Question : Nortel 2424 Load Balancing Switches Vs W2K NLB

Hello,

We are running a high demanding web/application server farm.  Our web servers run on ports 80TCP and some of our applications run on UDP ports.

We are currently load balancing our servers in the farm using Nortel 2424 Load Balancing Switches.  Since the servers are W2K Advanced Servers, I thought of NLB as a more cost effective alternative.

I could not find any documentations or newsgroup discussions about the performance difference between a hardware load balancer such as the 2424, and the Windows built in NLB.  When looking at it from a performance point of view, which one is better?  What's the difference really?  What happens under the hood?  I understand that the 2424 uses Virtual IPs that distributes to the servers' IPs.  NLB on the other hand is set by having all farm members share the same VIP.  Does that make it slower?  High Performance is very critical for us, but I'd still like to know if NLB is an option and why.

Thanks!
JM

Answer : Nortel 2424 Load Balancing Switches Vs W2K NLB

Well there are these several that are most used:

First we need to understand the setup:

- 2 or more servers are connected to the LB.
- 1 or more connections from users to the servers.

LB has a Virtual IP to which all connections are addressed.
It gets the packets and looks inside their contents and according to the contents it distributes them between the servers according to the LB algorithms that I am about to explain.

I will explain you here the LB on Layer 4 (transport) and Layer 7 (application).

Layer 4 switching (Load Balancing) is done in a following matter.

1. Round Robin: Connections are distributed between all servers one by one in a cyclic manner.
2. Hash or Persistent connections: all connections from the same user (IP address) are redirected to the same user.
3. Least Load : Load Balancer maintains the table of live connections and send each new connection to a least loaded server.
4. Least amount of connections
5. Least amount of users (each user can have more than 1 connection).

All these 3 mentioned above are LB for the same service type, meaning all service have the same functionality (Mirrors like).

Another is to distrbute connections according to service type or port number: Lets say we have an HTTP and SMTP service running behind the LB - all the connections will arrive to the same Virtual IP. So LB will accept the connection and will redirect it according to the service type or a port number to the correct server.

Also there are many other types of load balancing on different networking layers: from Ethernet to Applications layer. Different algorythms are suitable more or less to different types of traffic/applications and setups.

This is a liitle about load balancing.