What is IP Nexthop-List?

The next hop IP is the IP address of a nearby router or other device connected to the controller at Layer 2. If the controller uses policy-based routing to forward packets to the next-hop device and the device goes offline, packets that match the policy do not reach their destination. The next-hop list provides redundancy for next-hop devices by redirecting traffic to a backup next-hop device in the event of a failure. Traffic that matches a policy-based routing ACL is routed through the active next-hop in the list with the highest precedence when the active next-hop device in the list becomes inaccessible.

There can be up to four next hops in a next hop list. The sequence in which the next hops are selected can be determined by assigning a priority to each subsequent hop. The next highest priority active next hop is chosen for forwarding if the higher priority next-hop fails. The order is decided by the configuration of the following hops if all next hops are provided with the same priority. Traffic will be forwarded using conventional destination-based forwarding if all future hops are unavailable.

The default route uses only one of the following uplink hops to forward packets in typically multiple uplink deployment scenarios. If the next hop becomes inaccessible, packets will not reach it. If your implementation uses policy-based routing based on next-hop lists, any uplink next-hop can be used to forward traffic. For this to work, all next hops for policy-based routing must have valid ARP (route cache) entries in the system.

Site uplink can use DHCP to obtain IP addresses and default gateways in branch controller configuration. For such deployments, the VLAN ID for the uplink VLAN can be used to set up the next hop list. When a VLAN gets its IP address via DHCP and the VLAN interface determines the default gateway, the IP address of the gateway is used as the next hop IP address. Additionally, branch office deployments may require policy-based traffic redirection to different VPN tunnels. Select IPsec mapping from the Next Hop list to route traffic through the IPsec tunnel.

IP next-hop List:

Syntax:

ip nexthop-list <string>

ip {<ip-adddr>}|{dhcp vlan <id>} priority <0-255>

ipsec-map <name>

preemptive-failover

Parameter	Description
<name>	The nexthop list’s name.
ip <ip-addr>	Subsequent (next-hop) device IP address
ip dhcp vlan <id>	The next-hop device VLAN ID is: When a VLAN gets its IP address via DHCP and the VLAN interface determines the default gateway, the IP address of the gateway is used as the next hop IP address.
ipsec-map <map_name>	You can use ipsec map name to redirect packets through VPN tunnel.
preemptive-failover	The status of preemptive failover is displayed as Enabled or Disabled in this column. When preemption is enabled, packets are resent to the next hop with higher priority, making that next hop reachable again.

Example:

A list of next hops can be configured with the following command.

(host)(config)# ip nexthop-list list1
(host)(config-nexthop-list)#ip 10.1.1.41 priority 1
(host)(config-nexthop-list)#ip 172.21.18.170 priority 2
(host)(config-nexthop-list)#ip 192.18.140.20 priority 3