2 x 6509 running HSRP, VMware, MS TMG Array with NLB

[cornwallcollege]

We have a pair of 6509 switches (running HSRP) which have redundant trunk paths to our VMware servers.

There are 2 TMG boxes as guests on the VMware hosts currently using unicast NLB.

I was looking into NLB Multicast but found out (http://etherealmind.com/cisco-load-balancing-blue-coat-sgos/)
that our 6509's also support SLB. This seems like a better option but I was wondering how we go about configuring SLB to work with a pair of 6509s?

We would then be looking to get rid of NLB and get the 6509s to balance the traffic instead.

Hopefully someone here can advise...

Many thanks.

[Giuseppe Larosa]

Hello Cornwallcollege,

be aware that IP SLB is performed in software by using supervisor cpu resources.

This is explained in the link that you have provided:

"The IOS SLB feature in the C6500 performs well in excess of 500 Megabits per second in my experience on a Supervisor 720 at about 30% CPU utilisation. This suggests that peak performance could be much higher. On a Supervisor II I have seen up to 200 Mbps at about 25% average CPU, again implying a much higher maximum or peak rate."

So you need to understand the traffic volume of your traffic if it is within those figures you are fine, if traffic to be load balanced can be more then 1 Gbps I would suggest to avoid to use it.

How to use with two devices:  you should use HSRP groups in all vlans including server vlans with one C6500 the master in all groups so that it can perform the load balancing action

Hope to help

Giuseppe

[cornwallcollege]

Hi Giuseppe,

Thanks for the reply. From what I've read SLB can operate in 2 modes - directed and dispatched mode.

Although dispatched mode would be preferable given the lower resource usage I don't believe it would be the correct option for us - correct me if I'm wrong though. As we've got 2 6509s (Sup 720s) running HSRP for their Vlans and the VMware guest could be routed through either core - I presume we will need to run directed mode. The destination IP header rewrite and CRC recalculation shouldn't be an issue as we are well withing the limits described in the article.

Am I correct in thinking that we will need to place the same config on both 6509 switches and also that there are no additional commands we need to use as we're running HSRP? Something like this...

Router(config)# ip slb serverfarm serverfarm-name
Router(config-slb-sfarm)# real IP_address_core_a
Router(config-slb-real)# inservice
Router(config-slb-sfarm)# real IP_address_core_b
Router(config-slb-real)# inservice
Router(config)# ip slb vserver virtual-server-name
Router(config-slb-vserver)# serverfarm serverfarm-name
Router(config-slb-vserver)# virtual IP_address tcp 80
Router(config-slb-vserver)# inservice

Thanks.

[Giuseppe Larosa · Accepted solution]

Hello Cornwallcollege,

my practical experience is with service modules CSM and ACE inserted in C6509 chassis.

IOS SLB is very similar to configuration for CSM module.

>> Am I correct in thinking that we will need to place the same config on both 6509 switches and also that there are no additional commands we need to use as we're running HSRP?

I agree the same list of real servers, serverfarm and virtual server and so on should be configured on both C6509

for example see

http://www.cisco.com/en/US/docs/ios-xml/ios/slb/configuration/12-4t/Configuration_Examples_for_IOS_SLB.html#GUID-31F00EB3-AB9F-4E1F-BD7E-BAF626C82AFD

Directed mode if the virtual server is not known to real servers

see

http://www.cisco.com/en/US/docs/ios-xml/ios/slb/configuration/12-4t/Information_About_Cisco_IOS_SLB.html

Hope to help

Giuseppe

[cornwallcollege]

Hi Giuseppe,

Many thanks for your reply.