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I am helping a LAN party organisation set up their network. Because of a high number of attendees we think it would be better to use 2 separate wan connections (from different ISP's) using simple routers. Is there an "easy" way of balancing load between the 2 routers without buying hardware?

This is how our network looks like:

Internet -> router 1 & 2 -> 4x 24 gbit switches -> clients

Our first thought was to give each router a separate and limited DHCP scope so that a portion of the network would get router 1 as gateway and the other portion would get router 2. Will this work? (I do not really know which DHCP offer a client will accept if 2 are received)

We do have a Windows Server 2008 R2 machine that will run gameservers that we could use for DHCP/Routing/... but I would not know where to start looking first.

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This is the wrong way to go about things. With two routers responding to DHCP requests, one will inevitably respond faster than the other and then all load will go to that system.

What you want is a single router that can support dual WAN connections. Perhaps the most simple/cheap way for you to do this without spending much money is to grab a spare workstation, ensure it has (at least) three network cards in it, and then install pfSense. pfSense supports multi-wan out of the box, and you'll be up and running in no time.

Another problem with consumer-grade routers is that with the load you'll typically be experiencing, you'll run into state table exhaustion very quickly. pfSense, when running on even very modest hardware, will be able to track many more NAT state entries than a consumer-grade router.

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Perfect answer! – Tim Meers Oct 21 '11 at 18:38
I know it wouldnt be the perfect solution but if we work with limited dhcp scopes even if router 1 would get filled first the remaining clients would have use router 2 right? – Jens Oct 21 '11 at 19:22
With the release of pfSense 2.0 this is really easy to setup too. – 3dinfluence Oct 21 '11 at 20:05

I am assuming these are consumer-grade routers, which would limit our choices a bit... besides simpler is often better in situations like this...

Set up a couple of vlans and split the attendees between them. NAT should prevent asymetric routing concerns. This means that you need to set up DHCP so that attendees in Vlan A will go to router 1 and attendees in Vlan B will go out router 2. Router 1 will not handle Vlan B and Router 2 will not handle Vlan A. If you like you can set up a third (dedicated vlan between the routers for failover should the internet on one of them go down (this would not mitigate loss of LAN connection on either one though, since they are using dedicated Vlan connections.

The DHCP server will discriminate based on the source subnet of the DHCP request, and you will need to ensure that your routers forward the requests appropriately. Technically, you could issue DHCP from your routers locally for their respective Vlans and save configuration of the Win2008 for DHCP purposes.

All this is moot if you have "real" cisco routers... then load-balance using GLBP and it's a win all the way around.

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