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The Add Path Support in EIGRP feature enables hubs in a single Dynamic Multipoint VPN (DMVPN) domain to advertise multiple best paths to connected spokes when the Enhanced Interior Gateway Routing Protocol (EIGRP) is the routing protocol between the hubs and the spokes. This module provides information about the Add Path Support in EIGRP feature and explains how to configure it.
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.
All interfaces in an Enhanced Interior Gateway Routing Protocol (EIGRP) topology are by default configured with the next-hop-self command. This command enables EIGRP to set the local outbound interface as the next-hop value while advertising a route to a peer, even when advertising routes out of the interface on which the routes were learned. This default EIGRP behavior may interfere with the add-pathscommand that helps configure the Add Path Support in EIGRP feature. Therefore, before you configure this feature on a hub device in a Dynamic Multipoint VPN (DMVPN) domain, you must disable the next-hop-self command that is configured on the hub interface that connects to spokes in the DMVPN domain.
In most Dynamic Multipoint VPN (DMVPN) domains, two or more spokes are connected to the same LAN segment. These spokes connect to more than one hub (for hub redundancy) through different service providers (for service-provider redundancy). In a single DMVPN domain, a hub connects to all spokes through one tunnel interface. In Enhanced Interior Gateway Routing Protocol (EIGRP) topologies, when a hub has more than one path (with the same metric but through different spokes) to reach the same network, both paths are chosen as best paths. However, by default, EIGRP advertises only one path as the best path to connected spokes. With the implementation of the Add Path Support in EIGRP feature, hubs in an EIGRP-DMVPN domain can advertise up to four additional best paths to connected spokes, thereby allowing load balancing and path redundancy. This feature supports both IPv4 and IPv6 configurations.
Spoke-1 and Spoke-2 are connected to a LAN with the network address 192.168.1.0/24. Both these spokes are connected to both the hubs through two different service providers, and hence, these spokes advertise the same LAN network to both hubs. Typically, spokes on the same LAN advertise the same metric; therefore, based on the metric, Hub-1 and Hub-2 have dual Equal-Cost Multipath (ECMP) routes to reach network 192.168.1.0/24. However, because EIGRP is a distance vector protocol, it advertises only one best path to the destination. Therefore, in this EIGRP-DMVPN domain, the hubs advertise only one route (for example, through Spoke-1) to reach network 192.168.1.0/24. When clients in subnet 192.168.2.0/24 communicate with clients in subnet 192.168.1.0/24, all traffic is directed to Spoke-1. Because of this default EIGRP behavior, there is no load balancing on Spoke-3 and Spoke-4. Additionally, if Spoke-1 fails or if the network of Service-Provider 1 goes down, EIGRP must reconverge to provide connectivity to 192.168.1.0/24.
The Add Path Support in EIGRP feature enables EIGRP to advertise up to four additional paths to connected spokes in a single DMVPN domain. If you configure this feature in the example topology discussed above, both Spoke-1 and Spoke-2 will be advertised to Spoke-3 and Spoke-4 as best paths to network 192.168.1.0, thereby allowing load balancing among all spokes in this DMVPN domain.
1.
enable
2.
configure
terminal
3.
router
eigrp
virtual-name
4.
address-family
ipv4
autonomous-system as-number
5.
af-interface
{default
| interface-type interface-number}
6.
no next-hop-self
[no-ecmp-mode]
7.
add-paths
number
8.
end
9.
show
running-config
1.
enable
2.
configure
terminal
3.
ipv6
unicast-routing
4.
router
eigrp
virtual-name
5.
address-family
ipv6
autonomous-system as-number
6.
af-interface {default
| interface-type interface-number}
7.
no next-hop-self
[no-ecmp-mode]
8.
add-paths
number
9.
end
10.
show
running-config
Device(config)# router eigrp name Device(config-router)# address-family ipv4 autonomous-system 10 Device(config-router-af)# af-interface tunnel 0 Device(config-router-af-interface)# no next-hop-self no-ecmp-mode Device(config-router-af-interface)# add-paths 4 Device(config-router-af-interface)# end
Device(config)# ipv6 unicast-routing Device(config)# router eigrp name Device(config-router)# address-family ipv6 autonomous-system 10 Device(config-router-af)# af-interface tunnel 0 Device(config-router-af-interface)# no next-hop-self no-ecmp-mode Device(config-router-af-interface)# add-paths 4 Device(config-router-af-interface)# end
Related Topic |
Document Title |
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Cisco IOS commands |
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EIGRP commands |
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EIGRP FAQ |
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EIGRP technology white papers |
Description |
Link |
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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.
Feature Name |
Releases |
Feature Information |
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Add Path Support in EIGRP |
Cisco IOS XE Release 3.8S 15.2(1)E |
The Add Path Support in EIGRP feature enables a hub in a single Dynamic Multipoint VPN (DMVPN) domain to advertise multiple paths to connected spokes when the Enhanced Interior Gateway Routing Protocol (EIGRP) is the routing protocol between the hub and the spokes. The following command was introduced or modified: add-paths. |