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BGP Next Hop Propagation

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BGP Next Hop Propagation

Table Of Contents

BGP Next Hop Propagation

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

Command Reference

neighbor next-hop-unchanged


BGP Next Hop Propagation


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.

Feature History for BGP Next Hop Propagation

Release
Modification

12.0(16)ST

This feature was introduced.

12.2

This feature was integrated into Cisco IOS Release 12.2.

12.2(14)S

This feature was integrated into Cisco IOS Release 12.2(14)S.

12.0(22)S

This feature was integrated into Cisco IOS Release 12.0(22)S.


Finding Support Information for Platforms and Cisco IOS Software Images

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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

Command Reference

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.


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.

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

This section contains the following procedures:

Configuring the Route Reflector (required)

Configuring the Route Reflector Client (required)

Configuring the Route Reflector Client (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 

neighor 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

Enter 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 activate

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 EXEC 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. For more information about configuring BGP, route reflectors, route summarization, and filtering, refer to the Cisco IOS IP Routing Configuration Guide and the Cisco IOS IP Command Reference, Volume 2 of 4: Routing Protocols.

Cisco IOS IP Command Reference, Volume 2 of 4: Routing Protocols, Release 12.3T

Cisco IOS IP Configuration Guide, Release 12.3

iBGP multipath loadsharing—For internal BGP (iBGP) multipath load-sharing configuration and command reference information, refer to the iBGP Multipath Load Sharing feature document in the "New Features in Release 12.2(1)T" area of Cisco.com.

iBGP Multipath Load Sharing


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 obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at the following URL:

http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml


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

Technical Assistance Center (TAC) home page, containing 30,000 pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

http://www.cisco.com/public/support/tac/home.shtml


Command Reference

This section documents new commands. All other commands used with this feature are documented in the Cisco IOS command reference publications.

neighbor next-hop-unchanged

neighbor next-hop-unchanged

To enable an external BGP (eBGP) multihop peer to propagate the next hop unchanged, use the neighbor next-hop-unchanged command in address family or router configuration mode. To disable next hop propagation capabilities, use the no form of this command.

neighbor ip-address | peer-group-name next-hop-unchanged

no neighbor ip-address | peer-group-name next-hop-unchanged

Syntax Description

ip-address

The IP address of the next hop.

peer-group-name

The name of a BGP peer group that is the next hop.


Defaults

No default behavior or values

Command Modes

Address family configuration
Router configuration

Command History

Release
Modification

12.0(16)ST

This command was introduced.

12.2

This command was integrated into Cisco IOS Release 12.2.

12.2(14)S

This command was integrated into Cisco IOS Release 12.2(14)S.

12.0(22)S

This command was integrated into Cisco IOS Release 12.0(22)S.


Usage Guidelines

The neighbor next-hop-unchanged command is used to configured the propagate the next hop unchanged for multihop eBGP peering sessions. This command should not be configured on a route reflector, and the neighbor next-hop-self command should not be used to modify the next hop attribute for a route reflector when this feature is enabled for a route reflector client.

This command can be used 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.


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.

Examples

Route Reflector Configuration

In the following example, the local router is configured 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.

Router(config)# route-map NEXTHOP 
Router(config-route-map)# set ip next-hop 172.16.0.1 
Router(config-route-map)# exit 
Router(config)# router bgp 65534 
Router(config-router)# neighbor 10.0.0.100 remote-as 65412 
Router(config-router)# address-family ipv4 
Router(config-router-af)# neighbor 10.0.0.100 activate 
Router(config-router-af)# neighbor 10.0.0.100 ebgp-multihop 255 
Router(config-router-af)# neighbor 10.0.0.100 route-reflector-client 
Router(config-router-af)# neighbor 10.0.0.100 route-map NEXTHOP out 
Router(config-router-af)# end 

Route Reflector Client Configuration

In the following example, the local router (route-reflector client) is configured to establish peering with the route reflector and to propagate the next hop unchanged:

Router(config)# router bgp 65412 
Router(config-router)# neighbor 192.168.0.1 remote-as 65412 
Router(config-router)# address-family ipv4 
Router(config-router-af)# neighbor 192.168.0.1 activate 
Router(config-router-af)# neighbor 192.168.0.1 ebgp-multihop 255 
Router(config-router-af)# neighbor 192.168.0.1 next-hop-unchanged 
Router(config-router-af)# end 

Related Commands

Command
Description

address-family ipv4

Enters address family configuration mode for configuring routing sessions, such as BGP, RIP, or static routing sessions, that use standard IPv4 address prefixes.

address-family vpnv4

Enters address family configuration mode for configuring routing sessions, such as BGP, RIP, or static routing sessions, that use standard VPNv4 address prefixes.

neighbor ebgp-multihop

Accepts and attempts BGP connections to external peers residing on networks that are not directly connected.

neighbor route-map

Applies a route map to incoming or outgoing routes.

neighbor route-reflector-client

Configures the router as a BGP route reflector and configures the specified neighbor as its client.