GLBP Load Balancing Configuration Example

GLBP example with interface tracking

This document provide you the detail steps to configure GLBP between two locations. As we know that we can use GLBP for load balancing between two links or locations, so that there is no dependency on the single link.

If we have two links we can simply configure GLBP and load balancing works. But, if other location also have two links then how we will configure GLBP to achieve the same?

Refer the diagram above, In Core switch there is only one default route towards the router and the gateway will  be the  glbp ip. Now assume, if p2p link of router 1 of site A goes down then traffic will go through the router 2, but from site B they don't know that router 1 of site A is down and they will send traffic through both the router due to the default behavior (round robin) of GLBP and hence some systems from site B will not be able to access site A resources.

To resolve this issue we need to do IP SLA from both the side and need to track its gateway so that if any of the link goes down both the router connected through that link will know that there is no reachability let the traffic to go from other link.

So below is the configuration example

Configuration Details

Detailed Steps

Configuration on router 1

Enabling IP SLA

Steps	Command or Action
Step 1	Ssh or telnet to router
Step 2	Router> enable
Step 3	Router# configure terminal
Step 4	Router(config)# ip sla 1
Step 5	icmp-echo 10.10.1.2 source-interface GigabitEthernet0/1
Step 6	Router(config)# ip sla schedule 1 life forever start-time now

Track ip sla

To track the state of a Cisco IOS IP SLA operation and to enter tracking configuration mode, use the below command on configuration mode 

Step 7

router(config)#track 1 ip sla 1 reachability

GLBP Configuration

Steps	Command or Action
Step 1	Ssh or telnet to router
Step 2	Router> enable
Step 3	Router# configure terminal
Step 4	Router(config)# interface Gi 0/0
Step 5	Router(config)#ip address 10.10.10.9 255.255.255.0
Step 6	Router(config-if)# glbp 10 preempt
Step 7	Router(config-if)# glbp 10 ip 10.10.10.11
Step 8	Router(config-if)# glbp 10 weighting track 1 decrement 100
Step 9	Router(config-if)# exit

Configuration on router 2

Steps	Command or Action
Step 1	Ssh or telnet to router
Step 2	Router> enable
Step 3	Router# configure terminal
Step 4	Router(config)# ip sla 1
Step 5	icmp-echo 10.10.1.1 source-interface GigabitEthernet0/1
Step 6	Router(config)# ip sla schedule 1 life forever start-time now
Step 7	router(config)#track 1 ip sla 1 reachability

GLBP Configuration

Steps	Command or Action
Step 1	Ssh or telnet to router
Step 2	Router> enable
Step 3	Router# configure terminal
Step 4	Router(config)# interface Gi 0/0
Step 5	Router(config)#ip address 10.5.10.9 255.255.255.0
Step 6	Router(config-if)# glbp 10 preempt
Step 7	Router(config-if)# glbp 10 ip 10.5.10.11
Step 8	Router(config-if)# glbp 10 weighting track 1 decrement 100
Step 9	Router(config-if)# exit

Configuration on router 3

Steps	Command or Action
Step 1	Ssh or telnet to router
Step 2	Router> enable
Step 3	Router# configure terminal
Step 4	Router(config)# ip sla 1
Step 5	icmp-echo 10.10.2.1 source-interface GigabitEthernet0/1
Step 6	Router(config)# ip sla schedule 1 life forever start-time now
Step 7	router(config)#track 1 ip sla 1 reachability

GLBP Configuration

Steps	Command or Action
Step 1	Ssh or telnet to router
Step 2	Router> enable
Step 3	Router# configure terminal
Step 4	Router(config)# interface Gi 0/0
Step 5	Router(config)#ip address 10.10.10.10 255.255.255.0
Step 6	Router(config-if)# glbp 10 preempt
Step 7	Router(config-if)# glbp 10 ip 10.10.10.11
Step 8	Router(config-if)# glbp 10 weighting track 1 decrement 100
Step 9	Router(config-if)# exit

Configuration on router 4

Steps	Command or Action
Step 1	Ssh or telnet to router
Step 2	Router> enable
Step 3	Router# configure terminal
Step 4	Router(config)# ip sla 1
Step 5	icmp-echo 10.10.2.1 source-interface GigabitEthernet0/1
Step 6	Router(config)# ip sla schedule 1 life forever start-time now
Step 7	router(config)#track 1 ip sla 1 reachability

GLBP Configuration

Steps	Command or Action
Step 1	Ssh or telnet to router
Step 2	Router> enable
Step 3	Router# configure terminal
Step 4	Router(config)# interface Gi 0/0
Step 5	Router(config)#ip address 10.5.10.10 255.255.255.0
Step 6	Router(config-if)# glbp 10 preempt
Step 7	Router(config-if)# glbp 10 ip 10.5.10.11
Step 8	Router(config-if)# glbp 10 weighting track 1 decrement 100
Step 9	Router(config-if)# exit