IP Routing: EIGRP Configuration Guide, Cisco IOS XE Fuji 16.9.x
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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
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Prerequisites for Add Path Support in EIGRP
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-paths command 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.
Restrictions for Add Path Support in EIGRP
The Add Path Support in EIGRP feature can be enabled only in Enhanced Interior Gateway Routing Protocol (EIGRP) named mode
variance command should not be configured when the Add Path Support in EIGRP feature is enabled. The
variance command alters the metrics of routes in an EIGRP topology, thereby enabling EIGRP to balance traffic among desired paths.
Therefore, if you configure the
variance command on a hub device, the command may interfere with the configuration of this feature.
Information About Add Path Support in EIGRP
EIGRP Add Path Support Overview
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
How Add Path Support in EIGRP Works
A typical single Dynamic Multipoint VPN (DMVPN) domain consists of dual hubs (for hub redundancy) connected to more than one
service provider (for service-provider redundancy). In the figure below, two hub devices—Hub-1 and Hub-2—are connected through
tunnel interfaces to a DMVPN domain.
The DMVPN domain is in turn connected to two service providers—Service-Provider 1 and Service-Provider 2. Four spoke devices
in this DMVPN domain—Spoke-1, Spoke-2, Spoke-3, and Spoke-4. Spoke-1 and Spoke-3 are connected to Service-Provider 1, and
Spoke-2 and Spoke-4 are connected to Service-Provider 2. The Enhanced Interior Gateway Routing Protocol (EIGRP) is the routing
protocol between the hubs and the spokes over the tunnel interfaces.
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
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
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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.
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Table 1. Feature Information for Add
Path Support in EIGRP
Support in EIGRP
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.
command was introduced or modified: