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rdefuriaFlag for United States of America

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Combining two DSL connections for LAN connectivity

Hello,

I would like to have redundant DSL connections to my office, and be able to have both be active concurrently (transparent to my users, of course).  Hopefully, this will make my office connectivity less subject to the vagaries of a single DSL provider.

However, my existing DSL providers gives me static ip addresses, while the potential new providers only offer dynamic ip addresses.

What network configuration would make this work (e.g., dual port router with NAT on one of the ports, etc.)?

Additonal background:
1. My clients all have static ips and will retain those
2. Currently with single DSL connection I have a pretty simple setup as follows:

     dsl line <-> dsl router <-> firewall <-> switch <-> lan ... clients


Is there any other info needed?

-RD
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scraig84

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Heavens, no, we are not hosting anything from our office; all our production stuff is located at our data center (ostensibly much more robust than anything we could do internally).

My intention is just what you said - to keep office connectivity (web browsing and sending/receiving email, mainly) when our primary DSL goes down.

I was hoping for some slick solution that would work whether one or the other DSL providers was down.  If one went down, couldn't the cost of routes be adjusted so that no outgoing packets get lost?  I guess I am not following what you suggest...

-RD
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scraig84

Here is the problem.  DSL "modems" usually connect to the inside device via an Ethernet connection.  Even if the DSL link goes away, the Ethernet side stays up and keeps a link with the connected router or PC.  Therefore even if you have a router there, it has no way of ever determining if the route went down, because the link literally never dies.  So, it always thinks it has an active link and will never choose a secondary path.  If you want simple load balancing, a router can decide to share both by considering both links to be equal.  However, if one goes down, it still sends half of the packets to the side that's down.  Unless some DSL modems have a feature to bring down the Ethernet interface in the event that the DSL connection goes down (which I've never heard of), you aren't really left with any options.
I have to agree with scraig84, you can't get there from here
Radware LinkProof in between the LAN and 2 DSL routers ought to work. Doesn't need BGP, it just tries both routes and choses the faster one.
http://www.radware.com/content/products/link.asp
Oops, missed that you needed "receiving email". That may not be possible if you have a SMTP server recieving email.

You'd have to have 2 MX records, one resolving to your permanent IP address and the other (with higher number/lower preference) resolving to the dynamic IP supplying ISP's mail relay which can forward to your dynamic IP address through their mailserver knowing what IP address you have through their radius servers logs but they may not offer this service.

We are not accepting incoming smtp connections in the office.  That's done by our mail server in a data center.  We use pop-3 to read our email, and make outgoing smtp connections to send email.  That's what I meant by sending/receiving email (I should have more correctly said reading/sending email).

So will this device allow for one of my dsl providers giving me static ips, and the other giving me dynamic ips?

What happens if returning packets come back via the non-NATed path?

Will it recognize if one dsl connection is down and route all traffic the other way?

I am not sure I have a handle on whether this is really possible or not, or whether
I will have to split up my LAN and have some folks use one gateway and the rest use another gateway, and manually reconfigure if one of the providers goes down.


POP3 makes life easy.
The box itself does NAT so the packet will have the IP address of one of it's interfaces so the reply will come back to the same interface. Pretty sure it can handle mixture of static and dynamic ISP provided addresses. If one path is down (even if it's the ISP's backbone rather than the local DSL connection) it will notice this and use the other interface. Guess you might loose current sessions that were going through whichever ISP fails.
 I'm not a radware salesman but the box will do exactly what you want. Splitting the LAN by having half of clients with one gateway and half with the other doesn't solve the problem of www.foo1.com being faster through ISP1 and www.foo2.com being faster through ISP2 but this box does.

I am looking for a more cost-effective solution.  Would a linux box to do routing, NAT, firewalling, bridging, etc. be helpful in this scenario?

No cost-effective solution. scraig84 said it all in his first comment, I just added one of the products available as the thread was still open 2 days later. Don't give him less than an A just because it can't be done for free.

Thanks, everyone, for all the input and expertise!