I did a pretty cool little thing today with two 3750 Cisco switches. I have a customer that has two 3750s setup as a redundant core. If one fails, the other takes over. Its called HSRP, and it works pretty well. However, I noticed that on the primary (active) 3750, the cpu utilization was really at various times. So, I thought I would separate the traffic as best as I could so that the primary took most of the vlans and the secondary took one vlan in particular (vlan 102). I happened to know for sure that vlan 102 had a ton of traffic on it, so I made my decision based on that. So, instead of the primary taking all the heat while the secondary sat idle waiting on a failed primary, I decided to load share them. Here is what the config looks like:
*****PRIMARY SWITCH*****:
interface Vlan10 <----------- Active vlan on Primary
description 1st floor
ip address 10.232.10.250 255.255.255.0 <----------- Real IP address of vlan interface
no ip redirects
standby 10 ip 10.232.10.254 <------------ Virtual IP address shared between Primary and Secondary for vlan 10
standby 10 timers 3 7 <----------- Send hellos every 3 seconds, switch over to secondary after 7 seconds
standby 10 priority 110 <----------- Notice the priority command for vlan 10, higher than the default of the secondary switch
interface Vlan102 <----------- Not Active vlan on Primary
description 2nd floor
ip address 10.10.2.254 255.255.252.0 <----------- Real IP address of vlan interface
standby 102 ip 10.10.2.1 <------------ Virtual IP address shared between Primary and Secondary for vlan 102
*****SECONDARY SWITCH*****:
interface Vlan10 <----------- Not Active vlan on Secondary
description 1st floor
ip address 10.232.10.251 255.255.255.0 <----------- Real IP address of vlan interface
no ip redirects
standby 10 ip 10.232.10.254 <------------ Virtual IP address shared between Primary and Secondary for vlan 10
standby 10 timers 3 7
interface Vlan102 <----------- Active vlan on Secondary
description 2nd floor
ip address 10.10.2.253 255.255.252.0 <----------- Real IP address of vlan interface
standby 102 ip 10.10.2.1 <------------ Virtual IP address shared between Primary and Secondary for vlan 102
standby 102 timers 3 7 <----------- Send hellos every 3 seconds, switch over to secondary after 7 seconds
standby 102 priority 120 <----------- Notice the priority command for vlan 102, higher than the default of the primary switch
I like this. So lets look at the "show standby brief" command for both:
*****PRIMARY SWITCH*****
pricoreswitch#sho stand bri
P indicates configured to preempt.
|
Interface Grp Prio P State Active Standby Virtual IP
Vl10 10 110 P Active local 10.232.10.251 10.232.10.254 <-------------- Active
Vl102 102 100 Standby 10.10.2.253 local 10.10.2.1 <-------------- NOT Active
*****SECONDARY SWITCH*****
seccoreswitch#sh standby bri
P indicates configured to preempt.
|
Interface Grp Prio P State Active Standby Virtual IP
Vl10 10 100 Standby 10.232.10.250 local 10.232.10.254 <-------------- NOT Active
Vl102 102 120 P Active local 10.10.2.254 10.10.2.1 <-------------- Active
Now, we have a "load sharing" scenario between the two HSRP 3750 switches. Very cool.
Oh wait, what happens if I power down a switch? Well, here is what happens when I powered down the secondary 3750:
*****PRIMARY SWITCH*****
pricoreswitch#sho stand bri
P indicates configured to preempt.
|
Interface Grp Prio P State Active Standby Virtual IP
Vl10 10 110 P Active local 10.232.10.251 10.232.10.254 <-------------- Active
Vl102 102 120 P Active local 10.10.2.253 10.10.2.1 <-------------- Active
Secondary was powered off, so no readings there. Just like a real failure.
