IP Routing: BGP Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 920 Series)

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Book Title

IP Routing: BGP Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 920 Series)

Chapter Title

BGP Graceful Shutdown

Results

Updated:
November 22, 2018

Chapter: BGP Graceful Shutdown

BGP Graceful Shutdown

The BGP Graceful Shutdown feature reduces or eliminates the loss of traffic along a link being shut down for maintenance. Routers always have a valid route available during the convergence process. This feature is used primarily for maintenance on a link between a Provider Edge (PE), PE-PE, PE- Route Reflector (RR), PE-Customer Edge (CE) and CE.

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Information About BGP Graceful Shutdown

Purpose and Benefits of BGP Graceful Shutdown

There are times when planned maintenance operations cause routing changes in BGP. After the shutdown of eBGP and iBGP peering sessions between autonomous system border routers (ASBRs), BGP devices are temporarily unreachable during BGP convergence. The goal of gracefully shutting down one or more BGP sessions is to minimize traffic loss during the planned shutdown and subsequent reestablishment of the sessions.

The BGP Graceful Shutdown feature reduces or eliminates the loss of inbound or outbound traffic flows that were initially forwarded along the peering link that is being shut down for maintenance. This feature is primarily for PE-CE, PE-RR and PE-PE links. Lowering the local preference for paths received over the session being shutdown renders the affected paths less preferred by the BGP decision process, but still allows the paths to be used during the convergence while alternative paths are propagated to the affected devices. Therefore, devices always have a valid route available during the convergence process.

The feature also allows vendors to provide a graceful shutdown mechanism that does not require any router reconfiguration at maintenance time. The benefits of the BGP Graceful Shutdown feature are fewer lost packets and less time spent reconfiguring devices.

GSHUT Community

The GSHUT community is a well-known community used in conjunction with the BGP Graceful Shutdown feature. The GSHUT community attribute is applied to a neighbor specified by the neighbor shutdown graceful command, thereby gracefully shutting down the link in an expected number of seconds. The GSHUT community is always sent by the GSHUT initiator.

The GSHUT community is specified in a community list, which is referenced by a route map and then used to make policy routing decisions.

The GSHUT community can also be used in the show ip bgp community command to limit output to GSHUT routes.

How to Configure BGP Graceful Shutdown

Shutting Down a BGP Link Gracefully

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

router bgp autonomous-system-number

Example:


Device(config)# router bgp 5000

Configures a BGP routing process.

Step 4

neighbor {ipv4-address | ipv6-address } remote-as number

Example:


Device(config-router)# neighbor 2001:db8:3::1 remote-as 5500

Configures the autonomous system (AS) to which the neighbor belongs.

Step 5

neighbor {ipv4-address | ipv6-address | peer-group-name } shutdown graceful seconds {community value [local-preference value ] | local-preference value }

Example:


Device(config-router)# neighbor 2001:db8:3::1 shutdown graceful 600 community 1200 local-preference 300

Configures the device to gracefully shut down the link to the specified peer in the specified number of seconds; advertises the route with the GSHUT (Graceful Shutdown) community; and advertises the route with another community or specifies a local preference value for the route, or both.

  • Make sure to specify an adequate amount of time for iBGP peers to converge and to choose an alternate path as the best path.

  • If the graceful keyword is used in the neighbor shutdown command, at least one of the two attributes (a community or local preference) must be configured. You may configure both attributes.

  • If the graceful keyword is used in the neighbor shutdown command, the route is advertised with the GSHUT community by default. You may also set one other community for policy routing purposes.

  • In this particular example, the route to the neighbor is configured to shut down in 600 seconds, is advertised with the GSHUT community and community 1200, and is configured with a local preference of 300.

  • The device receiving the advertisement looks at the community value(s) of the route and optionally uses the community value to apply routing policy. Filtering routes based on a community is done with the ip community-list command and a route map.

  • During the graceful shutdown, the neighbor shutdown command is not nvgened. After the timer expires, SHUTDOWN is nvgened.

Step 6

end

Example:


Device(config-router)# end

Returns to EXEC mode.

Step 7

show ip bgp community gshut

Example:


Device# show ip bgp community gshut

(Optional) Displays information about the routes that are advertised with the well-known GSHUT community.

Filtering BGP Routes Based on the GSHUT Community

Perform this task on a BGP peer to the device where you enabled the BGP Graceful Shutdown feature.

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

router bgp autonomous-system-number

Example:


Device(config)# router bgp 2000

Configures a BGP routing process.

Step 4

neighbor {ipv4-address | ipv6-address } remote-as number

Example:


Device(config-router)# neighbor 2001:db8:4::1 remote-as 1000

Configures the autonomous system (AS) to which the neighbor belongs.

Step 5

neighbor {ipv4-address | ipv6-address } activate

Example:


Device(config-router)# neighbor 2001:db8:4::1 activate

Activates the neighbor.

Step 6

neighbor {ipv4-address | ipv6-address } send-community

Example:


Device(config-router)# neighbor 2001:db8:4::1 send-community

Enables BGP community exchange with the neighbor.

Step 7

exit

Example:


Device(config-router)# exit

Exits router configuration mode.

Step 8

route-map map-tag [permit | deny ] [sequence-number ]

Example:


Device(config)# route-map RM_GSHUT deny 10

Configures a route map to permit or deny routes for policy routing.

Step 9

match community {standard-list-number | expanded-list-number | community-list-name [exact ]}

Example:


Device(config-route-map)# match community GSHUT

Configures that the routes that match ip community-list GSHUT will be policy routed.

Step 10

exit

Example:


Device(config-route-map)# exit

Exits route-map configuration mode.

Step 11

ip community-list {standard | standard list-name} {deny | permit} gshut

Example:


Device(config)# ip community-list standard GSHUT permit gshut

Configures a community list and permits or denies routes that have the GSHUT community to the community list.

  • If you specify other communities in the same statement, there is a logical AND operation and all communities in the statement must match the communities for the route in order for the statement to be processed.

Step 12

router bgp autonomous-system-number

Example:


Device(config)# router bgp 2000

Configures a BGP routing process.

Step 13

neighbor address route-map map-name in

Example:


Device(config)# neighbor 2001:db8:4::1 route-map RM_GSHUT in

Applies the route map to incoming routes from the specified neighbor.

  • In this example, the route map named RM_GSHUT denies routes from the specified neighbor that have the GSHUT community.

Configuration Examples for BGP Graceful Shutdown

Example: Shutting Down a BGP Link Gracefully

Graceful Shutdown While Setting a Local-Preference

This example gracefully shuts down the link to the specified neighbor in 600 seconds, adds the GSHUT community to the route, and sets a local preference of 500 for the route. 


router bgp 1000
 neighbor 2001:db8:5::1 remote-as 2000
 neighbor 2001:db8:5::1 shutdown graceful 600 local-preference 500
 neighbor 2001:db8:5::1 send-community
 exit

Graceful Shutdown While Setting an Additional Community

This example gracefully shuts down the link to the specified neighbor in 600 seconds, and adds the GSHUT community and numbered community to the route. 


router bgp 1000
 neighbor 2001:db8:5::1 remote-as 2000
 neighbor 2001:db8:5::1 shutdown graceful 600 community 1400
 neighbor 2001:db8:5::1 send-community
 exit

Graceful Shutdown while Setting an Additional Community and Local-Preference

This example gracefully shuts down the link to the specified neighbor in 600 seconds, adds the GSHUT community and the numbered community to the route, and sets a local preference of 500 to the route. 


router bgp 1000
 neighbor 2001:db8:5::1 remote-as 2000
 neighbor 2001:db8:5::1 shutdown graceful 600 community 1400 local-preference 500
 neighbor 2001:db8:5::1 send-community
 exit

Example: Filtering BGP Routes Based on the GSHUT Community

In additional to being able to gracefully shut down a BGP route, another use of the GSHUT community is to configure a community list to filter routes with this community from getting into the BGP routing table.

This example illustrates how to use a community list to filter incoming BGP routes based on the GSHUT community. In this example, a route map named RM_GSHUT denies routes based on a standard community list named GSHUT. The community list contains routes with the GSHUT community. The route map is then applied to incoming routes from the neighbor at 2001:db8:4::1. 


router bgp 2000
 neighbor 2001:db8:4::1 remote-as 1000
 neighbor 2001:db8:4::1 activate
 neighbor 2001:db8:4::1 send-community
 exit
route-map RM_GSHUT deny 10
 match community GSHUT
 exit
ip community-list standard GSHUT permit gshut
router bgp 2000
 neighbor 2001:db8:4::1 route-map RM_GSHUT in

Additional References

Related Documents

Related Topic

Document Title

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

BGP commands

Cisco IOS IP Routing: BGP Command Reference

Standards and RFCs

Standard/RFC

Title

RFC 6198

Requirements for the Graceful Shutdown of BGP Sessions

Technical Assistance

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