Table Of Contents

BGP Next Hop Propagation

Finding Feature Information

Contents

Prerequisites for BGP Next Hop Propagation

Restrictions for BGP Next Hop Propagation

Information About Next Hop Propagation

BGP Next Hop Propagation Overview

Benefits of BGP Next Hop Propagation

How to Configure BGP Next Hop Propagation

Configuring the Route Reflector

Restrictions

Examples

What to Do Next

Configuring the Route Reflector Client

Examples

What to Do Next

Verifying BGP Next Hop Propagation

Configuration Examples for BGP Next Hop Propagation

Router Reflector: Example

Router Reflector Client: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for BGP Next Hop Propagation

BGP Next Hop Propagation

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First Published: 2005

Last Updated: May 4, 2009

The BGP Next Hop Propagation feature provides additional flexibility when designing and migrating networks. The BGP Next Hop Propagation feature allows a route reflector to modify the next hop attribute for a reflected route and allows Border Gateway Protocol (BGP) to send an update to an external BGP (eBGP) multihop peer with the next hop attribute unchanged.

Finding Feature Information

For the latest feature information and caveats, see 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 for BGP Next Hop Propagation" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for BGP Next Hop Propagation

•Restrictions for BGP Next Hop Propagation

•Information About Next Hop Propagation

•How to Configure BGP Next Hop Propagation

•Configuration Examples for BGP Next Hop Propagation

•Additional References

•Feature Information for BGP Next Hop Propagation

Prerequisites for BGP Next Hop Propagation

•BGP peering has been established, and the next hop is accessible.

Restrictions for BGP Next Hop Propagation

•BGP Next Hop Propagation can be configured only between multihop eBGP peers. The follow error message will be displayed if you attempt to configure this feature for a directly connect neighbor:

%BGP: Can propagate the nexthop only to multi-hop EBGP neighbor

•Do not use the neighbor next-hop-self command to modify the next hop attribute for a route reflector when this feature is enabled for a route reflector client. Using the neighbor next-hop-self command on the route reflector will modify next hop attributes only for routes that are learned from eBGP peers and not the intended routes that are being reflected from the route reflector clients. To modify the next hop attribute when reflecting a route, use an outbound route map.

Information About Next Hop Propagation

This section contains the following concepts:

•BGP Next Hop Propagation Overview

•Benefits of BGP Next Hop Propagation

BGP Next Hop Propagation Overview

The BGP Next Hop Propagation feature provides additional flexibility when designing and migrating networks. The BGP Next Hop Propagation feature allows a route reflector to modify the next hop attribute for a reflected route and allows BGP to send an update to an eBGP multihop peer with the next hop attribute unchanged.

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Caution Incorrectly setting BGP attributes for a route reflector can cause inconsistent routing, routing loops, or a loss of connectivity. Setting BGP attributes for a route reflector should be attempted only by an experienced network operator.

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The configuration of this feature in conjunction with the iBGP Multipath Load Sharing feature allows you to use an outbound route map to include BGP route reflectors in the forwarding path.

Benefits of BGP Next Hop Propagation

The BGP Next Hop Propagation feature allows you to perform the following tasks:

•Bring the route reflector into the forwarding path, which can be used with the iBGP Multipath Load Sharing feature to configure load balancing.

•Configure interprovider Multiprotocol Label Switching (MPLS) Virtual Private Networks (VPNs) by not modifying the next hop attribute when advertising routes to an eBGP peer.

•Turn off the next hop calculation for an eBGP peer. This feature is useful for configuring the end-to-end connection of a label-switched path.

How to Configure BGP Next Hop Propagation

The first two tasks in this section are required, the third task is optional.

•Configuring the Route Reflector (required)

•Configuring the Route Reflector Client (required)

•Verifying BGP Next Hop Propagation (optional)

Configuring the Route Reflector

In this section, the following tasks are completed:

•A route map is created to set the next hop that will be advertised to the router reflector client. The route map is applied only to outbound routes.

•eBGP peering is configured with the route reflector client.

Restrictions

Do not use the neighbor next-hop-self command to modify the next hop attribute for a route reflector when this feature is enabled for a route reflector client.

SUMMARY STEPS

1. enable

2. configure terminal

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

4. set ip next-hop ip-address [peer-address]

5. exit

6. router bgp as-number

7. address-family ipv4 [mdt | multicast | tunnel | unicast [vrf vrf-name] | vrf vrf-name]

8. neighbor ip-address activate

9. neighbor ip-address ebgp-multihop ttl

10. neighbor ip-address route-reflector-client

11. neighbor ip-address route-map map-tag in | out

12. end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	route-map map-tag [permit | deny] [sequence-number] Example: Router(config)# route-map NEXTHOP	Enter route map configuration mode to create or configure a route map. •The route map is create to set the next hop for the route reflector client.
Step 4	set ip next-hop ip-address [peer-address] Example: Router(config-route-map)# set ip next-hop 172.16.0.1	Specifies the next hop.
Step 5	exit Example: Router(config-route-map)# exit	Exits route-map configuration mode, and enters global configuration mode.
Step 6	router bgp as-number Example: Router(config)# router bgp 65535	Enters router configuration mode, and creates a BGP routing process.
Step 7	address-family ipv4 [mdt | multicast | tunnel | unicast [vrf vrf-name] | vrf vrf-name] Example: Router(config-router-af)# address-family ipv4	Enters address family configuration mode to configure BGP peers to accept address family specific configurations.
Step 8	neighbor ip-address activate Example: Router(config-router-af)# neighbor 10.0.0.100 activate	Enables the exchange of information with the address family peer.
Step 9	neighbor ip-address ebgp-multihop ttl Example: Router(config-router-af)# neighbor 10.0.0.100 ebgp-multihop 255	Configures the local router to accept and initiate connections to external peers that reside on networks that are not directly connected.
Step 10	neighbor ip-address route-reflector-client Example: Router(config-router-af)# neighbor 10.0.0.100 route-reflector-client	Configures the local router as a BGP route reflector, and configures the specified neighbor as a route-reflector client.
Step 11	neighbor ip-address route-map map-name out Example: Router(config-router-af)# neighbor 10.0.0.100 route-map NEXTHOP out	Applies the route map to outgoing routes.
Step 12	end Example: Router(config-router-af)# end	Exits address family configuration mode, and enters privileged EXEC mode.

Examples

The following example, starting in global configuration mode, configures the local router as a route reflector and configures the 10.0.0.100 multihop peer as a route reflector client. A route map is created to set the advertised next hop to 172.16.0.1.

route-map NEXTHOP 

 set ip next-hop 172.16.0.1 

 exit 

router bgp 65535

 address-family ipv4

 neighbor 10.0.0.100 activate 

 neighbor 10.0.0.100 ebgp-multihop 255

 neighbor 10.0.0.100 route-reflector-client

 neighbor 10.0.0.100 route-map NEXTHOP out

 end

What to Do Next

To complete this configuration, the neighbor next-hop-unchanged command is configured on the route reflector client. Proceed to the next section to see more information.

Configuring the Route Reflector Client

In this section, the following tasks are completed:

•eBGP peering is configured with the route reflector.

•The route-reflector client is configured to propagate the next hop unchanged.

SUMMARY STEPS

1. enable

2. configure terminal

3. router bgp as-number

4. address-family ipv4 [mdt | multicast | tunnel | unicast [vrf vrf-name] | vrf vrf-name]

5. neighbor ip-address activate

6. neighbor ip-address ebgp-multihop ttl

7. neighbor ip-address next-hop-unchanged

8. end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	router bgp as-number Example: Router(config)# router bgp 65412	Enters router configuration mode, and creates a BGP routing process.
Step 4	address-family ipv4 [mdt | multicast | tunnel | unicast [vrf vrf-name] | vrf vrf-name] Example: Router(config-router-af)# address-family ipv4	Enters address family configuration mode to configure BGP peers to accept address family specific configurations.
Step 5	neighbor ip-address activate Example: Router(config-router-af)# neighbor 192.168.0.1 activate	Enables the exchange of information with the address family peer.
Step 6	neighbor ip-address ebgp-multihop ttl Example: Router(config-router-af)# neighbor 192.168.0.1 ebgp-multihop 255	Configures the local router to accept and initiate connections to external peers that reside on networks that are not directly connected.
Step 7	neighbor ip-address next-hop-unchanged Example: Router(config-router-af)# neighbor 192.168.0.1 next-hop-unchanged	Configures the router to send BGP updates to BGP peers without modifying the next hop attribute.
Step 8	end Example: Router(config-router-af)# end	Exits address family configuration mode, and enters privileged EXEC mode.

Examples

The following example, starting in global configuration mode, configures the local router (route-reflector client) to establish peering with the route reflector and to propagate the next hop unchanged:

router bgp 65412

 address-family ipv4

 neighbor 192.168.0.1 activate 

 neighbor 192.168.0.1 ebgp-multihop 255

 neighbor 192.168.0.1 next-hop-unchanged 

 end

What to Do Next

Proceed to the next section to see commands that can be used to verify the configuration of the BGP Next Hop Propagation feature.

Verifying BGP Next Hop Propagation

The configuration of the BGP Next Hop Propagation feature can be verified with the show ip bgp neighbors command.

SUMMARY STEPS

1. enable

2. show ip bgp neighbors [neighbor-address] [received-routes | routes | advertised-routes | {paths regexp} | dampened-routes | received prefix-filter]]

3. show ip bgp [network] [network-mask] [longer-prefixes] [prefix-list prefix-list-name | route-map route-map-name] [shorter prefixes mask-length]

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	show ip bgp neighbors [neighbor-address] [received-routes | routes | advertised-routes | {paths regexp} | dampened-routes | received prefix-filter]] Example: Router# show ip bgp neighbors	Displays information about the TCP and BGP connections to neighbors. The output will display the status of the BGP Next Hop Propagation feature.
Step 3	show ip bgp [network] [network-mask] [longer-prefixes] [prefix-list prefix-list-name | route-map route-map-name] [shorter prefixes mask-length] Example: Router# show ip bgp	Displays entries in the BGP routing table. The displayed output will indicate if the neighbor next-hop-unchanged command has been configured for the selected address.

Configuration Examples for BGP Next Hop Propagation

The following examples show how to configure this feature:

•Router Reflector: Example

•Router Reflector Client: Example

Router Reflector: Example

The following example, starting in global configuration mode, configures the local router as a route reflector and configures the 10.0.0.100 multihop peer as a route reflector client. A route map is created to set the advertised next hop to 172.16.0.1.

route-map NEXTHOP 

 set ip next-hop 172.16.0.1 

 exit 

router bgp 65535

 address-family ipv4

 neighbor 10.0.0.100 activate 

 neighbor 10.0.0.100 ebgp-multihop 255

 neighbor 10.0.0.100 route-reflector-client

 neighbor 10.0.0.100 route-map NEXTHOP out

 end

Router Reflector Client: Example

The following example, starting in global configuration mode, configures the local router (route-reflector client) to establish peering with the route reflector and to propagate the next hop unchanged:

router bgp 65412

 address-family ipv4

 neighbor 192.168.0.1 activate 

 neighbor 192.168.0.1 ebgp-multihop 255

 neighbor 192.168.0.1 next-hop-unchanged 

 end 

Additional References

The following sections provide references related to the BGP Next Hop Propagation feature.

Related Documents

Related Topic	Document Title
BGP commands and configuration tasks—The BGP Next Hop Propagation feature is an extension of the BGP routing protocol. Information is included about configuring BGP, route reflectors, route summarization, and filtering.	Cisco IOS IP Routing Protocols Command Reference
iBGP multipath loadsharing—For internal BGP (iBGP) multipath load-sharing configuration and command reference information.	iBGP Multipath Load Sharing
Cisco IOS master command list, all  releases	Cisco IOS Master Command List, All Releases

Standards

Standards	Title
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.	—

MIBs

MIBs	MIBs Link
No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.	To locate and download MIBs for selected platforms, Cisco IOS XE software releases, and feature sets, use Cisco MIB Locator found at the following URL: http://www.cisco.com/go/mibs

RFCs

RFCs	Title
No new or modified RFCs are supported by this feature, and support for existing standards has not been modified by this feature.	—

Technical Assistance

Description

Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies. To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds. Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport

Feature Information for BGP Next Hop Propagation

Table 1 lists the features in this module and provides links to specific configuration information.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

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Note Table 1 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.

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Table 1 Feature Information for BGP Next Hop Propagation 

Feature Name	Releases	Feature Information
BGP Next Hop Propagation	Cisco IOS XE Release 2.1	This feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.

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