IOS SLB versus CSM

[amorgos]

Hi,

trying to figure out a possible solution for a 6500 and got a bit confused. According to my knowledge, IOS SLB is working either in L2 (MAC) or L3/4 (NAT), to ensure load balancing. CSM comes in the game, but offers much more, extending to L4/7. Are the two solutions substitude or complementary? Is it true that only with an CSM can you get HTTP probes to check your load balanced server farm? What other differences do you know about these two solutions?

In the paper http://www.cisco.com/en/US/partner/products/hw/modules/ps2706/products_configuration_example09186a0080094066.shtml

it is stated that "To run Cisco IOS SLB software, you must configure the mode using the show ip slb mode [csm | rp] command before any configuration. In the show ip slb mode command, the rp argument is default. You can only configure csm argument if you have the Content Switching Module (CSM)."

While in

http://www.cisco.com/en/US/partner/products/hw/modules/ps2706/products_configuration_example09186a008009452d.shtml

cisco states that "You cannot run Cisco IOS® SLB software on the same switch as the CSM."

Any ideas on that?

Thanks in advance

[Gilles Dufour]

there are 2 ways to configure the csm.

You can use the same ios slb command and just tell the switch that there is a csm with the command 'ip slb mode'.

Or you can use the 'module contentswitching ' command.

If you use the first method, you can't use both a CSM and ios slb on the same switch.

If you use the second method, it is ok to have both ios slb and csm.

IOS SLB offers L4-7 loadbalancing solution.

Just be aware that as soon as you do L7 or do some nating, you poor performance with ios slb compare to a CSM.

One advantage of ios slb is the capacity to do radius loadbalancing [inspecting radius packet to identify framed ip, ...]

This is why in CMX solution we combine both ios slb and csm.

IOS SLB is used to loadbalance radius and the CSM is used to loadbalance the rest of the traffic.

Personally, I would say if you just need some vpn or firewall loadbalancing, ios slb is enough.

If you need HTTP or any other traffic wthe CSM is a better choice.

Regards,

Gilles.

[seilsz]

IOS SLB is only intended for low volume load balancing with very limited functionality. The two (2) solutions are worlds apart from a performance perspective, and as you've read, the CSM has many, many more features (including HTTP probes for checking server availability).

Regarding your second question, it is possible to have both IOS SLB and the CSM running at the same time in the same 6500. To do that, you need to have the following command configured, which is the default:

ip slb mode rp

~Zach