Contents
This module describes configuration tasks for various advanced Border Gateway Protocol (BGP) features. BGP is an interdomain routing protocol that is designed to provide loop-free routing between organizations. This module contains tasks to configure BGP next-hop address tracking, BGP Nonstop Forwarding (NSF) awareness using the BGP graceful restart capability, route dampening, and Bidirectional Forwarding Detection (BFD) support for BGP.
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, 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.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Before configuring advanced BGP features you should be familiar with the "Cisco BGP Overview" module and the "Configuring a Basic BGP Network" module.
A router that runs Cisco IOS XE software can be configured to run only one BGP routing process and to be a member of only one BGP autonomous system. However, a BGP routing process and autonomous system can support multiple address family configurations.
Border Gateway Protocol (BGP) is an interdomain routing protocol designed to provide loop-free routing between separate routing domains that contain independent routing policies (autonomous systems). The Cisco software implementation of BGP version 4 includes multiprotocol extensions to allow BGP to carry routing information for IP multicast routes and multiple Layer 3 protocol address families including IP Version 4 (IPv4), IP Version 6 (IPv6), Virtual Private Networks version 4 (VPNv4), and Connectionless Network Services (CLNS).
BGP is mainly used to connect a local network to an external network to gain access to the Internet or to connect to other organizations. When connecting to an external organization, external BGP (eBGP) peering sessions are created. For more details about connecting to external BGP peers, see the "Connecting to a Service Provider Using External BGP" chapter.
Although BGP is referred to as an exterior gateway protocol (EGP) many networks within an organization are becoming so complex that BGP can be used to simplify the internal network used within the organization. BGP peers within the same organization exchange routing information through internal BGP (iBGP) peering sessions. For more details about internal BGP peers, see the "Configuring Internal BGP Features" chapter of the Cisco IOS IP Routing Configuration Guide.
Note |
BGP requires more configuration than other routing protocols and the effects of any configuration changes must be fully understood. Incorrect configuration can create routing loops and negatively impact normal network operation. |
To configure BGP next-hop address tracking, you should understand the following concepts:
The BGP next-hop address tracking feature is enabled by default when a supporting Cisco software image is installed. BGP next-hop address tracking is event driven. BGP prefixes are automatically tracked as peering sessions are established. Next-hop changes are rapidly reported to the BGP routing process as they are updated in the RIB. This optimization improves overall BGP convergence by reducing the response time to next-hop changes for routes installed in the RIB. When a best-path calculation is run in between BGP scanner cycles, only next-hop changes are tracked and processed.
BGP monitors the next hop of installed routes to verify next-hop reachability and to select, install, and validate the BGP best path. By default, the BGP scanner is used to poll the RIB for this information every 60 seconds. During the 60 second time period between scan cycles, Interior Gateway Protocol (IGP) instability or other network failures can cause black holes and routing loops to temporarily form.
BGP selective next-hop route filtering was implemented as part of the BGP Selective Address Tracking feature to support BGP next-hop address tracking. Selective next-hop route filtering uses a route map to selectively define routes to help resolve the BGP next hop.
The ability to use a route map with the bgp nexthop command allows the configuration of the length of a prefix that applies to the BGP Next_Hop attribute. The route map is used during the BGP bestpath calculation and is applied to the route in the routing table that covers the next-hop attribute for BGP prefixes. If the next-hop route fails the route map evaluation, the next-hop route is marked as unreachable. This command is per address family, so different route maps can be applied for next-hop routes in different address families.
Note |
Only match ip address and match source-protocol commands are supported in the route map. No set commands or other match commands are supported. |
The Next_Hop attribute identifies the next-hop IP address to be used as the BGP next hop to the destination. The router makes a recursive lookup to find the BGP next hop in the routing table. In external BGP (eBGP), the next hop is the IP address of the peer that sent the update. Internal BGP (iBGP) sets the next-hop address to the IP address of the peer that advertised the prefix for routes that originate internally. When any routes to iBGP that are learned from eBGP are advertised, the Next_Hop attribute is unchanged.
A BGP next-hop IP address must be reachable in order for the router to use a BGP route. Reachability information is usually provided by the IGP, and changes in the IGP can influence the forwarding of the next-hop address over a network backbone.
To configure BGP Nonstop Forwarding (NSF) awareness, you should understand the following concepts:
Cisco NSF is supported by the BGP, EIGRP, OSPF, and IS-IS protocols for routing and by Cisco Express Forwarding (CEF) for forwarding. Of the routing protocols, BGP, EIGRP, OSPF, and IS-IS have been enhanced with NSF-capability and awareness, which means that devices running these protocols can detect a switchover and take the necessary actions to continue forwarding network traffic and to recover route information from the peer devices.
In this document, a networking device is said to be NSF-aware if it is running NSF-compatible software. A device is said to be NSF-capable if it has been configured to support NSF; therefore, it would rebuild routing information from NSF-aware or NSF-capable neighbors.
Each protocol depends on CEF to continue forwarding packets during switchover while the routing protocols rebuild the Routing Information Base (RIB) tables. Once the routing protocols have converged, CEF updates the FIB table and removes stale route entries. CEF then updates the line cards with the new FIB information.
Note |
Currently, EIGRP supports only NSF awareness. |
A key element of NSF is packet forwarding. In a Cisco networking device, packet forwarding is provided by CEF. CEF maintains the FIB and uses the FIB information that was current at the time of the switchover to continue forwarding packets during a switchover. This feature reduces traffic interruption during the switchover.
During normal NSF operation, CEF on the active RP synchronizes its current FIB and adjacency databases with the FIB and adjacency databases on the standby RP. Upon switchover of the active RP, the standby RP initially has FIB and adjacency databases that are mirror images of those that were current on the active RP. For platforms with intelligent line cards, the line cards will maintain the current forwarding information over a switchover; for platforms with forwarding engines, CEF will keep the forwarding engine on the standby RP current with changes that are sent to it by CEF on the active RP. In this way, the line cards or forwarding engines will be able to continue forwarding after a switchover as soon as the interfaces and a data path are available.
As the routing protocols start to repopulate the RIB on a prefix-by-prefix basis, the updates in turn cause prefix-by-prefix updates for CEF, which it uses to update the FIB and adjacency databases. Existing and new entries will receive the new version (epoch) number, indicating that they have been refreshed. The forwarding information is updated on the line cards or forwarding engine during convergence. The RP signals when the RIB has converged. The software removes all FIB and adjacency entries that have an epoch older than the current switchover epoch. The FIB now represents the newest routing protocol forwarding information
The routing protocols run only on the active RP, and they receive routing updates from their neighbor routers. Routing protocols do not run on the standby RP. Following a switchover, the routing protocols request that the NSF-aware neighbor devices send state information to help rebuild the routing tables.
Note |
For NSF operation, the routing protocols depend on CEF to continue forwarding packets while the routing protocols rebuild the routing information. |
When an NSF-capable router begins a BGP session with a BGP peer, it sends an OPEN message to the peer. Included in the message is a declaration that the NSF-capable or NSF-aware router has graceful restart capability. Graceful restart is the mechanism by which BGP routing peers avoid a routing flap following a switchover. If the BGP peer has received this capability, it is aware that the device sending the message is NSF-capable. Both the NSF-capable router and its BGP peer(s) (NSF-aware peers) need to exchange the graceful restart capability in their OPEN messages, at the time of session establishment. If both the peers do not exchange the graceful restart capability, the session will not be graceful restart capable.
If the BGP session is lost during the RP switchover, the NSF-aware BGP peer marks all the routes associated with the NSF-capable router as stale; however, it continues to use these routes to make forwarding decisions for a set period of time. This functionality means that no packets are lost while the newly active RP is waiting for convergence of the routing information with the BGP peers.
After an RP switchover occurs, the NSF-capable router reestablishes the session with the BGP peer. In establishing the new session, it sends a new graceful restart message that identifies the NSF-capable router as having restarted.
At this point, the routing information is exchanged between the two BGP peers. Once this exchange is complete, the NSF-capable device uses the routing information to update the RIB and the FIB with the new forwarding information. The NSF-aware device uses the network information to remove stale routes from its BGP table. Following that, the BGP protocol is fully converged.
If a BGP peer does not support the graceful restart capability, it will ignore the graceful restart capability in an OPEN message but will establish a BGP session with the NSF-capable device. This functionality will allow interoperability with non-NSF-aware BGP peers (and without NSF functionality), but the BGP session with non-NSF-aware BGP peers will not be graceful restart capable.
BGP support for NSF requires that neighbor routers are NSF-aware or NSF-capable. NSF awareness in BGP is also enabled by the graceful restart mechanism. A router that is NSF-aware functions like a router that is NSF-capable with one exception: an NSF-aware router is incapable of performing an SSO operation. However, a router that is NSF-aware is capable of maintaining a peering relationship with a NSF-capable neighbor during a NSF SSO operation, as well as holding routes for this neighbor during the SSO operation.
The BGP Nonstop Forwarding Awareness feature provides an NSF-aware router with the capability to detect a neighbor that is undergoing an SSO operation, maintain the peering session with this neighbor, retain known routes, and continue to forward packets for these routes. The deployment of BGP NSF awareness can minimize the effects of Route Processor (RP) failure conditions and improve the overall network stability by reducing the amount of resources that are normally required for reestablishing peering with a failed router.
NSF awareness for BGP is not enabled by default. The bgp graceful-restart command is used to globally enable NSF awareness on a router that is running BGP. NSF-aware operations are also transparent to the network operator and BGP peers that do not support NSF capabilities.
Note |
NSF awareness is enabled automatically in supported software images for Interior Gateway Protocols, such as EIGRP, IS-IS, and OSPF. In BGP, global NSF awareness is not enabled automatically and must be started by issuing the bgp graceful-restart command in router configuration mode. |
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 neighbor ha-mode graceful-restart command, or a BGP peer can inherit a graceful restart configuration from a BGP peer-session template using the ha-mode graceful-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 bgp graceful-restart command, but the default values are set when the neighbor ha-mode graceful-restart or ha-mode graceful-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.
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.
For more details about BGP peer session templates, see the section "Configuring a Basic BGP Network."
To use a BGP peer session template to enable or disable BGP graceful restart, see the section "Enabling and Disabling BGP Graceful Restart Using BGP Peer Session Templates."
Route dampening is a BGP feature designed to minimize the propagation of flapping routes across an internetwork. A route is considered to be flapping when its availability alternates repeatedly.
For example, consider a network with three BGP autonomous systems: autonomous system 1, autonomous system 2, and autonomous system 3. Suppose the route to network A in autonomous system 1 flaps (it becomes unavailable). Under circumstances without route dampening, the eBGP neighbor of autonomous system 1 to autonomous system 2 sends a withdraw message to autonomous system 2. The border router in autonomous system 2, in turn, propagates the withdraw message to autonomous system 3. When the route to network A reappears, autonomous system 1 sends an advertisement message to autonomous system 2, which sends it to autonomous system 3. If the route to network A repeatedly becomes unavailable, then available, many withdrawal and advertisement messages are sent. This is a problem in an internetwork connected to the Internet because a route flap in the Internet backbone usually involves many routes.
Note |
No penalty is applied to a BGP peer reset when route dampening is enabled. Although the reset withdraws the route, no penalty is applied in this instance, even if route flap dampening is enabled. |
The route dampening feature minimizes the flapping problem as follows. Suppose again that the route to network A flaps. The router in autonomous system 2 (where route dampening is enabled) assigns network A penalty of 1000 and moves it to history state. The router in autonomous system 2 continues to advertise the status of the route to neighbors. The penalties are cumulative. When the route flaps so often that the penalty exceeds a configurable suppress limit, the router stops advertising the route to network A, regardless of how many times it flaps. Thus, the route is dampened.
The penalty placed on network A is decayed until the reuse limit is reached, upon which the route is once again advertised. At half of the reuse limit, the dampening information for the route to network A is removed.
The following terms are used when describing route dampening:
The routes external to an autonomous system learned via iBGP are not dampened. This policy prevent the iBGP peers from having a higher penalty for routes external to the autonomous system.
Bidirectional Forwarding Detection (BFD) is a detection protocol designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning will be easier, and reconvergence time will be consistent and predictable. The main benefit of implementing BFD for BGP is a marked decrease in reconvergence time.
Caution |
BFD and BGP Graceful Restart capability cannot both be configured on a router running BGP. If an interface goes down, BFD detects the failure and indicates that the interface cannot be used for traffic forwarding and the BGP session goes down, but graceful restart still allows traffic forwarding on platforms that support NSF even though the BGP session is down, allowing traffic forwarding using the interface that is down. Configuring both BFD and BGP graceful restart for NSF on a router running BGP may result in suboptimal routing. |
See also the "Configuring BGP Neighbor Session Options" chapter, the section "Configuring BFD for BGP IPv6 Neighbors."
For more details about BFD, see the Cisco IOS IP Routing: BFD Configuration Guide.
The tasks in this section show how configure BGP next-hop address tracking. BGP next-hop address tracking significantly improves the response time of BGP to next-hop changes in the RIB. However, unstable Interior Gateway Protocol (IGP) peers can introduce instability to BGP neighbor sessions. We recommend that you aggressively dampen unstable IGP peering sessions to reduce the possible impact to BGP. For more details about configuring route dampening, see "Configuring BGP Route Dampening."
Perform this task to disable BGP next-hop address tracking. BGP next-hop address tracking is enabled by default under the IPv4 and VPNv4 address families. Disabling next hop address tracking may be useful if you the network has unstable IGP peers and route dampening is not resolving the stability issues. To reenable BGP next-hop address tracking, use the bgp nexthop command with the trigger and enable keywords.
Perform this task to adjust the delay interval between routing table walks for BGP next-hop address tracking.
You can increase the performance of this feature by tuning the delay interval between full routing table walks to match the tuning parameters for the Interior Gateway protocol (IGP). The default delay interval is 5 seconds. This value is optimal for a fast-tuned IGP. In the case of an IGP that converges more slowly, you can change the delay interval to 20 seconds or more, depending on the IGP convergence time.
BGP next-hop address tracking significantly improves the response time of BGP to next-hop changes in the RIB. However, unstable Interior Gateway Protocol (IGP) peers can introduce instability to BGP neighbor sessions. We recommend that you aggressively dampen unstable IGP peering sessions to reduce the possible impact to BGP.
Perform this task to configure selective next-hop route filtering using a route map to filter potential next-hop routes. This task uses prefix lists and route maps to match IP addresses or source protocols and can be used to avoid aggregate addresses and BGP prefixes being considered as next-hop routes.
For more examples of how to use the bgp nexthop command, see "Examples: Configuring BGP Next-Hop Route Filtering."
Note |
Only match ip address and match source-protocol commands are supported in the route map. No set commands or other match commands are supported. > |
The following example from the show ip bgp command shows the next-hop addresses for each route:
BGP table version is 7, local router ID is 172.17.1.99 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path * 10.1.1.0/24 192.168.1.2 0 0 40000 i * 10.2.2.0/24 192.168.3.2 0 0 50000 i *> 172.16.1.0/24 0.0.0.0 0 32768 i *> 172.17.1.0/24 0.0.0.0 0 32768
The tasks in this section show how configure BGP Nonstop Forwarding (NSF) awareness using the BGP graceful restart capability. The first task enables BGP NSF globally for all BGP neighbors and suggests a few troubleshooting options. The second task describes how to adjust the BGP graceful restart timers although the default settings are optimal for most network deployments. The next three tasks demonstrate how to enable or disable BGP graceful restart for individual BGP neighbors including peer session templates and peer groups. The final task verifies the local and peer router configuration of BGP NSF.
Perform this task to enable BGP NSF awareness globally for all BGP neighbors. BGP NSF awareness is part of the graceful restart mechanism and BGP NSF awareness is enabled by issuing the bgp graceful-restart command in router configuration mode. BGP NSF awareness allows NSF-aware routers to support NSF-capable routers during an SSO operation. NSF-awareness is not enabled by default and should be configured on all neighbors that participate in BGP NSF.
Note |
The configuration of the restart and stale-path timers is not required to enable the BGP graceful restart capability. The default values are optimal for most network deployments, and these values should be adjusted only by an experienced network operator. |
Note |
Configuring both BFD and BGP graceful restart for NSF on a router running BGP may result in suboptimal routing. For more details, see the section "BFD for BGP." |
Command or Action | Purpose | |
---|---|---|
Step 1
|
enable
Example: Device> enable |
Enables privileged EXEC mode. |
Step 2
|
configure terminal
Example: Device# configure terminal |
Enters global configuration mode. |
Step 3
|
router bgp autonomous-system-number
Example: Device(config)# router bgp 45000 |
Enters router configuration mode and creates a BGP routing process. |
Step 4
|
bgp graceful-restart [restart-time seconds] [stalepath-time seconds]
Example: Device(config-router)# bgp graceful-restart |
Enables the BGP graceful restart capability and BGP NSF awareness. |
Step 5
|
end
Example: Device(config-router)# end |
Exits router configuration mode and enters privileged EXEC mode. |
To troubleshoot the NSF feature, use the following commands in privileged EXEC mode, as needed:
If the bgp graceful-restart command has been issued after the BGP session has been established, you must reset by issuing the clear ip bgp * command or by reloading the router before graceful restart capabilities will be exchanged. For more information about resetting BGP sessions and using the clear ip bgp command, see the "Configuring a Basic BGP Network" module.
Perform this task to adjust the BGP graceful restart timers. There are two BGP graceful restart timers that can be configured. The optional restart-time keyword and seconds argument determine how long peer routers will wait to delete stale routes before a BGP open message is received. The default value is 120 seconds. The optional stalepath-time keyword and seconds argument determine how long a router will wait before deleting stale routes after an end of record (EOR) message is received from the restarting router. The default value is 360 seconds.
Note |
The configuration of the restart and stale-path timers is not required to enable the BGP graceful restart capability. The default values are optimal for most network deployments, and these values should be adjusted only by an experienced network operator. |
Command or Action | Purpose | |||
---|---|---|---|---|
Step 1
|
enable
Example: Device> enable |
Enables privileged EXEC mode. |
||
Step 2
|
configure terminal
Example: Device# configure terminal |
Enters global configuration mode. |
||
Step 3
|
router bgp autonomous-system-number
Example: Device(config)# router bgp 45000 |
Enters router configuration mode and creates a BGP routing process. |
||
Step 4
|
bgp graceful-restart [restart-time seconds]
Example: Device(config-router)# bgp graceful-restart restart-time 130 |
Enables the BGP graceful restart capability and BGP NSF awareness.
|
||
Step 5
|
bgp graceful-restart [stalepath-time seconds]
Example: Device(config-router)# bgp graceful-restart stalepath-time 350 |
Enables the BGP graceful restart capability and BGP NSF awareness.
|
||
Step 6
|
end
Example: Device(config-router)# end |
Exits router configuration mode and enters privileged EXEC mode. |
If the bgp graceful-restart command has been issued after the BGP session has been established, you must reset the peer sessions by issuing the clear ip bgp * command or by reloading the router before graceful restart capabilities will be exchanged. For more information about resetting BGP sessions and using the clear ip bgp command, see the "Configuring a Basic BGP Network" module.
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--at Router A and Router E in the figure below--are identified. The first BGP peer at Router A is configured to inherit the first peer session template that enables BGP graceful restart, whereas the second BGP peer at Router E inherits the second template that disables BGP graceful restart. Using the optional show ip bgp neighbors command, the status of the BGP graceful restart capability is verified for each BGP neighbor configured in this task.
The restart and stale-path timers can be modified only using the global bgp graceful-restart command as shown in the figure. 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. |
Command or Action | Purpose | |
---|---|---|
Step 1
|
enable
Example: Device> enable |
Enables privileged EXEC mode. |
Step 2
|
configure terminal
Example: Device# configure terminal |
Enters global configuration mode. |
Step 3
|
router bgp autonomous-system-number
Example: Device(config)# router bgp 45000 |
Enters router configuration mode and creates a BGP routing process. |
Step 4
|
template peer-session session-template-name
Example: Device(config-router)# template peer-session S1 |
Enters session-template configuration mode and creates a peer session template. |
Step 5
|
ha-mode graceful-restart [disable]
Example: Device(config-router-stmp)# ha-mode graceful-restart |
Enables the BGP graceful restart capability and BGP NSF awareness.
|
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
|
template peer-session session-template-name
Example: Device(config-router)# template peer-session S2 |
Enters session-template configuration mode and creates a peer session template. |
Step 8
|
ha-mode graceful-restart [disable]
Example: Device(config-router-stmp)# ha-mode graceful-restart disable |
Enables the BGP graceful restart capability and BGP NSF awareness.
|
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
|
bgp log-neighbor-changes
Example: Device(config-router)# bgp log-neighbor-changes |
Enables logging of BGP neighbor status changes (up or down) and neighbor resets. |
Step 11
|
neighbor ip-address remote-as autonomous-system-number
Example: Device(config-router)# neighbor 192.168.1.2 remote-as 40000 |
Configures peering with a BGP neighbor in the specified autonomous system. |
Step 12
|
neighbor ip-address inherit peer-session session-template-number
Example: Device(config-router)# neighbor 192.168.1.2 inherit peer-session S1 |
Inherits a peer session template. |
Step 13
|
neighbor ip-address remote-as autonomous-system-number
Example: Device(config-router)# neighbor 192.168.3.2 remote-as 50000 |
Configures peering with a BGP neighbor in the specified autonomous system. |
Step 14
|
neighbor ip-address inherit peer-session session-template-number
Example: Device(config-router)# neighbor 192.168.3.2 inherit peer-session S2 |
Inherits a peer session-template. |
Step 15
|
end
Example: Device(config-router)# end |
Exits router configuration mode and enters privileged EXEC mode. |
Step 16
|
show ip bgp template peer-session [session-template-number]
Example: Device# show ip bgp template peer-session |
(Optional) Displays locally configured peer session templates. |
Step 17
|
show ip bgp neighbors [ip-address [received-routes | routes | advertised-routes | paths [regexp] | dampened-routes | flap-statistics | received prefix-filter | policy [detail]]]
Example: Device# show ip bgp neighbors 192.168.1.2 |
(Optional) Displays information about TCP and BGP connections to neighbors. |
The following example shows partial output from the show ip bgp neighbors 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 bgp graceful-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 show ip bgp neighbors 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
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 address family IPv4, 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 show ip bgp neighbors command is used.
Command or Action | Purpose | |
---|---|---|
Step 1
|
enable
Example: Device> enable |
Enables privileged EXEC mode. |
Step 2
|
configure terminal
Example: Device# configure terminal |
Enters global configuration mode. |
Step 3
|
router bgp autonomous-system-number
Example: Device(config)# router bgp 45000 |
Enters router configuration mode and creates a BGP routing process. |
Step 4
|
address-family ipv4 [unicast | multicast | vrf vrf-name]
Example: Device(config-router)# address-family ipv4 unicast |
Specifies the IPv4 address family and enters address family configuration mode.
|
Step 5
|
neighbor ip-address remote-as autonomous-system-number
Example: Device(config-router-af)# neighbor 172.21.1.2 remote-as 45000 |
Configures peering with a BGP neighbor in the specified autonomous system. |
Step 6
|
neighbor ip-address activate
Example: Device(config-router-af)# neighbor 172.21.1.2 activate |
Enables the neighbor to exchange prefixes for the IPv4 address family with the local router. |
Step 7
|
neighbor ip-address ha-mode graceful-restart [disable]
Example: Device(config-router-af)# neighbor 172.21.1.2 ha-mode graceful-restart |
Enables the BGP graceful restart capability for a BGP neighbor.
|
Step 8
|
end
Example: Device(config-router-af)# end |
Exits address family configuration mode and returns to privileged EXEC mode. |
Step 9
|
show ip bgp neighbors [ip-address [received-routes | routes | advertised-routes | paths [regexp] | dampened-routes | flap-statistics | received prefix-filter | policy [detail]]]
Example: Device# show ip bgp neighbors 172.21.1.2 |
(Optional) Displays information about TCP and BGP connections to neighbors. |
The following example shows partial output from the show ip bgp neighbors 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 bgp graceful-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
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, 172.16.1.2 at Router D in the figure above, is then identified and added as a peer group member and inherits the configuration associated with the peer group, which, in this example, disables BGP graceful restart.
Command or Action | Purpose | |
---|---|---|
Step 1
|
enable
Example: Device> enable |
Enables privileged EXEC mode. |
Step 2
|
configure terminal
Example: Device# configure terminal |
Enters global configuration mode. |
Step 3
|
router bgp autonomous-system-number
Example: Device(config)# router bgp 45000 |
Enters router configuration mode and creates a BGP routing process. |
Step 4
|
address-family ipv4 [unicast | multicast | vrf vrf-name]
Example: Device(config-router)# address-family ipv4 unicast |
Specifies the IPv4 address family and enters address family configuration mode.
|
Step 5
|
neighbor peer-group-name peer-group
Example: Device(config-router-af)# neighbor PG1 peer-group |
Creates a BGP peer group. |
Step 6
|
neighbor peer-group-name remote-as autonomous-system-number
Example: Device(config-router-af)# neighbor PG1 remote-as 45000 |
Configures peering with a BGP peer group in the specified autonomous system. |
Step 7
|
neighbor peer-group-name ha-mode graceful-restart [disable]
Example: Device(config-router-af)# neighbor PG1 ha-mode graceful-restart disable |
Enables the BGP graceful restart capability for a BGP neighbor.
|
Step 8
|
neighbor ip-address peer-group peer-group-name
Example: Device(config-router-af)# neighbor 172.16.1.2 peer-group PG1 |
Assigns the IP address of a BGP neighbor to a peer group. |
Step 9
|
end
Example: Device(config-router-af)# end |
Exits address family configuration mode and returns to privileged EXEC mode. |
Step 10
|
show ip bgp neighbors [ip-address [received-routes | routes | advertised-routes | paths [regexp] | dampened-routes | flap-statistics | received prefix-filter | policy[ detail]]]
Example: Device# show ip bgp neighbors 172.16.1.2 |
(Optional) Displays information about TCP and BGP connections to neighbors. |
The following example shows partial output from the show ip bgp neighbors 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 bgp graceful-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
Use the following steps to verify the local configuration of BGP NSF awareness on a router and to verify the configuration of NSF awareness on peer routers in a BGP network.
Step 1 |
enable Enables privileged EXEC mode. Enter your password if prompted. Example:
Device> enable
|
Step 2 |
show running-config [options] Displays the running configuration on the local router. The output will display the configuration of the bgp graceful-restart command in the BGP section. Repeat this command on all BGP neighbor routers to verify that all BGP peers are configured for BGP NSF awareness. In this example, BGP graceful restart is enabled globally and the external neighbor at 192.168.1.2 is configured to be a BGP peer and will have the BGP graceful restart capability enabled. Example:
Device# show running-config
.
.
.
router bgp 45000
bgp router-id 172.17.1.99
bgp log-neighbor-changes
bgp graceful-restart restart-time 130
bgp graceful-restart stalepath-time 350
bgp graceful-restart
timers bgp 70 120
neighbor 192.168.1.2 remote-as 40000
neighbor 192.168.1.2 activate
.
.
.
|
Step 3 |
show ip bgp neighbors [ip-address [received-routes | routes | advertised-routes | paths [regexp] | dampened-routes | flap-statistics | received prefix-filter | policy [detail]]] 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 Cisco IOS XE Release 2.1 or later releases, the ability to enable or disable the BGP graceful restart capability for an individual BGP neighbor, peer group or peer session template was introduced and output was added to this command to show the BGP graceful restart status. |
The tasks in this section configure and monitor BGP route dampening. Route dampening is designed to minimize the propagation of flapping routes across an internetwork. A route is considered to be flapping when its availability alternates repeatedly.
Command or Action | Purpose | |
---|---|---|
Step 1
|
enable
Example: Router> enable |
Enables privileged EXEC mode. |
Step 2
|
configure terminal
Example: Router# configure terminal |
Enters global configuration mode. |
Step 3
|
router bgp as-number
Example: Router(config)# router bgp 45000 |
Enters router configuration mode and creates a BGP routing process. |
Step 4
|
address-family ipv4 [unicast | multicast | vrf vrf-name]
Example: Router(config-router)# address-family ipv4 unicast |
Specifies the IPv4 address family and enters address family configuration mode.
|
Step 5
|
bgp dampening [half-life reuse suppress max-suppress-time] [route-map map-name]
Example: Router(config-router-af)# bgp dampening 30 1500 10000 120 |
Enables BGP route dampening and changes the default values of route dampening factors. |
Step 6
|
end
Example: Router(config-router-af)# end |
Exits address family configuration mode and enters privileged EXEC mode. |
Step 1 | enable Enables privileged EXEC mode. Enter your password if prompted. Example:
Router> enable
|
Step 2 | show ip bgp flap-statistics [regexp regexp | filter-list access-list | ip-address mask [longer-prefix]] Use this command to monitor the flaps of all the paths that are flapping. The statistics will be deleted once the route is not suppressed and is stable for at least one half-life. Example:
Router# show ip bgp flap-statistics
BGP table version is 10, local router ID is 172.17.232.182
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network From Flaps Duration Reuse Path
*d 10.0.0.0 172.17.232.177 4 00:13:31 00:18:10 100
*d 10.2.0.0 172.17.232.177 4 00:02:45 00:28:20 100
|
Step 3 | clear ip bgp flap-statistics [neighbor-address [ipv4-mask]] [regexp regexp | filter-list extcom-number] Use this command to clear the accumulated penalty for routes that are received on a router that has BGP dampening enabled. If no arguments or keywords are specified, flap statistics are cleared for all routes. Flap statistics are also cleared when the peer is stable for the half-life time period. After the BGP flap statistics are cleared, the route is less likely to be dampened. Example:
Router# clear ip bgp flap-statistics 172.17.232.177
|
Step 4 | show ip bgp dampened-paths Use this command to monitor the flaps of all the paths that are flapping. The statistics will be deleted once the route is not suppressed and is stable for at least one half-life. Example:
Router# show ip bgp dampened-paths
BGP table version is 10, local router ID is 172.29.232.182
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network From Reuse Path
*d 10.0.0.0 172.16.232.177 00:18:4 100 ?
*d 10.2.0.0 172.16.232.177 00:28:5 100 ?
|
Step 5 | clear ip bgp [ipv4 {multicast | unicast} | ipv6{multicast | unicast} | vpnv4 unicast] dampening [neighbor-address] [ipv4-mask] Use this command to clear stored route dampening information. If no keywords or arguments are entered, route dampening information for the entire routing table is cleared. The following example clears route dampening information for VPNv4 address family prefixes from network 192.168.10.0/24, and unsuppresses its suppressed routes. Example:
Router# clear ip bgp vpnv4 unicast dampening 192.168.10.0 255.255.255.0
|
You start a BFD process by configuring BFD on the interface. When the BFD process is started, no entries are created in the adjacency database, in other words, no BFD control packets are sent or received. The adjacency creation takes places once you have configured BFD support for the applicable routing protocols. The first two tasks must be configured to implement BFD support for BGP to reduce the BGP convergence time. The third task is an optional task to help monitor or troubleshoot BFD.
The steps in this procedure show how to configure BFD on the interface by setting the baseline BFD session parameters on an interface. Repeat the steps in this procedure for each interface over which you want to run BFD sessions to BFD neighbors.
Command or Action | Purpose | |
---|---|---|
Step 1
|
enable
Example: Router> enable |
Enables privileged EXEC mode.
|
Step 2
|
configure terminal
Example: Router# configure terminal |
Enters global configuration mode. |
Step 3
|
interface type number
Example: Router(config)# interface FastEthernet 6/0 |
Enters interface configuration mode. |
Step 4
|
bfd interval milliseconds min_rx milliseconds multiplier interval-multiplier
Example: Router(config-if)# bfd interval 50 min_rx 50 multiplier 5 |
Enables BFD on the interface. |
Step 5
|
end
Example: Router(config-if)# end |
Exits interface configuration mode. |
Perform this task to configure BFD support for BGP, so that BGP is a registered protocol with BFD and will receive forwarding path detection failure messages from BFD.
Command or Action | Purpose | |
---|---|---|
Step 1
|
enable
Example: Router> enable |
Enables privileged EXEC mode. |
Step 2
|
configure terminal
Example: Router# configure terminal |
Enters global configuration mode. |
Step 3
|
router bgp autonomous-system-number
Example: Router(config)# router bgp tag1 |
Specifies a BGP process and enters router configuration mode. |
Step 4
|
neighbor ip-address fall-over bfd
Example: Router(config-router)# neighbor 172.16.10.2 fall-over bfd |
Enables BFD support for fallover. |
Step 5
|
end
Example: Router(config-router)# end |
Returns the router to privileged EXEC mode. |
Step 6
|
show bfd neighbors [details]
Example: Router# show bfd neighbors detail |
Verifies that the BFD neighbor is active and displays the routing protocols that BFD has registered. |
Step 7
|
show ip bgp neighbors [ip-address [received-routes | routes | advertised-routes | paths [regexp] | dampened-routes | flap-statistics | received prefix-filter | policy [detail]]]
Example: Router# show ip bgp neighbors |
Displays information about BGP and TCP connections to neighbors. |
In the following example, next-hop address tracking is disabled under the IPv4 address family session:
router bgp 50000 address-family ipv4 unicast no bgp nexthop trigger enable
In the following example, the delay interval for next-hop tracking is configured to occur every 20 seconds under the IPv4 address family session:
router bgp 50000 address-family ipv4 unicast bgp nexthop trigger delay 20
The following example shows how to configure BGP selective next-hop route filtering to avoid using a BGP prefix as the next-hop route. If the most specific route that covers the next hop is a BGP route, then the BGP route will be marked as unreachable. The next hop must be an IGP or static route.
router bgp 45000 address-family ipv4 unicast bgp nexthop route-map CHECK-BGP exit exit route-map CHECK-BGP deny 10 match source-protocol bgp 1 exit route-map CHECK-BGP permit 20 end
The following example shows how to configure BGP selective next-hop route filtering to avoid using a BGP prefix as the next-hop route and to ensure that the prefix is more specific than /25.
router bgp 45000 address-family ipv4 unicast bgp nexthop route-map CHECK-BGP25 exit exit ip prefix-list FILTER25 seq 5 permit 0.0.0.0/0 le 25 route-map CHECK-BGP25 deny 10 match ip address prefix-list FILTER25 exit route-map CHECK-BGP25 deny 20 match source-protocol bgp 1 exit route-map CHECK-BGP25 permit 30 end
The following example enables BGP NSF awareness globally on all BGP neighbors. The restart time is set to 130 seconds and the stale path time is set to 350 seconds. The configuration of these timers is optional and the preconfigured default values are optimal for most network deployments.
configure terminal router bgp 45000 bgp graceful-restart bgp graceful-restart restart-time 130 bgp graceful-restart stalepath-time 350 end
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 in the figure below (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 in the figure below (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, 172.21.1.2 at Router C in the figure above, whereas the BGP graceful restart is disabled for the BGP neighbor 172.16.1.2 at Router D in the figure above 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.
router bgp 45000 template peer-session S1 remote-as 40000 ha-mode graceful-restart exit-peer-session template peer-session S2 remote-as 50000 ha-mode graceful-restart disable exit-peer-session bgp log-neighbor-changes bgp graceful-restart restart-time 150 bgp graceful-restart stalepath-time 400 address-family ipv4 unicast neighbor PG1 peer-group neighbor PG1 remote-as 45000 neighbor PG1 ha-mode graceful-restart disable neighbor 172.16.1.2 peer-group PG1 neighbor 172.21.1.2 remote-as 45000 neighbor 172.21.1.2 activate neighbor 172.21.1.2 ha-mode graceful-restart neighbor 192.168.1.2 remote-as 40000 neighbor 192.168.1.2 inherit peer-session S1 neighbor 192.168.3.2 remote-as 50000 neighbor 192.168.3.2 inherit peer-session S2 end clear ip bgp *
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, 192.168.1.2 at Router A 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.
router bgp 45000 bgp log-neighbor-changes bgp graceful-restart address-family ipv4 unicast neighbor PG2 peer-group neighbor PG2 remote-as 40000 neighbor PG2 ha-mode graceful-restart disable neighbor 192.168.1.2 peer-group PG2 end clear ip bgp *
The following example configures BGP dampening to be applied to prefixes filtered through the route-map named ACCOUNTING:
ip prefix-list FINANCE permit 10.0.0.0/8 ! route-map ACCOUNTING match ip address ip prefix-list FINANCE set dampening 15 750 2000 60 exit router bgp 50000 address-family ipv4 bgp dampening route-map ACCOUNTING end
Related Topic |
Document Title |
---|---|
BGP commands: complete command syntax, command mode, defaults, command history, usage guidelines, and examples |
Cisco IOS IP Routing: BGP Command Reference |
Overview of Cisco BGP conceptual information with links to all the individual BGP modules |
"Cisco BGP Overview" module of the IP Routing: BGP Configuration Guide. |
Conceptual and configuration details for basic BGP tasks. |
"Configuring a Basic BGP Network" module of the IP Routing: BGP Configuration Guide. |
Information about SNMP and SNMP operations. |
"Configuring SNMP Support" section of the Cisco IOS Network Management Configuration Guide. |
IPv6--NSF and Graceful Restart for MP-BGP IPv6 Address Family |
"IPv6--NSF and Graceful Restart for MP-BGP IPv6 Address Family" module of the IP Routing: BGP Configuration Guide. |
RFC |
Title |
---|---|
RFC 1657 |
Definitions of Managed Objects for the Fourth Version of the Border Gateway Protocol (BGP-4) using SMIv2 |
RFC 1771 |
A Border Gateway Protocol 4 (BGP-4) |
RFC 1772 |
Application of the Border Gateway Protocol in the Internet |
RFC 1773 |
Experience with the BGP Protocol |
RFC 1774 |
BGP-4 Protocol Analysis |
RFC 1930 |
Guidelines for Creation, Selection, and Registration of an Autonomous System (AS) |
RFC 2519 |
A Framework for Inter-Domain Route Aggregation |
RFC 2858 |
Multiprotocol Extensions for BGP-4 |
RFC 2918 |
Route Refresh Capability for BGP-4 |
RFC 3392 |
Capabilities Advertisement with BGP-4 |
RFC 4724 |
Graceful Restart Mechanism for BGP |
Description |
Link |
---|---|
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
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 www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 1 | Feature Information for Configuring Advanced BGP Features |
Feature Name |
Releases |
Feature Configuration Information |
---|---|---|
BGP Convergence Optimization |
Cisco IOS XE Release 2.1 |
This feature was introduced on the Cisco ASR 1000 Series Routers. |
BGP Graceful Restart per Neighbor |
Cisco IOS XE Release 2.1 |
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. This feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers. The following commands were introduced or modified by this feature: ha-mode graceful-restart, neighbor ha-mode graceful-restart, show ip bgp neighbors. |
BGP Nonstop Forwarding (NSF) Awareness |
Cisco IOS XE Release 2.1 |
Nonstop Forwarding (NSF) awareness allows a router to assist NSF-capable neighbors to continue forwarding packets during a Stateful Switchover (SSO) operation. The BGP Nonstop Forwarding Awareness feature allows an NSF-aware router that is running BGP to forward packets along routes that are already known for a router that is performing an SSO operation. This capability allows the BGP peers of the failing router to retain the routing information that is advertised by the failing router and continue to use this information until the failed router has returned to normal operating behavior and is able to exchange routing information. The peering session is maintained throughout the entire NSF operation. This feature was introduced on the Cisco ASR 1000 Series Routers. The following commands were introduced or modified by this feature: bgp graceful-restart, show ip bgp, show ip bgp neighbors. |
BGP Selective Address Tracking |
Cisco IOS XE Release 2.1 |
The BGP Selective Address Tracking feature introduces the use of a route map for next-hop route filtering and fast session deactivation. Selective next-hop filtering uses a route map to selectively define routes to help resolve the BGP next hop, or a route map can be used to determine if a peering session with a BGP neighbor should be reset when a route to the BGP peer changes. This feature was introduced on the Cisco ASR 1000 Series Routers. The following commands were modified by this feature: bgp nexthop, neighbor fall-over. |
BGP Support for BFD |
Cisco IOS XE Release 2.1 Cisco IOS XE Release 3.5S |
Bidirectional Forwarding Detection (BFD) is a detection protocol designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate, rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning will be easier, and reconvergence time will be consistent and predictable. The main benefit of implementing BFD for BGP is a significantly faster reconvergence time. This feature was introduced on the Cisco ASR 1000 Series Routers. In Cisco IOS XE Release 3.5S, support was added for the Cisco ASR 903 Router. The following commands were introduced or modified by this feature: bfd, neighbor fall-over, show bfd neighbors, show ip bgp neighbors. |
BGP Support for Next-Hop Address Tracking |
Cisco IOS XE Release 2.1 |
The BGP Support for Next-Hop Address Tracking feature is enabled by default when a supporting Cisco IOS XE software image is installed. BGP next-hop address tracking is event driven. BGP prefixes are automatically tracked as peering sessions are established. Next-hop changes are rapidly reported to the BGP routing process as they are updated in the RIB. This optimization improves overall BGP convergence by reducing the response time to next-hop changes for routes installed in the RIB. When a bestpath calculation is run in between BGP scanner cycles, only next-hop changes are tracked and processed. This feature was introduced on the Cisco ASR 1000 Series Routers. The following command was introduced in this feature: bgp nexthop. |
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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.