Dual NIC Teaming/failover/Load Balancing

[runboy]

I have a server (Power Edge 2650 with BroadCom Nics) with Dual Nics and was wanting to set up some form of Failover/Load balancing. The server/NICs are capable of this, but I am a little confused about how it works.

- Will the server still need at least two IP adresses or can it be represented by a single IP ? Either way, how is the Router/DNS setup ?
- Can two ports on a router be configured to use the same IP and if so isn't the load balancing actually made by the router ?

 

[Santa]

From what I understand about the broadcom line they have software to allow for failover configuration of the network adapters only. I don't think they have the ability to team them yet.

The failover will be done through software and both NICs would be configured identically but only one will be turned on and answer request unless it detects that the link goes down on the active card then it will disable that card and bring the other one online.

 

[spidey07]

here's how I use dual/quad port nics:

Its really the greatest thing in networks since sliced bread. The bonding/teaming/failover is handled at the driver level, hence the OS is completely clueless to any underlaying failures/activity.

That's a good thing. IP stacks and operating systems don't like severe changes in their stack/routing/switching/arp, etc...I could go on for days on why modern NICs and drivers are a godsend for performance and failover.

There are two approaches to operating mulitple NICS:
1) Do you want ultimate redundancy?
2) Or do you want ultimate performance with redundancy as a nice to have?

If you want 1) then -
Each of the network interfaces (NICs) plugs into a separate switch, with one being a primary. The primary performs all network communications. The secondary doesn't do much other than wait for a failure at which point it takes over comm duties. This is a very effective solution and I use it religiously in high-availibility networks. I can fail NICs, lose core switches, just about lose anything and the host is unaware of any changes. Truly incredible if you want 99.999% uptime. Only down side is only one NIC is active.

2) Performance is enhanced by using multiple NICs to a single switch that supports some kind of load balancing. Down side is you almost always have to attach both nics to a single switch. So you gain some performance, but you lose redundancy. Switches do fail, often.

As far as the OS is concerned...it needs only one IP address. The OS is only aware of a single NIC - the drivers handle all the underlying magic. Anytime you assign more than one IP address to a machine it is no longer doing any kind of load balancing or redundancy. (this is a very general statement). The job of performanc/redudancy is best left to the drivers. The OS normally gets confused and complicated when you have more than one NIC addressed to the same IP network.

Hope this helps.

 

[runboy]

Santa - Broadcom in the poweredge supports the following three team types:
- Smart load balancing and failover
- Link Aggregation (802.3ad)
- Generic Trunking (FEC/GEC)/802.3ad-Draft Static



spidey07 - This is a webserver. Let's say I want redundancy (I guess I could really have both failover and redundancy right). How would the switches/routers be set up using only one IP address on two different ports without having some kind load balancing at a higher level ? An outside request would need to know which of the ports to go to, how does that work without load balancing ?
I can see how it is done with two different IPs defined on the same domain nam, but that is not really load balancing, more a 50/50 request spilt.
Could it be that Broadcom by load balancing means only from the server and not to ?

 

[spidey07]

Runboy,

Any load balancing occurs at layer2. There is only one IP address so all requests have the same destination address. The switch is then configured for load balancing or ether channel and distributes the requests using a balancing algorithim.

Higer end switches distribute the load based on layer3 (like cisco 6500)

 

[Buddha Bart]

spidey, what nics/switchs/os's do you get the best results on this with?

 

[spidey07]

Originally posted by: Buddha Bart
spidey, what nics/switchs/os's do you get the best results on this with?

Sun Solaris using ip multipath and sun trunking. Switch is Cisco 6500.
On the wintel side Intel dual/quad port 10/100/1000s work well on 2000. Same switch.

The failover results in an outage of about 2 seconds. Its nice to know you can lose a 300 port switch and not affect anything.

 

[runboy]

spidey07 wrote:
.

Any load balancing occurs at layer2. There is only one IP address so all requests have the same destination address. The switch is then configured for load balancing or ether channel and distributes the requests using a balancing algorithim.

The is a webserver with multiple websites and I would like to not put all of them on the same IP. Since we are talking about the same machine, would there be anything wrong with assigning multiple IPs to the same two ports on the switch/router. Are the IPs assigned to the ports themselves or just the switch/router as a hole ?
How does the load balancing actually happen ? How does the NICs tell the switch/router that they are busy or is the load just distributed evenly ?

 

[spidey07]

your web server really only should have one ip address unless you're doing something funky like SSL.

try a search on "link aggregation" or search intels web page for "load balancing" or "teaming"

 

[runboy]

I can see many reason why you would want more than one IP and have used that for several years now. There is actually a slight overhead in IIS by using only one so it has to analyse the header. Many of customers also demand having their own IP , mostly for SSL reasons. Most likely the overhead in the OS by having several IPs is bigger than what is gained in IIS. I also have some specific security reasons why I use more than one IP, but I don't want to go into detail for obvious reasons.

 

[Buddha Bart]

regardless of how many IPs you want, you still want both of your nic's to have the same IP(s). The bonding is occuring at layer2.

bart