One-armed LB with Trunk

[cisco123456]

What are the downsides of using a one-armed LB solution? I am trunking multiple VLANs across one interface instead of using multiple interfaces to connect to my server farm. The servers still have their default gateway as the CSS.

[owillins]

The disadvantage of using one armed proxy could be reduction in the performance of the CSS 11000 considerably. The following document discusses the advantages and disadvantages as well as gives configuration details.

http://www.cisco.com/en/US/products/hw/contnetw/ps789/products_configuration_example09186a0080093dff.shtml

[Gilles Dufour]

I would like to add that if you are using a css11000 and not a css11500, you will only use FCB of the port you are using as trunk.

Therefore you limit the number of sessions the device can switch in hardware.

If you using fastethernet and css11000, you will limit the box to approximately 7500 active connection switched in hardware.

Regards,

Gilles.

[richard.troman]

Thee are performance issues if the CSS has to LB over one interface. These should not be under estimated !!

However if you are trunking in to the CSS, you may not have this. It depends on how you configure your "logical" network. You could use one physical interface, but run two vlans over it (a trunk), these vlans are two logical interfaces, so in fact you are not running true one-armed. On CSS the vlans bind to the circuits to form the interfaces, it is only when you are LB over one circuit that you get performance issues.

Hope that made sense :-)

[Gilles Dufour]

Richard, sorry, but I have to disagree with you.

The performance issue is linked to the FCB usage which determines how traffic is switched in hardware.

So, the impact occurs when you are using only 1 physical interface [even if trunking].

See my previous post.

Gilles.