We currently have 1 ISP and are adding a second. I need to load balance this into our current network so it shares the bandwidth between our 2 ISPs. We have a total of about 10 external IP addresses that will need to be able to route to the correct servers on our network.

Our network structure is an ASA5505 (and identical failover system) with unlimited users/security+ licenses. From here it just routes to the switches/patch panel and network.

I know there are hardware solutions that you can plug in. Like sonic wall does this.

But there’s also an exterior BGP/Multi homing option that can be used.

We are a company with 40+ employees and reliability to the internet is key for us as we are a software company.

  • Take a look at my answer on this question - I don't think it's directly applicable to your sitation, but may help to narrow down the questions that you have. Oct 26, 2011 at 17:32

1 Answer 1


For using multiple outgoing connections, all you need is something to route the traffic appropriately. There are a number of free linux/BSD router distros that will work fine, such as m0n0wall.

However, to share the same set of public IPs on multiple incoming connections, ISP participation is required.

This is indeed referred to as multi-homing, and requires the use of BGP, an assigned AS number, and ownership of an IP space.

This is not often feasible for such small IP spaces; you may be able to get a redundant link from one ISP, in which case they will take care of the multi-homing, but that doesn't protect you against that ISP going down...

An alternative is to host your critical services in a datacenter, which will be redundant in all respects (power, cooling, hardware, connectivity) - but you will have to compare costs.

  • so you guys would not recommend installing hardware and having it manage the ISPs?
    – Lbaker101
    Oct 26, 2011 at 17:52
  • @Lbaker, what adaptr is saying is, if you want your users to load balance when going out of your network, then you can use hardware and/or software to do this. If you want the world to reach your office and load balance between two ISP than you need those ISP to talk and configure accordingly.
    – Alex
    Oct 26, 2011 at 18:44
  • It actually doesn't require ownership of IP space or an assigned AS number if the two ISPs cooperate, are directly connected, and you don't mind losing the inability to load-balance inbound traffic or having the link between the two ISPs being a failure point. In that case, you can use a private AS that's only used between you and your two ISPs and you can announce a chunk of one ISP's space to the other ISP. (This announcement is only used to route traffic between you and your two ISPs.) Oct 26, 2011 at 21:24
  • Well, yes, but those are some big IFs...
    – adaptr
    Oct 27, 2011 at 7:22
  • Thank you for the help guys (^_^) i think I have a lot clearer picture now.
    – Lbaker101
    Oct 31, 2011 at 17:19

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