Configure "ip dhcp client route track" for Dual ISP Failover on ISR Routers

Introduction

This document describes the procedure to configure dual ISP failover with the use of DHCP on Cisco's Integrated Service Router (ISR) 2900 series.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

This document is not restricted to specific software and hardware versions.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Configure

Network Diagram

Configurations

This setup is useful when you have two ISP's terminate on the router and both get IP addresses via DHCP from the ISP.

CLIENT#sh ip int b 

Interface IP-Address OK? Method Status Protocol
Embedded-Service-Engine0/0 unassigned YES NVRAM administratively down down 
GigabitEthernet0/0 10.106.38.136 YES DHCP up up 
GigabitEthernet0/1 unassigned YES NVRAM up up 
GigabitEthernet0/1.100 1.1.1.4 YES DHCP up up 
GigabitEthernet0/1.200 2.2.2.4 YES DHCP up up 
GigabitEthernet0/2 unassigned YES NVRAM down down 
Loopback0 11.11.11.11 YES NVRAM up up 

interface gigabitethernet 0/1.100 and interface gigabitethernet 0/1.200 are two interfaces which are get dhcp ip address from two ISP's respectively.

interface  gigabitethernet 0/1.100 is primary and interface gigabitethernet 0/1.200 is secondary.

Static Route configurations: 

A secondary route with higher AD value:

ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1.200 dhcp 200
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1.100 dhcp

Interface configuration: 

CLIENT#sh run int GigabitEthernet0/1.100
Building configuration...

Current configuration : 112 bytes
!
interface GigabitEthernet0/1.100
 encapsulation dot1Q 100
 ip dhcp client route track 2         
 ip address dhcp
end

Note: You must configure the ip dhcp client command before you issue the ip address dhcp command on an interface. The ip dhcp client  command is checked only when an IP address is acquired from DHCP. If the ip dhcp client command is issued after an IP address has been acquired from DHCP, it will not take effect until the next time the router acquires an IP address from DHCP.

CLIENT#sh run int GigabitEthernet0/1.200
Building configuration...

Current configuration : 82 bytes
!
interface GigabitEthernet0/1.200
 encapsulation dot1Q 200
 ip address dhcp
end

IP Service Level Agreement (SLA): A route sourcing primary interface is tracked: 

CLIENT#sh run | sec ip sla
track 2 ip sla 2 reachability
ip sla 2
 icmp-echo 11.11.11.11 source-interface GigabitEthernet0/1.100
ip sla schedule 2 life forever start-time now
ip sla auto discovery

CLIENT#sh ip route

C 1.1.1.0/24 is directly connected, GigabitEthernet0/1.100
L 1.1.1.4/32 is directly connected, GigabitEthernet0/1.100
 2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 2.2.2.0/24 is directly connected, GigabitEthernet0/1.200
L 2.2.2.4/32 is directly connected, GigabitEthernet0/1.200

Verify

Use this section in order to confirm that your configuration works properly.

When the track is up, the default gateway points route towards primary: 

CLIENT#sh ip route track-table 
 ip route 0.0.0.0 0.0.0.0 1.1.1.1 254 track 2 state is [up]
 ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1.100 1.1.1.1 track 2 state is [up]

CLIENT#sh ip route

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP

       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 

       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

       E1 - OSPF external type 1, E2 - OSPF external type 2

       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

       ia - IS-IS inter area, * - candidate default, U - per-user static route

       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP

       + - replicated route, % - next hop override



Gateway of last resort is 1.1.1.1 to network 0.0.0.0



S*    0.0.0.0/0 [1/0] via 1.1.1.1, GigabitEthernet0/1.100

      1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C        1.1.1.0/24 is directly connected, GigabitEthernet0/1.100

L        1.1.1.5/32 is directly connected, GigabitEthernet0/1.100

      2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C        2.2.2.0/24 is directly connected, GigabitEthernet0/1.200

L        2.2.2.4/32 is directly connected, GigabitEthernet0/1.200

When the track goes down, default gateway points route towards secondary:

CLIENT#sh ip route track-table 

 ip route 0.0.0.0 0.0.0.0 1.1.1.1 254 track 2 state is [down]

 ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1.100 1.1.1.1 track 2 state is [down]


CLIENT#sh ip route

Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP

       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 

       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

       E1 - OSPF external type 1, E2 - OSPF external type 2

       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

       ia - IS-IS inter area, * - candidate default, U - per-user static route

       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP

       + - replicated route, % - next hop override



Gateway of last resort is 2.2.2.1 to network 0.0.0.0



S*    0.0.0.0/0 [200/0] via 2.2.2.1, GigabitEthernet0/1.200

      1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C        1.1.1.0/24 is directly connected, GigabitEthernet0/1.100

L        1.1.1.5/32 is directly connected, GigabitEthernet0/1.100

      2.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C        2.2.2.0/24 is directly connected, GigabitEthernet0/1.200

L        2.2.2.4/32 is directly connected, GigabitEthernet0/1.200

      10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C        10.106.38.0/24 is directly connected, GigabitEthernet0/0

L        10.106.38.136/32 is directly connected, GigabitEthernet0/0

Troubleshoot

There is currently no specific troubleshooting information available for this configuration.