighbor
The BGP
Graceful Restart per Neighbor feature enables or disables the BGP graceful
restart capability for an individual BGP neighbor, including using peer session
templates and BGP peer groups.
The following
commands were introduced by this feature:
ha-mode
graceful-restart, andneighbor ha-mode graceful-restart.
The following
command was modified by this feature:
show ip bgp
neighbors.
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