Load balancers...!

Answered Question

Hi Gurus,

I have one load balancers which has to load balance the traffic between two servers which are replica of each other. Kindly let me know how can i connect the load balancer to the switch and servers.

--gaurav

I have this problem too.
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Correct Answer by Konstantin Dunaev about 8 years 10 months ago

hm, I think the type of cable you should use depends on the vendor, I don't think that is depend on the L2 or L3 capability of LB, some of LB can work as L2 or L3 device, you should simply activate those capability. But as I remember all our LB (4 different vendors) used to use the stright-throuh cable for connection to the switch.

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caijunjie Wed, 01/30/2008 - 17:35

Hi

Depend on the what are u looking for, one way is to connect the lb and the servers to the sw and configure the lb to load balance between the servers that u have.

Some example of teh traffic would be.

A host trying to access from outside., It will pass the router and to the firewall, once it passes the fw, it will hit the lb, the lb will see wat the IP add of the server and it will load balance based on the algorithm configured.

Hope that help.

Alan

Konstantin Dunaev Thu, 01/31/2008 - 00:44

there are not to many ways to interconnect the LB, switch and serevrs.

first of all, is your LB layer2 or layer3?

1. you connect the realservers directly to LB and connect the LB to the switch. if your LB is layer3 you configure the defaultgateway on realserver to point to the LB, if LB is layer2 the defaultgateway points to the router.

This approach has a disadvantage- you can connect only so many realserevrs, as your LB port capacity. But you can use then the second switch to which are realservs are connected and then connect that switch to LB, it will solve the port capacity problem.

2. you connect the realserver to the switch, and LB to the switch as well, it's "single-arm" connection. With this approach the DSR (direct Server return) mode works a little bit more efficient, because the return traffic don't pass the loadbalancer and it saves its resources, but single-arm connection could have many issues and should be planned more carefully in regard to VLAN and defaultgateways.

Thanks a lot Sir, that was pretty informative to me.

Kindly give an example or scenario for configuring a cisco 3550 and cisco 4500 (IOS) switches for load balancers. Is it just the vlan which has to be same for the servers/LB switchports or there is something else to be configured? The server requests from clients/users would be using the IP of the LB and not the IP's of the real servers, isn't it?

--gaurav

Konstantin Dunaev Fri, 02/01/2008 - 00:00

hi,

I never used cisco routers for loadbalancing, that is why I can'T give an example, but it should be enouch I suppose on the cisco site.

if you use DSR, then yes, loadbalancer and the realserver should be in the same VLAN (loadbalancer just exchange the MAC address and keep the destination IP address, you need the hidden-loopback interface on the realserver), for the "NAT loadbalancing" the loadbalancer and realserver can be in different VLANs.

But I would recomend simply to install a linux serevr with simple loadbalancer - "keepalive". It doesn't have any funny features but simple loadbalancing works perfectly on them.

dongdongliu Fri, 02/01/2008 - 01:09

I have used other company`s LB equipment.

if LB equipment have enough interface, 2 server can be connected to LB equipment. if LB equipment do not have enough interface, 2 server can via SW to connedt LB equipment.

suspend LB equipment from SW is a good idea.

Just one more querry..

how can i get to know that the LB is a layer3 or a layer2 device? In other words, what cables are to be used to connect switch and load balancer, as far as my knowledge goes a layer2 and a layer3 devices (like a switch and a router) should be connected through a Straight through cable and two layer2 devices like two switches should be connected through a cross-cable, correct me if I'm wrong somewhere?

--gaurav

Correct Answer
Konstantin Dunaev Mon, 02/04/2008 - 00:07

hm, I think the type of cable you should use depends on the vendor, I don't think that is depend on the L2 or L3 capability of LB, some of LB can work as L2 or L3 device, you should simply activate those capability. But as I remember all our LB (4 different vendors) used to use the stright-throuh cable for connection to the switch.

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