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.
set ip next-hop 172.16.0.1
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
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:
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.
set ip next-hop 172.16.0.1
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
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:
neighbor 192.168.0.1 activate
neighbor 192.168.0.1 ebgp-multihop 255
neighbor 192.168.0.1 next-hop-unchanged
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.
|
Copyright © 2005 Cisco Systems, Inc. All rights reserved.
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