Currently with my servers, they all or almost all have 2 nics with one in use. Each NIC is is of course connected to a single switch.

What do I need to do to make this redundant in that both NICs are used and connected to different switches, but will have one IP with automatic failover.

Most of the servers are Dell Poweredge servers running either Windows Server 2003 or CentOS/Redhat 5ish.

I have never set this up before, but I am guessing the topic is a bit beyond one serverfault question, so I am just looking for the keywords (like NIC bonding?), links, book recommendations on this topic, and gotchas to watch out for.


You should be able to get and install either the Intel (proset) or Broadcom server utility - depending on which kind of NIC you have in your server.

Once you have that on your machine, you can configure fault tolerance on the server. At least with proset (don't have a broadcom server w/ the tool installed right now to look at) you would configure a new team, tell it what type of fault tolerance you want - Adapter, switch, load balancing, etc.

The only gotcha I can think of right now is if you are running MSCS on any of the servers they don't support NICs setup with fault tolerance in any way and the cluster verification will fail.

Some keywords for you to look for "Adapter Fault Tolerance" "NIC Fault Tolerance" "Adapter Load Balancing" "Adapter Fail over"

I think a picture says 1000 words. So you basically can have three situations.

1 - Switch redundancy, but no Router or ISP redundancy:

router spof http://www.brokenhaze.com/sf_images/router-spof.png

2 - Switch, and router redundancy, but no ISP redundancy:

isp spof http://www.brokenhaze.com/sf_images/router-isp-spof.png

3 - Finally, no SPOF - within your control:

no spof http://www.brokenhaze.com/sf_images/no-spof.png

Now each of these setups will obviously be more expensive than the last. For most small/medium sized companies option one holds the best risk/benefit ratio.

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  • Oh awesome, missed this edit, thanks for the great answer! – Kyle Brandt Feb 8 '10 at 18:12
  • What our ISP is matters in a SPOF scenario. For instance if you are using DSL and cable, there wouldn't be a SPOF. But if you are using 2 T-1s from the same local lec there would be. Similarly if you were using DSL and a T-1 still using the same local lec, therefore if you are worried about an upstream local carrier failure. – JamesBarnett Jan 5 '11 at 7:55
  • If you're considering multiple ISPs, make sure their lines are physically seperated. Otherwise you end up with Backhoe SPOF – devnul3 May 2 '12 at 18:57
  • 1
    Links are broken – Aheho Nov 9 '12 at 22:01
  • It would be great if you could re-upload your images to imgur or something, and edit your answer to point to them. – Chris L Dec 7 '14 at 22:25

one more keyword to look up would be NIC Teaming.

Just an additional note as well: if you are connecting to separate physical switches you are more likely limited to more Fault Tolerant solution as opposed to doing Load balancing of inbound/outbound data.

Unless you are running some of the more higher end switches (Cisco 6500 w/VSS, etc..) you won't be able to do full load balancing.

I know the HP NIC teaming utility will allow you to do Fault Tolerance with outbound load balancing, but all traffic to the server goes through a single link.

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For the RHEL/CentOS systems, you'll want to research "bonding". Red Hat has some decent documentation in their online manual, specifically the Channel Bonding section.

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